MBIO 10-K & 10-Q changes, risk factors and insider trading

We have a limited operating history. We have focused primarily on organizing, acquiring, developing and securing our proprietary technology and identifying and obtaining preclinical data or clinical data for various product candidates, with the goal of supporting regulatory approval for these product candidates. We have incurred losses since our inception in March 2015. Our net losses were $15.8$1.9 million and $51.6$15.8 million for the years ended December 31, 20242025 and 2023,2024, respectively, and we had an accumulated deficit of $396.7$398.6 million as of December 31, 2024.2025. We expect to continue to incur significant operating losses for the foreseeable future. We also do not anticipate that we will achieve profitability for a period of time after generating material revenues, if ever. If we are unable to generate revenues, we will not become profitable and may be unable to continue operations without continued funding.

Because of the numerous risks and uncertainties associated with developing pharmaceutical products, we are unable to predict the timing or amount of increased expenses or whenwhen, or ifif, we will be able to achieve profitability. Our net losses may fluctuate significantly from quarter to quarter and year to year. We anticipate that our expenses will increase substantially if:

There is substantial doubt regarding our ability to continue as a going concern. We willmay in the future need to raise substantial additional fundingfunding, (which may not be available on acceptable terms to us, or at all) and/or delay, limit or terminate our product development efforts or other operations.all. If we are unable to raise capital, we could be required to delay, limit or terminate our product development efforts or other operations, or seek bankruptcy protection or other alternatives that would likely result in our securityholders losing some or all of their investment in us.

We are currently advancing our programs in hematologic cancers, autoimmune diseases and solid tumors through clinical development. Developing and commercializing CAR T products is expensive, and we do not expect to generate meaningful product revenues in the foreseeable future until we obtain marketing approval for products in the United States and following any potential commercial launch. We will need to significantly increase our spending to advance the preclinical and clinical development of our product candidates and launch and commercialize any product candidates for which we may receive regulatory approval, including building our own commercial organizations to address certain markets. We will require substantial additional capital for the further development and, if approved, commercialization of our product candidates, as well as to fund our other operating expenses and capital expenditures.

As of December 31, 2024, our cash and cash equivalents were $6.8 million. Based on our current business plan, there is substantial doubt regarding our ability to continue as a going concern for a period of one year after the date that our financial statements for the year ended December 31, 2024, are issued. Our fundraising efforts to raise additional funding may divert our management from their day-to-day activities, which may adversely affect our ability to develop and commercialize our potential products following marketing approval if and when obtained. In addition, we cannot guarantee that financing will be available in sufficient amounts or on terms acceptable to us, if at all. Moreover, the terms of any financing may adversely affect the holdings or the rights of our stockholders and the issuance of additional securities, whether equity or debt, by us, or the possibility of such issuance, may cause the market price of our shares to decline. The sale of additional equity or convertible securities would dilute all of our stockholders. Potential indebtedness, if incurred, would result in increased fixed payment obligations, and we may be required to agree to certain restrictive covenants, such as limitations on our ability to incur additional debt, limitations on our ability to acquire, sell or license intellectual property rights and other operating restrictions that could adversely impact our ability to conduct our business. We could also be required to seek funds through arrangements with collaborative partners or otherwise at an earlier stage than otherwise would be desirabledesirable, and we may be required to relinquish rights to some of our technologies or product candidates or otherwise agree to terms unfavorable to us, any of which may have a material adverse effect on our business, operating results and prospects.

In addition, in order to address our current or future funding constraints, we may be required to further revise our business plan and strategy, which may result in us (i) further curtailing, delaying or discontinuing one or more of our research or development programs or the commercialization of any product candidates, (ii) selling certain of our assets and/or (iii) may result in our being unable to expand our operations or otherwise capitalize on our business opportunities. Such actions may become necessary whether or not we are able to raise additional capital. As a result, our business, financial condition, and results of operations could be materially affected. Furthermore, if we are unable to raise capital, the value of our stock could decline, or we could be required to wind down our operations or seek bankruptcy protection or other alternatives that would likely result in our securityholders losing some or all of their investment in us.

Our shortlimited operating history makes it difficult to evaluate our business and prospects.

We have been conducting operations only since our incorporation in March 2015. Our operations to date have been limited. We have not yet demonstrated an ability to successfully complete clinical trials, obtain regulatory approvals, manufacture a clinical scale or commercial scale product, or arrange for a third party to do so on our behalf, or conduct sales and marketing activities necessary for successful product commercialization. Consequently, any predictions about our future performance may not be as accurate as they could be if we had a history of successfully developing and commercializing pharmaceutical products.

Under current SEC regulations, if at the time we file our Annual Report on Form 10-K our public float is less than $75 million, and for so long as our public float remains less than $75 million, the amount we can raise through primary public offerings of securities in any twelve-month period using shelf registration statements is limited to an aggregate of one-third of our public float, which is commonly referred to as the baby shelf rules. SEC regulations permit us to use the highest closing sales price of our common stock (or the average of the last bid and last ask prices of our common stock) on any day within 60 days of sales under the registration statement to calculate our public float.

As of the date of this Form 10-K, our public float was less than $75 million. As a result, for sales following the date of this Form 10-K, and until we again have a public float with a value in exceedsexcess of $75 million, if ever, we only have the capacity to sell sharesan amount of securities up to one-third of our public float under shelf registration statements in any twelve-month period. If our public float decreases, the number of securities we may sell under our Form S-3 shelf registration statements will also decrease.

We have elected to take advantage of certain of the reduced reporting obligations available to us. We cannot predict whether investors will find our common stock less attractive if we rely on these exemptions. If some investors find our common stock less attractive as a result, there may be a less active trading market for our common stockstock, and our stock price may be reduced or more volatile.

Our ability to use our pre-change NOLsnet operating loss carryforwards and other pre-change tax attributes to offset post-change taxable income or taxes may be subject to limitation.

To date, we have invested a significant portion of our efforts and financial resources in the acquisition and development of our product candidates. We have not demonstrated our ability to perform the functions necessary for the successful acquisition, development or commercialization of the technologies we are seeking to develop. As an early stageearly-stage company, we have limited experience and have not yet demonstrated an ability to successfully overcome many of the risks and uncertainties frequently encountered by companies in new and rapidly evolving fields, particularly in the biopharmaceutical area. Our future success is substantially dependent on our ability to successfully develop, obtain regulatory approval for, and then commercialize such product candidates. Most of ourOur product candidates are currently in early stageearly-stage clinical trials. Our business depends entirely on the successful development and commercialization of our product candidates, which may never occur. We currently have no drug products for sale, currently generate no revenues from sales of any drug products, and may never be able to develop or commercialize a marketable product.

Our operations have historically been limited to organizing the Company, acquiring, developing and securing our proprietary technology and identifying and obtaining preclinical data or clinical data for various product candidates. These operations provide a limited basis for you to assess our ability to continue to develop our technology, identify product candidates, develop and commercialize any product candidates we are able to identify and enter into successful collaborative arrangements with other companies, as well as for you to assess the advisability of investing in our securities. Each of these requirements will require substantial time, effort and financial resources.

We have concentrated much of our research and development efforts on CAR T technology, and our future success is highly dependent on the successful development of T cell immunotherapies in general and our CAR T technology and product candidatescandidate in particular. Because CAR T is a relatively new approach to cancer immunotherapy and cancer treatment generally, developing and commercializing our CAR T product candidatescandidate, if approved, subjects us to a number of challenges, including, but not necessarily limited to:

Clinical trials are expensive and can take many years to complete, and the outcome is inherently uncertain. We cannot guarantee that any clinical trials will be conducted as planned or will be completed on schedule, if at all. A failure of one or more clinical trials can occur at any stagestage, and our future clinical trials may not be successful. The commencement or conduct of clinical trials can be delayed for a variety of reasons, including, but not necessarily limited to, delays in:

Suspensions or delays in the completion of clinical testing could result in increased costscosts, and delay or prevent our ability to complete development of that product candidate or generate product revenues, if approved.

With respect to foreign markets, approval procedures vary among countries and, in addition to the aforementioned risks, can involve additional product testing, administrative review periods and agreements with pricing authorities. In addition, rapid drug and biological development during the COVID-19 pandemic has raised questions about the safety and efficacy of certain marketed pharmaceuticals and may result in increased cautiousness by the FDA and comparable foreign regulatory authorities in reviewing new pharmaceuticals based on safety, efficacy or other regulatory considerations and may result in significant delays in obtaining regulatory approvals. Any delay in obtaining, or inability to obtain, applicable regulatory approvals would prevent us from commercializing our product candidates. It is also unclear what actions will be taken by the currentU.S. presidential administration or through legislative actiongovernment that could impact the FDA and our ability to obtain regulatory approvals.

If any of our product candidates are approved and wewe, or our contract manufacturer(s), fail to produce the product, or components of the product, in the volumes that we require on a timely basis, or fail to comply with stringent regulations applicable to pharmaceutical drug manufacturers, we may face delays in the commercialization of our product candidates, if approved, or be unable to meet market demand, and may lose potential revenues.

The manufacture of pharmaceutical products requires significant expertise and capital investment, including the development of advanced manufacturing techniques and process controls, and the use of specialized processing equipment. We may enter into development and supply agreements with contract manufacturers for the completion of pre-commercialization manufacturing development activities and, if approved, the manufacture of commercial supplies for one or more of our product candidates. Any termination or disruption of our relationships with our contract manufacturers may materially harm our business and financial condition and frustrate any commercialization efforts for each respective product candidate.candidate, if approved.

If the contract manufacturers upon whom we may rely to manufacture one or more of our product candidates, and any future product candidate we may in-license, failsfail to deliver the required commercial quantities on a timely basis at commercially reasonable prices, we would likely be unable to meet demand for our approved product and we would lose potential revenues.

If serious adverse or unacceptable side effectsevents are identified during the development of one or more of our product candidates or any future product candidate, we may need to abandon or limit the development of some of our product candidates.

If one or more of our product candidates or any future product candidate are associated with undesirable side effects or adverse events in clinical trials or have characteristics that are unexpected, we may need to abandon their development or limit development to more narrow uses or subpopulations in which the adverse events, undesirable side effectsevents or other characteristics are less prevalent, less severe or more acceptable from a risk-benefit perspective. In our industry, many compounds that initially showed promise in early stageearly-stage testing have later been found to causebe seriousassociated with adverse events that prevented further development of the compound. In the event that our clinical trials reveal a high or unacceptable severity and prevalence of adverse events, our trials could be suspended or terminated, and the FDA or comparable foreign regulatory authorities could order us to cease further development or deny approval of one or more of our product candidates or any future product candidate for any or all targeted indications. The FDA could also issue a letter requesting additional data or information prior to making a final decision regarding whether or not to approve a product candidate. The number of requests for additional data or information issued by the FDA in recent years has increased and has resulted in substantial delays in the approval of several new drugs. Adverse events orassociated undesirable side effects caused bywith one or more of our product candidates or any future product candidate could also result in the inclusion of unfavorable information in our product labeling or in denial of regulatory approval by the FDA or other regulatory authorities for any or all targeted indications, which would, in turn, prevent us from commercializing and generating market acceptance and revenues from the sale of that product candidate.candidate, if approved. Adverse events or side effects could affect patient recruitment or the ability of enrolled patients to complete the trial and could result in potential product liability claims.

Additionally, if one or more of our product candidates or any future product candidate receives marketing approval and we or others later identify undesirableadverse sideevents effectsassociated caused bywith this product, a number of potentially significant negative consequences could result, including:

Any of these events could prevent us from achieving or maintaining market acceptance of anyeither of our product candidates or any future product candidatecandidate, if approved, or could substantially increase our commercialization costs and expenses, which in turn could delay or prevent us from generating significant revenues, or any revenues, from their sale.

In addition, later discovery of previously unknown adverse events or other problems with our products, manufacturers or manufacturing processes, or failure to comply with regulatory requirements,requirements may yield various results, including:

The FDA’s policies may change, and additional government regulations may be enacted that could prevent, limit or delay regulatory approval of our product candidates, or negatively affect those products for which we may have already received regulatory approval, if any. There is added uncertainty in light of actions that may be taken by the current presidential administration or Congress with respect to the FDA. If we are slow or unable to adapt to changes in existing requirements or the adoption of new requirements or policies, or if we are not able to maintain regulatory compliance, we may be subject to the various actions listed above, including losing any marketing approval that we may have obtained.

A pharmaceutical product cannot be marketed in the U.S. or other countries until we have completed a rigorous and extensive regulatory review process, including approval of a brand name. Any brand names we intend to use for our product candidates will require approval from the FDA regardless of whether we have secured a formal trademark registration from the USPTO. The FDA typically conducts a review of proposed product brand names, including an evaluation of the potential for confusion with other product names. The FDA may also object to a product brand name if it believes the name inappropriately implies medical claims. If the FDA objects to any of our proposed product brand names, we may be required to adopt an alternative brand name for our product candidates. If we adopt an alternative brand name, we would lose the benefit of our existing trademark applications for such product candidate and may be required to expend significant additional resources in an effort to identify a suitable product brand name that would qualify under applicable trademark laws, not infringe the existing rights of third parties and be acceptable to the FDA. We may be unable to build a successful brand identity for a new trademark in a timely manner or at all, which would limit our ability to commercialize our product candidates.candidates, if approved.

In light of widely publicized events concerning the safety risk of certain drug products, the FDA, members of the U.S. Congress, the Government Accountability Office, medical professionals and the general public have raised concerns about potential drug safety issues. These events have resulted in the withdrawal of drug products, revisions to drug labeling that further limit use of the drug products and the establishment of risk management programs. The Food and Drug Administration Amendments Act of 2007, (“FDAAA”), grants significant expanded authority to the FDA, much of which is aimed at improving the safety of drug products before and after approval. In particular, the law authorizes the FDA to, among other things, require post-approval studies and clinical trials, mandate changes to drug labeling to reflect new safety information and require risk evaluation and mitigation strategies for certain drugs, including certain currently approved drugs. It also significantly expanded the federal government’s clinical trial registry and results databank, which we expect will result in significantly increased government oversight of clinical trials. Under the FDAAA, companies that violate these and other provisions of the law are subject to substantial civil monetary penalties, among other regulatory, civil and criminal penalties. The increased attention to drug safety issues may result in a more cautious approach by the FDA in its review of data from our clinical trials. Data from clinical trials may receive greater scrutiny, particularly with respect to safety, which may make the FDA or other regulatory authorities more likely to require additional preclinical studies or clinical trials. If the FDA requires us to conduct additional preclinical studies or clinical trials prior to approving any of our product candidates, our ability to obtain approval of this product candidate will be delayed. If the FDA requires us to provide additional clinical or preclinical data following the approval of any of our product candidates, the indications for which this product candidate is approved may be limited or there may be specific warnings or limitations on dosing, and our efforts to commercialize our product candidatescandidates, if approved, may be otherwise adversely impacted.

There is significant uncertainty related to the third-party coverage and reimbursement of newly approved drugs. Such third-party payors include government health programs such as Medicare, managed care providers, private health insurers and other organizations. We intend to seek approval to market our product candidates in the U.S., the European Union (“EU”) and other selected foreign jurisdictions. Market acceptance and sales of our product candidatescandidates, if approved, in both domestic and international markets will depend significantly on the availability of adequate coverage and reimbursement from third-party payors for any of our product candidates and may be affected by existing and future health care reform measures. Government and other third-party payors are increasingly attempting to contain healthcare costs by limiting both coverage and the level of reimbursement for new drugs and, as a result, they may not cover or provide adequate payment for our product candidates, if approved. These payors may conclude that our product candidates are less safe, less effective or less cost-effective than existing or future introduced products, and third-party payors may not approve our product candidates, if approved, for coverage and reimbursement or may cease providing coverage and reimbursement for these product candidates.

We currently do not have a marketing or sales organization for the marketing, sales and distribution of pharmaceutical products. In order to commercialize any approved product candidate, we would need to build marketing, sales, distribution, managerial and other non-technical capabilities or arrange for third parties to perform these services, and we may be unsuccessful in doing so. In the event of successful development and regulatory approval of any of our current or future product candidates, we expect to build a targeted specialist sales force to market or co-promote the product. There are risks involved with establishing our own sales, marketing and distribution capabilities. For example, recruiting and training a sales force is expensive and time consumingtime-consuming and could delay any product launch. If the commercial launch of a product candidatecandidate, if approved, for which we recruit a sales force and establish marketing capabilities is delayed or does not occur for any reason, we would have prematurely or unnecessarily incurred these commercialization expenses. This may be costly, and our investment would be lost if we cannot retain or reposition our sales and marketing personnel.

Public perception may be influenced by claims that one or more of the therapies underpinning our product candidates is unsafe, and such therapy may not gain the acceptance of the public or the medical community. More restrictive government regulations or negative public opinion would have a negative effect on our business or financial condition and may delay or impair the development and commercialization of our product candidates or demand for any products we may develop. Adverse events in our clinical trials, even if not ultimately attributable to our product candidates, and the resulting publicity, could lead to increased governmental regulation, unfavorable public perception, potential regulatory delays in the testing or approval of our potential product candidates, stricter labeling requirements for those product candidates that do obtain approval and/or a decrease in demand for any such product candidates. Concern about environmental spread of our products, whether real or anticipated, may also hinder the commercialization of our products.

We rely on our licensors to conduct some of our preclinical studies and some of our clinical trials for our product candidates and for future product candidates, and we rely on third-party CROs and site management organizations to conduct most of the remainder of our preclinical studies and all the rest of our clinical trials. We expect to continue to rely on third parties, such as our licensors, CROs, site management organizations, clinical data management organizations, medical institutions and clinical investigators, to conduct some of our preclinical studies and all of our clinical trials. The agreements with these third parties might terminate for a variety of reasons, including a failure to perform by the third parties. If we need to enter into alternative arrangements, that could delay our product development activities.

Our reliance on these third parties for research and development activities reduces our control over these activities but does not relieve us of our responsibilities. For example, we remain responsible for ensuring that each of our preclinical studies and clinical trials is conducted in accordance with the general investigational plan and protocols for the trial and for ensuring that our preclinical studies are conducted in accordance with good laboratory practices (“GLPs”) as appropriate. Moreover, the FDA requires us to comply with standards, commonly referred to as good clinical practices (“GCPs”) for conducting, recording and reporting the results of clinical trials to assure that data and reported results are credible and accurate and that the rights, integrity and confidentiality of trial participants are protected. Regulatory authorities enforce these requirements through periodic inspections of trial sponsors, clinical investigators and trial sites. If we or any ofthird ourparties CROson which we rely fail to comply with applicable GCPs, the clinical data generated in our clinical trials may be deemed unreliable and the FDA or comparable foreign regulatory authorities may require us to perform additional clinical trials before approving our marketing applications. We cannot assure you that upon inspection by a regulatory authority, such regulatory authority will determine that any of our clinical trials complies with GCP regulations. In addition, our clinical trials must be conducted with product produced under cGMP regulations. Our failure to comply with these regulations may require us to repeat clinical trials, which would delay the regulatory approval process. We also are required to register certain clinical trials and post the results of completed clinical trials on a government-sponsored database, ClinicalTrials.gov, within specified timeframes. Failure to do so can result in fines, adverse publicity and civil and criminal sanctions.

We are currently reliant on COH, Fred Hutch, Nationwide and UAB for all of our research and development efforts and the early clinical testing of our product candidates.

A substantial portion of our research and development has been and will continue to be conducted by COH, Fred Hutch, Nationwide, and UAB pursuant to a sponsored research agreement and/or clinical trial agreements between Mustang Bious and each of COH and Fred Hutch,COH, as well as a Memorandum of Understanding between Nationwide and UAB under which UAB is conducting its MB-108 Phase 1 clinical trials. As a result, our future success is heavily dependent on the results of research and development efforts of these institutions and their personnel. We have limited control over the nature or timing of their research and limited visibility into their day-to-day activities, and as a result can provide little assurance that their efforts will be successful.

We do not independently conduct our LV vector production and we currently rely, and expect to continue to rely, on third parties with respect to the manufacture of thesethis items.item.

Our reliance on these third parties for manufacturing LV vector reduces our control over these activities but will not relieve us of our responsibility to ensure compliance with all required regulations and study protocols. For products that we develop and, if approved, commercialize, we will remain responsible for ensuring that each of our IND-enabling studies and clinical studies is conducted in accordance with the study plan and protocols, and that our LV vectorsvector areis manufactured in accordance with GMP as applied in the relevant jurisdictions.

If these third parties do not successfully carry out their contractual duties, meet expected deadlines, conduct our studies in accordance with regulatory requirements or our stated study plans and protocols, or manufacture our LV vectors in accordance with GMP, we will not be able to complete, or may be delayed in completing, the preclinical and clinical studies and manufacturing process validation activities required to support future IND, market authorization application and BLA submissions and approval of our CAR T product candidates,candidate, or to support commercialization of our products,CAR T product, if approved. Many of our agreements with these third parties contain termination provisions that allow these third parties to terminate their relationships with us at any time. If we need to enter into alternative arrangements, our product development and commercialization activities could be delayed.

We may be forced to enter into an agreement with a different manufacturer, which we may not be able to do on reasonable terms, if at all. In some cases, the technical skills required to manufacture LV vector for our CAR T drug product candidatescandidate may be unique or proprietary to the original manufacturer, and we may have difficulty or there may be contractual restrictions prohibiting us from, transferring such skills to a back-up or alternate supplier, or we may be unable to transfer such skills at all. Any of these events could lead to clinical study delays or failure to obtain marketing approval or impact our ability to successfully commercialize our CAR T product candidatescandidate or any future CAR T product candidates, if approved. Some of these events could be the basis for FDA action, including injunction, recall, seizure or total or partial suspension of production.

A third party may hold intellectual property, including patent rights that are important or necessary to the development and commercialization of our products.product candidates and commercialization, if approved. It may be necessary for us to use the patented or proprietary technology of third parties, who may or may not be interested in granting such a license, to commercialize our products, in which case we would be required to obtain a license from these third parties on commercially reasonable terms, or our business could be harmed, possibly materially.

In the United States and certain foreign jurisdictions, there have been, and we expect there will continue to be, a number of legislative and regulatory changes to the healthcare system that could prevent or delay marketing approval of our product candidate,candidates, restrict or regulate post-approval activities, and affect our ability to profitably sell any product candidates for which we obtain marketing approval. The Patient Protection and Affordable Care Act, as amended by the Health Care and Education Reconciliation Act of 2010 (the “PPACA” or collectively, the “ACA”), substantially regulates the way healthcare is financed by both governmental and private insurers in the United States. Among other things, the ACA increased the minimum level of Medicaid rebates payable by manufacturers of brand name drugs from 15.1% to 23.1%; required collection of rebates for drugs paid by Medicaid managed care organizations; imposed a non-deductible annual fee on pharmaceutical manufacturers or importers who sell certain “branded prescription drugs” to specified federal government programs; implemented a new methodology under which rebates owed by manufacturers under the Medicaid Drug Rebate Program are calculated for drugs that are inhaled, infused, instilled, implanted, or injected; expanded the eligibility criteria for Medicaid programs; created a new Patient-Centered Outcomes Research Institute to oversee, identify priorities in, and conduct comparative clinical effectiveness research, along with funding for such research; and established a Center for Medicare and Medicaid Innovation (“CMMI”) at the CMS, to test innovative payment and service delivery models to lower Medicare and Medicaid spending, potentially including prescription drug spending.

Since its enactment, there have been executive, judicial, and Congressional challenges to certain aspects of the ACA, and we expect there will be additional challenges and amendments to the ACA in the future. Drug pricing continues to be a subject of debate at the executive and legislative levels of U.S. government. The American Rescue Plan Act of 2021 signed into law by President Biden onin March 14, 20212021, includes a provision that eliminated the statutory cap on rebates drug manufacturers pay to Medicaid beginning in January 2024. With the elimination of the rebate cap, manufacturers may be required to compensate states in an amount greater than what the state Medicaid programs pay for the drug. Additionally, the Inflation Reduction Act of 2022 (“IRA”) contains substantial drug pricing reforms, including the establishment of a drug price negotiation program within the U.S. Department of Health and Human Services that would require manufacturers to charge a negotiated “maximum fair price” for certain selected drugs or pay an excise tax for noncompliance, the establishment of rebate payment requirements on manufacturers of certain drugs payable under Medicare Parts B and D to penalize price increases that outpace inflation, and requires manufacturers to provide discounts on Part D drugs. Substantial penalties can be assessed for noncompliance with the drug pricing provisions in the IRA. Although the IRA exempts orphan drugs that treat only one rare disease from the drug pricing negotiation provisions, we do not know if additional drug pricing reforms could eliminate this exemption. The IRA could have the effect of reducing the prices we can charge and reimbursement we receive for our product candidates, if approved, thereby reducing our profitability, and could have a material adverse effect on our financial condition, results of operations, and growth prospects. The effect of the IRA on our business and the pharmaceutical industry in general is not yet known.

We expect that additional federal, state, and foreign healthcare reform measures will be adopted in the future, any of which could limit the amounts that federal and state governments will pay for healthcare products and services, which could result in limited coverage and reimbursement and reduced demand for our products, onceif approved, or additional pricing pressures.

We are a clinical-stage biopharmaceutical company focused on translating today’s medical breakthroughs into potential cures for difficult-to-treat cancers and autoimmune diseases.cancers. We aim to acquire rights to these technologies by licensing or otherwise acquiring an ownership interest in the technologies, funding their research and development and eventually either out-licensing or bringing the technologies to market.

Our pipeline is currently focused inon two core areas: CAR T therapies for hematologic malignancies and autoimmune diseases and CAR Tnovel therapies for solid tumors. For these therapies we have partnered with world class research institutions, including the City of Hope National Medical Center (“COH” or “City of Hope”), Fred Hutchinson Cancer Center (“Fred Hutch”), and Nationwide Children’s Hospital (“Nationwide”).

We expect to incur substantial expenses for the foreseeable future relating to research, development and commercialization of our potential products.products However,and may never achieve profitability. We do not have any products that are approved for commercial sale and, therefore, do not expect to generate any revenues from product sales in the foreseeable future, if ever. Additionally, there can be no assurance that we will be successful in securing additional resources when needed, on terms acceptable to us, if at all. Therefore, there exists substantial doubt about our ability to continue as a going concern. The financial statements included in this prospectus do not include any adjustments related to the recoverability of assets that might be necessary despite this uncertainty.

Our pipeline of CAR T therapies is being developed under exclusive licenses from several world class research institutions. Our strategy is to license these technologies, support preclinical and clinical research activities by our partners and transferdevelop thethese underlyingproduct technologycandidates through to ourpotential or our contract manufacturer’s cell processing facility in order to conduct our own clinical trials.approval.

WeIn partnership with COH, we are developing CAR T therapy for solid tumors in partnership with COH targeting IL13Rα2 (MB-101). In addition, we have partnered with Nationwide for a herpes simplex virus type 1 (“HSV-1”) oncolytic virus (MB-108) in order to enhance the activity of MB-101 for the treatment of patients with high-grade malignant brain tumors. The Phase 1 clinical trial sponsored by COH for MB-101 (ClinicalTrials.gov Identifier: NCT02208362) has completed the treatment phase and patients continue to be assessed for long-term safety. A Phase 1 clinical trial sponsored by the University of Alabama at Birmingham (“UAB”) for MB-108 (ClinicalTrials.gov Identifier: NCT03657576) has also completed the treatment phase and patients continue to be assessed for long-term safety. In October 2023, we announced that the FDA accepted our IND application for the combination of MB-101 and MB-108 – which is referred to as MB-109 – for the treatment of patients with IL13Rα2+ relapsed or refractory glioblastoma (“GBM”) and high-grade astrocytoma. Pursuant to termination of the lease for our cell processing center in Worcester, MA, we are exploring with COH and Nationwide the possibility of initiating this clinical trial as an investigator-sponsored single-institution study at COH in the fourthsecond quarter of 2025.2026.

In October 2023, we received a safe-to-proceed “approval”letter from the FDA for our MB-109 IND application allowing us to initiate a Phase 1, open-label, non-randomized, multicenter study of MB-109 in patients with IL13Rα2+ recurrent GBM and high-grade astrocytoma. ThisThe Phase 1 clinical study wasunder designedthat toIND would evaluate the combination of CAR-T cells (MB-101) and the herpes simplex virus type 1 oncolytic virus (MB-108) in patients with IL13Rα2+ high-grade gliomas. As originally written and approved by the FDA, the study involved first a lead-in cohort, wherein patients would have beenbe treated with MB-101 alone without prior MB-108 administration. This lead-in cohort was required by the FDA due to the change in cell processing site from COH to Mustang Bio, which would have involved methodological changes as well as the obvious change in equipment and personnel. After successful confirmation of the safety profile of MB-101 alone, the study would have then investigatedinvestigate increasing doses of intratumorally administered MB-108 followed by dual intratumoral (ICT) and intraventricular (ICV) administration of MB-101.

On November 7, 2024, we announced that the FDA granted Orphan Drug Designation to Mustang for MB-108, aan herpes simplex virus type 1 (“HSV-1”) oncolytic virus, for the treatment of malignant glioma. On July 7, 2025, we announced that the FDA granted Orphan Drug Designation to Mustang for MB-101, IL13Ra2-targeted CAR T-cells, for the treatment of recurrent diffuse and anaplastic astrocytoma (astrocytomas) and glioblastoma. The Orphan Drug Designation provides certain incentives, such as tax credits toward the cost of clinical trials upon approval and prescription drug user fee waivers. If a product receives Orphan Drug Status from the FDA, that product is entitled to seven years of market exclusivity for the disease in which it has Orphan Drug designation, which is independent from intellectual property protection.

We are currently exploring with COH and Nationwide the possibility of conducting an investigator-sponsored single-institution trial under the COH IND to treat patients with IL13Rα2+ recurrent GBM and high-grade astrocytoma with MB-109 that could potentially be initiated in the fourthsecond quarter of 2025.2026. Because cell processing for MB-101 will revert back to COH – where the product continues to be manufactured today for other investigator-sponsored clinical trials being conducted by COH in malignant brain tumors (NCT04003649, NCT04661384, NCT04510051), we believe that it is reasonable to assume that the FDA will not require the aforementioned lead-in cohort. Should this, indeed, be the case, the first patient enrolled will receive the combination of MB-101 and MB-108, which will represent a considerable savings of time and money – as well as afford the potential benefit of both therapies to every patient treated on study.

Terminated Product CandidatesCandidate (GeneCAR-T Therapies and in vivo CAR-TTherapy)

The closing of the transactions described above occurred on February 21, 2025 (the “Closing”), with AbbVie’s issuance of an Acceptance Notice (as defined in the Sale/Surrender Agreement) to us stating that a Sufficient Percentage (as defined in the Sale/Surrender Agreement) of the FF&E items listed in the Sale/Surrender Agreement are present in the Premises and functional for their intended purpose without the need for repair or replacement. On February 25, 2025, as a result of the issuance of the Acceptance Notice, pursuant to the terms of the Escrow Agreement, the Escrow Agent released the Purchase Price to us. On February 27, 2025, we announced the relocation of our corporate headquarters to 95 Sawyer Road, Waltham, Massachusetts.Massachusetts 02453.

We have a limited operating history. We have focused primarily on organizing, acquiring, developing and securing our proprietary technology and identifying and obtaining preclinical data for various product candidates, with the goal of supporting regulatory approval for these product candidates. We have incurred losses since our inception in March 2015. Our net losses were $1.0$2.0 million and $0.2$0.9 million for the threesix months ended MarchJune 31,30, 2026 and 2025, respectively, and we had an accumulated deficit of $399.6$400.7 million as of MarchJune 31,30, 2026. We expect to continue to incur significant operating losses for the foreseeable future. We also do not anticipate that we will achieve profitability for a period of time after generating material revenues, if ever. If we are unable to generate revenues, we will not become profitable and may be unable to continue operations without continued funding.

Since our inception, we have incurred substantial operating losses and expect to continue to incur significant operating losses for the foreseeable future, and we may never become profitable. To date, we have not generated positive cash flows from operations and have funded our operations primarily with the proceeds from sales of equity securities. As of MarchJune 31,30, 2026, we had an accumulated deficit of $399.6$400.7 million, and cash and cash equivalents of $16.3$15.2 million.

Under the terms of the Second Amended and Restated Founders Agreement (the “Founders Agreement”), which became effective July 22, 2016,Agreement, Fortress will receive a grant of shares of our common stock equal to two and one-half percent (2.5%) of the gross amount of any equity or debt financing. Additionally, the Class A Preferred Stock, as a class, will receive an annual dividend on January 1st, payable in shares of common stock in an amount equal to two and one-half percent (2.5%) of our fully-diluted outstanding capital stock as of the business day immediately prior to January 1st of such year. Fortress currently owns all outstanding shares of Class A Preferred Stock. These share issuances to Fortress and any other holder of Class A Preferred Stock will dilute your holdings in our common stock and, if the value of our Company has not grown proportionately over the prior year, would result in a reduction in the value of your shares. The Founders Agreement has a term of 15 years and renews automatically for subsequent one-year periods unless terminated by Fortress or upon a Change in Control (as defined in the Founders Agreement).

Additionally, trade policies and geopolitical disputes and other international conflicts can result in tariffs, sanctions and other measures that restrict international trade, and can materially adversely affect our business, particularly if these measures occur in regions where drug products are manufactured or raw materials are sourced. For example, tensions between the United States and China have led to a series of tariffs being imposed by the United States on imports from Chinamainland mainland,China, as well as other business restrictions. Countries may also adopt other measures, such as controls on imports or exports of goods, technology or data, that could adversely impact our operations and supply chain. As these tensions continue to rise, more targeted approaches by the U.S. or Chinese governments on certain products, industries or companies could significantly impact our development and commercialization efforts. The U.S. government may impose additional or higher tariffs, sanctions or other trade restrictions on goods imported from China and other countries which could increase the cost of goods needed to commercialize any products for which we obtain marketing authorization and continue development of our product candidates. Further, such actions by the U.S. could result in retaliatory action by those countries which could impact our ability to profitably commercialize any products for which we obtain marketing authorization in those jurisdictions. As a result, our business, operations, and financial condition could be materially harmed.

Our common stock is listed on the Nasdaq Capital Market under the symbol “MBIO.” The Nasdaq Capital Market requires that listed companies satisfy continued listing standards to maintain their listing. We are currently not in compliance with certain standards for continued listing on the Nasdaq Capital Market, namely, Nasdaq Listing Rule 5550(a)(2), which sets forth the minimum bid price requirement for continued listing on the Nasdaq Capital Market (the “Bid Price Rule”)., and as described below, we may not be in compliance with the newly adopted minimum Market Value of Listed Securities requirement, if and when such rule becomes effective.

On April 15, 2026, we received a notice (the “Letter”) from the Staff of Nasdaq’s Listing Qualifications Department (the “Staff”) of Nasdaq indicating that the bid price of our common stock had closed below $1.00 for 30 consecutive business days and, as a result, we were not in compliance with the Bid Price Rule. PursuantThe toLetter Nasdaqhas Listingno Ruleimmediate 5810(c)(3)(A),effect we have been afforded a 180-calendar day grace period, or until October 12, 2026, to regain compliance withon the Bid Price Rule, which necessitates a closing bid pricelisting of atthe leastCompany’s $1.00Common perStock shareon for a minimum of ten consecutive business days (but generally not more than 20 consecutive business days) by October 12, 2026.Nasdaq.

There can be no assurance that we will be able to regain compliance with Nasdaq’s continued listing rules. If we are unable to regain compliance, we may be delisted from Nasdaq.Nasdaq, and in the case of the MVLS Requirement, if and when it becomes effective, any such suspension and delisting could occur immediately and without a compliance period. In the event we are delisted from Nasdaq, there can be no assurance that our common stock will be eligible for trading on another stock exchange or quotation on an over-the-counter market. If we are not able to obtain a listing on another stock exchange or quotation service for our common stock, it may be extremely difficult or impossible for stockholders to sell their shares. Additionally, if we are delisted from Nasdaq, but obtain a substitute listing or quotation service for our common stock, it will likely be on a market with less liquidityliquidity, and our common stock may therefore experience potentially more price volatility than it has historically experienced on Nasdaq. Stockholders may not be able to sell their shares of common stock on any such substitute market in the quantities, at the times, or at the prices that could potentially be available on a more liquid trading market. As a result of these factors, if our common stock is delisted from Nasdaq, the value and liquidity of our common stock would likely be adversely affected. A delisting of our common stock from Nasdaq could also adversely affect our ability to obtain financing for our operations and/or result in a loss of confidence by investors, employees and/or business partners.

You should read the following discussion and analysis of our financial condition and results of operations in conjunction with our financial statements and the related notes included elsewhere in this Form 10-Q. Our financial statements have been prepared in accordance with U.S. GAAP. The following discussion and analysis contains forward-looking statements within the meaning of Section 27A of the Securities Act of 1933, as amended (the “Securities Act”), and Section 21E of the Securities Exchange Act of 1934, as amended (the “Exchange Act”), which are often indicated by terms such as “anticipate,” “believe,” “could,” “estimate,” “expect,” “goal,” “intend,” “look forward to,” “may,” “plan,” “potential,” “predict,” “project,” “should,” “will,” “would” and similar expressions, include, but are not limited to, any statements relating to our growth strategy and product development programs, including the Company’s expectations with respect to the consummation of the sale of its manufacturing facility, the timing of and our ability to make regulatory filings such as Investigational New Drug (“IND”) applications and other applications and to obtain regulatory approvals for our product candidates, statements concerning the potential of therapies and product candidates, and any other statements that are not historical facts. All forward-looking statements included in this document are based on information available to us on the date hereof, and we assume no obligation to update any such forward-looking statements. Our business and financial performance are subject to substantial risks and uncertainties. Actual results could differ materially from those projected in the forward-looking statements. In evaluating our business, you should carefully consider the information set forth under Part II, Item 1A “Risk Factors” herein.

In partnership with COH, we are developing CAR T therapy for solid tumors targeting IL13Rα2 (MB-101). In addition, we have partnered with Nationwide for a herpes simplex virus type 1 (“HSV-1”) oncolytic virus (MB-108) in order to enhance the activity of MB-101 for the treatment of patients with high-grade malignant brain tumors. The Phase 1 clinical trial sponsored by COH for MB-101 (ClinicalTrials.gov Identifier: NCT02208362) has completed the treatment phase and patients continue to be assessed for long-term safety. A Phase 1 clinical trial sponsored by the University of Alabama at Birmingham (“UAB”) for MB-108 (ClinicalTrials.gov Identifier: NCT03657576) has also completed the treatment phase and patients continue to be assessed for long-term safety. In October 2023, we announced that the FDA accepted our IND application for the combination of MB-101 and MB-108 – which is referred to as MB-109 – for the treatment of patients with IL13Rα2+ relapsed or refractory glioblastoma (“GBM”) and high-grade astrocytoma. Pursuant to termination of the lease for our cell processing center in Worcester, MA, weWe are exploring with COH and Nationwide the possibility of initiating thisthe MB-109 clinical trial for GBM and high-grade astrocytoma as an investigator-sponsored single-institution study at COH in the thirdfourth quarter of 2026.

We are currently exploring with COH and Nationwide the possibility of conducting an investigator-sponsored single-institution trial under the COH IND to treat patients with IL13Rα2+ recurrent GBM and high-grade astrocytoma with MB-109 that could potentially be initiated in the thirdfourth quarter of 2026. Because cell processing for MB-101 will revert back to COH after the termination of the lease for the cell processing center – where the product continues to be manufactured today for other investigator-sponsored clinical trials being conducted by COH in malignant brain tumors (ClinicalTrials.gov Identifiers: NCT04003649, NCT04661384, NCT04510051), we believe that it is reasonable to assume that the FDA will not require a lead-in cohort, wherein a cohort of patients would have to be treated with MB-101 alone prior to treatment of subsequent cohorts with the combination of MB-108 followed by MB-101. Should this, indeed, be the case, the first patient enrolled will receive combination therapy, which will represent a considerable savings of time and money – as well as afford the potential benefit of both therapies to every patient treated on study.

During the threesix months ended MarchJune 31,30, 2026, there were no new accounting pronouncements or updates to recently issued accounting pronouncements disclosed in the 2025 Form 10-K that are expected to materially affect our present or future financial statements.

Comparison of the Three Months Ended MarchJune 31,30, 2026 and 2025

For the three months ended MarchJune 31,30, 2026 and 2025, research and development expenses were approximately $0.2 million and $(1.0)$0.1 million, respectively. The increase of approximately $1.1$0.1 million is primarily attributed to $0.7a million$52,000 increase in personnel-related expenses and $51,000 of non-repeat savings recognized from the settlement of aged payables and $0.4 million non-repeat gain fromin the termination of the Plantation Street Facility lease that occurred during the firstsecond quarter of 2025.

For the three months ended MarchJune 31,30, 2026, and 2025, general and administrative expenses were $0.9 million and $1.2$0.8 million, respectively. The decreaseincrease of approximately $0.3$0.1 million is primarily attributed to a $0.2 million decreaseincrease in non-cash stock-based compensationpersonnel-related expenses, primarilyoffset related to the equity fee to Fortress, andby a $0.1 million decrease in outsideprofessional serviceservice-related costs, primarily related to financing activity that occurred in the first quarter of 2025.expenses.

For the three months ended MarchJune 31,30, 2026, and 2025, other income was $0.1 million and $0.1 million, respectively, all of which is related to interest income.

We have incurred substantial operating losses and expect to continue to incur significant operating losses for the foreseeable future and may never become profitable. To date, we have funded our operations primarily with the proceeds from various public and private offerings of our equity securities. As of MarchJune 31,30, 2026, we had an accumulated deficit of $399.6$400.7 million and cash and cash equivalents of $16.3$15.2 million.

During the three and six months ended MarchJune 31,30, 2026, there were no material changes in our contractual obligations and commitments, as described in our 2025 Form 10-K.

Cash Flows for the ThreeSix Months Ended MarchJune 31,30, 2026 and 2025

Net cash used in operating activities was $1.0$2.0 million for the threesix months ended MarchJune 31,30, 2026, compared to $1.4$2.7 million for the threesix months ended MarchJune 31,30, 2025.

Net cash used in operating activities for the threesix months ended MarchJune 31,30, 2026, was primarily due to approximately $1.0$2.0 million in net loss during the quarter.year.

Net cash used in operating activities for the threesix months ended MarchJune 31,30, 2025, was primarily due to approximately $0.2$0.9 million in net loss, $1.1$1.8 million change in operating assets and liabilities, inclusive of approximately $0.8 million of savings from the settlement of payables, and $0.4 million gain on the termination of the Plantation Street Facility lease, partially offset by $0.3 million of non-cash items, primarily related to the $0.2 million equity fee to Fortress for financing activity.

During the threesix months ended MarchJune 31,30, 2026, no cash was used in or provided by investing activities.

For the threesix months ended MarchJune 31,30, 2025, net cash provided by investing activities was $1.2 million which primarily reflects the proceeds from the sale of equipment to AbbVie.

Net cash providedused byin financing activities was $7.6approximately $0.1 million during the threesix months ended MarchJune 31,30, 2025,2026, primarily reflecting proceedsoffering fromcosts therelated February 2025 Equity Offering andto the ATM Agreement.