Cabaletta Bio Announces FDA Granted Orphan Drug Designation to CABA-201 for Treatment of Myositis PHILADELPHIA

Cabaletta Bio Announces FDA Granted Orphan Drug Designation to

CABA-201 for Treatment of Myositis

PHILADELPHIA, Feb. 1, 2024 Cabaletta Bio, Inc. (Nasdaq: CABA), a

clinical-stage biotechnology company focused on developing and launching the first curative targeted cell therapies for patients with autoimmune diseases, today announced that the U.S. Food and Drug Administration (FDA) has granted Orphan Drug

Designation (ODD) to CABA-201, a 4-1BB-containing fully human CD19-CAR T cell

investigational therapy, for the treatment of idiopathic inflammatory myopathies (IIM, or myositis). CABA-201 is in development as a potential treatment for autoimmune diseases driven by B cells. Four RESET (REstoring SElf-Tolerance) Phase 1/2 trials are advancing for the evaluation of CABA-201 across multiple autoimmune conditions, including the Phase 1/2

RESET-Myositis trial.

Myositis, believed to be driven by B cells, is a severe and

potentially fatal autoimmune disease for which no curative therapy exists. Current treatment options provide modest efficacy, with a significant portion of diagnosed patients having an inadequate response to treatment, thus, there is a clear need

for innovative medicines that can meaningfully change the treatment paradigm, said David J. Chang, M.D., Chief Medical Officer of Cabaletta. CABA-201 is designed to deeply and transiently deplete

CD19-positive B cells, which may enable an immune system reset, and has the potential to deliver durable remission off therapy in patients diagnosed with myositis and other autoimmune diseases where B cells play a role. Orphan Drug Designation is an

important recognition for investigational therapies for rare diseases and provides us with potentially valuable benefits as we seek to make a difference in the lives of patients and develop the first targeted, and potentially curative, cell therapy

for patients with autoimmune diseases.

The FDA grants Orphan Drug Designation to drugs or biologics intended to treat or prevent rare diseases or

conditions that affect fewer than 200,000 individuals in the United States. This designation qualifies Cabaletta for certain incentives, which may include partial tax credit for clinical trial expenditures, waived user fees and potential eligibility

for seven years of marketing exclusivity.

About the RESET-Myositis Trial

The RESET-Myositis trial is a Phase 1/2 open-label study of

CABA-201 in subjects with active idiopathic inflammatory myopathy (IIM, or myositis), including the subtypes of dermatomyositis (DM), anti-synthetase syndrome (ASyS) and immune-mediated necrotizing myopathy

(IMNM). Subjects will receive a one-time infusion of CABA-201 at a dose of 1 x 106 cells/kg, preceded by a standard

preconditioning regimen of fludarabine and cyclophosphamide. Key inclusion criteria include patients between ages 18 to 65 (inclusive), evidence of active disease and disease activity despite prior or current treatment with standard of care

treatments. Key exclusion criteria include cancer-associated myositis, significant lung or cardiac impairment, treatment with a B cell depleting agent within the prior approximately six months or treatment with a biologic agent within the prior

approximately three months. As part of Cabaletta s CARTA (Chimeric Antigen Receptor T cells for Autoimmunity) strategy, this trial is intended to evaluate the potential ability of CABA-201 to transiently,

but fully, eliminate B cells, potentially enabling durable remissions via a reset of the immune system.

CABA-201 is designed to deeply and transiently deplete CD19-positive B cells following a

one-time infusion, which may enable an immune system reset with the potential for durable remission off therapy in patients with autoimmune diseases. To date, Cabaletta has received clearance from

the FDA for Investigational New Drug (IND) applications for CABA-201 in multiple autoimmune conditions including systemic lupus erythematosus (SLE), myositis, systemic sclerosis (SSc) and generalized

myasthenia gravis (gMG). Cabaletta is conducting four Phase 1/2 clinical trials with a total of nine cohorts that can advance simultaneously, employing a similar parallel cohort design and starting dose of 1 x 106 cells/kg without a dose escalation requirement.

Myositis refers to a group of autoimmune diseases characterized by inflammation and muscle weakness. In some cases, myositis may also affect other organs and

systems in the body, such as the lungs, heart, or skin. Myositis is classified into several subtypes based on the underlying immune mechanisms and clinical characteristics. Although the pathogenesis of myositis is not well understood, there are

several subtypes thought to be driven by B cells, including dermatomyositis (DM), anti-synthetase syndrome (ASyS) and immune-mediated necrotizing myopathy (IMNM). These three subtypes impact approximately 66,000 patients in the US alone, and

typically affect middle-aged individuals, particularly women. All three subtypes can lead to severe functional impairment and may be life-threatening. Current treatment typically involves medications to suppress the immune system and/or chronic

intensive therapies such as intravenous immunoglobulin, or IVIg. Despite these therapies, a significant portion of myositis patients have disease that remains refractory to existing medications.

Cabaletta Bio (Nasdaq: CABA) is a

clinical-stage biotechnology company focused on the discovery and development of engineered T cell therapies that have the potential to provide a deep and durable, perhaps curative, treatment for patients with autoimmune diseases. The CABA platform encompasses two strategies: the CARTA (chimeric antigen receptor T cells for autoimmunity) strategy, with CABA-201, a 4-1BB-containing fully human CD19-CAR T, as the lead product candidate being evaluated in the RESET (REstoring SElf-Tolerance) clinical trials in systemic lupus erythematosus, myositis, systemic sclerosis and generalized myasthenia gravis, and the CAART (chimeric autoantibody receptor T cells)

strategy, with multiple clinical-stage candidates, including DSG3-CAART for mucosal pemphigus vulgaris and MuSK-CAART for MuSK myasthenia gravis. The expanding CABA platform is designed to

develop potentially curative therapies that offer deep and durable responses for patients with a broad range of autoimmune diseases. Cabaletta Bio s headquarters and labs are located in Philadelphia, PA.

Forward-Looking Statements

This press release contains

forward-looking statements of Cabaletta Bio within the meaning of the Private Securities Litigation Reform Act of 1995, as amended, including without limitation, express or implied statements regarding: Cabaletta s ability to retain

and recognize and its expectations around the intended incentives conferred by Orphan Drug Designation for CABA-201 for the treatment of idiopathic inflammatory myopathies; Cabaletta s ability to retain

and recognize the intended incentives conferred by Fast Track Designations for CABA-201 in multiple autoimmune diseases; Cabaletta s expectations around the potential success and therapeutic benefits of CABA-201, including its belief that CABA-201 may enable an immune

system reset and provide deep and durable responses in patients across an increasing number of autoimmune diseases; Cabaletta s belief that it is making meaningful progress toward the

development and potential launch of the first targeted, and perhaps curative, cellular therapies for patients with autoimmune diseases; the Company s advancement of separate Phase 1/2 clinical trials of

CABA-201 in patients with SLE, myositis, SSc and gMG; Cabaletta s ability to leverage its research and translational insights; and the Company s expectations for the efficiency of the trial design

for its Phase 1/2 clinical trials of CABA-201.

Any forward-looking statements in this press release are based on

management s current expectations and beliefs of future events, and are subject to a number of risks and uncertainties that could cause actual results to differ materially and adversely from those set forth in or implied by such forward-looking

statements. These risks and uncertainties include, but are not limited to: risks related to regulatory filings and potential clearance; the risk that signs of biologic activity or persistence may not inform long-term results; Cabaletta s

ability to demonstrate sufficient evidence of safety, efficacy and tolerability in its preclinical studies and clinical trials of CABA-201; the risk that the results observed with the similarly-designed

construct employed in the recent academic publications, including due to the dosing regimen, are not indicative of the results we seek to achieve with CABA-201; risks related to clinical trial site activation

or enrollment rates that are lower than expected; risks related to unexpected safety or efficacy data observed during clinical studies; risks related to volatile market and economic conditions and public health crises; Cabaletta s ability to

retain and recognize the intended incentives conferred by Orphan Drug Designation and Fast Track Designation for its product candidates, as applicable; risks related to Cabaletta s ability to protect and maintain its intellectual property

position; risks related to fostering and maintaining successful relationships with Cabaletta s collaboration and manufacturing partners; uncertainties related to the initiation and conduct of studies and other development requirements for its

product candidates; the risk that any one or more of Cabaletta s product candidates will not be successfully developed and/or commercialized; and the risk that the initial or interim results of preclinical studies or clinical studies will not

be predictive of future results in connection with future studies. For a discussion of these and other risks and uncertainties, and other important factors, any of which could cause Cabaletta s actual results to differ from those contained in

the forward-looking statements, see the section entitled Risk Factors in Cabaletta s most recent annual report on Form 10-K as well as discussions of potential risks, uncertainties, and other

important factors in Cabaletta s other filings with the Securities and Exchange Commission. All information in this press release is as of the date of the release, and Cabaletta undertakes no duty to update this information unless required by

Chief Financial Officer

Stern Investor Relations, Inc.