Cabaletta Bio Reports First Quarter 2024 Financial Results and Provides Business Update No CRS or ICANS of any grade observed during the 28-day DLT observation window for either of the first patients dosed with CABA-201

Cabaletta Bio Reports First Quarter 2024 Financial Results and Provides Business Update

No CRS or ICANS of any grade observed during the 28-day DLT observation window for either of

the first patients dosed with CABA-201 in the RESET-Myositis and RESET-SLE trials

Initial clinical data from each of the first patients

in the RESET-Myositis and RESET-SLE trials to be presented at a satellite symposium at the EULAR 2024 Congress in June

Evaluating CABA-201 without preconditioning by initiation of the RESET-PV sub-study within the ongoing DesCAARTes trial in

PHILADELPHIA, May 15, 2024 Cabaletta Bio, Inc. (Nasdaq: CABA), a clinical-stage

biotechnology company focused on developing and launching the first curative targeted cell therapies designed specifically for patients with autoimmune diseases, today reported financial results for the first quarter ended March 31, 2024, and

provided a business update.

With no CRS or ICANS of any grade observed in either of the first patients from the RESET-Myositis and RESET-SLE trials, we look forward to presenting initial translational and clinical data from both patients during a satellite symposium at the EULAR 2024 Congress on June 14th, said Steven Nichtberger, M.D., Chief Executive Officer and Co-founder of Cabaletta. In addition to implementing our development path for CABA-201, we have made substantial progress on two innovations designed to optimize the patient and physician experience. First, we are evaluating CABA-201 without

preconditioning through the incorporation of the RESET-PV sub-study within the ongoing DesCAARTes trial in patients with pemphigus vulgaris, expanding CABA-201 development into dermatology. Second, we demonstrated the potential to eliminate the need for apheresis by using a blood draw to obtain the starting material for the

CABA-201 manufacturing process as presented at the ASGCT meeting. We are evaluating the opportunity to incorporate an apheresis-free process into our ongoing CABA-201

clinical program. By executing on our CABA-201 development strategy and integrating these types of innovations, we believe that we are well positioned to deliver on the full potential of the targeted cell

therapies that we are developing to provide durable, drug-free remissions for patients with a broad range of autoimmune diseases.

Operational Highlights and Upcoming Anticipated Milestones

Chimeric Antigen Receptor T cells for Autoimmunity (CARTA) Strategy

CABA-201: Autologous, engineered T cells designed with a chimeric antigen receptor containing a fully human CD19

binder and a 4-1BB co-stimulatory domain as a potential treatment for a broad range of autoimmune diseases across multiple therapeutic portfolios where B cells

contribute to the initiation and/or maintenance of disease.

Rheumatology Portfolio

Dermatology Portfolio

Past and Upcoming External Scientific Presentations

Chimeric AutoAntibody Receptor T (CAART) cells Strategy

Cabaletta plans to participate in the following upcoming investor conferences:

First Quarter 2024 Financial Results

The Company expects that its cash, cash equivalents

and short-term investments as of March 31, 2024, will enable it to fund its operating plan into the first half of 2026.

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 without chronic therapy in patients with autoimmune diseases.

Cabaletta is evaluating CABA-201 in multiple autoimmune conditions including systemic lupus erythematosus (SLE), myositis, systemic sclerosis (SSc), generalized myasthenia gravis (gMG) and pemphigus vulgaris

(PV). Cabaletta is conducting four Phase 1/2 RESET clinical trials evaluating CABA-201 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. CABA-201 is also being

evaluated in the absence of preconditioning in a separate sub-study within the DesCAARTes trial for patients with PV.

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 in the

RESET-PV sub-study within the DesCAARTes clinical

trial in pemphigus vulgaris, along with 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-associated 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 grow its autoimmune pipeline; Cabaletta s future plans and strategies for its CAAR T and CARTA technologies and the company s

business plans and objectives as a whole; statements regarding regulatory filings for its development programs, including the planned timing of such regulatory filings and potential review by regulatory authorities; Cabaletta s ability to

retain and recognize and its expectations around the intended incentives conferred by Fast Track Designation and/or Orphan Drug Designation for CABA-201 for the treatment of multiple autoimmune diseases;

Cabaletta s ability to retain and recognize and its expectations around the potential benefits and incentives provided by FDA s rare pediatric disease designation for CABA-201; 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 with the

potential for durable remission without chronic therapy in 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 and advancement of a RESET-PV sub-study within the ongoing DesCAARTes trial in PV, including updates related to status, safety data, or otherwise and the

expected timing of the related data read-outs; Cabaletta s plans to eliminate the need for apheresis by using a simpler collection process to obtain the starting material for the CABA-201 manufacturing

process; Cabaletta s ability to accelerate its pipeline, develop meaningful therapies for patients and leverage its research and translational insights; the Company s expectations for the efficiency of the trial design for its Phase 1/2

clinical trials of CABA-201 and for its RESET-PV sub-study within the ongoing DesCAARTes trial in PV; Cabaletta s planned

initial clinical data read-out at the EULAR 2024 Congress in June 2024 for patients with myositis and SLE treated with CABA-201; Cabaletta s additional planned

initial clinical data read-outs for patients with SSc and gMG treated with CABA-201 or otherwise; Cabaletta s advancement of the process to activate clinical trial sites and pursue patient enrollment for

the RESET-SLE trial in Canada; Cabaletta s planned assessment of its DesCAARTes and

MusCAARTes trials; use of capital, expense and other financial results in the future; ability to fund operations into the first half of 2026 and the anticipated contribution of the members

of Cabaletta s executives to the company s operations and progress.

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 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, delays in

enrollment generally or enrollment rates that are lower than expected; delays related to assessment of clinical trial results; 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 or other designations 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, including in

light of recent legislation; 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 law.

SELECTED FINANCIAL DATA

(unaudited; in thousands, except share and per share data)

Statements of Operations

Selected Balance Sheet Data

Chief Financial Officer

Stern Investor Relations, Inc.