Cabaletta Bio Reports First Quarter 2023 Financial Results and Provides Business Update IND application cleared within 30 days for clinical trial of CABA-201 in patients with LN and SLE and Fast Track Designation granted

Cabaletta Bio Reports First Quarter 2023 Financial Results and Provides Business Update

IND application cleared within 30 days for clinical trial of CABA-201 in patients with LN and

SLE and Fast Track Designation granted by the FDA for CABA-201 to deplete CD19-positive B cells and improve disease activity in patients with LN and SLE

Phase 1/2 trial planned to evaluate CABA-201 in six patients with active LN and six patients

with SLE without renal involvement in parallel cohorts at an initial dose of 1.0 x 106 cells/kg in each cohort

Invited, oral presentation on CD19-CAR T in SLE and poster presentations for CABA-201 and DSG3-CAART to be presented at the upcoming ASGCT 26th Annual Meeting

May 11, 2023 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

reported financial results for the first quarter ended March 31, 2023, and provided a business update.

The recent clearance of our first IND

application to evaluate CABA-201 in patients with LN and SLE occurring within six months of in-licensing of the CABA-201 binder,

as well as the subsequent Fast Track Designation to deplete CD19-positive B cells and improve disease activity in patients with LN and SLE granted by the FDA, underscore the continued ability of our team to rapidly and effectively execute. Since we

announced CABA-201 in October 2022, our clinical team has been working with sites across the US, including many where we have existing clinical trials actively enrolling for our CAART programs, in preparation

for the CABA-201 IND clearance to continue our efforts in ensuring a timely opening of sites for the initial CABA-201 clinical trial, said Steven Nichtberger,

M.D., Chief Executive Officer of Cabaletta. We believe that we are competitively positioned to rapidly advance CABA-201 to patients because we have a product candidate specifically designed for

autoimmune patients and engineered to potentially replicate the findings of recent academic studies coupled with an efficient clinical trial design. Clinical trial implementation is being facilitated by our uniquely experienced team with a track

record of successful execution in logistically complicated, interdisciplinary cell therapy studies with the goal of bringing the potential of CABA-201 closer to patients with autoimmune disease.

Recent Operational Highlights and Upcoming Anticipated Milestones

Chimeric Antigen Receptor T cells for Autoimmunity (CARTA) Strategy

CABA-201: Autologous, engineered T cells 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 where B cells contribute to the initiation and/or maintenance

Chimeric AutoAntibody Receptor T (CAART) cells Strategy

DSG3-CAART: Desmoglein 3 chimeric autoantibody receptor T (DSG3-CAART) cells as a potential treatment for patients with mucosal pemphigus vulgaris

MuSK-CAART: Muscle-specific kinase (MuSK) chimeric autoantibody receptor T (MuSK-CAART) cells as a potential treatment for patients with

MuSK-associated myasthenia gravis.

First Quarter 2023 Financial Results

The Company expects that its cash and cash equivalents as of March 31, 2023,

will enable it to fund its operating plan into the first quarter of 2025.

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 CD19-CAR T, as the

lead product candidate, 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 for patients with a broad range of autoimmune diseases. Cabaletta Bio s headquarters 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 its expectations regarding:

Cabaletta s ability to grow its autoimmune-focused pipeline; its plans around CABA-201, including its ability to enroll the requisite number of patients, dose each dosing cohort in the intended manner and

trial is planned in its Phase 1/2 clinical trial of CABA-201 as well as leverage the potential benefits from using the initial dose used in the September

2022 Nature Medicine publication; Cabaletta s ability to retain and recognize the intended incentives conferred from the Fast Track Designation for CABA-201; the company s business plans and

objectives; the progress and results of its DesCAARTes Phase 1 trial and MusCAARTes Phase 1 trial, including Cabaletta s

ability to enroll the requisite number of patients, dose each dosing cohort in the intended manner, and progress the trial; statements regarding anticipated significance of, and timing of release of, efficacy endpoints and tolerability data for CABA-201 and its safety and persistence data and combination sub-study cohort data for its DesCAARTes trial; statements regarding regulatory filings for its development

programs, including the planned timing of such regulatory filings and potential review by such regulatory authorities; the expectation that Cabaletta Bio may improve outcomes for patients suffering from SLE, mPV, MG, or other autoimmune diseases as

well as its expected therapeutic benefits; the ability to accelerate Cabaletta s pipeline and develop meaningful therapies for patients, including in collaboration with academic and industry partners and the ability to optimize such

collaborations on its development programs; use of capital, expenses, future accumulated deficit and other financial results in the future; availability of funding for existing programs; and ability to fund operations into the first quarter of 2025.

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 DSG3-CAART, MuSK-CAART and CABA-201; the risk that the results observed with the similarly-designed construct employed in the recent Nature Medicine

publication, 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; risks related to the impact of public health epidemics affecting countries or regions in which

Cabaletta has operations or does business, such as COVID-19; 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 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.