Cabaletta Bio Reports Second Quarter 2024 Financial Results and Provides Business Update Nine patients enrolled as of

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

Nine patients enrolled as of August 5, 2024 across the RESET clinical

development program, including four since EULAR in June, with 22 U.S. clinical sites now enrolling

clinical data from the RESET-Myositis and RESET-SLE trials as well as initial clinical data

from the RESET-SSc and RESET-MG trials anticipated in 2H24

Initial clinical and translational data from each of the first patients in the RESET-Myositis and

RESET-SLE trials presented at EULAR in June 2024

An LN patient with very

active, refractory disease dosed with CABA-201 in late June experienced a protocol-defined dose-limiting toxicity of Grade 4 ICANS, which resolved rapidly following standard management; the independent data

monitoring committee recommended the study to proceed as designed, without delay, at the current dose

Lonza and Cellares agreements support progression into next stage of manufacturing strategy to support expansion of clinical supply while preparing to efficiently scale commercial supply for CABA-201

Cash, cash equivalents and short-term investments total $203.2 million as of June 30, 2024, expected to support

operations into the first half of 2026

PHILADELPHIA, Aug. 8, 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 second quarter ended June 30, 2024, and

provided a business update.

We have seen increased enrollment and additional clinical sites open since presenting positive initial clinical and

translational data for the first two patients dosed with CABA-201 at the EULAR 2024 Congress in June. We look forward to sharing additional clinical data on CABA-201 in

the second half of this year, said Steven Nichtberger, M.D., Chief Executive Officer of Cabaletta. In addition, we have recently advanced our manufacturing strategy for CABA-201 through a new CDMO

agreement with Lonza and by expanding our existing fully automated manufacturing collaboration with Cellares. We have also added Sarah Yuan, Ph.D., as our Chief Technology Officer. Sarah brings substantial cell therapy development and commercial

launch experience, including at bluebird bio and 2seventy bio, where she was instrumental in the regulatory approval process for Abecma and two other cell therapy medicines. With the

momentum and milestones achieved in the second quarter and recent period, we believe we are well positioned to realize our vision of developing and launching the first curative targeted cell therapy for patients with autoimmune diseases.

Recent 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 where B cells contribute to the initiation and/or maintenance

Rheumatology Portfolio

Dermatology Portfolio

External Scientific Presentations and Publications

Chimeric AutoAntibody Receptor T (CAART) cells Strategy

Manufacturing Leadership and Strategy Updates

The Company expects that its cash, cash equivalents and short-term

investments as of June 30, 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 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 within five disease-specific company sponsored INDs including myositis (idiopathic inflammatory myopathy, or IIM), systemic lupus

erythematosus (SLE), systemic sclerosis (SSc), generalized myasthenia gravis (gMG), and pemphigus vulgaris (PV; a sub-study to evaluate CABA-201 without

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 myositis, systemic lupus

erythematosus, systemic sclerosis, 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 business plans and objectives as a whole; Cabaletta s ability to realize its vision of launching the first curative targeted cell therapy for patients with autoimmune diseases; Cabaletta s ability

to successfully complete research and further development and commercialization of its drug candidates in current or future indications; the uncertainties inherent in clinical testing and accruing patients for clinical trials; the timing and results

of Cabaletta s clinical trials, as well as its ability to conduct and complete clinical trials; expectation that clinical results will support CABA-201 s safety and activity profile; statements

regarding the expectations of trial modifications and prophylactic measures, continued trial operations; statements regarding the timing of regulatory filings and interactions with regulatory authorities, including such authorities review of

safety information from Cabaletta s ongoing clinical trials; Cabaletta s ability to retain and recognize and its expectations around the intended incentives conferred by Fast Track Designation for

CABA-201 for the treatment of 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 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 ability to accelerate

its pipeline, develop meaningful therapies for patients and leverage its research and translational insights and its expanding manufacturing partnerships; Cabaletta s ability to execute its manufacturing strategy to enable expansion of clinical

supply and efficiently scale commercial supply for CABA-201; Cabaletta s planned additional clinical data read-out for patients with myositis and SLE treated with CABA-201; Cabaletta s planned initial clinical data read-outs for patients with SSc and gMG treated with CABA-201 or otherwise; Cabaletta s ability to increase

enrollment from its rapidly expanding clinical network in the RESET clinical program; 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 that modifications to trial design or approach may not have the intended benefits and that the

trial design may need to be further modified; 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

SELECTED FINANCIAL DATA

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

Statements of Operations

Selected Balance Sheet Data

Chief Financial Officer