Cabaletta Bio Reports Second Quarter 2021 Financial Results and Provides Business Update Company continues to make progress on the DesCAARTes trial for DSG3-CAART; expects to report second and third cohort safety data in

Cabaletta Bio Reports Second Quarter 2021 Financial Results and Provides Business Update

Company continues to make progress on the DesCAARTes trial for DSG3-CAART;

expects to report second and third cohort safety data in 3Q21 and 4Q21, respectively, and data on target engagement 3 to 6 months after each completed cohort

Investigational New Drug (IND) application submission to U.S. Food and Drug Administration (FDA) for MuSK-CAART expected in 2H21 and pre-IND meeting request submitted to FDA for PLA2R-CAART

PHILADELPHIA, August 5,

2021 Cabaletta Bio, Inc. (Nasdaq: CABA), a clinical-stage biotechnology company focused on the discovery and development of engineered T cell therapies for patients with B cell-mediated autoimmune diseases, today reported financial

results for the second quarter ended June 30, 2021, and provided a business update.

During the quarter, we did not observe any clinically

relevant adverse events in the first, low-dose patient cohort of the DesCAARTes clinical trial for DSG3-CAART, our lead clinical product candidate for

the treatment of patients with mucosal-dominant pemphigus vulgaris. We remain well-positioned to achieve multiple near-term clinical milestones for this program, including our plan to report safety data from the higher dose second and third patient

cohorts in the third and fourth quarters of 2021, respectively, as well as target engagement data 3 to 6 months after each cohort is completed. said Steven Nichtberger, M.D., Chief Executive Officer and

Co-founder of Cabaletta. Additionally, we remain on track to submit an IND to the FDA for MuSK-CAART, our lead preclinical product candidate, and we expect to conduct a

pre-IND meeting with the FDA to discuss the development path for PLA2R-CAART in the second half of 2021.

Autoimmune Disease-Focused Pipeline Highlights and Anticipated Upcoming Milestones

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

Specific Kinase (MuSK) chimeric autoantibody receptor T (MuSK-CAART) cells as a potential treatment for patients with MuSK-associated myasthenia gravis.

Phospholipase A2 receptor (PLA2R) chimeric autoantibody receptor T (PLA2R-CAART) cells as a potential treatment for patients with PLA2R-associated membranous nephropathy.

Corporate Highlights

Upcoming Events in the Third Quarter of 2021

Second Quarter 2021 Financial Results

The Company expects that its cash, cash equivalents and investments as of June 30, 2021, will enable it to fund its operating plan through at least the

fourth quarter of 2022.

Cabaletta Bio is a clinical-stage biotechnology company focused on the discovery and development of engineered T cell therapies, and exploring their potential

to provide a deep and durable, perhaps curative, treatment for patients with B cell-mediated autoimmune diseases. The Cabaletta Approach to selective B cell Ablation (CABA ) platform, in

combination with Cabaletta s proprietary technology, utilizes Chimeric AutoAntibody Receptor (CAAR) T cells that are designed to selectively bind and eliminate only specific autoantibody-producing B cells while sparing normal antibody-producing

B cells, which are essential for human health. The Company s lead product candidate, DSG3-CAART, is being evaluated in the DesCAARTes Phase 1 clinical trial as a potential treatment for

patients with mucosal pemphigus vulgaris, a prototypical B cell-mediated autoimmune disease. The FDA granted Fast Track Designation for DSG3-CAART in May 2020. For more information about the

DesCAARTes Phase 1 clinical trial, please see www.clinicaltrials.gov. The Company s lead preclinical product candidate, MuSK-CAART, is in

IND-enabling studies and is designed as a potential treatment for patients with MuSK-associated myasthenia gravis. For more information, visit www.cabalettabio.com.

Forward-Looking Statements

This press release contains

forward-looking statements of Cabaletta within the meaning of the Private Securities Litigation Reform Act of 1995, as amended, including without limitation, express or implied statements regarding expectations regarding: the progress

and results of its DesCAARTes Phase 1 trial, including Cabaletta s ability to enroll the requisite number of patients, progress of the trial, results and expected timing to report

additional data for the second and third cohorts in the third and fourth quarters of 2021, respectively, in addition to target engagement data 3 to 6 months after dosing of each cohort is completed; the expectation that Cabaletta may improve

outcomes for patients suffering from mPV; the effectiveness and timing of product candidates that Cabaletta may develop, including in collaboration with academic partners; the safety, efficacy and tolerability of DSG3-CAART for the treatment of mPV;

the progress of its MuSK-CAART program, including the completion and expected results of its ongoing IND-enabling studies and plans to submit an IND application or equivalent regulatory filing for MuSK-CAART

in the second half of 2021; Cabaletta s plans to conduct a pre-IND meeting with the FDA for PLA2R-CAART in the second half of 2021; presentation of additional data at upcoming scientific conferences,

and other preclinical data; expectations regarding the design, implementation, timing and success of its current and planned clinical trials and the successful completion of nonclinical studies; planned potential timing and advancement of its

preclinical studies and clinical trials and related regulatory submissions; ability to replicate results achieved in preclinical studies or clinical trials in any future studies or trials; ability to continue its growth and realize the anticipated

contribution of the members of its board of directors and executives to its operations and progress; expectations of the potential impact of COVID-19 on strategy, future operations, and the timing of its

clinical trials, including the potential impacts on enrollment and initiation of its DesCAARTes Phase 1 trial; statements regarding regulatory filings regarding its development programs; use

of capital, expenses, future accumulated deficit and other financial results in the future; and ability to fund operations through the fourth quarter of 2022.

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 the impact of COVID-19 affecting countries or regions in which we have operations or do business, including potential negative impacts on our employees,

customers, supply chain and production as well as global economies and financial markets; risks related to Cabaletta s ability to protect and maintain its intellectual property position; Cabaletta s ability to demonstrate sufficient

evidence of safety, efficacy and tolerability in its clinical trials of DSG3-CAART; 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 Cabaletta s ability to protect and maintain its intellectual property position; uncertainties related to the initiation and conduct of studies and other development requirements for its product candidates; and

the risk that the 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.