Cabaletta Bio Reports Fourth Quarter and Full Year 2020 Financial Results and Provides a Business Update PHILADELPHIA

Cabaletta Bio Reports Fourth Quarter and Full Year 2020

Financial Results and Provides a Business Update

PHILADELPHIA, March 16, 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 announced financial results for the fourth quarter and full year ended December 31, 2020.

At the end of 2020, we achieved an important milestone when we dosed the first patient without any dose limiting toxicities in our Phase 1 clinical

trial for DSG3-CAART, our lead product candidate being developed for the treatment of patients with mucosal pemphigus vulgaris. This is the first time a highly targeted, antigen specific cell therapy has been dosed in a patient with an autoimmune

disease. We continue to expect to report acute safety data from the initial cohort in this study in the first half of 2021 followed by additional topline data on any completed dose cohorts throughout the second half of 2021, said Steven

Nichtberger, M.D., Chief Executive Officer and Co-founder of Cabaletta. We also continue to advance our pipeline, and as such, remain on track to submit the Investigational New Drug Application for

MuSK-CAART in the second half of 2021. To support this effort, we have secured a long-term commercial manufacturing partnership.

Disease-Focused Pipeline Highlights and Anticipated Upcoming Milestones

DSG3-CAART: Desmoglein 3 chimeric autoantibody receptor T (DSG3-CAART)

cells as potential treatment for patients with mucosal pemphigus vulgaris (mPV).

MuSK-CAART: Muscle Specific Kinase (MuSK) chimeric autoantibody receptor T (MuSK-CAART) cells as

potential treatment for patients with MuSK-associated myasthenia gravis.

Corporate Highlights

Fourth Quarter and Full Year 2020 Financial Results

The Company expects that its cash and cash equivalents and investments as of December 31, 2020 will enable it to fund its operating plan through at least

the third 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 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 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 beliefs and

expectations regarding its: expectations of the potential impact of COVID-19 on strategy, future operations, IND submissions, contract manufacturing agreements, collaboration, and the timing of its clinical

trials, as well as potential impacts on enrollment and initiation; DesCAARTesTM phase 1 clinical trial, including the progress, results and ability to enroll the requisite number of patients and

the results and expected timing to report clinical acute safety data from the initial cohort by the first half of 2021 and additional topline data on any completed dosing cohorts in the second half of 2021; 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; 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 and the potential to successfully maintain or secure the necessary cell processing capacity and supply for its product

candidates for clinical trials, including Cabaletta s planned development and timing of next generation T cell engineering tools and process advancement; 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; ability to optimize the impact of its collaborations on its

development programs; statements regarding the timing of 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 third 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; risks related to Cabaletta s relationship with third parties, including its licensors and licensees; risks related to the ability of its licensors to protect

and maintain their intellectual property position; 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 commercialized; 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.