Cabaletta Bio Reports Fourth Quarter and Full-Year 2019 Financial Results and Provides Business Update DSG3-CAART IND clearance received in October 2019 and Orphan Drug Designation granted by the FDA for the treatment of

Cabaletta Bio Reports Fourth Quarter and Full-Year 2019 Financial Results and Provides Business Update

PHILADELPHIA, March 30, 2020 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, 2019.

2019 was a foundational year highlighted by the FDA clearance of the IND for our lead product candidate, DSG3-CAART, for patients with mucosal pemphigus

vulgaris (mPV). We obtained intellectual property protection and engaged with key partners to enable the rapid startup of this program, while at the same time making meaningful progress on our broader pipeline of additional programs,

said Steven Nichtberger, M.D., Chief Executive Officer and Co-founder of Cabaletta. With respect to the COVID-19 pandemic, our top priority is to ensure the

safety of our employees, collaborators, and others involved in our research and development efforts. As a result, we now anticipate a delay in reporting the acute safety data from the first cohort in the Phase 1 DesCAARTesTM trial. Once we have visibility on the impact of the pandemic, possibly during the second quarter of this year, we expect to issue revised guidance on our timeline for reporting the acute safety data

from this trial. The recent extension of our cash runway until at least the end of the third quarter of 2022, two quarters beyond previous guidance, provides additional flexibility for the business.

Recent Business 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

MuSK-CAART: Muscle Specific Kinase (MuSK) chimeric autoantibody receptor T cells as potential treatment for patients with MuSK-associated

Fourth Quarter and Full Year 2019 Financial Results

a clinical-stage biotechnology company focused on the discovery and development of engineered T cell therapies 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 in development as a potential treatment for a prototypical B cell-mediated autoimmune disease, mucosal pemphigus vulgaris. For more information, visit

www.cabalettabio.com.

Forward-Looking Statements

This press release contains forward-looking statements of Cabaletta Bio, Inc. ( Cabaletta or the Company ) within

the meaning of the Private Securities Litigation Reform Act of 1995. These forward-looking statements include, but are not limited to, express or implied statements regarding Cabaletta s beliefs and expectations regarding its: expectations of

the potential impact of COVID-19 on strategy, future operations, contract manufacturing agreements, collaboration, and the timing of its clinical trials, as well as potential impacts on enrollment and

initiation; plans to initiate patient dosing in an open-label Phase 1 clinical trial to evaluate DSG3-CAART safety and tolerability in relapsed/refractory mPV patients, including the potential timing of the initiation of patient dosing; potential

manner and timing of data readouts of its ongoing and planned clinical trials; plans to initiate IND-enabling studies of MuSK-CAART in 2020; 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 tolls 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 2019 financial results or 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 public health epidemics affecting countries or regions in which we have operations or do business, such as COVID-19, which has been labelled a pandemic by

the World Health Organization, 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 quarterly report on Form 10-Q 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.