Cabaletta Bio Reports Fourth Quarter and Full Year 2021 Financial Results and Provides Business Update DesCAARTes trial progressing in cohort A5 with presentation of DSG3-CAART clinical and translational data from cohort

Cabaletta Bio Reports Fourth Quarter and Full Year 2021 Financial Results and Provides Business Update

DesCAARTes trial progressing in cohort A5 with presentation

of DSG3-CAART clinical and translational data from cohorts A3 and A4 and 28-day safety data for cohort A5 expected at upcoming scientific meetings in mid-2022

MuSK-CAART Investigational New Drug (IND) application cleared and Fast Track Designation granted by the U.S. Food and Drug

Administration (FDA); planning to initiate first-in-human trial in 2022

Ended 2021 with $122.2 million in cash on hand to fund operations through 3Q 2023

PHILADELPHIA, March 17, 2022 Cabaletta Bio, Inc. (Nasdaq: CABA), a clinical-stage biotechnology company focused on the

discovery and development of targeted cell therapies for patients with autoimmune diseases, today reported financial results for the fourth quarter and full year ended December 31, 2021, and provided a business update.

We are encouraged by early data from the DesCAARTes trial in patients with mucosal

pemphigus vulgaris, including the dose-dependent increase in persistence seen in cohort A3 relative to the two low dose cohorts throughout the 28 days following DSG3-CAART infusion and the absence of dose limiting toxicities observed through cohort

A4 as well as continued investigator engagement and patient interest. We look forward to reporting DSG3-CAART clinical and translational data from the middle dose cohorts A3 and A4 along with 28-day safety

data from cohort A5 at scientific meetings in mid-2022, said Steven Nichtberger, M.D., Chief Executive Officer and Co-founder of Cabaletta. Learnings from

the DesCAARTes trial have provided platform-based insights for our growing autoimmune-focused pipeline, including the

MusCAARTes trial for patients with MuSK-associated myasthenia gravis. MuSK-CAART was recently granted Fast Track Designation by the FDA to improve activities of daily living and muscle

strength in patients with MuSK-associated myasthenia gravis, and with our now-cleared IND application, we plan to initiate the MusCAARTes trial in

2022 as we continue to advance our mission of delivering deep, durable, and potentially curative, responses for patients with autoimmune diseases.

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 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.

PLA2R-CAART: Phospholipase A2 receptor (PLA2R) chimeric autoantibody receptor T (PLA2R-CAART) cells as a potential

treatment for patients with PLA2R-associated membranous nephropathy.

Corporate Highlights

Fourth Quarter and Full Year 2021 Financial Results

The Company expects that its cash and cash equivalents as of December 31, 2021, will enable it to fund its operating plan through the third quarter of

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, in combination with Cabaletta Bio s proprietary technology, has advanced a growing pipeline that currently includes potential treatments for patients with mucosal

pemphigus vulgaris, MuSK-associated myasthenia gravis, PLA2R-associated membranous nephropathy, mucocutaneous pemphigus vulgaris and hemophilia A with FVIII alloantibodies. Cabaletta Bio s headquarters are located in Philadelphia, PA. For more

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 expectations regarding: Cabaletta s ability to grow its autoimmune-focused pipeline; the progress and results of its DesCAARTes 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; the expected timing and

significance around the announcement of 28-day safety for cohort A5 and biologic activity data for cohorts A3 and A4 in mid-2022; the expected timing and significance

around additional clinical data updates from the DesCAARTes trial at scientific meetings throughout 2022 and 2023; the expectation that Cabaletta may improve outcomes for patients suffering

from mPV; the ability of Oxford

Biomedica to supply Cabaletta with a sufficient quantity and/or quality of lentiviral vector; expectations regarding the intended incentives conferred by Fast Track Designation for MuSK-CAART to

improve activities of daily living and muscle strength in patients with MuSK antibody-positive myasthenia gravis; the expectation that Cabaletta Bio may improve outcomes for patients suffering from MuSK MG; plans to initiate patient dosing in an

open-label Phase 1 clinical trial to evaluate MuSK-CAART safety and tolerability in MuSK MG patients in 2022; Cabaletta s ability to enroll the requisite number of patients, dose each dosing cohort in the intended manner, and progress the

MusCAARTes trial; the ability of MuSK-CAART to target B cells that differentiate into antibody secreting cells, which produce autoantibodies against muscle-specific kinase; the ability

of WuXi Advanced Therapies to supply sufficient quality and quantity of MuSK-CAART for the planned MusCAARTes trial; Cabaletta s plans to advance development of its preclinical

pipeline; the effectiveness and timing of product candidates that Cabaletta may develop, including in collaboration with academic partners; 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 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; the impact of COVID-19 on the timing, progress, interpretability of data, and results of ongoing or planned preclinical and clinical trials; 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 2023.

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: the risk that

signs of biologic activity may not inform long-term results; Cabaletta s ability to demonstrate sufficient evidence of safety, efficacy and tolerability in its preclinical and 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 the impact of public health epidemics, such as the ongoing COVID-19 pandemic, affecting countries or regions in which we have operations or do business; Cabaletta s ability to retain and recognize the intended incentives conferred by Orphan Drug Designation and Fast

Track Designation for DSG3-CAART for improving healing of mucosal blisters in patients with mucosal pemphigus vulgaris; Cabaletta s ability to retain and recognize the intended incentives conferred by Fast Track Designation for MuSK-CAART to

improve activities of daily living and muscle strength in patients with MuSK antibody-positive myasthenia gravis; Cabaletta s ability to demonstrate sufficient evidence of safety, efficacy and tolerability in its preclinical and clinical trials

of DSG3-CAART and MuSK-CAART; risks related to fostering and maintaining successful relationships with Cabaletta s manufacturing partners; 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; the risk that any one or more of Cabaletta s product candidates will not be successfully developed and 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.