Cabaletta Bio Reports Third Quarter 2021 Financial Results and Provides Business Update Dose dependent increase in DSG3-CAART persistence observed in the third dose cohort with 500 million DSG3-CAART cells relative to th

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

Dose dependent increase in DSG3-CAART persistence observed in the third dose cohort with 500 million DSG3-CAART cells relative

to the first two low dose cohorts in DesCAARTes Phase 1 clinical trial throughout the 28 days following infusion

No dose limiting toxicities (DLTs) or clinically relevant adverse events observed as of October 31, 2021, in the first three dose

Dosing initiated in fourth patient cohort at a dose of 2.5 billion DSG3-CAART cells. DesCAARTes trial advancing toward key milestones; top-line biologic activity data from first two low dose cohorts expected to be announced in 4Q21

Lead preclinical program, MuSK-CAART, Investigational New Drug (IND) submission on track for 4Q21; PLA2R-CAART preclinical data to be

presented at the American Society of Nephrology s Kidney Week that show potential as a precision therapy for patients with PLA2R membranous nephropathy

Ended the quarter with $119.3M in cash, extending the cash runway to fund operations through at least 1Q23

PHILADELPHIA, Nov. 1, 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 third quarter ended September 30, 2021, and provided a business update.

The DesCAARTes trial for DSG3-CAART for patients with mucosal-dominant pemphigus vulgaris has

demonstrated encouraging momentum, with continued strong patient enrollment as well as new site and investigator engagement. Dose dependent increases in DSG3-CAART persistence in the third cohort through 28 days following infusion have been

observed, as well as the continued absence of any DLTs or clinically relevant adverse events for the first three cohorts as of October 31, 2021. Our next anticipated data readout will include top-line

biologic activity data from the first two low dose cohorts, which we expect to announce in the fourth quarter of 2021. We look forward to continuing to generate data on potential biologic activity as we proceed to higher dosing cohorts, with the

goal of providing a targeted, highly effective, and potentially curative, therapy without generalized immunosuppression, said Steven Nichtberger, M.D., Chief Executive Officer and Co-founder of

Cabaletta. We are operating under a strengthened balance sheet as a result of $32 million in additional gross proceeds through our at-the-market

(ATM) equity offering program. In addition to advancing the DesCAARTes trial, we are also focused on growing our novel pipeline. To that end, we expect to progress our two lead preclinical

programs in the balance of the year with the submission of an IND to the FDA for MuSK-CAART being developed for patients with the MuSK form of myasthenia gravis, and a pre-IND interaction with the FDA to align

on a development path for PLA2R-CAART being developed for patients with PLA2R-associated membranous nephropathy.

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 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

Upcoming Events in the Fourth Quarter of 2021

Third Quarter 2021 Financial Results

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

the first quarter of 2023.

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 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 visit our website (DesCAARTes Phase 1 Trial). 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.

University of Pennsylvania Financial Disclosure

Dr. Payne is a University of Pennsylvania (Penn) faculty member, scientific collaborator, key advisor, and

co-founder of Cabaletta Bio. As such, she holds an equity stake in the Company, her laboratory at Penn receives sponsored research funding from Cabaletta Bio, and as an inventor of the licensed technology she

may receive additional future financial benefits under licenses granted by Penn to Cabaletta Bio. The University of Pennsylvania may also receive future financial benefit under licenses it has granted to Cabaletta Bio.

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: 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 the fourth dose cohort in the first quarter of 2022 and top-line

biologic activity data for the first two low dose cohorts in the fourth quarter of 2021; the expectation that Cabaletta may improve outcomes for patients suffering from 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 fourth quarter of 2021; Cabaletta s plans to conduct

a pre-IND interaction with the FDA for PLA2R-CAART in the fourth quarter of 2021; 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; the impact of COVID-19 on the timing, progress, interpretability of data, and results of ongoing or planned preclinical and clinical trials;

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 at least the first 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 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 Fast

Track Designation for DSG3-CAART for improving healing of mucosal blisters in patients with mucosal pemphigus vulgaris, respectively; 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 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.