Disclaimer The following presentation, including any printed or electronic copy of these slides, the talks given by the presenters, the information communicated during any delivery of the presentation and any question an

Corporate Presentation September 2023

Disclaimer The following presentation,

including any printed or electronic copy of these slides, the talks given by the presenters, the information communicated during any delivery of the presentation and any question and answer session and any document or material distributed at or in

connection with the presentation (collectively, the "Presentation") has been prepared by Cabaletta Bio, Inc. ("we," "us," "our," "Cabaletta" or the "Company") and is made for

informational purposes only. This Presentation does not purport to be a prospectus, to be complete or to contain all of the information you may desire. Statements contained herein are made as of the date of this Presentation unless stated otherwise,

and this Presentation shall not under any circumstances create an implication that the information contained herein is correct as of any time after such date or that information will be updated or revised to reflect information that subsequently

becomes available or changes occurring after the date hereof. This Presentation may contain "forward-looking statements" within the meaning of the Private Securities Litigation Reform Act of 1995 relating to our business, operations, and

financial conditions, and include, but are not limited to, express or implied statements regarding our current beliefs, expectations and assumptions regarding: our business, future plans and strategies for our CAAR T and CARTA technologies and

CABA platform; our ability to grow our autoimmune-focused pipeline; the ability to capitalize on and potential benefits resulting from the translational research partnership with Professor Georg Schett and the exclusive license agreement with

IASO Bio; our expectations around the potential success and therapeutic benefits of CABA-201, including our belief that CABA-201 may enable an "immune system reset" and provide deep and durable responses for patients with autoimmune

diseases; our plans for (i) a Phase 1/2 clinical trial of CABA-201 in patients with SLE, including our anticipated progress, clinical trial design, ability to leverage our experience in autoimmune cell therapy and lupus product development and (ii)

a Phase 1/2 clinical trial of CABA-201 in patients with myositis, including our anticipated progress, clinical trial design and ability to leverage our experience in autoimmune cell therapy; our planned initial clinical data read-out in the first

half of 2024 for patients treated with CABA-201; our ability to enroll the requisite number of patients, dose each dosing cohort in the intended manner, and advance the trial as planned in our Phase 1/2 clinical trials of CABA-201; the ability to

retain and recognize the intended incentives conferred by any Fast Track Designations for CABA-201; the timing any planned regulatory filings for our development programs; the progress and results of our DesCAARTes Phase 1 trial, including

the significance and impact around reported safety and clinical and translational data of cohorts from our DesCAARTes trial, and our ability to advance dose escalation and initiate combination cohorts and to optimize our targeted cell

therapy; our ability to implement a pre-treatment regimen, the outcomes of such pre-treatment regimen and the potential ability to enhance in vivo DSG3-CAART exposure; the therapeutic potential and clinical benefits of our product candidates; the

expectation that Cabaletta may improve outcomes for patients suffering from systemic lupus erythematosus, myositis, mucosal pemphigus vulgaris, myasthenia gravis, or other autoimmune diseases; our ability to escalate dosing as high as 15 billion

cells in cohort A6m, initiate dosing in a combination cohort or otherwise; our ability to evaluate, and the potential significance of, the relationship between DSG3-CAART persistence and potential clinical responses in patients with mPV; our ability

to safely retreat additional patients and whether we will continue to observe a lack of immune-mediated clearance of DSG3-CAART cells after retreatment and repeat dosing of patients; our ability to successfully complete our preclinical and clinical

studies for our product candidates, including our ability to enroll the requisite number of patients, dose each dosing cohort in the intended manner, and progress the trial; the ability of MuSK-CAART to target B cells that differentiate into

antibody secreting cells, which produce autoantibodies against muscle-specific kinase; our ability to obtain and maintain regulatory approval of our product candidates, including our expectations regarding the intended incentives conferred by and

ability to retain Orphan Drug Designation and Fast Track Designation for our product candidates, as applicable; the further expansion and development of our modular CABA platform across a range of autoimmune diseases; our ability to contract

with third-party suppliers and manufacturers, implement an enhanced manufacturing process and further develop our internal manufacturing strategy, capabilities and facilities; our potential commercial opportunities, including value and addressable

market, for our product candidates; our expectations regarding our use of capital and other financial results; and our ability to fund operations into the fourth quarter of 2025. Words such as, but not limited to, "look forward to,"

"believe," "expect," "anticipate," "estimate," "intend," "plan," "would," "should" and "could," and similar expressions or words, identify

forward-looking statements. Various risks, uncertainties and assumptions could cause actual results to differ materially from those anticipated or implied in our forward-looking statements. Such risks and uncertainties include, but are not limited

to, risks related to the success, cost, and timing of our product candidate development activities and preclinical studies and clinical trials, risks related to our ability to demonstrate sufficient evidence of safety, efficacy and tolerability in

our preclinical studies and clinical trials of CABA-201, DSG3-CAART and MuSK-CAART, the risk that the results observed with the similarly-designed construct, including, but not limited to, due to dosing regimen, are not indicative of the results we

seek to achieve with CABA-201, our plans to evaluate additional cohorts in the DesCAARTes trial, including a cohort implementing a pre-treatment regimen, the risk that signs of biologic activity or persistence may not inform long-term

results, the risk that persistence observed with effective CART-19 oncology studies in combination with lymphodepletion is not indicative of, or applicable to, clinical responses in patients with mPV, risks related to clinical trial site activation

or enrollment rates that are lower than expected, our ability to protect and maintain our intellectual property position, risks related to our relationships with third parties, uncertainties related to regulatory agencies' evaluation of

regulatory filings and other information related to our product candidates, our ability to retain and recognize the intended incentives conferred by any Orphan Drug Designations and Fast Track Designations, risks related to regulatory filings and

potential clearance, the risk that any one or more of our product candidates will not be successfully developed and commercialized, the risk that the results of preclinical studies or clinical studies will not be predictive of future results in

connection with future studies, and risks related to volatile market and economic conditions and public health crises. New risks and uncertainties may emerge from time to time, and it is not possible to predict all risks and uncertainties. Except as

required by applicable law, we do not plan to publicly update or revise any forward-looking statements contained herein, whether as a result of any new information, future events, changed circumstances or otherwise. Although we believe the

expectations reflected in such forward-looking statements are reasonable, we can give no assurance that such expectations will prove to be correct. Accordingly, you are cautioned not to place undue reliance on these forward-looking statements. No

representations or warranties (expressed or implied) are made about the accuracy of any such forward-looking statements. For a discussion of these and other risks and uncertainties, and other important factors, any of which could cause our actual

results to differ materially from those contained in the forward-looking statements, see the section entitled "Risk Factors" in our most recent annual report on Form 10-K, as well as discussions of potential risks, uncertainties, and other important

factors in our other and subsequent filings with the Securities and Exchange Commission. Certain information contained in this Presentation relates to or is based on studies, publications, surveys and other data obtained from third-party sources and

the Company's own internal estimates and research. While the Company believes these third-party sources to be reliable as of the date of this Presentation, it has not independently verified, and makes no representation as to the adequacy,

fairness, accuracy or completeness of, any information obtained from third-party sources. The Company is the owner of various trademarks, trade names and service marks. Certain other trademarks, trade names and service marks appearing in this

Presentation are the property of third parties. Solely for convenience, the trademarks and trade names in this Presentation are referred to without the and TM symbols, but such references should not be construed as any indicator that their

respective owners will not assert, to the fullest extent under applicable law, their rights thereto.

Develop and launch the first curative

targeted cellular therapies for patients with autoimmune diseases

Leveraging years of experience with

cellular therapy in autoimmunity to initiate CABA-201 clinical trials Cabaletta : Pursuing cures for a broad range of autoimmune diseases CARTA - Chimeric Antigen Receptor T cells for Autoimmunity; CAART - Chimeric AutoAntibody

Receptor T cells; IND - Investigational New Drug; SLE - Systemic lupus erythematosus; DM - Dermatomyositis; ASyS - Anti-synthetase syndrome; IMNM - Immune-mediated necrotizing myopathy; Flu - Fludarabine; Cy

- Cyclophosphamide Mackensen, Andreas, et al. "Anti-CD19 CAR T cell therapy for refractory systemic lupus erythematosus." Nature Medicine (2022): 1-9. M ller, Fabian, et al. "CD19-targeted CAR T cells in refractory antisynthetase

syndrome." The Lancet (2023). Dai, Zhenyu, et al. "Development and functional characterization of novel fully human anti CD19 CARs for T cell therapy." Journal of Cellular Physiology 236.8 (2021): 5832-5847. Assumes no dose-limiting

toxicities are observed in the cohort and uninterrupted enrollment occurs in the trials. Reported as of 2Q 2023 10-Q. Advancing myositis & SLE trials with efficient designs, including starting dose & parallel cohorts 1.0 x 106 cells/kg

initial dose of CABA-201 is identical to dose used in academic myositis and SLE studies1,2 Parallel cohorts with 6 patients each - Myositis study with 1) DM, 2) ASyS & 3) IMNM; SLE study with 1) LN & 2) Non-renal SLE CABA-201 has been

specifically engineered for patients with autoimmune diseases Fully human CD19 binder with data in ~20 oncology patients - clinical safety profile supporting further evaluation in autoimmunity Same 4-1BB costimulatory domain and similar CD19

binder affinity3 as used in the academic myositis and SLE studies1,2 Potential to cure a broad range of autoimmune diseases where B cells have a role initiating or maintaining disease Additional clinical data from academic institutions reinforcing

potential of CD19-CAR T in autoimmunity with early industry studies underway Opportunity to address unmet need in rheumatology as well as in other therapeutic areas, including neurology, nephrology & dermatology DesCAARTes trial of

DSG3-CAART in mucosal pemphigus vulgaris - IVIg / Flu / Cy cohort enrolling MusCAARTes trial in MuSK myasthenia gravis - leveraging insights from experience with DSG3-CAART CARTA Strategy | CABA-201 (4-1BB CD19-CAR T) to be

evaluated in parallel myositis & SLE Phase 1/2 studies CAART Strategy | DSG3-CAART & MuSK-CAART clinical studies evaluating combination regimens Initial CABA-201 3 mo. clinical efficacy & tolerability data expected by 1H244 | $176M cash5

with runway into 4Q25

One CABA platform, two

strategies to address autoimmune diseases Complementary strategies to optimize clinical outcomes using cellular therapies in autoimmune diseases Mackensen, Andreas, et al. "Anti-CD19 CAR T cell therapy for refractory systemic lupus erythematosus."

Nature Medicine (2022): 1-9. M ller, Fabian, et al. "CD19-targeted CAR T cells in refractory antisynthetase syndrome." The Lancet (2023). Ellebrecht, Christoph T., et al. "Reengineering chimeric antigen receptor T cells for targeted therapy of

autoimmune disease." Science 353.6295 (2016): 179-184. Fully Human Anti-CD19 Targeting Domain CARTA Chimeric Antigen Receptor T cells for Autoimmunity CAART Chimeric AutoAntibody Receptor T cells CABA-201 4-1BB Costimulatory Domain &

CD3-Zeta Signaling Domain DSG3-CAART Potential to reset the immune system' in patients with autoimmune diseases driven by B cells, through generalized transient B cell depletion and repopulation of healthy B cells1,2 In autoimmune

diseases with a limited number of well-defined pathogenic autoantibodies, permanent antigen-specific B cell depletion may provide an elegant biologic solution to disease3 Autoantigen Targeting Domain 4-1BB Costimulatory Domain & CD3-Zeta

Biologic opportunity for cure or

treatment may be possible in dozens of autoimmune diseases* CABA platform may apply across a range of autoimmune diseases Pemphigus Vulgaris1,2,3 Pemphigus Foliaceus1,2,3 Epidermolysis Bullosa Acquisita3 Bullous Pemphigoid1,2,3 Lupus

Nephritis3,4 Membranous Nephropathy1,2,3 Goodpasture's Syndrome1,2,3,4 Myasthenia Gravis1,2,3,5 Multiple Sclerosis6 Neuromyelitis Optica3 CIDP (Chronic Inflammatory Demyelinating Polyneuropathy)1.2 Anti-NMDAR Encephalitis3,6 Lambert-Eaton

Syndrome5 Systemic Lupus Erythematosus3,4,5,6 Rheumatoid Arthritis2,3,4 Myositis5 Systemic sclerosis6 ANCA-Associated Vasculitis3,4,5 Immune Thrombocytopenic Purpura3 Thrombotic Thrombocytopenic Purpura1,2,3 Antiphospholipid Syndrome4,5 Autoimmune

Hemolytic Anemia3 Type 1 Diabetes3,6 Graves' Disease3,5 Hashimoto's Disease5 Illustrative list of autoimmune diseases where B cells may play a role in initiating or maintaining disease, and where biologic opportunity for cure or

treatment with CAART or CARTA approach may be possible. Diseases in bold represent where clinical studies are underway or plan to be initiated by Cabaletta or by Professor Schett Koneczny, Inga. "Update on IgG4-mediated autoimmune diseases: new

insights and new family members." Autoimmunity Reviews (2020): 102646. Huijbers, Maartje G., et al. "IgG4-mediated autoimmune diseases: a niche of antibody-mediated disorders." Annals of the New York Academy of Sciences 1413.1 (2018): 92. Ludwig,

Ralf J., et al. "Mechanisms of autoantibody-induced pathology." Frontiers in immunology 8 (2017): 603. Suurmond, Jolien, and Betty Diamond. "Autoantibodies in systemic autoimmune diseases: specificity and pathogenicity." The Journal of clinical

investigation 125.6 (2015): 2194-2202. Xiao, Ze Xiu, Joseph S. Miller, and Song Guo Zheng. "An updated advance of autoantibodies in autoimmune diseases." Autoimmunity Reviews (2020): 102743. Hampe, Christiane S. "B cells in autoimmune diseases."

Scientifica 2012 (2012). Dermatology Nephrology Neurology Rheumatology Hematology Endocrinology

CABA Platform Indication

Program Discovery Preclinical Phase 1/2 Phase 2/3 CARTA Chimeric Antigen Receptor T cells for Autoimmunity Myositis (IIM, Idiopathic Inflammatory Myopathy)1 Dermatomyositis CABA-201 4-1BB CD19-CAR T Anti-Synthetase Syndrome Immune-Mediated

Necrotizing Myopathy CARTA Chimeric Antigen Receptor T cells for Autoimmunity Systemic Lupus Erythematous (SLE)1 Lupus Nephritis CABA-201 4-1BB CD19-CAR T Non-Renal SLE Multiple Undisclosed Indications CAART2 Chimeric AutoAntibody Receptor T cells

Mucosal Pemphigus Vulgaris DSG3-CAART3 MuSK Myasthenia Gravis MuSK-CAART3 Pipeline targeting autoimmune diseases where cure is possible CABA-201 is being evaluated in separate clinical trials for myositis and SLE. Additional CAART pipeline

candidates include PLA2R-CAART in preclinical stage for PLA2R membranous nephropathy, DSG3/1-CAART in discovery stage for mucocutaneous pemphigus vulgaris & 2 undisclosed targets in discovery stage. Currently being evaluated in a Phase 1 trial.

IND cleared IND cleared

Chimeric Antigen Receptor T Cells for

Autoimmunity CABA-201

Emerging clinical data with 4-1BB

CD19-CAR T1 in SLE - Systemic lupus erythematosus; SLEDAI-2K - Systemic Lupus Erythematosus Disease Activity Index 2000 The construct utilized in these studies has a similar design to CABA-201, sharing the 4-1BB costimulatory

domain, but is a different construct. Mackensen, Andreas, et al. "Anti-CD19 CAR T cell therapy for refractory systemic lupus erythematosus." Nature Medicine (2022): 1-9. Taubmann, J., et al. "OP0141 Long Term Safety and Efficacy Of CAR-T Cell

Treatment in Refractory Systemic Lupus Erythematosus-Data from the First Seven Patients." (2023): 93-94. M ller, Fabian, et al. "CD19-targeted CAR T cells in refractory antisynthetase syndrome." The Lancet (2023). Taubmann, Jule, et al. "Rescue

therapy of antisynthetase syndrome with CD19-targeted CAR-T-cells after failure of several B cell depleting antibodies." Rheumatology (Oxford, England) (2023): kead330. Pecher, Ann-Christin, et al. "CD19-Targeting CAR T Cells for Myositis and

Interstitial Lung Disease Associated With Antisynthetase Syndrome." JAMA 329.24 (2023): 2154-2162. Bergmann, Christina, et al. "AB0816 Treatment of a Patient with Severe Diffuse Systemic Sclerosis (Ssc) Using CD19-targeting CAR-T-cells." (2023):

1621-1621. 9 Promising clinical responses observed across several autoimmune diseases in academic CD19-CAR T trial Academic data: Immune system reset in autoimmune patients Robust improvement in clinical disease activity within 3 months of CD19-CAR

T treatment Rapid and deep CD19+ B cell depletion Return of healthy B cells within 7 months Favorable safety data with CD19-CAR T regimen Clinical SLE responses up to 24 mo with no relapses reported3 7 Systemic lupus erythematosus patients2,3 3

Myositis patients (anti-synthetase subtype)4-6 1 Systemic sclerosis patient7 SLE (N=5)2 SLEDAI-2K Published data as of Sept 5, 2023 100% of patients with objective clinical disease response Total improvement score Myositis (N=1)4

Cabaletta's CD19 binder with

similar in vitro & in vivo activity to FMC631,2 (binder used in academic studies3,4) CABA-201: CD19-targeting CAR T therapy for autoimmune diseases SLE - Systemic lupus erythematosus; IIT - Investigator-initiated trial; Flu/Cy

- Fludarabine/Cyclophosphamide; CRS - Cytokine release syndrome; ICANS - Immune effector cell-associated neurotoxicity syndrome Peng, Binghao J, et al. "Preclinical specificity and activity of CABA-201, a fully human 4-1BB

containing CD19 CAR T therapy for treatment-resistant autoimmune disease." Poster presented at: American Society Gene and Cell Therapy 26th Annual Meeting; 2023 May 19; Los Angeles, CA. Dai, Zhenyu, et al. "Development and functional

characterization of novel fully human anti CD19 chimeric antigen receptors for T cell therapy." Journal of Cellular Physiology 236.8 (2021): 5832-5847. Mackensen, Andreas, et al. "Anti-CD19 CAR T cell therapy for refractory systemic

lupus erythematosus." Nature Medicine (2022): 1-9. M ller, Fabian, et al. "CD19-targeted CAR T cells in refractory antisynthetase syndrome." The Lancet (2023). Evaluated as part of CT120, a dual-CD19xCD22 CAR T product candidate under

development by Nanjing IASO Biotherapeutics, Co., Ltd. (IASO Bio). Fully human anti-CD19 binder 4-1BB costimulatory domain CD3-Zeta signaling domain CABA-201 Similar in vitro & in vivo biologic activity to FMC631 Same co-stimulatory domain as

used in academic studies CD19-CAR Construct Clinical data reported by IASO using licensed CD19 binder in oncology5 Fully human binder Evaluated as dual-CAR combined with CD22 binder with standard Flu/Cy preconditioning Data reported in ~20 patients

to date B cell leukemia and lymphoma in IIT in China Safety data supports autoimmune development CABA-201 In vitro In vivo CABA-201 CD19 binder used in academic studies3,4