ASGCT 2026: AFTX-201: A Novel Investigational AAV Gene Therapy for the Treatment of BAG3-Associated Dilated Cardiomyopathy

Giri Murlidharan, Ph.D. Sr. Director, Head of Translational Biology 29th Annual Meeting of the American Society of Gene and Cell Therapy, Boston, Massachusetts May 14th, 2026 AFTX-201: A Novel Investigational AAV Gene Therapy for the Treatment of BAG3-Associated Dilated Cardiomyopathy 2 Disclosures ▪ I am an employee of Affinia Therapeutics Functional BAG3 protein Cardiac contractility Dilated heart Patient exercise capacity 59.7 50.3 67.6 32.9 64.3 3.6 0 10 20 30 40 50 60 70 80 LVEF % LVEDD mm NYHA Class I % ↓ ejection fraction ↑ heart dilation ↓ exercise capacity Low BAG3 associated with reduced cardiac contractility in Dilated Cardiomyopathy BAG3 mutation Martin et al., Nature Communications, 2021; Dominguez et al., JACC, 2018; Myers et al., JACC Basic Transl Sci., 2018; Ozes et al., P130, 2023 ASGCT Meeting; Kirk, JACC, 2023; LVEF: Left Ventricle Ejection Fraction; LVEDD: Left Ventricle End-Diastolic Diameter; NYHA: New York Heart Association BAG3 plays critical role in protein quality control & sarcomeric integrity Healthy Dilated LVEF% LVEDD mm NYHA Class I% No DCM BAG3 DCM Low BAG3 associated with ↓ Cardiac Contractility Increasing BAG3 expression (quartiles) Cardiomyocyte force generation Fmax (mN/mm2) 4 Left: Human iPSC-derived cardiomyocytes 96-well assay; 50K cells per well; 72h incubation; in duplicate Right: %Cardiomyocytes +ve for GFP in heart left ventricles after IV dose 3e13 vg/kg and 28-day in life in NHPs Engineered ATC-187 capsid was selected for AFTX-201 based on superior cardiomyocyte transduction vs. AAV9 5 BAG3 cKO+/- conditional haploinsufficiency mouse model of Dilated Cardiomyopathy recapitulates human disease BAG3 cKO+/- mouse model characterization at 10 weeks of age; ****P<0.0001 Myers J Cell Physiol. 2018 In BAG3 cKO+/- mice, the AFTX-201 MED of 9e11 vg/kg IV increases cardiac BAG3 protein and normalizes ejection fraction 8 weeks post-dose 6 AFTX-201 dose-ranging efficacy study in BAG3 cKO+/- mice dosed at 10 weeks of age with AFTX-201 9e11 vg/kg IV, or with vehicle compared to wild type mice (N=15/arm) with echocardiography 8 weeks post-dose AFTX-201-derived human BAG3 protein is increased in heart Wild type mice BAG3 cKO+/- mice, Vehicle-treated BAG3 cKO+/- mice, AFTX-201-treated AFTX-201 normalizes ejection fraction to wild type EF (%) Wild type mice BAG3 cKO+/- mice, Vehicle-treated BAG3 cKO+/- mice, AFTX-201-treated P = NS P <0.05 AFTX-201 dose at 10 weeks of age after phenotype confirmation Measure echocardiogram 8- weeks post-injection AFTX-201 is dosed post- phenotype confirmation in BAG3 cKO+/- mice In BAG3 cKO+/- mice, AFTX-201 also reverses the structural defects of the heart that are hallmark features of the disease 7 AFTX-201 normalizes Fractional Shortening (FS) to wild type AFTX-201 normalizes Left Ventricular Internal Diameter, systolic (LVIDs) to wild type AFTX-201 normalizes Posterior Wall Thickness, systolic (LVPWs) to wild type FS (%) LVIDs (mm) LVPW (mm) P = NS P <0.05 P = NS P <0.05 P = NS P <0.05 Wild type mice BAG3 cKO+/- mice, Vehicle-treated BAG3 cKO+/- mice, AFTX-201-treated AFTX-201 dose-ranging efficacy study in BAG3 cKO+/- mice dosed at 10 weeks of age with AFTX-201, 9e11 vg/kg IV, or with vehicle compared to wild type mice (N=15/arm) with echocardiography 8 weeks post-dose 8 In BAG3 cKO+/- mice, AFTX-201-derived BAG3 DNA, RNA, and protein are sustained through the end of the study which is representative of the lifespan of the mice AFTX-201 biodistribution and expression kinetics in BAG3 cKO+/- mice, 9.5e11 vg/kg IV, n=5 per group Dotted line in DNA and RNA graphs = Average background level across tested tissues from naïve BAG3 cKO+/- mice In NHPs, AFTX-201 shows safety advantages in dose-limiting systemic toxicities related to the AAV class Left: Adult Cyno NHPs treated with AFTX-201 IV, n=3 per dose level, 180-days in life Right Adult Cyno NHPs treated with AFTX-201 with HA tag IV (N=2), 28-day in life, 4x magnification 9 ✓ No liver enzyme excursions or complement-mediated toxicity seen Heart: >90% cells+ (HA tag for hBAG3) Liver: <15% cells+ (HA tag for hBAG3) ▪ Planned doses in the clinic are 5 – 10-fold lower than for conventional capsids ▪ No significant safety findings − No AFTX-201 related mortality or clinical sequelae − ALT and AST below upper limit of normal − No evidence of complement-mediated toxicity ▪ Compelling BAG3 pharmacodynamic measures in heart − % cells+ − DNA − RNA − Protein In NHPs, AFTX-201 shows no LFTs excursions, or evidence of complement-mediated toxicity without prophylactic immunosuppressants AFTX-201 IV dosing in NHPs, n=3 per dose-level, Data shown for 3-month in-life duration ULN=upper limit; LLN=lower limit; WNL= Within Normal Limits of normal published in Park et al. Lab Anim Res 2016: 32(2), 79-86 10 11 In a head-to-head study, AFTX-201 was efficacious in BAG3 cKO+/- mice at 9e11 vg/kg (MED), effect not seen with rh74-based construct AFTX-201 (HA-tagged) vs rh74 capsid comparison efficacy study in 10 WoA BAG3 cKO+/-; ****P<0.0001, ***P<0.001, **P<0.01, *P<0.05; MED: Minimum effective dose; similar results of superior therapeutic efficacy were seen in head-to-head study vs AAV9 12 Phase 1b/2 multicenter, open-label, dose-exploration and dose- expansion trial of AFTX-201 in adults with BAG3–associated DCM (UPBEAT © trial) Cohort 1 (Dose 1), n=3-5 Cohort 2 (Dose 2), n=3-5 Expansion Cohort 3 (Dose tbd), n=6-12 UPBEAT Study Design DSMB review 6-mo observational run-in DSMB review ▪ Background: • The UPBEAT © trial measures myocardial BAG3 restoration and cardiac functional outcomes following a single systemic dose of AFTX-201 • FDA IND and Health Canada CTA approvals have been obtained, multiple sites across US and Canada to support clinical development • Eligibility: • Male or female, 18-55 years of age with truncating BAG3 mutation, DCM with LVEF <45%, NYHA Class II or III heart failure symptoms • Primary Outcome Measures: • Safety and tolerability of AFTX-201 over 12 months post dose ▪ Secondary Outcome Measures: • Assessment of the extent of AFTX-201 transduction, myocardial BAG3 protein expression at baseline, 3 and 12 months • Cardiovascular function (LVEF, pVO2) and structure. Clinical features of heart failure including functional classification byNYHA class and quality of life over 12 months • Safety and tolerability of AFTX-201 over 60 months post dose UPBEAT© AFTX-201 clinical trial complete study design: Poster 2363 All outcomes compare pre-dose assessment to ongoing post-dose assessment https://clinicaltrials.gov/study/NCT07426419 13 AFTX-201: Summary ✓ Efficacy: increased BAG3 expression normalized DCM phenotype in BAG3 cKO+/- disease model – Minimum effective dose identified to be 9e11 vg/kg in BAG3 cKO+/- disease model ✓ Differentiation vs conventional capsids – Superior efficacy and pharmacodynamics with AFTX-201 (vs dose and cargo matched AAVrh74 and AAV9) ✓ Durability: Stable pharmacodynamics in BAG3 cKO+/- disease model – Up to study duration, 140 days, representing the model lifespan ✓ Nonhuman primate studies: – Dose-dependent increase in biodistribution and expression – Safety demonstrated through comprehensive toxicological evaluation in absence of prophylactic immunosuppression • No LFT elevation, complement activation or histopathological findings at proposed clinical doses ✓ Regulatory filings: – IND approved in January 2026, and Health Canada CTA approved March 2026 – Fast Track Designation by FDA ▪ UPBEAT© AFTX-201 clinical trial study design: Poster 2363 – Contact: [email protected]; NCT07426419 Acknowledgements – Mayara Ribeiro – Bryan Mastis – Kyle Chamberlain – Charles Gualtieri – Tyler Ironside – Cynthia Pryce – Elizabeth Scott – Nicholas Robinson – Emily Grandell – Amanda Berry – Paul Freeman – Matt Bennett – Shahrzad Parker – Matt Edwards – Anthony DeMarco – Ramin Kamran Sami Correspondence: ▪ Giri Murlidharan, Sr. Dir., Head of Translational biology [email protected] – John Reece-Hoyes – Roberto Calcedo – Sherry Cao – Charles F. Albright – Hideo Makimura – Laura K. Richman Affinia Therapeutics Team 15

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