Adicet Bio, Inc.

Data highlights as of the August 28, 2026 cut-off date were as follows:

•

22 patients (16 LN and 6 extra renal SLE) were evaluated with follow-up ranging from 6-21 months.

•

Efficacy endpoints. Prula-cel treatment yielded high rates of immunosuppressant-free responses in a heavily pretreated population. Patients had a mean baseline of Systemic Lupus Erythematosus Disease Activity Index 2000 (SLEDAI-2K) of 13 and those with LN had mean urine protein-to-creatinine ratio (UPCR) of 2.8, and all had received at least three prior therapies (71% received four or more). At the 12-month mark, 50% of evaluable lupus nephritis patients achieved a complete renal response (CRR) and 54% of evaluable patients achieved DORIS remission. All 12-month responses were ongoing at 12 to 21 months of follow-up, except 1 patient with UPCR 0.65 g/g who remains off immunosuppressants. Reductions in mean SLEDAI-2K and Physician’s Global Assessment (PGA) were rapid and sustained, consistent with autologous alpha beta CD19 CAR-T therapies, and 85% of patients with 12-month follow-up achieved a PGA score below 0.5.

•

Safety Profile. As of August 28, 2026, prula-cel was generally well tolerated and showed a favorable safety profile appropriate for outpatient dosing. Across the 24 safety-evaluable patients dosed with prula-cel, there was no cytokine release syndrome (CRS) greater than Grade 2. Grade 1 or 2 CRS occurred in 25% of patients. There were no dose-limiting toxicities (DLTs), no immune effector cell-associated hemophagocytic lymphohistiocytosis-like syndrome (IEC-HS), and no Immune Effector Cell-Associated Neurotoxicity Syndrome (ICANS). Infections were reported in 54% of patients, with Grade 3 or higher in 8.3%. There were no cases of graft vs host disease (GvHD) observed. Per alignment with the U.S. Food and Drug Administration (FDA), this profile supports outpatient administration.

•

Immunosuppression and steroids. All patients discontinued immunosuppressants, and all but one tapered background steroids to 5 mg or less of prednisone equivalent.

•

Immune reset. Multiple independent biomarkers provided evidence of an immune reset. All efficacy evaluable patients (22 of 22) achieved undetectable CD19+ B cells, followed by naïve-dominant B-cell reconstitution. Reductions in anti-dsDNA antibodies were observed in 91% (10 of 11) of baseline-positive patients, and 90% (9 of 10) of patients with low baseline complement demonstrated complement recovery.

The Company approached the FDA regarding a pivotal study in lupus nephritis and aligned on a single-arm study in lupus nephritis patients with inadequate response to at least two immunosuppressants. The study is expected to enroll a double digit number of patients and the primary efficacy endpoint will be complete renal response at 12 months. The Company plans to initiate start-up activities for a pivotal study in LN in the fourth quarter of 2026.

The high DORIS remission rate observed to date may support the potential inclusion of lupus patients without nephritis in the single arm pivotal study, subject to regulatory alignment. The company plans to discuss with the FDA such potential expansion of the pivotal study to include lupus without nephritis in the fourth quarter of 2026.

There are approximately 35,000 LN patients and 35,000 patients with non-renal SLE who have organ/life threatening disease in the U.S. alone. Based on prula-cel enrollment track record to date and the level of interest expressed by patients and investigators in prula-cel, Adicet expects rapid enrollment to the pivotal study.

Anticipated milestones for prula-cel include:

•

Fourth quarter of 2026: Initiate pivotal start up activities and align with FDA on the pivotal study population, including potential inclusion of SLE