Adicet Bio Announces Positive Safety and Efficacy Data from Prula-cel (formerly ADI-001) Study in Patients with Systemic Lupus Erythematosus with or without Lupus Nephritis[...]

Adicet Bio Announces Positive Safety and Efficacy Data from Prula-cel (formerly ADI-001) Study in Patients with Systemic Lupus Erythematosus with or without Lupus Nephritis

- Prula-cel shown to be generally well tolerated with no CRS greater than Grade 2 and no IEC-HS or ICANS -

-At 12-months, 54% of evaluable patients achieved DORIS remission and 50% of patients achieved CRR-

-All patients discontinued immunosuppressants -

- All but one patient tapered background steroids to ≤5 mg prednisone equivalent per day-

-Rapid reductions in SLEDAI-2K and PGA scores, consistent with autologous alpha beta CAR-T cell therapies-

-Plan to initiate pivotal lupus nephritis trial start-up activities in 4Q/2026; high DORIS remission rate may support expansion of pivotal study to include lupus without nephritis based on regulatory precedent-

-Company to host investor webcast at 8:00am ET today-

REDWOOD CITY, Calif. - September 28, 2026 - Adicet Bio, Inc. (Nasdaq: ACET), a clinical-stage biotechnology company discovering and developing allogeneic gamma delta CAR-T cell and in vivo CAR-T therapies for autoimmune diseases, hematologic malignancies and solid tumors, today announced safety and efficacy data from the Phase 1 study evaluating prulacabtagene leucel (prula-cel) as a potential treatment for patients with systemic lupus erythematosus (SLE) with or without lupus nephritis (LN). The data cut as of August 28, 2026 includes 22 efficacy evaluable patients (16 LN patients and 6 extra-renal SLE patients). All patients have follow-up of at least 6 months, and 13 patients have at least 12 months of follow-up. Based on these findings, the Company plans to initiate start-up activities for a pivotal study in LN in the fourth quarter of 2026. Given the high Definition of Remission in Systemic lupus (DORIS) remission rate observed in the study, the pivotal study may expand to include lupus patients without nephritis.

"We are excited to report clinical data for prula-cel reinforcing its potential to deliver meaningful, lasting remission after a single treatment for patients with SLE, including those with lupus nephritis," said Lloyd Klickstein, M.D., Ph.D., Interim Chief Medical Officer and a Member of the Board of Directors. "We observed complete renal responses and DORIS remissions after a single dose of prula-cel in patients who had failed multiple prior therapies. Notably, these remissions were achieved off immunosuppression and were accompanied by biological evidence of an immune reset. In a disease where chronic therapy with limited efficacy and significant tolerability and safety considerations remains the standard of care, the prospect of durable, treatment-free remission after a single treatment could be transformative for individuals living with lupus."

"Today's results mark an exciting step forward for Adicet and for lupus patients with or without nephritis. The data suggests prula-cel has the potential to offer lupus patients a highly differentiated treatment option: a single dose, off-the-shelf therapy, with a favorable safety profile, that may lead to immunosuppressant free remission," said Chen Schor, President and Chief Executive Officer of Adicet Bio "Importantly, the compelling efficacy data observed to date has been accompanied by a generally favorable safety profile with no cases of IEC-HS, no ICANS and no CRS beyond Grade 2 reported in the study. Combined with the FDA's support of outpatient administration of prula-cel, and the scalability of our off-the-shelf manufacturing, these findings support the potential of prula-cel to redefine the treatment expectations for patients living with systemic lupus erythematosus with or without lupus nephritis. We look forward to progressing towards a potentially pivotal study by the end of 2026."

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

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:

For more information about the Phase 1 study, please visit: Study Details | NCT06375993 | A Phase 1 Study of Prulacabtagene Leucel (Prula-cel, Formerly ADI-001) in Autoimmune Disease | ClinicalTrials.gov

Webcast/Conference Call Information Adicet will host a webcast presentation on Monday, September 28, 2026 at 8:00am ET. The live webcast of the presentation can be accessed by registering via this link or under "Presentations & Events" in the investors section of the Company's website at https://www.adicetbio.com. An archived replay will be available for 30 days following the presentation. The archived webcast will be available on the Company's website beginning approximately two hours after the event.

About Prulacabtagene leucel (prula-cel)

Prula-cel is an investigational allogeneic gamma delta chimeric antigen receptor (CAR) T cell therapy targeting B-cells via an anti-CD20 CAR. ADI-001 was granted Fast Track Designation by the U.S. Food and Drug Administration (FDA) for the potential treatment of relapsed/refractory class III or class IV lupus nephritis (LN), refractory systemic lupus erythematosus (SLE) with extrarenal involvement and systemic sclerosis (SSc).

About Adicet Bio, Inc.

Adicet Bio, Inc. is a clinical-stage biotechnology company discovering and developing a broad pipeline of allogeneic gamma delta T cell therapies, engineered with chimeric antigen receptors (CARs), alongside differentiated in vivo CAR-T therapies with the potential to redefine treatment across autoimmune diseases, hematologic malignancies and solid tumors. For more information, please visit our website at https://www.adicetbio.com.