Adicet's lupus CAR-T data lands and ACET drops 29.6%. Adicet Bio's allogeneic CAR-T improved lupus symptoms in an early trial and a pivotal study is planned, yet ACET shares closed down 29.60% at 6.35 on Sept. 28, 2026. Adicet Bio said its off-the-shelf CAR-T therapy improved symptoms in lupus patients in an early-stage study and that it plans to begin a pivotal trial soon, but its shares closed 29.60% lower at 6.35 on Sept. 28, 2026. Adicet Bio (ACET) told investors on Monday that its off-the-shelf CAR-T therapy improved symptoms in lupus patients in an early-stage study, and that it intends to move the program into a pivotal trial soon. The market responded by taking roughly a third off the company's value. Shares finished the session at 6.35, down 29.60% from the prior close of 9.02, with a day range of 6.25 to 7.96 as of the last trade at 20:00 GMT on Sept. 28, 2026. That gap between a readout described as promising and a share price that behaved as though the news were bad is the story. It is also a familiar one in cell therapy, where the bar for what counts as a surprise has moved faster than the bar for what counts as clinical progress. What the Bay Area company actually reported. Adicet, based in the Bay Area, is working on allogeneic CAR-T - cell therapy manufactured from donor cells and held ready for use, rather than made to order from each patient's own T cells. The autologous approach that produced the first approved CAR-T drugs in cancer requires collecting a patient's cells, engineering them, and shipping them back, a process that takes weeks and carries a manufacturing cost that has kept the therapies confined to severe disease. Lupus is the application that has reframed the field. Systemic lupus erythematosus is an autoimmune disease in which B cells drive damage across organs; the logic of CAR-T in this setting is that deeply depleting those B cells can reset the immune system rather than merely suppress it. If that works with an off-the-shelf product, the treatable population expands enormously, because an autoimmune indication involves far more patients than any single blood cancer and far fewer of them are willing to wait weeks for a bespoke manufacturing run. Adicet reported symptom improvement in an early-stage study and said a pivotal trial - the registrational study that a regulator would weigh for approval - is close. Those are the two facts the company put on the table, and both are, on their face, constructive. Why a 29.60% decline follows good-looking data. Early-stage autoimmune cell therapy readouts are small by design. A handful of patients, followed for a limited period, can show that symptoms improved without establishing how long the benefit lasts once the engineered cells clear, or how consistently B cells come back and whether disease returns with them. Durability is the variable that decides whether a lupus CAR-T is a one-time reset or an expensive temporary effect, and it is exactly the variable an early study is least equipped to answer. There is also the question of what was already in the price. A stock that closes at 9.02 ahead of a readout is carrying expectations, and in cell therapy those expectations have become specific: investors want to see drug-free remission, clean safety without the cytokine-release problems that complicated oncology CAR-T, and evidence that the allogeneic construct persists long enough to do its job. Data that meet the clinical definition of encouraging can still land below the commercial definition, and the reaction on Monday suggests the market read the numbers against the second standard. Competitive positioning compounds it. Adicet is not alone in pointing allogeneic cell therapy at autoimmune disease, and several groups - including companies pursuing autologous CAR-T and others working on bispecific antibodies that deplete B cells without any cell manufacturing at all - are chasing the same patients. A promising early result that does not clearly separate a platform from the pack is, in valuation terms, a neutral event dressed as a positive one. Endpoints News first reported the readout and the share reaction. The session around it offered no cover. A promising early result that does not clearly separate a platform from the pack is, in valuation terms, a neutral event dressed as a positive one. Monday was not a day when a small-cap biotech could hide inside a rising tape. The S&P 500, tracked by SPY, closed at $765.61, down 0.74% from the prior close of $771.35. The Nasdaq 100 proxy QQQ finished at $736.53, off 1.07% from $744.50, and DIA closed at $514.02, down 0.67%. Broad risk appetite was mildly negative across all three, which means essentially none of Adicet's decline can be attributed to the index backdrop; the move was company-specific, and the size of it - a fall of 2.67 from the prior close, or nearly 30% - puts it in single-stock event territory. For context on how leveraged the move is to sentiment rather than fundamentals: the intraday high of 7.96 was itself well below the prior close, meaning the stock never traded green after the news hit. Sellers set the tone from the open and the low of 6.25 came near the close. What determines whether this repairs. Three things are worth tracking from here. First, the design of the pivotal trial: its size, the primary endpoint, how long patients are followed, and whether the comparator is standard immunosuppression. A registrational study built around a durable, drug-free response is a different proposition from one built around a symptom score at a fixed timepoint. Second, extended follow-up from the early study. If the patients reported on Monday hold their improvement as months accumulate, the same dataset becomes a materially stronger asset without a single new patient being dosed. Third, the balance sheet. Pivotal trials in cell therapy are expensive, and a company whose shares have just fallen 29.60% faces a costlier financing market than it did on Friday. The gap between announcing a pivotal trial and funding one is where clinical-stage biotech stories are frequently decided, and it is the constraint that a promising readout does nothing by itself to relieve. Key facts. * ACET last close: 6.35, down 29.60% (as of 20:00 GMT, Sept. 28, 2026) * Prior close / day range: 9.02; range 6.25-7.96 * Clinical news: Off-the-shelf CAR-T improved symptoms in early-stage lupus study * Next step: Pivotal trial planned to begin soon Frequently asked questions. What did Adicet Bio report? Adicet Bio said its off-the-shelf, or allogeneic, CAR-T cell therapy improved symptoms in lupus patients in an early-stage clinical study. The Bay Area company also said it plans to begin a pivotal trial soon - the registrational study a regulator would weigh in an approval decision. The company did not release data beyond that early-stage readout. How far did ACET shares fall? ACET closed at 6.35 on Sept. 28, 2026, a decline of 29.60% from the previous close of 9.02, based on the last trade at 20:00 GMT. The stock traded between 6.25 and 7.96 during the session, meaning it never traded above the prior close after the readout was published. Why would a stock drop on positive trial data? Early-stage studies are small and short, so they can show symptom improvement without proving durability. If a stock has already priced in a strong result, data that merely meet expectations can trigger selling. Competitive dynamics matter too: a result that does not clearly differentiate a platform from rivals is effectively neutral for valuation. What is off-the-shelf CAR-T and why does it matter in lupus? Off-the-shelf, or allogeneic, CAR-T uses engineered cells made from donor material and held ready for use, rather than manufactured individually from each patient's own cells over several weeks. In lupus, an autoimmune disease with a large patient population, avoiding bespoke manufacturing is what could make cell therapy practical at scale. Was the decline related to the broader market? Only marginally. On the same session the S&P 500 proxy SPY closed at $765.61, down 0.74%, QQQ at $736.53, down 1.07%, and DIA at $514.02, down 0.67%. Those are modest declines, so almost all of Adicet's roughly 30% fall was company-specific rather than driven by the index backdrop. What should investors watch next? Three items: the design of the planned pivotal trial, including its size, endpoint and follow-up duration; extended follow-up data from the early-stage study showing whether symptom improvement persists; and how the company funds a pivotal program after a sharp share-price decline, since cell therapy trials are capital-intensive.

Adicet Bio to participate in fireside chat at Canaccord Genuity 46th Annual Growth Conference. July 22, 2026 | REDWOOD CITY, Calif.-(BUSINESS WIRE)-Adicet Bio, Inc. (Nasdaq: ACET), a clinical stage biotechnology company discovering and developing allogeneic gamma delta T cell therapies for autoimmune diseases and cancer, today announced that Chen Schor, President and Chief Executive Officer, will participate in a fireside chat at the Canaccord Genuity 46th Annual Growth Conference being held from August 11-13, 2026, in Boston. Details of the event are as follows: Date: Tuesday, August 11, 2026 Time: 10:30 a.m. ET The live audio webcast can be accessed on the Investors section of Adicet Bio's website at https://www.adicetbio.com. An archived replay will be available for 30 days following the presentation. About Adicet Bio, Inc. Adicet Bio, Inc. is a clinical stage biotechnology company discovering and developing allogeneic gamma delta T cell therapies for autoimmune diseases and cancer. Adicet is advancing a pipeline of "off-the-shelf" gamma delta T cells, engineered with chimeric antigen receptors (CARs), to facilitate durable activity in patients. For more information, please visit our website at https://www.adicetbio.com. Adicet Bio, Inc. Investor and Media Contacts Anne Bowdidge [email protected] Penelope Belnap Precision AQ [email protected]