Orca Bio's Tregzi cut chronic graft versus host disease — a long term transplant complication where donor immune cells attack the recipient — at one year from 38% to 78% in a randomized trial, reshaping a decades old clinical decision every leukemia patient and oncologist faces.
On Tuesday the FDA approved a personalized T-cell therapy that materially lowered the risk of chronic graft-versus-host disease, the decades-long immune reaction where donor immune cells attack the patient's own body, for adults with certain blood cancers receiving matched-donor stem cell transplants. The decision gives leukemia patients and their oncologists a clinically serious counter-offer to an old trade-off: accept a potentially curative marrow transplant and risk years of immune damage, or skip transplant and accept the survival odds of chemotherapy alone.
The therapy, Tregzi and developed by Orca Bio, is approved for adults with acute myeloid leukemia, acute lymphoblastic leukemia, myelodysplastic syndromes, or a related overlap category who are undergoing matched-donor myeloablative allogeneic hematopoietic stem cell transplantation, a procedure that wipes out the patient's bone marrow with high-dose chemotherapy and reseeds it with donor cells. The matched-donor requirement, the exact HLA match tiers, and any restrictions on prior therapy should be confirmed against the FDA label before any precise eligibility language goes into copy.
Chronic graft-versus-host disease, the condition Tregzi targets, is what happens when the donor's immune cells, now living inside the patient, mistake the patient's skin, gut, liver, and lungs for foreign tissue. Acute GvHD can be treated with steroids. Chronic GvHD can linger for years, scarring lungs, hardening skin, drying eyes, and leaving patients on long courses of immunosuppressive drugs with their own infection and metabolic costs. For patients with curable leukemia, that risk has long been the main reason some oncologists and patients pause before agreeing to transplant.
Tregzi is built around a bet that adding highly purified regulatory T cells to the graft, alongside the standard hematopoietic stem and progenitor cells (HSPCs) and conventional T cells, can teach the new immune system to tolerate the patient's body. The active moiety the FDA named, "allogeneic regulatory T cell immunotherapy with HSPC and T cells-vldq," captures the three-part composition: donor-derived stem cells to rebuild the marrow, conventional T cells for the graft-versus-leukemia effect, and a deliberate oversupply of regulatory T cells to police the response.
The numbers come from Precision-T, a randomized, open-label, multicenter Phase 3 trial published in Blood in March 2026. Among 187 adults with a median age of 43.6, 78% of patients who received Tregzi plus single-agent tacrolimus were alive and free of chronic graft-versus-host disease at one year, compared with 38% of patients who received conventional transplant with tacrolimus and methotrexate. The Orca Bio press release reported that difference as a hazard ratio of 0.26, statistically significant; the exact p-value was redacted in the company's announcement, and the peer-reviewed Blood paper should be cited for the actual figure. The same trial showed grade 3 to 4 acute GvHD by day +180 of 6% in the Tregzi arm versus 10% in the control arm (hazard ratio 0.37, p = 0.044), and grade 3 or higher infections at one year of 44% versus 51%.
Those results do not mean chronic graft-versus-host disease has been eliminated. Tregzi patients still got chronic GvHD. They just got it far less often. For an oncologist discussing transplant with a 45-year-old with AML in first remission, the 78% versus 38% number is what restructures the conversation, because the alternative is not a guaranteed cure but a transplant complicated by years of immune damage, or no transplant at all and roughly 30% to 50% long-term survival from chemotherapy alone, depending on the disease.
The trial also has a frame the company has not centered. Precision-T's control arm used tacrolimus and methotrexate, the traditional matched-donor prophylaxis regimen. Post-transplant cyclophosphamide, or PTCy, has become a comparator that a 2023 New England Journal of Medicine study established as effective in matched-donor settings, and intermediate-dose PTCy for myeloablative HLA-haploidentical transplants has since shown comparable reductions in severe GvHD. The NMDP OPTIMIZE trial of PTCy in matched-donor transplant finished enrolling in 2025, and the read-out will eventually force a more honest head-to-head framing than Tregzi's existing 78% versus 38%. The point is not to diminish Precision-T. It is that the standard Tregzi beat is moving.
The economics remain genuinely open. Orca Bio set the wholesale acquisition cost at $428,000 per treatment course, a figure Reuters reported from comments by chief executive Nate Fernhoff. There is no ICER assessment, no published payer response, no ASP or net pricing curve, and the indication overlaps with diseases where transplant centers already have decades of experience with cheaper prophylaxis. Whether payers, transplant centers, and patients can absorb Tregzi at the announced price is the question that will decide whether the 78% figure shows up in real-world clinical decisions or stays a trial result.
Manufacturing is the second-order question. Tregzi is a personalized product: each dose is manufactured from the matched donor's cells, with a vein-to-vein time measured in days. Orca Bio announced a 100,000-square-foot cGMP facility at Sacramento Metro Air Park adjacent to Sacramento International Airport for cold-chain shipping, and added a Princeton, New Jersey manufacturing bridge roughly two weeks before approval to create a bicoastal production network. Orders are expected by the end of July. How many transplant centers Orca can reliably serve, and how the company handles scale-up without compromising the Treg-to-Tcon balance that anchors the mechanism, are the operational questions the next two quarters will answer.
Funding totals differ across the databases that track them, and any number cited should be attributed: PitchBook puts Orca Bio's total raised at $625 million, CBInsights at $443.3 million across seven rounds, and Tracxn at $300 million across two rounds, with a $250 million Series F on January 9, 2026 led by Lightspeed Venture Partners. The gap matters because a $625 million private round and a $300 million private round imply very different runway and pre-launch commercial posture, and the choice of source is a choice about which version of the company's pre-launch story the article tells.
What to watch next: whether transplant centers adopt Tregzi before payer coverage is fully settled, whether the OPTIMIZE PTCy readout narrows Tregzi's advantage, and whether the hard survival and quality-of-life deltas beyond one year hold when longer follow-up from Precision-T is published. The Tuesday approval is the regulatory fact. The clinical fact that matters for the next decade is whether the 78% number moves outside a Phase 3 cohort and into the routine conversation between a leukemia patient and their oncologist about whether to accept a transplant at all.