Background
Phase 3, multicenter, open-label RCT (PRECISION-T; NCT05316701) of Orca-T — a precision-engineered allogeneic cell therapy product comprising purified donor regulatory T cells (Tregs), conventional T cells, and CD34+ stem cells from G-CSF–mobilized peripheral blood — used as the graft for myeloablative HLA-matched alloHSCT. The hypothesis was that Treg-enriched grafts permit durable engraftment with less immunosuppression and lower GVHD than conventional grafts with Tac/MTX. 187 adults with AML, ALL, or MDS undergoing first MAC alloHSCT from 8/8 HLA-matched donors were enrolled across U.S. centers.
Interventions and follow up
Arm A (Orca-T): Precision-engineered allogeneic graft (purified donor Tregs followed by CD34+ stem cells and conventional T-cell product) + single-agent tacrolimus only (no methotrexate)
Arm B (Control): Conventional unmanipulated G-CSF–mobilized PBSC graft + tacrolimus + methotrexate (Tac/MTX)
Conditioning: Myeloablative (TBI- or busulfan-based) in both arms
Primary endpoint: Moderate-to-severe chronic GVHD-free survival (cGFS) at 1 year
Median follow-up: ~12 months
Arm B (Control): Conventional unmanipulated G-CSF–mobilized PBSC graft + tacrolimus + methotrexate (Tac/MTX)
Conditioning: Myeloablative (TBI- or busulfan-based) in both arms
Primary endpoint: Moderate-to-severe chronic GVHD-free survival (cGFS) at 1 year
Median follow-up: ~12 months
Results
1-year cGFS (Orca-T vs Tac/MTX): 78.0% (95% CI 65–87) vs 38.4% (95% CI 26–51), HR 0.26, 95% CI 0.14–0.47, P<.001
1-year moderate–severe cGVHD: 12.6% vs 44.0%, Gray test P<.001
1-year GRFS: 63.1% vs 30.9%, P<.001
1-year non-relapse mortality (NRM): 3.4% vs 13.2%, P=.03
1-year overall survival: 93.9% vs 83.1%, P=.12 (not significant)
1-year moderate–severe cGVHD: 12.6% vs 44.0%, Gray test P<.001
1-year GRFS: 63.1% vs 30.9%, P<.001
1-year non-relapse mortality (NRM): 3.4% vs 13.2%, P=.03
1-year overall survival: 93.9% vs 83.1%, P=.12 (not significant)
Adverse events
Infectious/non-relapse mortality: Substantially fewer serious infectious complications and lower NRM (3.4% vs 13.2%) with Orca-T despite less immunosuppression
Engraftment/graft-related: Engraftment kinetics comparable between arms; no new safety signals attributable to the engineered graft
Engraftment/graft-related: Engraftment kinetics comparable between arms; no new safety signals attributable to the engineered graft
Conclusions
Orca-T met its primary endpoint of improved moderate-to-severe cGVHD-free survival versus standard Tac/MTX prophylaxis with conventional allografts in MAC HLA-matched alloHSCT, with significantly lower moderate–severe cGVHD, higher GRFS, and lower NRM, supporting Orca-T as a low-toxicity option for GVHD prophylaxis. Overall survival showed a numerical advantage that did not reach significance at the 1-year cut.
Key Limitations
Open-label design; primary outcome reported at 12 months (longer follow-up needed for late cGVHD, relapse, and OS). Restricted to 8/8 HLA-matched donors and MAC conditioning — generalizability to mismatched/haploidentical donors and RIC regimens not established. Orca-T requires centralized GMP manufacturing with ~72-hour vein-to-vein turnaround, posing logistical and access constraints. Comparator was Tac/MTX rather than the PTCy/Tac/MMF standard from BMT CTN 1703, leaving a head-to-head comparison with PTCy unanswered.
Clinical Context
First phase 3 RCT of an engineered T-cell graft product for GVHD prophylaxis. If approved, Orca-T would offer an alternative paradigm to pharmacologic prophylaxis (Tac/MTX, PTCy/Tac/MMF) by reshaping graft composition itself. Per ASTCT/BMT CTN 1703, PTCy/Tac/MMF is the current benchmark for matched-donor GVHD prophylaxis; a future RCT of Orca-T versus PTCy will be needed to position this product within practice. Published Blood 2026;147(11):1168–1177.