Orca-T, a Precision Treg-Engineered Donor Product, Prevents Acute Gvhd with Less Immunosuppression in an Early Multicenter Experience with Myeloablative HLA-Matched Transplants

BACKGROUND

GVHD remains a frequent and serious complication of HSCT despite the decades-long use of standard immunosuppression, such as tacrolimus and methotrexate, as prophylaxis against GVHD. Preclinical models have shown that the timed infusion of donor-derived high-purity CD4⁺CD25⁺FOXP3⁺ regulatory T cells (T_reg) preceding adoptive transfer of conventional T cells (T_con) prevents GVHD and maintains anti-cancer immunity without the need of pharmacologic agents. Early clinical trials using purified T_reg-engineered graft showed safety and feasibility, but more extensive clinical studies are needed to test scalability and efficacy. Orca-T is an industry-manufactured, precision-engineered CD34-selected, T_reg-engineered graft made in a central GMP laboratory and distributed to multiple centers in the U.S. We present our early patient experience with Orca-T in an ongoing single center phase 2 trial and a multicenter Phase Ib trial and report a pre-planned evaluation of patients randomized to receive Orca-T plus single-agent GVHD prophylaxis (PPX) or Orca-T and no PPX.

METHODS

51 patients with high risk or active hematologic malignancies undergoing myeloablative conditioning were enrolled on two trials: a single-center Phase I/II (n=40, NCT01660607) and a multicenter Phase Ib (n=11; NCT04013685) study. Patients received CD34-selected cells infused with highly purified T_reg (target dose: 3.0 x 10⁶ cells/kg) followed 2 days later by the infusion of T_con (3.0 x 10⁶ cells/kg). Initial GMP manufacturing was demonstrated at Stanford (n=9 grafts; 2016 - 2019) and then transferred to Orca Bio in 2019 for scaled production.

We evaluated the 34 patients beyond dose escalation since July 2016 who received Orca-T grafts from either matched related (n=25) or unrelated (n=9) donors and single agent GVHD PPX with either tacrolimus (n=28) or sirolimus (n=6). For comparative analysis, we identified a contemporaneous SOC cohort at Stanford (n=138) with both matched related (n=79) and unrelated (n=59) transplant recipients who received unmanipulated PBSC products (median f/u 546 days) and methotrexate plus tacrolimus.

In April 2019, enrollment on a phase 2, stage 1 pre-planned subgroup of 24 patients were randomized to test whether all GVHD PPX could be removed: Orca-T plus either single-agent PPX (Arm 1, n=12) or no PPX (Arm2, n=12).

RESULTS

The Orca-T drug products were manufactured reliably with high T_reg purity (93.8% +/- 3.1%) and a dose of 2.6 +/- 0.4 x 10⁶ per kg (equivalent between arms and trials). Central lab turn-around times were 25.3 +/- 3.0 hours and all vein-to-vein times were less than 72 hrs (Table 1). For trial participants, there were no manufacturing failures, engraftment failures or treatment related mortality. Orca-T patients vs. SOC showed earlier neutrophil (median of 11 days vs. 14 days, p<0.0001 by Mann-Whitney U) and platelet engraftment (11 vs 17 days, p<0.0001) and a shorter hospital stay (15 vs 19 days, p=0.0002).

Patients across 4 clinical sites received Orca-T plus single agent GVHD PPX (n=34; median f/u 261 days) had an acute GVHD grade 2-4 incidence of 0% as compared to 33% in the SoC cohort (n=138, p=0.0018 by Log-rank Mantel-Cox test, Fig. 1). The rate of moderate to severe chronic GVHD for Orca-T patients was 4% vs. 44% in the SoC cohort (p=0.016).

In a preliminary subset of evaluable Orca- T patients, GVHD & relapse free survival (GRFS) at one year was higher for Orca-T patients vs SoC (69% versus 33%, p=0.006) while relapse and overall survival did not appear to differ. We observed no differences in infectious complications.

In patients randomized to PPX vs. no PPX, the incidence of aGVHD grade 2-4 was 0% in Arm 1 and 58% in Arm 2 (p <0.0001, Log-rank Mantel-Cox test), with 17% of these events being Grade 3-4. All GVHD in Arm 2 responded to steroids with no GVHD-related deaths.

CONCLUSIONS

Manufacture of high precision Orca-T T_reg-engineered donor products were successfully scaled in a central GMP with reliable distribution to centers. Patients who received Orca-T and single agent PPX had no grade 2 or greater acute GVHD acute and very little chronic GVHD when compared to SOC. Patients randomized to Orca-T and no PPX showed an increased incidence of acute GVHD vs. those with Orca-T and single agent PPX. Engineered T_reg grafts show promise to improve GFRS and other transplant outcomes. Orca-T has been granted RMAT status by the FDA and evaluation continues in an ongoing multicenter clinical trial.

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