CD25+ Regulatory T CELL-Depleted DONOR Lymphocyte Infusion for Relapse After Allogeneic Transplantation – A PHASE 1 Study

Donor CD4⁺CD25⁺FOXP3⁺ regulatory T cells (Treg) are capable of suppressing immune-mediated graft-versus-leukemia (GvL) and graft-versus-host disease (GvHD) responses.  We undertook a dose-finding phase 1 study of CD25-depleted donor lymphocyte infusions (DLI) to treat post-transplantation relapse.  Methods:  24 subjects with disease relapse after HLA-matched allogeneic transplantation (9 AML, 4 ALL, 4 HD, 2 MDS, 2 NHL) were enrolled.  Patients had no evidence of GvHD, were on no systemic immunosuppressants, and had received no salvage chemotherapy in the 4 weeks preceding DLI.  Donor lymphocytes were CD25+ depleted via the CliniMACS system (Miltenyi).  Primary objectives were feasibility and safety.  Secondary objective was response.   Results - Feasibility:  3 patients came off study for insufficient numbers of donor CD3+ cells or GvHD onset prior to DLI.  In the remainder, 10 had persistent or progressive disease, 7 were in PR, and 4 were in CR at study entry.  CD25-depleted DLI doses were 1x10⁷ CD3⁺ cells/kg (level 1; n=5) and 3x10⁷ CD3⁺ cells/kg (level 2; n=16).  8 DLIs were from unrelated donors, 13 from related donors.  Median log-reductions of CD25⁺ and CD4⁺CD25⁺FOXP3⁺Treg cells in the infusion products were 1.24 (range 0.72-7.75) and 2.10 (range 1.17-6.46), respectively.    Safety: 16 of 21 subjects were evaluable for toxicity.  In 3 evaluable subjects at DLI Level 1, there were no DLTs.   Dose Level 2 was the MTD, with 1 case of fatal acute GvHD in 13 evaluable subjects.  Among all subjects, rates of acute or chronic GvHD were 19% by 8 weeks and 38% by 1 year following DLI.  Response:  Median follow-up is 29.5 months.  All subjects at Dose level 1 had progressive disease at 8 weeks; 1 experienced extensive chronic GvHD.  At Dose level 2, 8 subjects (50%) had a response (1 PR, 7 CR), including 6 who had evidence of disease at DLI.   6 subjects, including 5 responders, manifested GvHD by day 100.  1 year survival was 8/16 (50%) in the MTD cohort, with 4 of the initial 8 week responders still in CR.  Median survival was 15.4 months.  Conclusions:  Use of CD25⁺ Treg depleted DLI appears feasible, safe and capable of inducing GvL without excessive GvHD in hematologic malignancies relapsed after allotransplantation.  Its safety and preliminary efficacy is promising but needs future prospective evaluation.