Effect of Graft Engineering and Post-Transplantation Immunosuppression Regimen on Immunophenotypic Recovery in Recipients of Unrelated Donor Bone Marrow (T-Cell Depletion Trial) in a Multicenter Randomized Phase II-III Trial.

T cell depletion (TCD) of donor allogeneic blood or marrow grafts can reduce the incidence and severity of acute graft-versus-host disease (GvHD) but may place the patient at risk for disease relapse. This multicenter randomized trial examined the impact of selective depletion of αβ T cells (αβTCD) + cyclosporine immunosuppression in recipients of unrelated marrow grafts vs. T-replete marrow grafts + methotrexate and cyclosporine immunosuppression. Previously reported data from this trial have shown that 3-year disease-free survival (DFS) did not differ between these groups, although the αβTCD group showed improved neutrophil recovery, decreased incidence of acute GvHD, and reduced grade III-IV toxicities. In order to further clarify these findings, we examined the impact of each graft manipulation and immunosuppression strategy on lymphocyte subset recovery and associated outcomes. Lymphocyte recovery was assessed at 1, 3, 6, 12, 18, and 24 months post-SCT. Of all patients accrued, only patients that had survived for at least one year and who had at least four separate immunophenotyping assessments were included in this analysis (unmanipulated grafts = 66/206 32.0%; αβTCD grafts 57/203 28.1%). Non-parametric pair wise tests were used to compare recovery of absolute cell counts at each measurement period. We also fit a mixed model to each individual’s data to estimate the rate of change in cell counts in the two groups. The slope estimate for each subject obtained from the mixed model was then used as a variable in models to assess DFS. The Cox proportional hazards test was used to examine associations between recovery of individual cell subsets and DFS. Recovery of total absolute CD3, αβ, γδ, CD3+CD4+, CD3+CD8+ T cell count as well as the absolute B cell count did not significantly differ between groups for at each measurement period. CD3+CD4+CD45RA naive T cell recovery remained below the expected adult normal range for all time points in both groups but was improved in patients who received unmanipulated grafts. Interestingly, NK cell absolute count recovery was significantly improved in patients that received TCD grafts over those who received unmanipulated grafts (p = 0.001) through the first year post-SCT. Analysis of the impact of individual cell subset recovery on DFS revealed that an absolute γδ T cell count greater than 1.75 x 10⁵/ml at any time during the first year predicted for improved DFS regardless of treatment group (p = 0.05) consistent with previous single-institution reports. Although the αβTCD regimen did not result in improved DFS in this trial, these findings show that αβTCD is a reasonable graft engineering strategy that can reduce the incidence of acute GvHD without producing a significant negative impact on lymphocyte subset recovery. Indeed, patients in the αβTCD group showed markedly improved NK recovery. Approaches that are currently in early-phase trials such as post-SCT targeted T and/or NK cell therapies could be used to supplement the αβTCD regimen, potentially improving relapse-free survival.