Poster: CT-098 Impact of T-Cell Dose on Outcome of T Cell–Replete HLA-Mismatched Allogeneic Peripheral Blood Stem Cell Transplantation

The outcome of allogeneic hematopoietic cell transplantation (HCST) relies on both disease-related factors and transplant-related factors including the conditioning regimen and immunotherapy exploiting the graft-versus-tumor (GVT) effect. CD3+ T cells are the main player in the GVT process, but an increased dose of these cells results in an increased risk of acute graft-versus-host disease (GVHD). We aimed to study whether the T-cell dose of allogeneic peripheral blood stem cell (PBSC) products influences transplantation outcomes in our patient population. This is a retrospective chart review study including patients over 18 years of age, diagnosed with AML, ALL, or MDS, who underwent PBSC mismatched allogeneic transplant, including haploidentical, one-antigen mismatched related, or 2-alleles mismatched related transplants at the King Hussein Cancer Center's bone marrow transplant program between January 2010 and December 2020. We calculated the median CD3 cell dose and divided all patients into 2 groups (Low and High dose groups) and then measured the cumulative incidence of acute GVHD, chronic GVHD, and 1- and 2-year overall survival (OS). Thirty-five patients were stratified according to the median CD3+ cell dose into the Low CD3 group, which included 18 (51%) patients with a mean dose of 13.7×10/kg (range: 2.8-19.7), and the High CD3 group, which included 17 (49%) patients with a mean dose of 29.7×10/kg (range: 19.8-93.1) (P-value: 0.000). The cumulative incidence of acute GVHD was 60% (n=12) in the Low CD3 group and 40% (n=8) in the High CD3 group (P-value: 0.24). The cumulative incidence of chronic GVHD was 64% (n=9) in the Low CD3 group and 35% (n=5) in the High CD3 group (P-value: 0.26). The overall survival for the cohort (n=35) at 12 months was 60.9% and reached 49.6% at 24 months. The 12-month OS for the Low and High CD3 groups was 66.7% and 52.9%, respectively. The 24-month OS for the Low and High CD3 groups was 66.7% and 33.1%, respectively (P-value: 0.084). Although the study showed a trend toward better OS in the Low CD3+ dose group, the difference was not statistically significant.