Enhanced immune reconstitution of γδ T cells after allograft overcomes negative impact of pre-transplant MRD positive status in AML patients.: γδ T cells and MRD+ AML

BACKGROUND Minimal residual disease (MRD) prior to allogeneic stem cell transplantation (allo-SCT) in AML is a poor risk factor for outcome. The γδ T cells represents a unique minority lymphocyte population which is preferentially located in peripheral tissues, can recognize antigens in non-MHC restricted manner and plays a "bridging" role between innate and adaptive immune system. OBJECTIVES In this study, we investigated a potential graft-vs-leukaemia effect of γδ T cells reconstitution post-transplant in AML patients with pre-transplant positive minimal/measurable disease status (MRD+). STUDY DESIGN We investigated a potential graft-vs-leukaemia effect of γδ T cells reconstitution post-transplant in AML patients with pre-transplant positive MRD+. MRD assessment was performed in 202 patients (MRD+, n=100) with multicolored flow cytometry ("different from normal" strategy). Analysis for absolute concentrations of CD3+, CD4+, CD8+, NK, and γδ T cells were performed by flow cytometry according to an internal protocol at day +30 and +100 post-transplant. Differences between categorical and continuous variables were determined by Chi-square and Student's T-test, respectively. The Mann-Whitney test was used to compare medians of continuous variables. Spearman correlation was used for nonparametric assessment of correlation between different cell subsets during immune reconstitution. Kaplan Meier survival analysis and Cox regression analysis were used to investigate the associations between immune reconstitution and survival outcomes. Grays' analysis was used to compute incidences of relapses, non-relapse mortality (NRM) and graft-vs-host disease (GvHD). RESULTS Follow-up for survivors was 28 months (3-59). Younger age (≤58) of recipient and donor (