Phenotypic and Functional Analysis of T-Cells Mobilized in HLA-Matched Sibling Donors Following Treatment with the Chemokine Antagonist AMD3100.

We are currently evaluating a novel method for the procurement of peripheral blood stem cells from HLA matched sibling donors using a direct antagonist of the CXCR4/SDF-1 interaction called AMD3100 (A). Donors receive a single subcutaneous injection of A and then undergo a 20 liter leukapheresis (LP) four hours later. The LP product is then cryopreserved and subsequently transplanted following ablative conditioning. To date, we have performed 15 transplants with allografts collected following A alone. In comparison to allografts collected following five days of G-CSF, A mobilized allografts contain approximately 50% less CD34+ cells but 2–3 times more CD3+ cells. Nevertheless, the kinetics of neutrophil and platelet engraftment have been virtually identical to that observed following G-mobilized allografts and grades 2–4 acute GVHD has been observed in only 20% of recipients. We sought to analyze the functional and phenotypic properties of T cells collected following A alone to understand the relatively low rates of acute GVHD despite the transplantation of higher T-cell doses. In 3 donors, extensive T cell phenotyping was performed on donor peripheral blood prior to A, 6 hours following A, and also on the LP product collected after A. Specifically, we were seeking to determine whether any alteration in CD4+ or CD8+ subsets had occurred. We analyzed T-cell subsets using well described markers for central memory, effector memory, naïve, and effector memory RA phenotypes. We also assessed expression of CD62L, CD127, CCR7, and SLAM family members (CD48, CD150, and CD244) on both CD4+ and CD8+ cells. The activation status on CD4 and CD8 cells was assessed using markers for CD25, CD30, and CD69. Finally we assessed for quantitative changes in the mobilization of regulatory T cells by assaying the proportion of CD4+CD25+FoxP3+ cells mobilized following A. In none of these analyses could we detect any significant alteration in the relative ratios of CD4 or CD8 subsets mobilized by A. Finally, the functional capacity of purified CD3+ cells collected following A was assessed using a NOD/SCID xenogeneic GVHD model we have recently developed. In that model, survival of mice transplanted with A mobilized T-cells was similar to that observed with untreated T cells, suggesting that A mobilized T cells retain their GVHD-inducing capacity. In summary, these preliminary data suggest that AMD3100 induces a “pan-mobilization” of T cell subsets without any apparent skewing toward a particular subset. These studies are in contrast to others suggesting subtle phenotypic and functional changes in donor T cells after mobilization with G-CSF. Further studies evaluating A mobilized allografts are ongoing.