Graft-facilitating doses of ex vivo activated γδ T cells do not cause lethal murine graft-vs.-host disease

Abstract

The purpose of this study was to examine the ability of γδ T cells to cause graft-vs.-host disease (GVHD) after allogeneic bone marrow transplantation (BMT) and to determine whether these cells offered any therapeutic advantages relative to αβ T cells. Due to the paucity of naive γδ T cells in mice and humans, γδ T cells (obtained from αβ T cell-deficient murine donors) were ex vivo activated and expanded in interleukin (IL)-2 so as to achieve sufficient cell numbers and to serve as a more clinically feasible strategy. After transplantation into lethally irradiated hosts, donor γδ T cells were detected in target organs of GVHD such as the spleen and intestines 2 weeks after BMT and constituted the primary T cell subpopulation. Large doses (150 × 106) of activated γδ T cells, which we have previously shown capable of facilitating engraftment in MHC-disparate recipients, failed to cause fatal GVHD in lethally irradiated recipients of MHC-incompatible donor marrow grafts (C57BL/6 [H-2b]→B10.BR [H-2k] and C57BL/6 [H-2b]→B6D2F1 [H-2b/d]). The absence of GVHD was confirmed by histologic analysis of target organs, splenic B cell reconstitution, and appropriate negative selection in the thymus, that were all comparable to those observed in mice transplanted with T cell-depleted BM only. While early splenic reconstitution was attributable to donor γδ T cells, analysis of durably engrafted chimeras 2 months posttransplant revealed that the vast majority of donor splenic T cells expressed the αβ T cell receptor. The results of secondary adoptive transfer assays showed that these cells were tolerant of recipient alloantigens in vivo, demonstrating that γδ T cells did not prevent the subsequent development of donor anti-host tolerance in BM-derived αβ T cells. When comparatively evaluated, the minimal number of naive αβ T cells necessary for donor engraftment caused significantly more fatal GVHD than the corresponding minimal dose of activated γδ T cells and thus had a superior therapeutic index. These studies indicate that doses of activated γδ T cells that are able to promote alloengraftment do not cause lethal GVHD in mice transplanted with MHC-incompatible marrow grafts.