The Pentostatin Plus Cyclophosphamide (PC) Non-myeloablative Regimen Induces Durable Host T Cell Functional Deficits and Prevents Murine Marrow Allograft Rejection

摘要

In this manuscript, we characterize for the first time an animal model of non-myeloablative bone marrow transplantation (BMT) using the purine analog pentostatin [P]. Other cohorts of mice received a distinct purine analog, fludarabine [F], which we and others have previously evaluated in non-myeloablative murine models. In this project, we have characterized pentostatin for its ability to: (1) operate synergistically with cyclophosphamide [C] to induce host T cell depletion; (2) induce host T cell suppression, as defined by modulation of cytokine secretion in vitro and abrogation of host-versus-graft reactivity (HVGR) in vivo; (3) constrain host T cell recovery post-chemotherapy; and (4) prevent the rejection of T-cell depleted (TCD), fully MHC mismatched bone marrow allografts. Relative to single-agent regimens, combination PC or FC regimens worked synergistically to deplete host CD4⁺ and CD8⁺ T cells; PC and FC regimens were developed that yielded similar levels of host T cell and myeloid cell depletion. In the setting of these generally comparable states of host T and myeloid cell depletion, the PC regimen was found to be highly immune suppressive, as evidenced by reduced host T cell capacity to: (1) secrete IL-2 and IFN-γ in vitro; (2) mediate HVGR in vivo; and (3) recover numerically and functionally during a two-week observation period post-chemotherapy. Finally, using B6 hosts treated with the 14-day chemotherapy regimens, the PC regimen more consistently prevented the rejection of BALB/c TCD-allografts than the FC regimen (rate of alloengraftment, 14/15 [93%] of PC-treated recipients vs. 8/14 [57%] of FC-treated recipients; p<0.05); similar results were observed using an 8-day conditioning regimen. These data suggest that host T cell suppression, distinct from T cell depletion, may therefore represent a critical determinant of engraftment after purine analog-based regimens and may also be preferentially attained by use of pentostatin.