Factors governing the activation of adoptively transferred donor T cells infused after allogeneic bone marrow transplantation in the mouse

Murine models of bone marrow transplantation were used to study the mechanisms governing the activation of donor lymphocyte infusions (DLIs) manifesting as lymphohematopoietic graft-versus-host (LH-GVH) and graft-versus-leukemia (GVL) reactivities. We demonstrate here that established mixed chimerism influences the potency of DLI-mediated alloreactivity only in the MHC-mismatched but not MHC-matched setting. In the MHC-matched setting, high levels (≥ 40%) of residual host chimerism correlated negatively with DLI-mediated alloreactivity irrespective of the timing of their administration, the donor's previous sensitization to host antigens, or the level of residual host APCs. In vivo administration of Toll-like receptor (TLR) ligands was required to maximize DLI-mediated LH-GVH and GVL reactivities in chimeras with low levels (≤ 15%) of residual host chimerism. In contrast, coadministration of DLI with antigen-presenting cell (APC) activators was insufficient to augment their LH-GVH response in the presence of high levels of host chimerism unless the host's T cells were transiently depleted. Together, these results show the cardinal influence of donor-host incompatibility on DLI-mediated GVH responses and suggest that in MHC-matched chimeras, the induction of optimal alloreactivity requires not only donor T cells and host APCs but also TLR ligands and in the presence of high levels of host chimerism depletion of host T cells.