Critical Role for CCR1:CCL5 (RANTES) Receptor Ligand Interactions in Modulating Allogeneic T Cell Responses Following Bone Marrow Transplantation.

Acute graft versus host disease (GVHD) and leukemic relapse are the most serious complications of allogeneic (allo) stem cell transplantation (SCT), and separating desirable graft-versus-leukemia (GVL) effects from GVHD remains the ultimate challenge to successful outcomes. The recruitment of activated T cells to host target tissues (GVHD) or sites of leukemic infiltration (GVL) is likely mediated by chemokine receptor:ligand interactions. CCR1 is a chemokine receptor that binds to CC chemokines including RANTES (CCL5), and is expressed on a variety of cells including activated T cells, monocytes, and macrophages. We have previously shown that mRNA expression of both CCR1 and RANTES is increased in GVHD target tissues following allo-SCT. Using a well established murine SCT model (B6->B6D2F1) and mice deficient in CCR1, we examined the contribution of CCR1 expression to allo T cell responses in vitro and to GVH and GVL effects in vivo. Lethally (1100cGy) irradiated B6D2F1 mice received SCT either from syngeneic (B6D2F1) or allogeneic (B6) CCR1+/+ or CCR1−/− donors. The severity of GVHD was assessed by survival and a well described clinical scoring system. Syngeneic SCT recipients all survived and were indistinguishable from naïve, untransplanted controls, whereas animals receiving allo-SCT from CCR1+/+ donors developed significant GVHD. By contrast, allo-SCT with CCR1−/− donor cells resulted in significantly improved survival (92% vs. 50%) and less severe clinical GVHD (p<0.01) by day 35 compared to allo-CCR1+/+ controls. GVL effects were next assessed by adding 500 P815 tumor cells (H-2^d and syngeneic to host) to the bone marrow inoculum on day 0. F1 recipients of syngeneic BMT all died from tumor infiltration by day +15. Although all allo-SCT recipients effectively rejected their tumor, mice receiving CCR1-/− SCT had significantly improved leukemia free survival (45% vs. 5%) by day 60 compared to allo controls. At higher tumor doses, significant GVL activity remained in CCR1−/− SCT recipients, but the survival advantage was lost. Further examination of allo T cell responses in vivo revealed that day 7 splenic T cell expansion and serum IFNγ levels were significantly lower following CCR1−/− SCT (p < 0.01). Surprisingly, proliferation and IFNγ secretion were also reduced by ~70% when CCR1−/− T cells were stimulated with host antigens in vitro, whereas CTL activity remained equivalent to CCR1+/+ controls. The reduction in proliferation was not secondary to a migration defect, but was dependent on interactions between CCR1 and RANTES; neutralization of RANTES with a monoclonal antibody significantly reduced proliferation of CCR1+/+ T cells in a dose dependent manner. Finally, we found that GVHD mortality was also less when RANTES−/− mice were used as recipients in a second, MHC-disparate, SCT model (p = 0.03). Collectively these data demonstrate a critical role for CCR1 in donor T cell alloreactivity following SCT. These responses contribute to both GVHD and GVL effects in vivo and are likely dependent upon interactions between CCR1 and the chemokine ligand RANTES.