ALBERT

Description: Allogeneic (allo) bone marrow transplantation (BMT) is the only curative option for many patients with malignant and non-malignant diseases. Acute graft versus host disease (GVHD) is the major complication of allo-BMT and limits the utility of this treatment strategy. The induction of GVHD fundamentally depends upon the activation of donor T cells by host antigen presenting cells (APCs), and the prevailing hypothesis is that these critical interactions occur in secondary lymphoid organs, such as lymph nodes (LN) Peyer’s patches (PP), and spleen (SP). We tested this hypothesis by using a well established, MHC disparate, murine SCT system (Balb/c → B6) and homozygous aly/aly (alymphoplasia) mice that are deficient in all LN and PP and heterozygous aly/+ littermate controls. Lethally irradiated, splenectomized, aly/aly mice (LN/PP/SP −/ −) and aly/+ sham mice (LN/PP/SP +/+) received BMT either from syngeneic (aly/aly) or allo (Balb/c) donors. In some experiments, wild-type B6 recipients of B6 or Balb/c BMT served as additional negative and positive GVHD controls respectively. The severity of GVHD was assessed by survival and well-described scoring systems of both clinical and target organ disease. As expected, greater than 95% of syngeneic (syn) BMT recipients survived and were indistinguishable from naïve, un-transplanted controls, whereas LN/PP/SP +/+ mice receiving allo-BMT showed significant signs of GVHD with ~40% mortality by day 49. All LN/PP/SP −/ − allo-BMT recipients also survived, but surprisingly, examination demonstrated that they too developed significant clinical GVHD compared to syn controls (score: 3.2 vs. 0.85) that was comparable in severity to LN/PP/SP +/+ mice (3.1). Moreover, histopathologic analysis demonstrated that LN/PP/SP −/ − allo-BMT recipients developed significantly greater GVHD target tissue damage in the liver, intestinal tract and skin compared to syn controls. In fact, LN/PP/SP −/ − allo-BMT recipients developed more severe hepatic GVHD compared to allo littermate (LN/PP/SP +/+) controls (30.8±1.9 vs. 20.7±2.2; p 〈 0.01). Similar differences in liver GVHD was also seen between allo groups as early as day 7 (16.0±2.2 vs. 7.3±0.9; p 〈 0.01). We next tested the ability of host aly/aly and aly/+ APCs to stimulate donor Balb/c T cells in vitro. No differences in proliferation, IFN γ production or CTL generation were detected, thus showing that the allo-stimulatory capacity of host APCs was not different between groups. In order to ascertain what extra-lymphoid host tissues might serve as initial sites for allo-antigen exposure, we examined donor T cell expansion (CD3+), activation (CD69+) and proliferation (CFSE) in the bone marrow compartment 3 days after BMT. We found that in each case, LN/PP/SP −/ − allo-BMT recipients had significantly higher numbers / divisions compared to allo, littermate, (LN/PP/SP +/+) controls. Collectively, these data challenge the paradigm that secondary lymphoid tissues are required for GVHD induction, and suggest that the bone marrow may represent an alternative site for allo-antigen recognition and donor T cell activation.

Description: Acute graft-versus-host disease (GVHD) and leukemic relapse are serious complications of allogeneic stem-cell transplantation (SCT). Recruitment of activated T cells to host target tissues or sites of leukemic infiltration (graft-versus-leukemia [GVL]) is likely mediated by chemokine receptor–ligand interactions. We examined the contribution of donor cell CCR1 expression to the development of GVHD and GVL using a well-established murine SCT model (B6 → B6D2F1) and CCR1-deficient mice (CCR1−/−). Allo-SCT with CCR1−/− donor cells significantly reduced systemic and target organ GVHD severity, and CCR1 expression on both T cells and accessory cells contributed to GVHD mortality. Significant GVL activity was preserved following CCR1−/− SCT, but the survival advantage diminished with increasing tumor burden. We then explored the effects of CCR1 expression on allo-specific T-cell responses. Although cytolytic effector function was maintained on a per-cell basis, T-cell proliferation and IFNγ secretion were significantly reduced both in vivo and in vitro. T-cell function was partially dependent on interactions between CCR1 and CCL5. Collectively, these data demonstrate that CCR1 expression on donor cells contributes to the development of both GVHD and GVL, and suggest that CCR1/CCL5 receptor-ligand interactions modulate allo-specific T-cell responses occurring in this context.