Tissue-specific effects of anti-CD4 therapy in induction of allograft unresponsiveness in high and low responder rats

Natural killer group 2 member D cell recruitment driven by major histocompatibility complex class I chain-related antigens A and B: a possible mechanism during acute intestinal allograft rejection in the mouse

Intestinal allograft rejection occurs frequently despite potent T-cell depletion protocols. We investigated the interaction of major histocompatibility complex class I chain-related antigens A and B (MICA/B; a ligand for natural killer [NK] cells) and NK group 2 member D (NKG2D) cells as an alternative mechanism for acute rejection (AR) of the intestinal graft. Heterotopic intestinal allotransplantation was performed from BalbC to C57Bl mice. Samples of grafted and native intestine were obtained at days 1, 3, 6, and 8 after transplantation (n = 4-6). We performed immunostaining for MICA/B and NKG2D. Moderate AR with increased crypt apoptosis was observed at day 6 and advanced AR with crypt destruction and mucosal sloughing was present by day 8. Low MICA/B levels were observed in grafted and native intestines on day 1. MICA/B expression gradually increased in the grafts during AR but not in the native intestines. The up-regulation was found mostly in the crypts. NKG2D+ cell counts that increased in the graft colocalized with MICA/B. The increase was most prominent in the crypt and villus. Together, these results suggest that MICA/B up-regulation and its subsequent interaction with the NK cells may represent an important link between innate and adaptive immune responses early after intestinal transplantation.

CD4 T cell-mediated cardiac allograft rejection requires donor but not host MHC class II

Numerous studies indicate that CD4 T cells are required for acute cardiac allograft rejection. However, the precise role for CD4 T cells in this response has remained ambiguous owing to the multipotential properties of this T-cell subpopulation. In the current study, we demonstrate the capacity of CD4 T cells to serve as direct effector cells of cardiac allograft rejection. We show that CD4 T cells are both necessary and sufficient for acute graft rejection, as indicated by adoptive transfer experiments in immune-deficient SCID and rag1(-/-) recipients. We have analyzed the contribution of direct (donor MHC class II restricted) and indirect (host MHC class II restricted) antigen recognition in CD4-mediated rejection. Acute CD4 T cell-mediated rejection required MHC class II expression by the allograft, indicating the importance of direct graft recognition. In contrast, reciprocal experiments indicate that CD4 T cells can acutely reject allogeneic cardiac allografts established in rag1(-/-) hosts that were also MHC class II deficient. This latter result indicates that indirect presentation of donor antigens by host MHC class II is not required for acute CD4-mediated rejection. Taken together, these results indicate that CD4 T cells can serve as effector cells for primary acute cardiac allograft rejection, predominantly via direct donor antigen recognition and independent of indirect reactivity.

Prolongation of cardiac graft survival with anti-CD4Ig plus hCTLA4Ig in primates

BACKGROUND

The aim of this study was to determine whether the use of combined immunotherapy with a brief course of humanized anti-CD4Ig and hCTLA4Ig would prolong heterotopic cardiac allograft survival in primates (rhesus monkeys). This model was based on work in "high responder" rats where a brief course of depletive anti-CD4mAb plus hCTLA4Ig was successful in inducing transplantation tolerance.

METHODS

Heterotopic cardiac transplants were performed in rhesus recipients. Donor/recipient pairs between groups were confirmed to be reactive prior to transplantation by MLR matching. Humanized anti-CD4Ig, a recently developed anti-CD4mAb, was given at a dose of 20 mg/kg i.v. on days -3, -2, -1, and 0. hCTLA4Ig was administered at 6 mg/kg/dose i.v. on days 0 and 2 for the first recipient and days 0, 2, 4, and 6 for the second recipient. No further immunosuppression was administered. The treated (n = 2) or untreated (n = 5) recipients were followed for graft function by daily palpitation.

RESULTS

Treatment with anti-CD4Ig plus hCTLA4Ig resulted in a significant prolongation of heart graft survival (42 days for the first recipient and 52 days for the second recipient) compared to untreated recipients (7 days x 4, 11 days x 1). FACS analysis demonstrated CD4 depletion of anti-CD4 treated animals to <2% on posttransplant day 1. The CD4+ T cells gradually repopulated to 50-70% pretransplant levels just prior to rejection. No adverse responses (fever, tachypnea, tachycardia, infections) were observed.

CONCLUSIONS

These are the first results demonstrating that a brief course of combined specific induction immunotherapy with humanized anti-CD4Ig plus hCTLA4Ig, in the absence of adjuvant posttransplant immunosuppression, was well tolerated and resulted in marked prolongation of cardiac allograft survival in primates.

CD4+ but not CD8+ cells are essential for allorejection

The generation of knockout mice with targeted gene disruption has provided a valuable tool for studying the immune response. Here we describe the use of CD4 and CD8 knockout mice to examine the role of CD4+ and CD8+ cells in initiating allotransplantation rejection. Pretreatment with a brief course of depletive anti-CD4 monoclonal antibody therapy allowed permanent survival of heart, but not skin, allografts transplanted across a major histocompatibility barrier. However, skin as well as heart grafts were permanently accepted in the CD4 knockout mice. Transfer of CD4+ cells into CD4 knockout recipient mice 1 d before skin engraftment reconstituted rejection, demonstrating that CD4+ cells are necessary for initiating rejection of allogeneic transplants. Major histocompatibility complex disparate heart and skin allografts transplanted into CD8 knockout recipients were rejected within 10 d. This study demonstrates that CD4+ but not CD8+ T cells are absolutely required to initiate allograft rejection.