A CD8 DE loop peptide analog prevents graft-versus-host disease in a multiple minor histocompatibility antigen-mismatched bone marrow transplantation model.

Donor CD8(+) T cells can be potent mediators of graft-versus-host disease (GVHD) after allogeneic hematopoietic cell transplantation to either major histocompatibility complex (MHC) class I-or multiple minor histocompatibility antigen-mismatched recipients. To develop small molecular inhibitors of CD8(+) T-cell activity, theoretical structural analysis of the human CD8 alpha molecule was previously used to identify potential functional surface epitopes that interact with the MHC class I molecule. The DE loop (p71-78) was identified as such a target region, and a panel of synthetic cyclized peptide mimics of this region were tested for their inhibitory effects on cytotoxic T lymphocyte activity in human cell-mediated lympholysis assays. Peptide 1109 (CKRLGDTFVC) was most effective at inhibiting specific target cell lysis. Accordingly, studies were conducted to determine whether there was sufficient cross-species homology in the DE loop region and its nonpolymorphic interactive site on the beta(2)-microglobulin domain of the MHC class I molecule to allow similar inhibition of murine CD8(+) cytotoxic T lymphocyte activity. On the basis of strong in vitro inhibitory activity of 1109 in the murine system, the capacity of the peptide to inhibit in vivo CD8(+) T-cell effector functions in skin and hematopoietic stem cell transplantation models was examined. In the C57BL/6 anti-bm1 skin allograft rejection model, across an MHC class I barrier, a single injection of 1109 at the time of transplantation significantly prolonged graft survival. Moreover, 1109 administered at the time of transplantation in the multiple minor histocompatibility antigen-disparate B10.BR-->CBA GVHD model significantly prolonged the survival of lethally irradiated mice that underwent transplantation with donor bone marrow cells and CD8(+) T cells. Histopathologic analysis confirmed that mice treated with the synthetic peptide exhibited diminution of epithelial target cell injury. Specificity of the peptide effect was evidenced by draining lymph node cells from B10.BR mice that had been challenged with CBA lymphocytes and simultaneously treated with 1109. These cells could not generate secondary proliferative responses in vitro upon stimulation with CBA splenocytes but could respond to third-party C57BL/6 stimulation. Thus, the 1109 peptide has potential application in the prevention of CD8-mediated GVHD development.