Structure-based designed CD8 peptide analogs inhibit both in vitro and in vivo CD8(+) T cell responses
CD8$\sp+$ T cells recognize antigen presented by major histocompatibility complex (MHC) class I molecules on target cells via the T cell receptor (TCR) complex, resulting in activation in the presence of interleukin (IL-2) and subsequent development into cytotoxic T lymphocytes (CTL). CD8 molecules function as coreceptors by interacting with a nonpolymorphic region of the MHC class I a3 domain. The murine CD8 protein, consisting of an $\alpha/\beta$ heterodimer, has been shown to play a major role in both the activation of mature T-cells and in the thymic differentiation process. The CDR-like regions of the variable immunoglobulin domain of the murine CD8-$\alpha$ chain are important in determining the surface conformations involved in protein-protein interactions of this receptor and its ligand. Homology modeling was employed to develop a three dimensional model of the D1 domain of murine CD8$\alpha$ chain based on the known structure of human CD8. A structure-based design approach was used to develop a panel of ten peptide analogs from this structural model of the mouse CD8$\alpha$ molecule to identify surfaces involved in MHC class I interaction. These analogs were conformationally restricted and covalently cyclized by introducing artificial disulfide bonds. The peptide analogs demonstrated the ability to inhibit in vitro CD8 dependent lysis of EL-4 tumor cells by AKR/J splenocytes primed with irradiated C57BL/6J splenocytes. In addition to inhibiting the effector stage of cytotoxic T cell mediated lympholysis, the peptides were tested for the ability to inhibit the generation of cytotoxic T-cells in vitro. Peptide analog SC4 (p54-59) significantly inhibited both the generation and effector stages of cytotoxic T-lymphocytes, whereas SC7 (p63-71) inhibited only the generation phase. Thus, a peptide analog was developed as a potential inhibitor of CD8 T cell responses. The SC4 peptide also proved to be effective in vivo in a MHC class I-restricted skin allograft rejection mouse model. A single dose of SC4 administered at the time of transplantation significantly prolonged graft survival. Also, SC4-Scr (SC4 peptide with random amino acid sequence) was ineffectual in prolonging allograft survival. Importantly, SC4 was found to be specific in its effect as it was unable to prolong allograft survival in a CD4-dependent and MHC class II-restricted skin transplantation model. Peptide treated mice with bm1 skin transplants are capable of vigorously rejecting third party grafts while showing prolonged survival of the bm1 grafts. In addition, lymph node T cells derived from peptide treated hosts with bm1 grafts show diminished lympholysis of bm1 targets. These results indicate that SC4 and SC7 may be capable of disrupting the activation and effector function of CD8+ T-cells. Moreover, this indirectly implicates the CDR2-like domain of CD8 in determining the biological significance of CD8 in cytotoxic T cells. Thus, structure-base designed CD8 peptide analogs may have therapeutic potential as immunoregulators of CTL responses.
Immunology|Cellular biology|Genetics|Molecular biology
Choksi, Swati, "Structure-based designed CD8 peptide analogs inhibit both in vitro and in vivo CD8(+) T cell responses" (1997). ETD Collection for Thomas Jefferson University. AAI9730316.