Immunization with a carbohydrate mimicking peptide augments tumor-specific cellular responses

The metastatic potential of some tumor cells is associated with the expression of the neolactoseries antigens sialyl-Lewis x (sLex) and sialyl-Lewis a (sLea) as they are ligands for selectins. We have recently shown that peptide mimetics of these antigens can potentiate IgG2a antibodies, which are associated with a Th1-type cellular response. As L-selectin is preferentially expressed on CD4+ Th1 and CD8+ T cell populations, specific induction of these phenotypes could augment a response to L-selectin ligand-expressing tumor cells. Here we demonstrate that immunization with a multiple antigen peptide (MAP) mimetic of sugar constituents of neolactoseries antigens induces a MHC-dependent peptide-specific cellular response that triggers IFN-gamma production upon peptide stimulation, correlating with IgG2a induction. Surprisingly, T lymphocytes from peptide-immunized animals were activated in vitro by sLex, also triggering IFN-gamma production in a MHC-dependent manner. Stimulation by peptide or carbohydrate resulted in loss of L-selectin on CD4+ T cells confirming a Th1 phenotype. We also observed an enhancement in cytotoxic T lymphocyte (CTL) activity in vitro against sLex-expressing Meth A cells using effector cells from Meth A-primed/peptide-boosted animals. CTL activity was inhibited by both anti-MHC class I and anti-L-selectin antibodies. These results further support a role for L-selectin in tumor rejection along with the engagement by the TCR for most likely processed tumor-associated glycopeptides, focusing on peptide mimetics as a means to induce carbohydrate reactive cellular responses.