G(D2) OLIGOSACCHARIDE - TARGET FOR CYTOTOXIC T-LYMPHOCYTES

Carbohydrate antigens rarely provide target epitopes for cytotoxic T lymphocytes (CTL). Disialoganglioside G(D2) is a glycolipid expressed at high levels in human tumors and a small group of murine lymphomas (EL4, RBL5, RMA, RMA-S, A13, and BALBRVE). Immunization of C57Bl/6 mice with irradiated EL4 cells stimulated a specific CTL response and protected these animals from engraftment of EL4 lymphoma. The CTL activity resided in the CD4(-)CD8(+) population, was dependent on T cell receptor alpha/beta, and was not removed by anti-natural killer cell immunoabsorption, but was restricted to G(D2) and H-2(b) bearing targets. CTL activity could be completely inhibited by G(D2)-oligosaccharide-specific monoclonal antibodies and their F(ab')(2) fragments, but not by immunoglobulin G(3) myelomas or antibodies against G(D3) or G(M2). Soluble G(D2) did not inhibit specific tumor lysis. RMA-S lymphoma cells (G(D2)(+)H-2b(-)TAP(2) deficient) were resistant to G(D2)-specific CTL. Sialic acid-containing peptides eluted from EL4 lymphoma cells could (a) stabilize H-2 molecules on RMA-S cells and (b) sensitize them for G(D2)-specific CTL. Control peptides (derived from vesicular stomatitis virus nucleoprotein peptide and G(D2)-negative lymphomas) could also stabilize H-2 on RMA-S, but were resistant to G(D2)-specific CTL. These H-2-binding peptides could be purified by anti-G(D2) affinity chromatography. We postulate a new class of naturally occurring epitopes for T cells where branched-chain oligosaccharides are linked to peptides with anchoring motifs for the major histocompatibility complex class I pocket. While analogous to the haptens trinitrophenyl and O-beta-linked acetyl-glucosamine, the potential implications of natural carbohydrates as antigenic epitopes for CTL in biology are considerable.