The tumor antigen NGcGM3 is a human CD1d ligand capable of mediating B cell and NKT interaction

PEREZ, M.E; ARANA, E; GENTILINI, M.V.; FAINBOIM, L; FERNANDEZ, P

Melbourne

Congreso; International Congress of Immunology; 2016

The ganglioside NGcGM3 is a tumor antigen (Ag). Some people have circulating Ag specific IgGs, capable of complement mediated cytotoxicity against NGcGM3 positive cells,relevant for tumor surveillance. Considering the Ag's chemical nature, we postulated it as a candidate ligand for CD1d. We aimed to assess whether the immune mechanism involved in the generation of anti-NGcGM3 Abs entailed an interaction between B cells (Bc) and invariant NKT cells (iNKT). We set up a cell free Ag presentation assay using a recombinant CD1d-IgG1 fusion on NGcGM3-coated plates and tested whether there were differences in the binding of the fusion and an IgG1 isotype control. Differences between them were reproducibly significant (p< 0.01), which was also true for differences with uncoated control wells. The results were confirmed through alternative biochemical assays including competitive ELISA with a known CD1d ligand (IC50 1.2 mmol/L). Using FACS, we demonstrated that human Bc present NGcGM3 in a CD1d context and paraformaldehyde treatment of cells expressing CD1d affects the presentation. Finally, by co-culturing primary human Bc with autologous iNKT and measuring Ki-67 expression, we detected a significant increment in the proliferation of both cell populations when Ag was on the medium, which was abrogated by blocking CD1d. Our findings identify a novel, endogenous, human CD1d ligand, which is sufficiently competent to stimulate iNKT. We postulate that CD1d-restricted Bc presentation of NGcGM3 drives effective iNKT activation, a mechanism involved in the antitumor response that has not been previously described for humans, which may contribute to understanding anti-NGcGM3 occurrence.