HSP70-mediated antigen-dependent nonclassical MHC class Ib-restricted anti-tumor responses in the frog Xenopus laevis (170.15)

Abstract The heat shock proteins (hsps) hsp70 are highly conserved molecular chaperones that elicit potent T cell responses against the antigens (Ags) they chaperone in both mammals and Xenopus. We have shown that frogs immunized with hsp70 generate CD8 T cell responses against the Xenopus thymic tumor 15/0 that expresses several nonclassical MHC class Ib genes, but not classical MHC class Ia. Therefore, we hypothesized that hsp70 can prime class Ib-mediated anti-tumor unconventional CD8 T cells in an Ag-dependent manner. To test this, we produced Xenopus recombinant tagged hsp70 proteins (both the cognate hsc73 and the inducible hsp72) from stable 15/0 tumor transfectants. Antigenic peptides can be easily removed from both hsps by ATP treatment. We used a cross-presentation assay to adoptively transfer hsp-pulsed antigen presenting cells and showed that both hsp72 and hsc73-Ag complexes, but not ATP treated Ag-negative hsp70s, elicit class Ib-mediated CD8 T cells responses resulting in protection from 15/0 tumor challenge. From expression studies, we further postulate that these responses involve one or a few class Ib gene products among which XNC10 is the prime candidate due to its lymphoid tissue distribution. To further elucidate the role of class Ib molecules in anti-tumor immunity, we developed a reverse genetic approach combining transgenesis and siRNA technology and obtained F1 Xenopus clones with silenced expression of class Ib in vivo that will be used for further analysis.