MHC class I-restricted cytotoxic lymphocyte responses induced by enterotoxin-based mucosal adjuvants

The ability of enterotoxin-based mucosal adjuvants to induce CD8(+) MHC: cl ass I-restricted CTL responses to a codelivered bystander Ag was examined. Escherichia coli heat-labile toxin (LT), or derivatives of LT carrying muta tions in the A subunit (LTR72, LTK63), were tested in parallel with cholera toxin (CT) or a fusion protein consisting of the Al subunit of CT fused to the Ig binding domain of Staphylococcus aureus protein A (called CTA1-DD), Intranasal (i.n.) immunization of C57BL/6 mice with CT, CTA1-DD, LT, LTR72 , LTK63, but not rLT-B, elicited MHC class I-restricted CD8(+) T cell respo nses to coadministered OVA or the OVA CTL peptide SIINFEKL (OVA(257-264)), CT, LT, and LTR72 also induced CTL responses to OVA after s.c. or oral coim munization whereas LTK63 only activated responses after s.c. coimmunization . rLT-B was unable to adjuvant CTL responses to OVA or OVA(257-264) adminis tered by any route, Mice treated with an anti-CD4 mAb to deplete CD4(+) T c ells mounted significant OVA-specific CTL responses after i.n. coadministra tion of LT with OVA or OVA(257-264) Both Cr-51 release assays and IFN-gamma enzyme-linked immunospot assays indicated that IFN-gamma(-/-) and IL-12 p4 0(-/-) gene knockout mice developed CTL responses equivalent to those detec ted in normal C57BL/6 mice, The results highlight the versatility of toxin- based adjuvants and suggest that LT potentiates CTL responses independently of IL-12 and IFN-gamma and probably by a mechanism unrelated to cross-prim ing.