Absence of the CD1 molecule up-regulates antitumor activity induced by CpG oligodeoxynucleotides in mice

The role of NKT cells on antitumor activity of CpG oligodeoxynucleotides (ODNs) was evaluated by peritumoral injections of CpG-ODNs in s.c. melanoma-bearing mice of strains differing in the number of NKT cells (athymic nude mice, recombination-activating gene^-/-/transgenic Vα14/Vβ8.2 mice that generate NKT cells; Jα281^-/- mice and CD1^-/- mice, which both have a strongly reduced number of NKT cells; and C57BL/6 wild-type mice). Tumor growth was significantly inhibited in strains enriched or depleted of NKT cells. The two murine strains having a reduced number of NKT cells differed significantly in the CpG-dependent tumor growth inhibition: in Jα281^-/- mice this inhibition was superimposable to that observed in C57BL/6 mice, while in CD1^-/- mice the inhibition was dramatic. The increased tumor inhibition in CD1^-/- correlated with a significantly higher ratio of IFN-γ-IL-4 production in response to CpG as compared with C57BL/6 and Jα281^-/- mice. Experiments in which preparations of APCs and lymphocytes of the three strains were mixed showed that in the presence of APCs not expressing CD1, the production of CpG-ODN-induced type 1 cytokines was higher. Phenotype analysis of IFN-γ- and IL-4-producing cells revealed that the differences between CD1^-/- and C57BL/6 in the production of these two cytokines were mainly due to CD3⁺ T lymphocytes. These data point to a regulatory role for the CD1 molecule in antitumor activity induced by danger signals, independently of Vα14 NKT cells. The identification of a CD1-dependent suppressive subpopulation(s) might have important implications for the study of tolerance in the context of cancer, autoimmunity, and transplantation.