4-1BB and OX40 stimulation enhance CD8 and CD4 T-cell responses to a DNA prime, poxvirus boost vaccine

The expression and the regulatory role of OX40 and 4-1BB heterodimer in activated human T cells

OX40 and 4-1BB are members of the tumor necrosis factor (TNF) family of costimulatory receptors whose signaling is important for differential immune responses mediated by CD4+ or CD8+ T cells. Although activated T cells may acquire OX40/4-1BB double-positive phenotype and signaling from each receptor is expected to influence cell functions, the relevance between OX40 and 4-1BB has never been investigated before. While we were investigating the expression of OX40 and 4-1BB on activated human T cells, we found that they colocalize. The study of receptor gene–transfected cells showed that both receptors coendocytose and the complex of OX40 and 4-1BB was detected by specific ligands or antibodies (Abs). The heterodimer of OX40 and 4-1BB was identified by sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) under nonreduced conditions and was associated with the tumor receptor–associated factor (TRAF) family proteins in a unique manner. Furthermore, the stimulation of OX40/4-1BB rendered cells sensitive to apoptosis induced by TNF-α that accompanied reduced activation of nuclear factor-κB (NF-κB). Finally, the OX40/4-1BB stimulation repressed the mitogen response in activated CD25+CD4+ T cells and preactivated CD8+ T cells. Thus, the OX40/4-1BB heterodimer appears to represent a unique regulatory receptor in activated T cells.

Liposome-encapsulated CpG oligodeoxynucleotides as a potent adjuvant for inducing type 1 innate immunity

Unmethylated cytosine-phosphorothioate-guanine oligodeoxynucleotides (CpG-ODNs) exhibit potent immunostimulating activity by binding with Toll-like receptor 9 (TLR9) expressed on antigen-presenting cells. Here, we show that CpG-ODN encapsulated in cationic liposomes (CpG-liposomes) improves its incorporation into CD11c(+) dendritic cells (DCs) and induces enhanced serum interleukin (IL)-12 levels compared with unmodified CpG-ODN. CpG-liposome potently activated natural killer (NK) cells (84.3%) and NKT cells (48.3%) to produce interferon-gamma (IFN-gamma), whereas the same dose of unmodified CpG-ODN induced only low numbers of IFN-gamma-producing NK cells (12.7%) and NKT cells (1.6%) to produce IFN-gamma. In contrast with the NKT cell agonist alpha-galactosylceramide, which induces both IFN-gamma and IL-4 production by NKT cells, CpG-liposome only induced IFN-gamma production by NKT cells. Such potent adjuvant activities of CpG-liposome were absent in TLR9-deficient mice, indicating that CpG-liposome was as effective as CpG-ODN in stimulating type 1 innate immunity through TLR9. In addition to TLR9, at least two other factors, IL-12 production by DCs and direct contact between DCs and NK or NKT cells, were essential for inducing type 1 innate immunity by CpG-liposome. Furthermore, ligation of TLR9 by CpG-liposome coencapsulated with ovalbumin (OVA) caused the induction of OVA-specific CTLs, which exhibited potent cytotoxicity against OVA-expressing tumor cells. These results indicate that CpG-liposome alone or combined with tumor antigen protein provides a promising approach for the prevention or therapy of tumors.