OK-432 is a lyophilized preparation of Streptococcus pyogenes that binds TLR-2, TLR-4, and/or TLR-9 and activates APCs, making it attractive for potential use as an adjuvant

of cancer vaccine [29-33]. OK-432–matured DCs effectively prime antigen-specific T cells in vitro [29, 34]. Importantly, OK-432 has already been used for many years as a direct anticancer agent, particularly in Japan, and has a well-established clinical safety profile. However, while it is considered that OK-432 may inhibit Treg-cell suppressive activity by stimulating several TLR signaling pathways, its influence on Treg cells has not yet been shown. In this study, we addressed whether OK-432 inhibits Treg-cell suppressive function and could be a promising adjuvant of cancer vaccines. To address whether OK-432 inhibited CD4+CD25+ Treg-cell suppression, we employed the Neratinib purchase standard in vitro suppression

system. CD4+CD25− T cells and CD4+CD25high Treg cells (highest 3% of CD4+CD25+ cells) were isolated from PBMCs of healthy individuals. CD4+CD25− T cells were cultured with irradiated autologous APCs (CD4-depleted PBMCs) and anti-CD3 Ab in the presence or absence Gefitinib of CD4+CD25high Treg cells. CD4+CD25− T-cell proliferation was analyzed as described in the Materials and methods. In accordance with previous reports [7], CD4+CD25high Treg cells markedly suppressed the proliferation of CD4+CD25− T cells (Fig. 1A and B). In sharp contrast, when OK-432 was added in the culture, suppressive activity of CD4+CD25high T cells was significantly inhibited (Fig. 1A and B). In addition, OK-432 did not induce death of CD4+CD25high Treg cells as the frequency of Annexin V+ and 7-AAD+ cells was not significantly increased in the presence of OK-432 (data

not shown). Instead, CD4+CD25high Treg cells exhibited marginal RANTES proliferation in the presence of OK-432 (Fig. 1A). These data indicate that addition of OK-432 impairs the suppressive activity of CD4+CD25high Treg cells and partially reverses anergy status of Treg cells. Since OK-432 reportedly induces TLR-2, TLR-4, and/or TLR-9 activation and subsequent production of proinflammatory cytokines [29-33], we examined the involvement of cytokines in this inhibition of Treg-cell suppression. To this end, Abs against several candidate cytokines were added to cultures. Among cytokines tested, only blocking Ab against IL-12 significantly abrogated the inhibition of Treg-cell suppression by OK-432 (Fig. 2A). To confirm the importance of IL-12, we next analyzed whether the addition of IL-12 could inhibit Treg-cell suppression as observed by OK-432. CD4+CD25− T cells were cultured with CD4+CD25high Treg cells, irradiated autologous APCs and anti-CD3 Ab in the presence of IL-12. Treg-cell suppressive activity was significantly inhibited by the addition of IL-12, but not IL-6 or IFN-γ (Fig. 2B).