| Research Abstract |
A lipoteichoic acid-related molecule OK-PSA, an active component of a streptococcal immunotherapeutic agent OK-432, is an effective inducer of TM-type cytokines, and elicits anti-tumor activity in tumor-bearing mice. DCs are potent antigen-presenting cells which promote immune responses against tumor cells. In the current study, we first examined the effect of OK-PSA on maturation of dendritic cells (DCs) in vitro. Immature DCs derived from 5 healthy donors and 10 patients with head and neck cancer with or without the expression of Toll-like receptor 4 (TLR4) or MiD-2 mRNA were treated with OK-PSA for 2 days, then the expression of surface molecules, cytokine production, T lymphocyte-stimulating activity of the DCs were analyzed. Treatment with OK-PSA of healthy donor-derived immature DCs effectively increased the surface expression of MHC class II, CD80, CD83 and CD86. OK-PSA-stimulated DCs markedly secreted the cytokines and chemokines that can induce Th1-type T-cell response. In add
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ition, OK-P SA-activated DCs enhanced the proliferation of allogeneic CD3+T cells and induced allo-specific cytotoxic T lymphocytes (CTLs). OK-PSA also activated DCs, derived from the patients which expressed both TLR4 arid MD-2 mRNAs. while OK-PSA-stimulated DCs from the patients in whom the expression of TLR4 or MID-2 mRNA was absent, did not induce CTL activity. Furthermore, TLR4-deficient DCs transfected with TLR4 expression vector showed the response to OK-PSA to produce IL-12 as well as to stimulate allogeneic T cells. OK-PSA induced DC maturation via TLR4 signaling. OK-PSA may be a useful therapeutic application as an adjuvant for DC-based cancer immunotherapy. Thus, we next tested the significance of expression of TLR4 on the DCs in in vivo anti-tumor effect of intratumoral administration of syngeneic DCs followed by OK-PSA against established tumors in mice. C57BL/6 mice, which express wild-type TLR4, and C57BL/6-derived TLR4-knockout (TLR4-/-) mice were used for the present experiments. Although OK-PSA markedly augmented anti-tumor effect of an intratumoral DC administration in wild-type mice bearing Lewis lung carcinomas LL/2, anti-tumor effect of OK-PSA as well as of the combination therapy with DCs and OK-PSA was not significant in TLR4-/-mice. Interestingly, an administration of wild-type-mouse-derived DCs followed by OK-PSA exhibited a marked anti-tumor effect even in LL/2-bearing TLR4-/-mice. Cytotoxic activities of tumor-infiltrating lymphocytes and of draining lymph node cells against LL/2, as well as interferon-γ secretion, were significantly increased by the therapy with DCs and OK-PSA in wild-type mice but not in TLR4-/-mice. These activities in LL/2-bearing TLR4-/-mice were also enhanced by intratumoral injection of wild-type-mouse-derived DCs and OK-PSA. These findings suggest that OK-PSA may be a potential adjuvant for local DC therapy, and that DC therapy followed by OK-PSA is able to elicit anti-tumor activity even in a TLR4-deficient host when TLR4 is expressed only in intratumorally transferred DCs. Less
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