Prothymosin a and a prothymosin α-derived peptide enhance TH1-type immune responses against defined HER-2/neu epitopes

Background: Active cancer immunotherapies are beginning to yield clinical benefit, especially those using peptide-pulsed dendritic cells (DCs). Different adjuvants, including Toll-like receptor (TLR) agonists, commonly co-administered to cancer patients as part of a DC-based vaccine, are being widely tested in the clinical setting. However, endogenous DCs in tumor-bearing individuals are often dysfunctional, suggesting that ex vivo educated DCs might be superior inducers of anti-tumor immune responses. We have previously shown that prothymosin alpha (qproT alpha) and its immunoreactive decapeptide proT alpha(100-109) induce the maturation of human DCs in vitro. The aim of this study was to investigate whether proT alpha- or proT alpha(100-109)-matured DCs are functionally competent and to provide preliminary evidence for the mode of action of these agents. Results: Monocyte-derived DCs matured in vitro with proT alpha or proT alpha(100-109) express co-stimulatory molecules and secrete pro-inflammatory cytokines. ProT alpha- and proT alpha(100-109)-matured DCs pulsed with HER-2/neu peptides induce T(H)1-type immune responses, prime autologous naive CD8-positive (+) T cells to lyse targets expressing the HER-2/neu epitopes and to express a polyfunctional profile, and stimulate CD4+ T cell proliferation in an HER-2/neu peptide-dependent manner. DC maturation induced by proT alpha and proT alpha(100-109) is likely mediated via TLR-4, as shown by assessing TLR-4 surface expression and the levels of the intracellular adaptor molecules TIRAP, MyD88 and TRIF. Conclusions: Our results suggest that proT alpha and proT alpha(100-109) induce both the maturation and the T cell stimulatory capacity of DCs. Although further studies are needed, evidence for a possible proT alpha and proT alpha(100-109) interaction with TLR-4 is provided. The initial hypothesis that proT alpha and the proT alpha-derived immunoactive decapeptide act as "alarmins", provides a rationale for their eventual use as adjuvants in DC-based anti-cancer immunotherapy.