Abstract 5325: Inhibition of CD4+CD25+ regulatory T cell suppression to anti-tumor responses by OK-432 (lyophilized Streptococcus pyogenes)

Abstract

Abstract It is important to control the suppressive activity to anti-tumor immune responses mediated by CD4+CD25+ regulatory T cell (Treg) for effective immunological cancer treatment. Recently, a number of studies have shed new light on recognition of pathogen-associated molecular patterns through toll like receptors (TLRs) to break the suppressive environment present at the tumor local site. TLR signals are not only able to block the suppressive activity of CD4+CD25+ Tregs but can also break CD8+ tolerance even in the presence of CD4+CD25+ Tregs. Recently, we reported that while high-avidity NY-ESO-1-specific CD4+ T cell precursors are indeed present in naïve T cell populations, their activation following peptide vaccination is kept under the strict control of Tregs, resulting in a selective activation/expansion of low-avidity NY-ESO-1 peptide-specific CD4+ T cells. Additionally, following DNA vaccination, high-avidity NY-ESO-1-specific CD4+ T cells can only be observed transiently and become rapidly suppressed by Tregs. Here, we focused on OK-432 (lyophilized preparation of Streptococcus pyogenes) that can stimulate TLRs and explored 1) whether OK-432 administrated into tumor-associated exudate fluids (chest or abdominal cavity) inhibits local Treg function and accumulation, and 2) whether OK-432 used as an adjuvant of cancer vaccine can break Treg suppression and induce the activation of high-avidity tumor antigen-specific T cell precursors. Levels of Tregs in cells collected from pleural effusion or ascites of cancer patients treated with OK-432 were assessed by staining with antibodies for CD4, CD25 and Foxp3. The frequency of Foxp3+ Tregs significantly decreased after OK-432 administration. Furthermore, suppressive function of Tregs from patients also decreased after OK-432 treatment. PBMCs were collected from patients receiving vaccination with tumor antigens (HER2 and NY-ESO-1), formulated in choresteryl hydrophobized pullulan (CHP) together with OK-432 and the presence of high-avidity NY-ESO-1-specific CD4+ T cells in effector/memory (CD25-CD45RO+) T cell population was examined. NY-ESO-1-specific CD4+ T cells were detected within CD45RO+ memory T cell population after vaccination. In contast to peptide vaccination, CD4+ T cell clones induced from these NY-ESO-1-protein vaccinated patients in the presence of OK-432 had high-affinity T cell receptors and recognized naturally-processed NY-ESO-1 protein presented by dendritic cells. Taken together, OK-432 appears to inhibit Treg function and contribute to the durable differentiation of high-avidity tumor antigen-specific naive T cell precursors into effector/memory T cells with relative resistance to Tregs. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 5325.