Abstract 1908: TH2 cells interact with tumor cells to facilitate recruitment of regulatory T cells into the tumor microenvironment in human B-cell lymphomas

Abstract

Abstract Immunosuppressive Foxp3+ regulatory T cells (Tregs) were shown to be markedly increased in the tumor microenvironment in patients with B-cell non-Hodgkin lymphomas and may impair the efficacy of immunotherapeutic strategies. While the induction of Tregs from conventional T cells by tumor B-cells may be one reason for the increased number, we hypothesized that Tregs may also be actively recruited into the lymphoma tumor microenvironment. Here, we used a combination of genomic and immunologic approaches to elucidate the mechanism of recruitment of Tregs into the tumor microenvironment in various human B-cell lymphomas, including follicular lymphoma, diffuse large B-cell lymphoma, mantle cell lymphoma, and splenic marginal zone lymphoma. To determine whether human lymphoma tumor cells hyperexpressed specific chemokines, we analyzed cDNA microarray data on enriched tumor B-cells and compared them with those on enriched B-cells from normal tonsils. We observed that lymphoma tumor cells hyperexpressed CCL17 and CCL22 but not other chemokines compared with tonsillar B-cells, a finding confirmed by real-time PCR. CCL17 and CCL22 are known chemotactic factors for Tregs but are not known to be constitutively expressed by B cells. Since production of CCL17 and CCL22 was previously shown to be induced by IL-4 and/or IL-13 in various tissues, we reasoned that the expression of these chemokines by lymphoma tumor cells is induced by IL-4 and/or IL-13 produced in the tumor microenvironment. Using immunohistochemical studies, we observed that IL-4 is hyperexpressed in the B-cell lymphoma tumor tissues compared with normal tonsillar tissues. Using cytokine induction assay and intracellular cytokine assay, we showed that IL-4 and/or IL-13 are produced by intratumoral TH2 cells but not by TH1 or tumor B-cells. IL-4 and/or IL-13 induced secretion of CCL17 and CCL22 by primary human B-cell lymphoma tumor cells. The expression of CCL17 and CCL22 by tumor B-cells was dependent on STAT6 since knock-down of STAT6 using siRNA inhibited the production of the chemokines. Finally, we observed that culture supernatants from IL-4-treated lymphoma tumor cells, significantly enhanced the migration of Tregs compared with non-Tregs in a transwell chemotaxis assay. The chemotaxis of Tregs in response to culture supernatants was abrogated in the presence of neutralizing antibodies against CCL17 and/or CCL22 in a dose-dependent manner. Tregs migration was also inhibited by anti-CCR4 blocking antibody suggesting that the chemotaxis of Tregs is mediated via CCR4, the receptor for CCL17 and CCL22. Taken together, these results suggest that the TH2 cells produce IL-4 and IL-13 which in turn exert a paracrine effect on tumor B-cells and induce production of CCL17 and CCL22 to facilitate recruitment of Tregs into the lymphoma tumor microenvironment. 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 1908.