CD25+ Regulatory T Cell Depletion Augments Immunotherapy of Micrometastases by an IL-21-Secreting Cellular Vaccine

Abstract

IL-21 is an IL-2-like cytokine, signaling through a specific IL-21R and the IL-2R γ-chain. Because the TS/A mammary adenocarcinoma cells genetically modified to secrete IL-21 (TS/A-IL-21) are strongly immunogenic in syngeneic mice, we analyzed their application as vaccine. In mice bearing TS/A-parental cell (pc) micrometastases, vaccination with irradiated TS/A-IL-21 cells significantly increased the animal life span, but cured only 17% of mice. Spleen cells from cured mice developed CTL activity and produced IFN-γ in response to stimulation by the AH1 epitope of the gp70env Ag of TS/A-pc. We tested whether the low therapeutic outcome might be due to CD4+CD25+ regulatory T cells (Treg) present in TS/A-pc tumors and draining lymph nodes and whether IL-21 had any effect on these cells. Indeed, CD4+CD25+ cells suppressed IFN-γ production by splenocytes from immune mice in response to stimulation by the AH1 peptide. Low concentrations of IL-21 (10 ng/ml) failed to reverse the inhibitory activity of CD4+CD25+ cells in an allogeneic MLR, whereas 60 ng/ml rIL-21 partially restored responder T cell proliferation. IL-21R expression on CD25− lymphocytes suggested that IL-21 could be more effective in mice depleted of CD25+ cells. Depletion of Treg cells by a single dose of anti-CD25 mAb combined with TS/A-IL-21 cell vaccine cured >70% of mice bearing micrometastases, whereas anti-CD25 mAb treatment alone had no effect. Successful combined immunotherapy required NK cells, CD8+ T cells, and IFN-γ. In conclusion, immunotherapy of micrometastases by an IL-21-based cellular vaccine is strongly potentiated by CD25+ cell depletion.

IL-21 Counteracts the Regulatory T Cell-Mediated Suppression of Human CD4+ T Lymphocytes

“…Consistently, a decreased number and/or defective activity of Treg has been documented in autoimmune and allergic diseases (10). In contrast, Treg may sabotage effective immune responses against microbes and tumors (7,8).…”

“…Although they were initially described to modulate self-tolerance and to protect against autoimmunity, more recent studies have suggested that Treg may also be implicated in suppressing immune responses in infective and neoplastic diseases (7,10). Concomitantly, several authors have shown that Treg activity can be differently modulated by inflammatory molecules, bacterial products, and tumor-derived molecules, thus raising the possibility that we can either enhance or inhibit Treg function for therapeutic purposes.…”

“…Moreover, mice overexpressing IL-21 exhibit inflammatory infiltrates in several tissues (6), thus raising the possibility that IL-21 may play an important role in the induction and/or perpetuation of immuneinflammatory processes. In contrast, IL-21 exerts antitumor effects in vivo (1,7), suggesting that this cytokine may have therapeutic potential.…”

“…Collectively, our data indicate that IL-21 counteracts the regulatory effects of CD4 ϩ CD25 ϩ T cells by providing human CD4 ϩ CD25 Ϫ T cells signals that raise their threshold for suppression by CD4 ϩ CD25 ϩ T cells. While this manuscript was in preparation, Comes et al (7) showed that IL-21 partially reverts the immunosuppressive activity of CD4 ϩ CD25 ϩ Treg isolated from tumor-draining lymph nodes, and that such cells fail to proliferate in response to IL-21 and alloantigen or anti-CD3 stimulation.…”

L’interleukine-21, un nouvel adjuvant contre le cancer ?

“…En effet, de nombreux groupes ont montré dans des études indépendantes que la transfection de l'ADNc codant pour l'IL-21 dans des cellules tumorales murines (issues de cancer du côlon, de mélanome, de fibrosarcome, de cancer mammaire, de cancer de la vessie, de gliome, de carcinome rénal et de neuroblastome) ralentit leur croissance ou entraîne le rejet total de ces tumeurs [4]. De plus, une straté-gie vaccinale, via l'injection de cellules tumorales exprimant l'IL-21 et irradiées dans un modèle murin d'adénocarcinome mammaire, a démontré un allongement de la survie de ces souris [5]. Des résultats identiques sur la réduction de la croissance tumorale et la survie des souris ont été obtenus dans les modèles B16 de méla-nome ou de fibrosarcome, en présence d'un plasmide codant pour l'IL-21 [7].…”