Abstract 3964: Appropriate conditioning of CD4+T cells for antitumor immunotherapy.

Abstract

Abstract It is now evident that lymphodepleting cytotoxic regimens augment antitumor immunity. We and others have demonstrated that transfer of naïve T cells after sublethal whole body irradiation induces antitumor effector T cells and inhibits tumor progression. We recently reported that CD4+CD25+Foxp3+ regulatory T cells (Treg) largely increased after whole body irradiation and suppressed the development of antitumor immune responses during recovery from lymphopenia. Depletion of these radio-resistant Treg following lymphodepletion significantly enhanced antitumor immunity (Baba J, et al. 2012, Blood). The combination of lymphodepletion and transfer of naïve T cells seems to be a promising approach for antitumor immunotherapy. But harvesting sufficient number of T lymphocytes from tumor-bearing patients is difficult. To obtain enough number of T cells that were capable of recognizing tumor-antigens, we expanded naïve T cells in vitro with culturing in CM containing several cytokines. CD4 or CD8 T cells from naïve spleens were activated with immobilized anti-CD3 mAbs for 2 days. Stimulated cells were maintained in CM with the combination of IL-2 (16 U/ml), IL-7 (10 ng/ml), IL-15 (10 ng/ml) and IL-23 (2 ng/ml) for additional 7 days. TCR-Vβ expressions of cultured T cells revealed that they maintained TCR diversity. To evaluate antitumor effects of these cells, mice were irradiated with 500 cGy to deplete lymphocytes and were transferred i.v. with the cultured T cells (4 x 107). On the same day, mice were inoculated s.c. with MCA205 tumor cells (1 x 105). We found that expanded CD4+ T cells mediated regression of s.c. tumors. In contrast, CD8+ T cells alone did not have therapeutic effects even combined with depletion of Treg. Next, we examined T cells proliferation by labeling with the CFSE and evaluated IFN-γ production after stimulation with specific tumor cells. Cultured CD4+ T cells proliferated rapidly and developed into tumor-specific effector T cells after transfer into lymphopenic hosts. Because CD4+ T cells from OT-II mice, that recognize Ovalbumin peptide specifically, did not show any antitumor effects after transfer into lymphopenic mice, this antitumor activity of CD4+ T cells is more likely to be tumor-antigen specific. Interestingly, using irradiated Rag-2 knockout mice as recipient abrogated antitumor effects of transferred cultured CD4+ T cells. Our results indicated that the combination of lymphodepletion and transfer of in vitro expanded CD4+ T cells has a potent antitumor efficacy, and recipient cells from irradiated hosts play a role in this treatment model. Citation Format: Tomohiro Tanaka. Appropriate conditioning of CD4+ T cells for antitumor immunotherapy. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3964. doi:10.1158/1538-7445.AM2013-3964