The therapeutic efficacy of anthracyclines relies on antitumor immune responses elicited by dying cancer cells. How chemotherapy-induced cell death leads to efficient antigen presentation to T cells, however, remains a conundrum. We found that intratumoral CD11c(+)CD11b(+)Ly6C(hi) cells, which displayed some characteristics of inflammatory dendritic cells and included granulomonocytic precursors, were crucial for anthracycline-induced anticancer immune responses. ATP released by dying cancer cells recruited myeloid cells into tumors and stimulated the local differentiation of CD11c(+)CD11b(+)Ly6C(hi) cells. Such cells efficiently engulfed tumor antigens in situ and presented them to T lymphocytes, thus vaccinating mice, upon adoptive transfer, against a challenge with cancer cells. Manipulations preventing tumor infiltration by CD11c(+)CD11b(+)Ly6C(hi) cells, such as the local overexpression of ectonucleotidases, the blockade of purinergic receptors, or the neutralization of CD11b, abolished the immune system-dependent antitumor activity of anthracyclines. Our results identify a subset of tumor-infiltrating leukocytes as therapy-relevant antigen-presenting cells.

Immunomodulators are effective in controlling hematologic malignancy by initiating or reactivating host antitumor immunity to otherwise poorly immunogenic and immune suppressive cancers. We aimed to boost antitumor immunity in B-cell lymphoma by developing a tumor cell vaccine incorporating ␣-galactosylceramide IntroductionHematologic malignancies typically express the necessary machinery for eliciting antitumor immunity, such as costimulatory molecules, yet many tumors are poorly immunogenic. Therapeutic vaccination strategies that incorporate immune adjuvants are likely to enhance immune recognition and targeting of hematologic cancers, an example being in mice vaccinated against mouse lymphomas with whole tumor cells loaded with CpG adjuvant. 1 Natural killer T (NKT) lymphocytes represent an immune regulatory population with recognized capacity for inducing innate (eg, NK cells) and adaptive (eg, CD8 T cell) antitumor immunity, [2][3][4] by their unique ability to rapidly produce large quantities of cytokines on TCR ligation, in particular IFN-␥. 5,6 As a result, the synthetic CD1d-dependent NKT cell ligand ␣-galactosylceramide (␣-GalCer) has been used for its NKT cell-mediated immune adjuvant properties in anticancer therapies. [7][8][9][10] Initial attempts to stimulate NKT cells in situ were to simply infuse soluble ␣-GalCer, which briefly inhibited the tumor growth, but had limited effects on survival. 11,12 In addition, multiple injections of ␣-GalCer led to deleterious effects including long-term NKT cell functional anergy or unresponsiveness. 12 Subsequently, ␣-GalCer was loaded onto dendritic cells (DCs) as a vaccine. This approach induced more potent antitumor effects than soluble ␣-GalCer injections, mainly by prolonging NKT cell IFN-␥ production and preventing induction of NKT cell anergy, and was able to significantly improve the activity of the DC vaccine if coadministered with tumor antigens. 10,13,14 The cumbersome nature of inducing and expanding DC from patients' peripheral blood monocytes for autologous ␣-GalCerpulsed DC therapy stimulated the use of irradiated tumor cells as a vehicle to deliver ␣-GalCer in vivo. [15][16][17] Here a full complement of tumor antigens (including undefined ones) and ␣-GalCer are codelivered, thus allowing generation of innate immunity and potentially long-term tumor-specific T-cell adaptive immunity. In a prophylactic setting, whole tumor cells loaded with ␣-GalCer were able to protect mice against subsequent challenge with live tumor cells 15,16 and were also shown to be partially effective at inhibiting growth of established solid tumors 17 (S.R.M., K.S., M. Li, H.D., S.F. Ngiow, M.J.S., Transient Foxp3 ϩ regulatory T cell depletion enhances therapeutic anticancer vaccination targeting the immunestimulatory properties of NKT cells, manuscript submitted, August 2012), demonstrating the ability of this vaccine to work successfully in a The online version of this article contains a data supplement.The publication costs of this article were defrayed in part by ...

The natural killer T (NKT) cell ligand, alpha-galactosylceramide (α-GalCer), represents a potential adjuvant to boost immunotherapeutic vaccination strategies against poorly immunogenic cancers. The objective of this study was to assess the therapeutic potential of an α-GalCer-loaded tumor-cell vaccine against solid tumors in mice and to enhance the effectiveness of this approach by removing immune suppression associated with the activity of Foxp3(+) regulatory T cells (Tregs). In the B16F10 melanoma model, we show that single vaccination with irradiated, α-GalCer-loaded tumor cells resulted in suppression of established subcutaneous (s.c.) B16F10 tumor growth, which was mediated by NKT cell-dependent IFN-γ production and enhanced in the absence of IL-17 A. Selective depletion of Foxp3(+) Tregs in transgenic DEpletion of REGulatory T cells (DEREG) mice led to significant inhibition of B16F10 tumor growth and enhanced survival of mice receiving vaccination. Short-term elimination of Foxp3(+) Tregs (<7 days) was sufficient to boost vaccine-induced immunity. Enhanced antitumor activity with combination therapy was associated with an increase in systemic NK cell and effector CD8(+) T-cell activation and IFN-γ production, as well as infiltration of effector CD8(+) T cells into the tumor. Overall, these findings demonstrate that transient depletion of Foxp3(+) Tregs constitutes a highly effective strategy to improve the therapeutic efficacy of anticancer vaccination with NKT cell adjuvants.