The indispensable role of CCR5 for in vivo suppressor function of tumor-derived CD103+ effector/memory regulatory T cells.

CD103 is a marker for identification of effector/memory regulatory T cells (Tregs). CD103(+) Tregs are potent suppressors of tissue inflammation in several infectious diseases, autoimmune diseases, and cancers. However, the underlying mechanisms for this potent suppression ability remain unclear. The current study was designed to clarify this issue. Unexpectedly, we found both CD103(+) and CD103(-) Tregs had similar suppression capacity in vitro. We then chose a murine tumor model for investigation of the in vivo behavior of these Tregs. The suppression ability in vivo against the anti-tumor ability of CD8(+) T cells was restricted to CD103(+) Tregs although both Tregs had equal in vitro suppression ability. In addition, CD103(+) Tregs expressed significantly higher levels of CCR5 than those of CD103(-) Tregs and accumulated more in tumors than did CD103(-) Tregs. Furthermore, blockade of CCR5 signaling, either by CCR5(-/-)CD103(+) Tregs or by CCL5 knockdown tumor, could reduce the migration of CD103(+) Tregs into tumors and impair their in vivo suppression ability. In conclusion, these results indicate that the potent in vivo suppression ability of CD103(+) Tregs is due to the tissue-migration ability through CCR5 expression.

Low-pressure pulsed focused ultrasound with microbubbles promotes an anticancer immunological response.

BACKGROUND: High-intensity focused-ultrasound (HIFU) has been successfully employed for thermal ablation of tumors in clinical settings. Continuous- or pulsed-mode HIFU may also induce a host antitumor immune response, mainly through expansion of antigen-presenting cells in response to increased cellular debris and through increased macrophage activation/infiltration. Here we demonstrated that another form of focused ultrasound delivery, using low-pressure, pulsed-mode exposure in the presence of microbubbles (MBs), may also trigger an antitumor immunological response and inhibit tumor growth. METHODS: A total of 280 tumor-bearing animals were subjected to sonographically-guided FUS. Implanted tumors were exposed to low-pressure FUS (0.6 to 1.4 MPa) with MBs to increase the permeability of tumor microvasculature. RESULTS: Tumor progression was suppressed by both 0.6 and 1.4-MPa MB-enhanced FUS exposures. We observed a transient increase in infiltration of non-T regulatory (non-Treg) tumor infiltrating lymphocytes (TILs) and continual infiltration of CD8+ cytotoxic T-lymphocytes (CTL). The ratio of CD8+/Treg increased significantly and tumor growth was inhibited. CONCLUSIONS: Our findings suggest that low-pressure FUS exposure with MBs may constitute a useful tool for triggering an anticancer immune response, for potential cancer immunotherapy.

Apoptosis of tumor infiltrating effector TIM-3+CD8+ T cells in colon cancer.

TIM-3 functions to enforce CD8+ T cell exhaustion, a dysfunctional state associated with the tolerization of tumor microenvironment. Here we report apoptosis of IFN-γ competent TIM-3+ population of tumor-infiltrating CD8+ T cells in colon cancer. In humans suffering from colorectal cancer, TIM-3+ population is higher in cancer tissue-resident relative to peripheral blood CD8+ T cells. Both the TIM-3+ and TIM-3- cancer tissue-resident CD8+ T cells secrete IFN-γ of comparable levels, although apoptotic cells are more in TIM-3+ compared to TIM-3- population. In mouse CT26 colon tumor model, majority of tumor-infiltrating CD8+ T cells express TIM-3 and execute cytolysis function with higher effector cytokine secretion and apoptosis in TIM-3+ compared to TIM-3- population. The tumor cells secrete galectin-9, which increases apoptosis of tumor-infiltrating CD8+ T cells. Galectin-9/TIM-3 signaling blockade with anti-TIM-3 antibody reduces the apoptosis and in addition, inhibits tumor growth in mice. The blockade increases therapeutic efficacy of cyclophosphamide to treat tumor in mice as well. These results reveal a previously unexplored role of TIM-3 on tumor-infiltrating CD8+ T cells in vivo.

Tumor-derived chemokine CCL5 enhances TGF-ß-mediated killing of CD8(+) T cells in colon cancer by T-regulatory cells.

Chemokine CCL5/RANTES is highly expressed in cancer where it contributes to inflammation and malignant progression. In this study, we show that CCL5 plays a critical role in immune escape in colorectal cancer. We found that higher levels of CCL5 expression in human and murine colon tumor cells correlated with higher levels of apoptosis of CD8+ T cells and infiltration of T-regulatory cells (T(reg)). In mouse cells, RNA interference (RNAi)-mediated knockdown of CCL5 delayed tumor growth in immunocompetent syngeneic hosts but had no effect on tumor growth in immunodeficient hosts. Reduced tumor growth was correlated with a reduction in T(reg) infiltration and CD8(+) T-cell apoptosis in tumors. Notably, we found that CCL5 enhanced the cytotoxicity of T(reg) against CD8(+) T cells. We also found tumor growth to be diminished in mice lacking CCR5, a CCL5 receptor, where a similar decrease in both T(reg) cell infiltration and CD8(+) T-cell apoptosis was noted. TGF-ß signaling blockade diminished apoptosis of CD8(+) T cells, implicating TGF-ß as an effector of CCL5 action. In support of this concept, CCL5 failed to enhance the production of TGF-ß by CCR5-deficient T(reg) or to enhance their cytotoxic effects against CD8(+) T cells. CCR5 signaling blockade also diminished the in vivo suppressive capacity of T(reg) in inhibiting the antitumor responses of CD8(+) T cells, in the same way as CCL5 signaling blockade. Together, our findings establish that CCL5/CCR5 signaling recruits T(reg) to tumors and enhances their ability to kill antitumor CD8(+) T cells, thereby defining a novel mechanism of immune escape in colorectal cancer.