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The tumor microenvironment in leukemia and solid tumors induces a shift of activated CD8+ cytotoxic T cells to an exhausted state, characterized by loss of proliferative capacity and impaired immunologic synapse formation. Efficient strategies and targets need to be identified to overcome T-cell exhaustion and further improve overall responses in the clinic. Here, we took advantage of the Eμ-TCL1 chronic lymphocytic leukemia (CLL) and B16 melanoma mouse models to assess the role of the homophilic cell-surface receptor SLAMF6 as an immune-checkpoint regulator. The transfer of SLAMF6+ Eμ-TCL1 cells into SLAMF6−/− recipients, in contrast to wild-type (WT) recipients, significantly induced expansion of a PD-1+ subpopulation among CD3+CD44+CD8+ T cells, which had impaired cytotoxic functions. Conversely, administering anti-SLAMF6 significantly reduced the leukemic burden in Eμ-TCL1 recipient WT mice concomitantly with a loss of PD-1+CD3+CD44+CD8+ T cells with significantly increased effector functions. Anti-SLAMF6 significantly reduced leukemic burden in the peritoneal cavity, a niche where antibody-dependent cellular cytotoxicity (ADCC) is impaired, possibly through activation of CD8+ T cells. Targeting of SLAMF6 affected tumor growth not only in B cell–related leukemia and lymphomas but also in nonhematopoietic tumors such as B16 melanoma, where SLAMF6 is not expressed. In vitro exhausted CD8+ T cells showed increased degranulation when anti-human SLAMF6 was added in culture. Taken together, anti-SLAMF6 both effectively corrected CD8+ T-cell dysfunction and had a direct effect on tumor progression. The outcomes of our studies suggest that targeting SLAMF6 is a potential therapeutic strategy.

Purpose: Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine tumor, often metastatic at presentation, for which current chemotherapeutic regimens are largely ineffective. As its pathogenesis is still unknown, we hypothesized that deregulation of signaling pathways commonly activated in cancer may contribute to MCC tumorigenesis and may provide insights into targeted therapy approaches for this malignancy.Experimental Design: We retrospectively profiled 60 primary MCC samples using a SNaPshot-based tumor genotyping assay to screen for common mutations in 13 cancer genes.Results: We identified mutations in 9 (15%) MCC primary tumors, including mutations in TP53 (3 of 60) and activating mutations in the PIK3CA gene (6 of 60). Sanger sequencing of the primary MCC tumors detected one additional PIK3CA mutation (R19K) that had not been previously described in cancer. Merkel cell polyoma virus (MCPyV) was detected in 38 (66%) MCC cases and patients with MCPyV-positive cancers showed a trend toward better survival. With one exception, the presence of MCPyV and activating mutations in PIK3CA appeared mutually exclusive. We observed that signaling through the PI3K/pAKT pathway was active in one MCPyV-positive and in all MCPyV-negative MCC cell lines, as evidenced by AKT phosphorylation. Importantly, the presence of a PIK3CA-activating mutation was associated with sensitivity to treatment with ZST474, a specific phosphoinositide 3-kinase (PI3K) inhibitor, and to NVP-BEZ235, a dual PI3K/mTOR inhibitor, targeted agents under active clinical development.Conclusions: PI3K pathway activation may drive tumorigenesis in a subset of MCC and screening these tumors for PIK3CA mutations could help identify patients who may respond to treatment with PI3K pathway inhibitors. Clin Cancer Res; 18(5); 1227–36. ©2012 AACR.

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The tumor microenvironment in leukemia and solid tumors induces a shift of activated CD8+ cytotoxic T cells to an exhausted state, characterized by loss of proliferative capacity and impaired immunologic synapse formation. Efficient strategies and targets need to be identified to overcome T-cell exhaustion and further improve overall responses in the clinic. Here, we took advantage of the Eμ-TCL1 chronic lymphocytic leukemia (CLL) and B16 melanoma mouse models to assess the role of the homophilic cell-surface receptor SLAMF6 as an immune-checkpoint regulator. The transfer of SLAMF6+ Eμ-TCL1 cells into SLAMF6−/− recipients, in contrast to wild-type (WT) recipients, significantly induced expansion of a PD-1+ subpopulation among CD3+CD44+CD8+ T cells, which had impaired cytotoxic functions. Conversely, administering anti-SLAMF6 significantly reduced the leukemic burden in Eμ-TCL1 recipient WT mice concomitantly with a loss of PD-1+CD3+CD44+CD8+ T cells with significantly increased effector functions. Anti-SLAMF6 significantly reduced leukemic burden in the peritoneal cavity, a niche where antibody-dependent cellular cytotoxicity (ADCC) is impaired, possibly through activation of CD8+ T cells. Targeting of SLAMF6 affected tumor growth not only in B cell–related leukemia and lymphomas but also in nonhematopoietic tumors such as B16 melanoma, where SLAMF6 is not expressed. In vitro exhausted CD8+ T cells showed increased degranulation when anti-human SLAMF6 was added in culture. Taken together, anti-SLAMF6 both effectively corrected CD8+ T-cell dysfunction and had a direct effect on tumor progression. The outcomes of our studies suggest that targeting SLAMF6 is a potential therapeutic strategy.

Purpose: Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine tumor, often metastatic at presentation, for which current chemotherapeutic regimens are largely ineffective. As its pathogenesis is still unknown, we hypothesized that deregulation of signaling pathways commonly activated in cancer may contribute to MCC tumorigenesis and may provide insights into targeted therapy approaches for this malignancy. Experimental Design: We retrospectively profiled 60 primary MCC samples using a SNaPshot-based tumor genotyping assay to screen for common mutations in 13 cancer genes. Results: We identified mutations in 9 (15%) MCC primary tumors, including mutations in TP53 (3 of 60) and activating mutations in the PIK3CA gene (6 of 60). Sanger sequencing of the primary MCC tumors detected one additional PIK3CA mutation (R19K) that had not been previously described in cancer. Merkel cell polyoma virus (MCPyV) was detected in 38 (66%) MCC cases and patients with MCPyV-positive cancers showed a trend toward better survival. With one exception, the presence of MCPyV and activating mutations in PIK3CA appeared mutually exclusive. We observed that signaling through the PI3K/pAKT pathway was active in one MCPyV-positive and in all MCPyV-negative MCC cell lines, as evidenced by AKT phosphorylation. Importantly, the presence of a PIK3CA-activating mutation was associated with sensitivity to treatment with ZST474, a specific phosphoinositide 3-kinase (PI3K) inhibitor, and to NVP-BEZ235, a dual PI3K/mTOR inhibitor, targeted agents under active clinical development. Conclusions: PI3K pathway activation may drive tumorigenesis in a subset of MCC and screening these tumors for PIK3CA mutations could help identify patients who may respond to treatment with PI3K pathway inhibitors. Clin Cancer Res; 18(5); 1227–36. ©2012 AACR.

Background: Merkel cell carcinoma (MCC) is a rare, aggressive cutaneous neuroendocrine tumor, often metastatic at presentation, with a median survival time of 6.8 months for stage IV disease. Current chemotherapeutic regimens are largely ineffective. It is still unknown whether established oncogenes or tumor suppressors are major players in the pathogenesis of MCC. Recently, a new polyomavirus has been identified in 50 to 80% of MCC, but a mechanistic role for this virus in the pathogenesis of MCC has not yet been demonstrated. We hypothesized that deregulation of signaling pathways that are commonly activated in cancer may contribute to MCC tumorigenesis and may provide insights into targeted therapy approaches for this malignancy. Design: We retrospectively profiled 60 primary MCC samples diagnosed at the MGH from 1995 to 2010 using a recently developed SNaPshot genotyping assay to screen for the presence of common mutations in 13 cancer genes, many of which are targeted by FDA approved drugs or by targeted agents undergoing clinical trials. In addition, all MCC samples were tested for the presence of Merkel cell polyomavirus (MCPyV) using PCR. Results: The SnaPshot assay identified mutations in 15% (9/60) of MCC primary tumors. The TP53 tumor suppressor gene was mutated in 3 of 60 cases and activating mutations in the p110 alpha subunit of the phosphatidylinositol 3-kinase (PIK3CA) gene were found in 6 of 60 cases. Sanger sequencing of the primary MCC tumors identified one additional PIK3CA mutation (R19K) that has not been previously described in cancer. In primary MCC cell lines, we observed that the presence of a PI3KCA activating mutation was associated with sensitivity to treatment with NVP-BEZ-235, a dual PI3K-mTOR inhibitor currently under active clinical development. Clinical correlations with PIK3CA mutational status and the presence of MCPyV are ongoing. Conclusions: We discovered that a subset of patients with MCC (10%) carry activating mutations in PIK3CA. Furthermore, we found that a MCC cell line harboring a PIK3CA mutation is selectively sensitive to a PI3K inhibitor under clinical development. Our results suggest the relevance of screening patients with MCC for activation of the PI3K pathway, as these cancers may be particularly sensitive to PI3K pathway inhibitors. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 102nd Annual Meeting of the American Association for Cancer Research; 2011 Apr 2-6; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2011;71(8 Suppl):Abstract nr 2210. doi:10.1158/1538-7445.AM2011-2210