Chemokines expressed in melanoma metastases associated with T cell infiltration

Abstract

8501 Background: Despite frequent induction of tumor antigen-specific T cells in melanoma patients following vaccination, tumor regressions remain rare. This observation prompted systematic analysis of the melanoma tumor microenvironment to identify factors that may influence the effector phase of the anti-tumor immune response. Methods: Gene expression profiling using the Affymetrix platform was performed on a series of melanoma metastases, melanoma cell lines, and primary melanocyte cell lines. Confirmatory assays were done by real-time RT-PCR, protein array, immunohistochemistry (IHC), and in vitro chemokine migration assays. Results: Non- supervised hierarchical clustering revealed 3 major subsets of tumors, with the main clustering based on differential expression of T cell-derived transcripts. The presence of CD8+ T cells was confirmed by IHC. Tumors that contained T cells uniquely expressed high levels of multiple chemokines. Protein array confirmed high expression of CCL2, CCL4, and CCL5; real-time RT-PCR additionally confirmed relatively high levels of CXCL9, CXCL10, and CCL3 transcripts. Transwell assays confirmed that each of these 6 chemokines recruited CD8+ effector cells in vitro. Conclusions: We have identified a set of 6 chemokines that likely regulates recruitment of activated T cells into melanoma metastases. Tumors that lack such chemokines might not be capable of supporting the effector phase of the anti-tumor immune response. We suggest that chemokine profiling of tumor sites should be performed in clinical trials of active immunotherapy. No significant financial relationships to disclose.