Uveal Melanoma Cell-Based Vaccines Activate Tumor-Cytolytic T Lymphocytes

Abstract

Purpose: : Uveal melanoma metastasizes in approximately 50% of patients and there is currently no therapy that either, prevents the development of metastases, or prolongs the survival of patients with metastases. We are exploring immunotherapy as an alternative or adjunctive treatment for uveal melanoma patients with liver metastases. Uveal melanoma may be particularly appropriate for immunotherapy because primary tumors arise in an immune privileged site, and may express antigens to which the host is not tolerized. Because of the key role of CD4⁺ T cells in (i) optimizing CD8⁺ T cell immunity, (ii) facilitating immune memory, and (iii) preventing tolerance, we developed cell-based uveal melanoma vaccines that target the activation of CD4⁺ T lymphocytes. The vaccines consist of tumor cells that constitutively express Major Histocompatibility Class I (MHC I), and are transduced with MHC Class II (MHC II) and costimulatory molecule CD80. Our previous data established that vaccines prepared from primary uveal melanomas boosted CD4⁺ T cells from either healthy donors, or uveal melanoma patients. Tumor-specific cytolytic T lymphocytes are critical for successful elimination of progressively growing tumors. Since the vaccine cells co-express MHC I, MHC II, and CD80, and activate tumor-specific CD4⁺ T cells, we hypothesized that uveal melanoma cell-based vaccines would also activate tumor-cytolytic CD8⁺ T lymphocytes.Methods and

Results: : To test this hypothesis, PBMC from healthy donors and uveal melanoma patients were in vitro primed with the vaccine and subsequently stimulated with IL-15. As determined by ⁵¹Cr-release assays, vaccine-primed PBMC non-specifically lysed all target cells. Since we observed that IL-15 non-specifically activated CD56⁺ lymphocytes (CD56⁺/CD3^- NK and CD56⁺/CD3⁺ NKT cells), we depleted CD56⁺ T cells prior to the cytotoxicity assay using magnetic bead sorting. As confirmed by flow cytometry, the remaining cell populations were CD3⁺/CD4⁺ and CD3⁺/CD8⁺ T lymphocytes. CD56^- PBMC specifically lysed unmodified target cells from either primary, or metastatic uveal melanomas, and did not lyse normal human foreskin fibroblasts.

Keywords: melanoma • tumors • immunomodulation/immunoregulation