032 Suppressor of cytokine signaling 2 directs early tumor-immune escape of skin cancer

S | Adaptive Immunity & Vaccination 031 Experimental therapeutic melanoma vaccination by ECP-generated dendritic cells A Ventura, A Vassal, E Robinson, J Wang, K Meeth, L Bianchi, S Chimenti, M Bosenberg and R Edelson 1 Dermatology, Yale University, New Haven, CT and 2 Dermatology, University of Rome Tor Vergata, Rome, Italy Extracorporeal Photochemotherapy (ECP) is a widely used immunotherapy for cutaneous T cell lymphoma, as well as an immunomodulatory treatment for graft versus host disease (GVHD) and rejection of allografts. We hypothesized that ECP’s physiologic induction of large-scale monocyte-to-dendritic antigen presenting cell (DC-E) conversion is mechanistically responsible for both its anti-cancer effect (immunizing mature DC-E) and its tolerogenic impact in the transplant setting (8-MOP-maturationally truncated DC-E). To interrogate this possibility, we developed an ECP device that is scalable from mouse to man and tested its capacity to produce DC that, when advantageously tuned and tumor antigen-loaded, can limit the growth of otherwise lethal tumors in the engineered Yale University Mouse Melanoma(YUMM1.7) model (driven by PTEN loss and BRAF activation). Untreated control mouse tumors (N1⁄4217) were 10-fold (p 50% reduction of dermally-implanted B16 (p 80% reduction in EL4 thymoma growth (p<.01) with higher antigen-specific IFNg-producing T cells detected in tumor draining LNs and spleen (p<.01). Acute DC-specific loss of SOCS2 in DC at the time of tumor implantation resulted in <50% B16 tumor growth (p<.001) with enhanced CD8/Treg ratio in TILS in a therapeutic model and expanded antigen-specific T cell activity in a model of anti-tumor immunization. Global and DC-specific (but not T cell-specific) loss of SOCS2 during immune priming with proteinimmunization reveals SOCS2 regulates adaptive T effector activity distinctly from memory T cell proliferation suggesting drugs which target SOCS2 could be used in combination with current immunotherapy including anti-PD1 blockade. Collectively, these data identify SOCS2 as a critical determinant of tumor-immune escape and target for immunotherapy. 033 CCL22 to divert regulatory T cells and control melanoma tumor growth S Henning, F Navarro, P Farhangi Oskuei, K Tobin, M Fernandez, J Eby, J Klarquist, S Chatterjee, S Mehrotra, J Clark and I Le Poole 1 Loyola University Chicago, Maywood, IL, 2 Cincinnati Children’s Hospital, Cincinnati, OH, 3 Medical University of South Carolina, Charleston, SC and 4 Loyola University Medical Center, Maywood, IL An abundance of regulatory T-cells (Tregs) in melanoma tumors correlates with poor prognosis, while serving to avert autoimmunity in other tissue sites. This prompted our efforts to reduce intratumoral Treg content in melanoma while keeping autoimmune side effects at bay. Probing chemokine expression in tumors we observed overexpression of Treg chemoattractant CCL22 (5-fold) and CCL1 (8-fold) in melanoma tumors when compared to unaffected skin, accompanied by infiltrating FoxP3 T cells. When assessing chemokine receptor expression on circulating Treg, a two-fold, significantly enhanced expression of CCR4 was evident among a greater proportion of Tregs in melanoma. As CCR4 overexpression was not found among CD8 T cells, Treg may be selectively redirected away from tumors that otherwise defy immune surveillance, while also suppressing autoimmune side effects of treatment. A marked increase in FOXP3 Treg migration to skin sites can be achieved in response to CcL22 vaccination in mice. When mice were subjected to repeated gene gun vaccinations and challenged with melanoma cells before monitoring pulmonary melanoma growth, 2.5-fold greater tumor counts and 6.5-fold greater Treg densities were found in untreated mice. Vaccination is accompanied by relatively increased cutaneous Treg abundance, which cannot be assigned to intratumoral conversion to Treg. Repeated treatment may be necessary for sustained and complete tumor surveilance, yet these findings demonstrate the treatment potential of topical CCL22 introduced to support anti-tumor responses while suppressing autoimmune side effects in the treatment of metastatic melanoma. 034 Recombinant replication competent attenuated vaccinia virus expressing human Flt3L for cancer immunotherapy W Wang, P Dai, S Shuman, T Merghoub, JD Wolchok and L Deng 1 Dermatology Service/Department of Medicine, Memorial Sloan Kettering Cancer Center, New York, NY, 2 Molecular Biology Program, Memorial Sloan Kettering Cancer Center, New York, NY and 3 Department of Medicine/Immunology Program, Memorial Sloan Kettering Cancer Center, New York, NY Poxviruses, such as engineered vaccinia viruses, are in the forefront as oncolytic therapy for metastatic cancers. Poxviruses are well suited as vectors to express multiple transgenes in cancer cells and tumor microenvironment and thus to enhance therapeutic efficacy. Preclinical studies and clinical trials have demonstrated efficacy of using oncolytic vaccinia viruses for treatment of advanced cancers refractory to conventional therapy. Here we report that we have constructed a replication competent attenuated vaccinia virus with the deletion of the Z-DNA-binding domain of E3L gene as well as the viral thymidine kinase gene (E3LD83N-TK), expressing human Flt3L (Fms-like tyrosine kinase 3 ligand). E3LD83N is 1,000-fold more attenuated than wild-type (WT) vaccinia and the deletion of TK allows more tumor selective replication of the virus. In addition, Flt3L plays a critical role in the development of DC subsets, including CD8a/CD103 DCs. We find that intratumoral injection of E3LD83N-TK-hFlt3L viruses is more efficacious than E3LD83N-TK in the eradication of injected tumors and regression of distant non-injected tumors, as well as in extending the survival of treated mice, in a bilateral B16-F10 murine melanoma implantation model. We also find that the combination of intratumoral delivery of virotherapy and systemic delivery of immune checkpoint blockade such as anti-CTLA-4 or anti-PD-1/PD-L1 antibodies results in enhanced antitumor effects than either agent alone. We find that the survived mice have developed systemic anti-tumor immunity and are capable of rejecting the challenge of an intravenously delivered lethal dose of B16-F10 melanoma cells. Taken together, our innovative design based on our knowledge of virus-host interaction improves the efficacy and safety of poxvirus-based oncolytic and immunotherapeutics.