Persistent expression of Merkel cell polyomavirus (MCPyV) T antigen oncoproteins is required for the growth of most Merkel cell carcinomas (MCCs). MCPyV oncoproteins are thus attractive tumor antigens for evaluating the feasibility of antigen-specific adoptive T-cell therapy in MCC. Importantly, unlike mammalian tumor associated antigens that have some degree of expression within normal tissues, MCPyV oncoprotein expression is restricted to MCCs. We have recently identified several dozen MCC-associated viral peptides recognized by T cells. However, a major challenge for T cell therapy is that MCCs often downregulate HLA-I expression (51% of 114 tumors). We report that a single dose of either radiotherapy (2-8 Gy) or intralesional interferon reverses HLA-I downregulation in MCCs and can be used as an adjuvant in combination with virus-specific T cells for a multi-modality approach to target MCC.

The feasibility and efficacy of this combined treatment has been explored in a 68 year-old man. He initially presented with a primary MCC on the hip that expressed low levels of HLA-I, high levels of MCPyV oncoprotein, and contained MCPyV-specific CD8 T cells. Based on rising antibody titers to MCPyV T-antigen, he was later found to have peri-pancreatic metastases. Blood-derived virus-specific T cells failed to respond to peptide challenge and expressed high levels of T cell exhaustion markers PD-1 and Tim-3. We used a novel approach to generate functional, polyclonal virus-specific therapeutic T cells. Lymphocytes from blood were cultured with peptide-loaded autologous dendritic cells, IL-2, IL-7, and IL-21, then sorted using an HLA-I/peptide tetramer and further expanded. 86% of these polyclonal CD8+ T cells were virus-specific and killed appropriate target cells. 24h after injecting interferon-beta into a pancreatic metastasis, the patient received 10^10 T cells/m2. Four weeks later, a single 8 Gy dose of radiation was given to the tumor area and was followed by a second T cell infusion 24h later. Treatment was well tolerated. After 2 treatments, all 3 metastatic lesions had markedly responded (>60% shrinkage by RECIST). No new distant disease has been detected at 456 days after the first metastasis (far beyond a median of 200 days for historical stage-matched controls). At >140 days after initiation of therapy, each of the following parameters remained markedly increased (relative to pre-treatment baseline) among virus-specific T cells in the blood: frequency, proliferation (Ki-67) and antigen-induced interferon-gamma production. TCR sequence analysis was used to track the prevalence and tumor infiltration of infused T cell clonotypes. After treatment, an increased fraction of virus-specific T cells was observed in the metastasis compared to a pre-treatment biopsy of the primary tumor. The use of polyclonal T cells may have been important because we observed that only a subset of the infused clones effectively infiltrated the sampled metastasis. This study represents a first-in-man treatment of a carcinoma using T cells targeting an oncogenic viral antigen and benefitted from the ability to accurately track adoptively transferred T cells specific for a non-self tumor antigen.

Citation Format: Olga Afanasiev, Aude Chapuis, Jayasri Iyer, Kotaro Nagase, Kelly Paulson, Aaron Seo, Ivy Lai, Ilana Roberts, Erik Farrar, Joo Ha Hwang, Upendra Parvathaneni, David Koelle, Cassian Yee, Paul Nghiem. Merkel cell carcinoma therapy with viral oncoprotein-specific T cells in combination with immunostimulatory adjuvants. [abstract]. In: Proceedings of the AACR Special Conference on Tumor Immunology: Multidisciplinary Science Driving Basic and Clinical Advances; Dec 2-5, 2012; Miami, FL. Philadelphia (PA): AACR; Cancer Res 2013;73(1 Suppl):Abstract nr IA17.