Abstract LB-430: Anti-polyomavirus CTL targeting Merkel cell carcinoma combined with MHC class I upregulation induces tumor regression (2012)

Abstract Merkel cell carcinoma (MCC) represents a highly aggressive neuroendocrine skin malignancy with 46% 5 year disease-associated mortality making it 3x as lethal as melanoma. Merkel cell polyomavirus (MCPyV), a recently discovered viral agent related to SV40, is clonally integrated into ∼80% of MCC tumors. MCPyV produces T Antigen (T-Ag) oncoproteins that are persistently expressed, necessary for survival and proliferation of most MCCs, representing an optimal target for immunotherapy. An HLA A*2402-restricted T-Ag epitope recognized by autologous CD8+ T-cells was identified in a patient with MCC. The presence of a small endogenous population (0.1% of CD8+ T-cells) of MCC-specific CD8+ T-cells failed to prevent new metastases, and responses may have been impaired by MHC class I down-regulation observed in the patient's tumor. As adoptively transferred antigen-specific T cells (CTL) have demonstrated clinical benefit in other tumor settings, we set out to examine the safety, in vivo persistence and anti-tumor effect of CTL targeting MCC. Autologous polyclonal antigen-specific CD8+ T cells targeting the HLA A*2402-restricted epitope of the MCPyV T-Ag oncoprotein were generated for this patient. Ex-vivo cultures were supplemented with the γc-chain cytokine IL-21, which has been demonstrated to promote less terminal differentiation of cultured cells as a means to increase CTL in vivo survival. To induce tumor MHC class I up-regulation with minimal confounding therapeutic effect, the patient received a single intra-lesional injection of 3.3 x 106 IU IFNβ 1B to 1 of 3 measurable metastatic lesions 24h prior to a first infusion of 1010/m2 of polyclonal multimer sorted MCPyV-specific CTL. Four weeks later, a single 8Gy dose of radiation to detectable disease was followed 24h later by a second T cell infusion. Both infusions were followed by low-dose IL-2 (500,000 IU/m2 s.c. x 14 days). The patient experienced no treatment-associated side effects. Four weeks after the first infusion, the metastatic lesion infused with IFNβ 1B regressed by 40% whereas the non-infused lesions increased by an average of 32%. Eight weeks after the second infusion, all lesions had regressed by an average of 62% with complete disappearance of the metastatic lesion previously infused with IFNβ 1B, and no development of new systemic lesions. Infused CTL peaked at 8% of total CD8+ T cells 7 days after infusions and persisted at ≥1% for at least 6 weeks. Infused CTL remained polyfunctional (secretion of IFNγ, TNFα and IL-2 in response to cognate antigen) over the observed period. Overall, this first-in-human trial suggests infusion of IL-21 derived polyclonal CTL targeting MCPyV is safe, and combined with up-regulation of tumor MHC class I, promotes in vivo tumor regression. Plans are underway to extend this investigational treatment to MCC patients with a broader array of MHC-restricted viral epitopes. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-430. doi:1538-7445.AM2012-LB-430