Tanapoxvirus expressing interleukin-2 is capable of human melanoma regression in the absence of T cells
Tiantian Zhang, Karim Essani*
Lab of Virology, Department of Biology, Western Michigan University, Kalamazoo, MI, 49008, USA
Background: Melanoma is the deadliest skin cancer with ever-increasing incidence. Oncolytic viruses (OVs) represent a novel approach for cancer therapy by causing tumor lysis and inducing host antitumor immune response. Tanapoxvirus (TPV), which is a benign human virus, appears as a promising OV candidate. Interleukin-2 (IL-2) is a pleiotropic cytokine that activates T cells, natural killer cells and macrophages.
Objectives: We sought to generate a recombinant TPV expressing mouse IL-2 (TPV66R-/mIL-2) via replacing the 66R gene with mIL-2 transgene. By assessing the efficacy of TPV66R-/mIL-2 in regressing melanoma in athymic (T cell deficient) nude mice, we aimed to determine if IL-2 expression would increase the therapeutic efficacy of TPV via a T cell independent mechanism.
Experimental approaches: TPV66R-/mIL-2 was generated via transfecting the wtTPV-infected cells with the engineered plasmid, which targets TPV-66R gene for replacement with mIL-2 transgene. The expression of mIL-2 was confirmed by western blot. Melanoma tumors were induced in nude mice by injecting human melanoma SK-MEL-3 cells subcutaneously. When the tumor volumes reached 45±4.5 mm3, mice were treated with intratumoral injection of viruses.
Results: In cell culture, the expression of IL-2 attenuated virus replication of not only TPV66R-/mIL-2, but also other mutant TPVs when coinfecting with TPV66R-/mIL-2. We show that IL-2 inhibits virus replication through intracellular components and without activating interferon-signaling pathway. Our in vivo results show that TPV66R-/mIL-2 more remarkably regresses the melanoma tumors than wtTPV and TPV66R-. Histopathological studies show that more cell degeneration and increased mononuclear cells such as macrophages are present in the tumors treated with TPV66R-/mIL-2.
Conclusions: The results suggest that TPV66R-/mIL-2 is effectively therapeutic for human melanoma in the absence of T cells.