Tumor-targeted IL-2 amplifies T cell-mediated immune response induced by gene therapy with single-chain IL-12

Induction, maintenance, and amplification of tumor-protective immunity afte r cytokine gene therapy is essential for the clinical success of immunother apeutic approaches. We investigated whether this could be achieved by singl e-chain IL-12 (scIL-12) gene therapy followed by tumor-targeted IL-2 using a fusion protein containing a tumor-specific recombinant anti-ganglioside G D(2) antibody and IL-2 (ch14.18-IL-2) in a poorly immunogenic murine neurob lastoma model. Herein, we demonstrate the absence of liver and bone marrow metastases after a lethal challenge with NXS2 wild-type cells only in mice (five of six animals) vaccinated with scIL-12-producing NXS2 cells and give n a booster injection of low-dose ch14.18-IL-2 fusion protein. This tumor-p rotective immunity was effective 3 months after initial vaccination, in con trast to control animals treated with a non-specific fusion protein or an e quivalent mixture of antibody and IL-2, Only vaccinated mice receiving the tumor-specific ch14.18-IL-2 fusion protein revealed a reactivation of CD8() T cells and subsequent MHC class I-restricted tumor target cell lysis in vitro. The sequential increase in the usage of TCR chains V beta 11 and -13 in mouse CD8(+) T cells after vaccination and amplification with ch14.18-I L-2 suggests that the initial polyclonal CD8(+) T cell response is effectiv ely boosted by targeted IL-2. In conclusion, we demonstrate that a successf ul boost of a partially protective memory T cell immune response that is in duced by scIL-12 gene therapy could be generated by tumor-specific targetin g of IL-2 with a ch14.18-IL-2 fusion protein. This approach could increase success rates of clinical cancer vaccine trials.