IFN-gamma-inducible protein-10 is essential for the generation of a protective tumor-specific CD8 T cell response induced by single-chain IL-12 gene therapy

The successful induction of T cell-mediated protective immunity against poo rly immunogenic malignancies remains a major challenge for cancer immunothe rapy. Here, we demonstrate that the induction of tumor-protective immunity by IL-12 in a murine neuroblastoma model depends entirely on the CXC chemok ine IFN-gamma -inducible protein 10 (IP-10). This was established by in viv o depletion of IP-10 with mAbs in mice vaccinated against NXS2 neuroblastom a by gene therapy with a linearized, single-chain (sc) version of the heter odimeric cytokine IL-12 (scIL-12). The efficacy of IP-10 depletion was indi cated by the effective abrogation of scIL-12-mediated antiangiogenesis and T cell chemotaxis in mice receiving s.c. injections of scIL-12-producing NX S2 cells. These findings were extended by data demonstrating that IP-10 is directly involved in the generation of a tumor-protective CD8(+) T cell-med iated immune response during the early immunization phase. Four lines of ev idence support this contention: First, A/J mice vaccinated with NXS2 scIL-1 2 and depleted of IP-10 by, two different anti-IP-10 mAbs revealed an abrog ation of systemic-protective immunity against disseminated metastases. Seco nd, CD8(+) T cell-mediated MHC class I Ag-restricted tumor cell lysis was i nhibited in such mice. Third, intracellular IFN-gamma expressed by prolifer ating CD8(+) T cells was substantially inhibited in IP-10-depleted, scIL-12 NXS2-vaccinated mice. Fourth, systemic tumor protective Immunity was compl etely abrogated in mice depleted of IP-10 in the early immunization phase, but not if IP-10 was depleted only in the effector phase. These findings su ggest that IP-10 plays a crucial role during the early immunization phase i n the induction of immunity against neuroblastoma by scIL-12 gene therapy.