GENERATION OF AN ANTITUMOR IMMUNE-RESPONSE IN A NONIMMUNOGENIC TUMOR - HSVTK KILLING IN-VIVO STIMULATES A MONONUCLEAR CELL INFILTRATE AND ATH1-LIKE PROFILE OF INTRATUMORAL CYTOKINE EXPRESSION

Direct delivery of the herpes simplex virus thymidine kinase (HSVtk) g ene, in combination with the prodrug ganciclovir (GC), has been used f or the treatment of localised, inoperable tumours. Several groups have shown that when rodent tumours are ablated in vivo with suicide genes , antitumour immunity can also be generated, Hence, this approach may also be useful in treating disseminated disease. Here we have studied the mechanisms associated with this anti-tumour immunity. In B16 HSVtk (+) tumours being killed in vivo with GC treatment, we observed the in duction of a pronounced intratumoural infiltrate of macrophages, CD4() and CD8(+) T cells. In addition, using reverse transcriptase polymer ase chain reaction, expression of interleukin (IL)-2, IL-12, interfero n-gamma (IFN-gamma), tumor necrosis factor-alpha (TNF-alpha) and granu locyte/macrophage colony-stimulating factor (GMCSF) but not IL-4, IL-6 or IL-IO, was observed, a profile of cytokine expression which resemb les that of a Th I immune response, To complement these findings, we a lso investigated the mechanisms by which expression of HSVtk leads to cell death. Our data show that B16/HSVtk(+) cells die predominantly by necrosis, rather than apoptosis, on exposure to GC, a process which m ay be associated with the generation of anti-tumour inflammatory respo nses. From these data we propose a model for the induction of anti-tum our immunity using suicide genes and discuss the development of improv ed vectors for gene therapy to augment these effects in vivo. (C) 1997 Wiley-Liss, Inc.