Purpose: Many human tumors lose responsiveness to IFN-gamma, providing a possible mechanism for the tumor to avoid immune recognition and destruction. Here we investigate the importance of tumor responsiveness to IFN-gamma in the successful immunotherapy of TC1 tumors that were immortalized with human papillomavirus proteins E6 and E7.
Methods: To investigate the role of IFN-gamma in vivo, we constructed a variant of TC1, TC1.mugR, that is unresponsive to IFN-gamma due to overexpression of a dominant negative IFN-gamma receptor.
Results: Using recombinant Listeria monocytogenes that express HPV-16 E7 (Lm-LLO-E7) to stimulate an antitumor response, we demonstrate that sensitivity to IFN-gamma is required for therapeutic efficacy in that Lm-LLO-E7 induces regression of TC1 tumors but not TC1.mugR. In addition, we show that tumor sensitivity to IFN-gamma is not required for inhibition of tumor angiogenesis by Lm-LLO-E7 or for trafficking of CD4+ and CD8+ T cells to the tumor. However, it is required for penetration of lymphocytes into the tumor mass in vivo.
Conclusions: Our findings identify a role for IFN-gamma in immunity to TC1 tumors and show that loss of tumor responsiveness to IFN-gamma poses a challenge to antigen-based immunotherapy.