Canarypox Virus-Mediated Interleukin 12 Gene Transfer into Murine Mammary Adenocarcinoma Induces Tumor Suppression and Long-Term Antitumoral Immunity

Abstract

The antitumoral activity of recombinant canarypox virus vectors (ALVAC) expressing murine interleukin 12 (IL-12) was evaluated in the syngeneic, nonimmunogenic murine mammary adenocarcinoma model (TS/A). Seven-day preestablished subcutaneous tumors (5- to 6-mm mean diameters) were injected on days 7, 10, 14, 17, 21, and 24 with the vector ALVAC-IL12 at 2.5 × 10⁵ TCID₅₀ (50% tissue culture infective dose). Total tumor regression occurred in 40 to 50% of the treated mice. Furthermore, 100% of the cured mice were protected against a contralateral subsequent challenge with the TS/A parental cells on day 28. The ALVAC-IL12 treatment is not effective in nude mice, suggesting the critical role of T cells. CD4 and CD8 T cells infiltrated the tumors treated with ALVAC-IL12 in the BALB/c model. Furthermore, in vivo depletion of CD4⁺ T cells totally abrogated the induction of the long-term antitumoral immune response by ALVAC-IL12. Interestingly, some tumor growth inhibition was also observed with ALVAC-βGal treatment and a vaccinal effect was found in 33% of the treated animals, suggesting an adjuvant effect of the vector itself. Other ALVAC vectors expressing murine cytokines (IL-2, GM-CSF, IFN-γ) were evaluated in the same model. Major antitumoral activity was observed with ALVAC-GM-CSF. However, a combination of ALVAC-GM-CSF and AL-VAC-IL12 had no synergistic effect. These results suggest that in vivo gene transfer with canarypox virus expressing IL-12 may provide an effective and safe strategy for the treatment of human cancers.

Overview summary

In the present study, we evaluated the antitumoral effect of direct in vivo gene therapy, using a canarypox virus recombinant vector expressing IL-12 (ALVAC-IL12), in a poorly immunogenic tumor model. In humans, the recombinant ALVAC vectors expressing foreign viral proteins have already been shown to be safe and efficient for vaccination. Their ability to induce cytotoxic T lymphocyte (CTL) priming has led to interest in their use for cancer immunotherapy. We demonstrate here the antitumoral and vaccinal effects of repeated intratumoral injections of ALVAC-IL12 in a murine mammary adenocarcinoma (TS/A). The adjuvant effect of the vector, combined with the local secretion of the cytokine, induced the eradication of preestablished tumors and led to a long-term antitumoral immune response. Other ALVAC constructs expressing IL-2, GM-CSF, or IFN-γ were evaluated in the same model. Antitumoral activity was also observed with ALVAC-GM-CSF. These results support the feasibility of in vivo gene therapy with ALVAC-IL12 for the treatment of human cancer.