Direct Intratumoral Injection of an Adenovirus Expressing Interleukin-12 Induces Regression and Long-Lasting Immunity That Is Associated with Highly Localized Expression of Interleukin-12

Abstract

Mice bearing breast tumors were treated with a single dose of an adenovirus expressing interleukin-12 (AdmlL-12.1) injected intratumorally, which produced regressions in greater than 75% of the treated tumors; approximately one-third of the animals remained tumor free. Complete regression was associated with immunity to secondary challenge with fresh tumor cells. Analysis of local cytokine expression demonstrated maximum expression of IL-12 within the tumor between 24 and 72 hr post-injection, reaching 600–800 ng per tumor, with elevated local levels of IL-12 detectable for at least 9 days. This expression was highly localized as serum IL-12 peaked at 40–60 ng/ml at 24 hr and was less than 10 ng/ml from day 3 onward. Interferon-γ (IFN-γ) concentrations were markedly increased within the tumor following AdmIL-12.1 administration, demonstrating that IL-12 was acting locally. Tumor-draining lymph node cells spontaneously produced IFN-γ following AdmIL-12.1 treatment, suggesting these cells were activated by IL-12. These data demonstrate that AdmIL-12.1 can be used to deliver very high levels of localized cytokine production. Moreover, we have confirmed that the IL-12 produced from our vector actually affects the local cytokine environment of the tumor and activates responder cells present within the tumor. The systemic toxicities associated with many recombinant cytokines can limit their use in vivo for cancer immunotherapy. We have directly infected murine tumors in vivo with an adenoviral vector expressing interleukin-12 (IL-12) to generate high intratumoral cytokine levels. This treatment lead to tumor regression and long-term immunity in those animals whose tumors regressed completely. The expression of IL-12 was localized primarily to the tumor, resulted in an increase in interferon-γ(IFN-γ) levels within the tumor, and promoted IFN-γ expression in the cells from the draining lymph node. These data demonstrate that adenoviral vectors can be used to produce very high levels of cytokine locally. Moreover, we have confirmed that intratumoral IL-12 production can alter the local cytokine environment of the tumor and activate responder cells present within the tumor.