Intratumoral IL-12 gene electrotransfer-mediated regression of established B16F10 melanoma protects against rechallenge

Abstract

Abstract Melanoma is an aggressive tumor with limited treatment options and poor prognosis. Interleukin-12 (IL-12) is a potent cytokine mediating antitumor activity. However, it has only achieved modest antitumor effects in clinical trials, often accompanied by unacceptable adverse events. We evaluated whether intratumoral delivery of a plasmid encoding IL-12 using gene electrotransfer (GET) to control the dose could induce rejection of an established poorly immunogenic tumor and avoid dose dependent toxicities. We treated B16F10 murine melanoma 3 times in 1 week by intratumoral injection of pUMVC3mIL-12 plasmid (pmIL-12, 50 μg) followed by GET. The GET protocols were; EP1 (six 300 V/cm, 100 μs pulses with an array of 6 penetrating electrodes), EP2 (ten 600 V/cm, 5ms pulses with non-penetrating caliper electrodes). Localized delivery of pmIL-12 with GET in the tumor microenvironment, significantly delayed disease development and prolonged disease free survival and induced long term immune memory protecting against rechallenge. The response was associated with a significant reduction in Treg and MDSC infiltration in B16F10 melanoma and increase of Granzyme B. Mice treated with pmIL-12 EP1 that achieved protection against rechallenge were observed to have CD62LlowCD44high memory T cells. Interestingly, pmIL-12 demonstrated stronger anti-tumor effects than pmIL-12 delivered by EP2. By manipulation of GET parameters the onset, level and duration of IL-12 protein expression can be controlled, resulting in meaningful therapeutic effects without associated IL-12 toxicities. Furthermore, the approach induced systemic antitumor immune activity and memory and therefore might have an impact against other types of metastatic disease.