Induction of anti-tumor responses via adoptively transferred, cytokine-gene transduced A-NK cells

Despite successes in animals, cytokine gene expression selectively in human tumors is difficult to achieve due to lack of efficient delivery methods. We previously demonstrated that adoptively transferred, IL-2 activated natural killer (A-NK) cells are very effective in trafficking to, infiltrating and, subsequently, reducing B16 lung tumors in tumor-bearing animals. We therefore speculated that the tumor-seeking A-NK cells could be used for the delivery of cytokines selectively to the tumor microenvironment. However, tumor infiltration by A-NK cells depends on high and often toxic doses of IL-2 to support the transferred A-NK cells' survival and anti-tumor functions. To address this problem, we hypothesized that A-NK cells transduced to express pro-NK cell cytokines would become less dependent on high and potentially toxic amounts of IL-2. Assessments of transduction efficiency in vitro demonstrated that adenoviral transduction consistently resulted in high (>60%) transduction rates and substantial expression of transgenes such as GFP, luciferase, and mIL-12 for at least 4 days. In vivo experiments illustrated that mIL-12 transduced A-NK cells localized and survived significantly better than mock transduced cells within lung metastases than in the surrounding normal lung tissue when supported with low, non-toxic doses of IL-2. The intratumoral survival of non-transduced "bystander" A-NK cells also increased when they were co-injected with IL-12 gene-transduced A-NK cells. The enhanced survival of exogenously delivered, IL-12 gene-transduced A-NK cells resulted in greater anti-tumor responsiveness. This led to a 7-10 day increase in median survival time compared to tumor-bearing mice receiving mock-transduced A-NK cells. These data show that the presence of IL-12 around tumor-infiltrating A-NK cells enhances their anti-tumor activity while reducing their requirement for systemically administered IL-2. This A-NK cell delivered IL-12 has lead to an enhanced host anti-tumor reactivity, which appeared to be mediated through cytokine involvement, namely IFNγ, rather than T, B, and NK cellular activity. Thus, adoptive transfer of A-NK cells represents an efficient method for targeting products of genes to tumor sites and eliciting anti-tumor responses