Synergistic activity between IL-15 signaling and checkpoint blockade drives enhanced NK cell expansion and tumor control in ovarian cancer

Survival in ovarian cancer patients has not improved in the past 40 years, stressing a need for new lines of therapy. NK cell immunotherapy in ovarian cancer has not been extensively explored due to limited data showing defective NK cell function in these patients. Our previous work shows that an IL-15 super-agonist (NANT N-803 (formerly ALT-803)) can bypass some of the deficiencies. However, we show here that though N-803 enhances NK cell activation, it also induces NK PD-1 expression and inflammatory cytokines secreted by the NK cells induce PD-L1 expression on ovarian tumors. To bypass this negative feedback we combined N-803 with an anti-PD-L1 antibody (Avelumab) and show a potent increase in NK cell activation and long-term real-time in vitro tumor killing. Furthermore, combined N-803/Avelumab induces robust killing of ovarian cancer tumor spheroids, not seen with individual treatments. To evaluate the benefits of this combined treatment in vivo we tested them in a xenogeneic model of ovarian cancer containing human ovarian cancer cells (MA148lucs or OVCAR8lucs) and human NK cells. Our data clearly shows reduced tumor burden, by bioluminescent imaging, and potently increased NK cell expansion with the combined treatment when compared to individual treatments. Since Avelumab is capable of driving antibody dependent cell-mediated cytotoxicity (ADCC) we wanted to evaluate the impact of checkpoint signals in the synergy excluding ADCC using an anti-PD-1 antibody (Pembrolizumab). Combination of N-803 with Pembrolizumab yielded similar tumor control and NK cell expansion in the in vivo model, indicating that the synergy lies in checkpoint signals and IL-15 signaling, and not just in amplification of ADCC via N-803.