Evaluation of membrane bound IL-21 expanded natural killer cells for chronic lymphocytic leukemia therapy

Abstract

Abstract Chronic lymphocytic leukemia (CLL) is the most prevalent adult leukemia and remains incurable despite recent therapeutic advances. Natural killer (NK) cells have potent anti-cancer effects, but efforts to use NK cell therapy in CLL have been limited by poor NK cell growth and anti-leukemia activity. We sought to determine if stimulating NK cells ex vivo with K562-based feeder cells expressing membrane-bound IL-21 (mbIL-21) (Denman et al., 2012) could overcome the limitations of prior techniques to create an effective therapy for CLL. Our data demonstrate that healthy donor-derived mbIL-21 expanded NK cells have increased antibody-dependent cellular cytotoxicity (ADCC) and direct cytotoxicity (DC; without targeting antibody) against CLL cell lines. This technique can also overcome CLL-induced NK suppression – CLL patient-derived NK cells expanded equally and were as potent as normal donor-derived NKs, including against both allogeneic and autologous CLL tumor cells. CLL tumor cells are not susceptible to DC but are very vulnerable to ADCC with anti-CD20 antibodies (rituximab or obinutuzumab). The lack of direct cytotoxicity of tumor cells was correlated to low NK:CLL quantitative conjugate formation, suggesting a lack of tumor target recognition. Blocking antibodies to FasL, TNFα, and TRAIL show that only TRAIL contributes modestly to anti-CLL tumor cytotoxicity, while application of folimycin demonstrates that perforin/granzyme release is the major mechanism of cytotoxicity. In vivo, treatment with expanded NK cells plus obinutuzumab significantly prolongs survival in the OSU-CLL human xenograft model. Based on these data, we are planning a clinical trial of mbIL-21 expanded NK cells plus obinutuzumab in CLL patients.