OPTIMIZATION OF ALLOGENEIC NK CELLS FOR ADOPTIVE TRANSFER THERAPY IN SOLID TUMOR PATIENTS

Adva Kubi ¹ Gal Markel ^1,2 Tzipi Shoham ³ Orit Harari-Steinberg ^1,4 Naama Zabari ^1,2 Rona Ortenberg ^1,2 Arkadi Yakirevitch ⁵ Arnon Nagler ⁶ Roni Loewenthal ⁷ Jacob Schachter ¹ Michal J. Besser ^1,2

¹Ella Institute for Melanoma, Sheba Medical Center, Ramat Gan
²Clinical Microbiology and Immunology, Sackler School of Medicine, Tel Aviv University, Tel Aviv
³GreenOnyx, GreenOnyx, Tel Aviv
⁴Pediatric Stem Cell Research Institute, Sheba Medical Center, Ramat Gan
⁵Otolaryngology and Head and Neck Surgery, Sheba Medical Center, Ramat Gan
⁶Bone Marrow Transplantation, Sheba Medical Center, Ramat Gan
⁷Tissue Typing Laboratory, Sheba Medical Center, Ramat Gan

Background

Natural killer (NK) cells have long been considered as potential agents for adoptive cell therapy for solid cancer patients. Triggering of effector NK function depends on the balance of inhibitory (mostly Killer-Ig-like Receptors; KIR) and stimulatory (NK Lysis Receptors; NKLR) signals. Although NK cells are able to eliminate malignant cells without prior antigenic stimulation, most clinical studies utilized autologous NK cells yielded disappointing results.

Aims

To develop the most efficient strategy employing allogeneic NK cells for adoptive cell transfer in solid tumors.

Results

In agreement with previous models, we could show that melanoma cells were more efficiently killed by allogeneic NK cells derived from KIR-ligand mismatched donors. Specific anti-tumor activity of NK cells could further be enhanced by the addition of antibody-dependent-cell-cytotoxicity (ADCC) inducing antibodies. The ADCC effect was independent from the KIR-ligand mismatched setting and only observed in NK cells overnight pre-activated with Interleukin-2 (IL-2), but not in fresh ones. To investigate the efficacy of ex-vivo expanded NK cells, we developed a clinically-compliable expansion protocol. Expanded NK cells displayed an enhanced killing activity of melanoma cells compared to overnight incubation with IL-2, as well as in the mismatched setting, as compared to the matched setting. The improved killing activity of expanded NK cells could be explained by the up-regulation of NK lysis receptors, mainly NKG2D and NKp30. Addition of ADCC-inducing antibody modestly increased the killing activity of already expanded NK cells.

Conclusions

NK cell ex vivo expansion and activation, and optimization of NKLR expression seem to be the most potent strategy for adoptive transfer trials with allogeneic NK cells, followed by ADCC induction and lastly by KIR-ligand mismatching. This study rationalizes a clinical trial that combines adoptive transfer of highly potent ex vivo expanded allogeneic NK cells from selected donors and antibody therapy in patients with solid tumors.