Bringing natural killer cells to the clinic: ex vivo manipulation

Abstract

Recently, there has been a substantial gain in our understanding of the role that natural killer (NK) cells play in mediating innate host immune responses against viruses and cancer. Although NK cells have long been known to be capable of killing cancer cells independently of antigen recognition, the full therapeutic potential of NK cell-based immunotherapy has yet to be realized. Here we review novel methods to activate and expand human NK cells ex vivo for adoptive transfer in humans, focusing on the important phenotypic and functional differences observed among freshly isolated, cytokine activated, and ex vivo-expanded NK populations. Natural killer cell therapy for cancer: a new hopeThe ability of natural killer (NK) cells to kill tumor cells without the need to recognize a tumor-specific antigen provides advantages over T cells and makes them appealing for investigation as effectors for immunotherapy. 1,2 There has recently been a substantial gain in our understanding of the role that NK cells play in mediating innate host immune responses against viruses and cancer. Although NK cells have long been known to be capable of killing cancer cells independently of antigen recognition, the full therapeutic potential of NK cell-based immunotherapy has yet to be realized. Here we review novel methods to activate and expand human NK cells ex vivo for adoptive transfer in humans, focusing on the important phenotypic and functional differences observed among freshly isolated, cytokine activated, and ex vivo-expanded NK populations. Ex vivo NK cell activation and expansionUnlike T cells, NK cells represent only a minor fraction of human lymphocytes. NK cells are defined by their CD3 Ϫ /CD56 ϩ phenotype, comprising 5% to 15% of circulating lymphocytes, and are commonly divided into CD56 dim CD16 ϩ (90%) and CD56 bright CD16 Ϫ (10%) subpopulations with distinct effector functions. Recently, investigators have shown that NK cell tumor cytotoxicity can be enhanced by disrupting NK cell signaling through inhibitory receptors such as KIR, PD-1, and NKG2A. 3,4 Furthermore, exposing tumors to drugs that down-regulate ligands for NK cell inhibitory receptors or up-regulate death receptors for NK cell effector molecules or ligands that bind NK cell-activating receptors can be used as a strategy to sensitize tumors to NK cell-mediated apoptosis. Recently, anti-PD-1 and anti-PD-L1 monoclonal antibodies and the immunomodulatory drug lenalidomide were shown to enhance both NK cell tumor trafficking and NK cell-mediated antibody-dependent cell-mediated cytotoxicity, and cytokine release against tumors while simultaneously suppressing regulatory T cell function. [5][6][7][8] Similarly, anti-CTLA-4 monoclonal antibodies have been shown to augment NK cell antibody-dependent cellmediated cytotoxicity and TNF␣ release against melanoma cells by Fc␥RIII (CD16) binding to antibody-bound tumor cells, as well as through regulatory T cell inactivation. 9-11 These data suggest these agents could be used in conjunction with autologous NK cell inf...

Acute GVHD in patients receiving IL-15/4-1BBL activated NK cells following T-cell–depleted stem cell transplantation

“…[44][45][46][47][48][49] Using a K562-based aAPC with membrane-bound IL-15 (K562-mb15-41BBL), Fujisaki first reported, 47 and we confirmed using a similar aAPC, 46 that coculture of NK cells with recombinant human IL-15 (rhIL-15) plus aAPC expressing 4-1BBL and IL15Ra results in NK expansion, upregulation of activating receptors, and enhanced cytotoxicity against a wide range of malignant cells, including pediatric solid tumors. 46,48 IL-15/4-1BBL-activated NK cells display a distinct gene expression profile and more potent killing capacity in vitro compared with resting and IL-2-activated NK cells.…”

Umbilical cord blood graft engineering: challenges and opportunities

“…110 Adoptive transfer of NK cells has previously been limited by the small numbers of circulating NK cells (5-15% of the total lymphocytes) and consequently low numbers obtained in an apheresis procedure. 111 Methods of NK expansion include: NK cells can be generated from HSCs, including CB 122 and show similar phenotype and activity against leukemic targets to peripheral blood-derived NK cells. 123 These can be generated using aAPCs derived from K562 cell lines 116,120 or in feeder cell-free conditions.…”

Expansion of NK cells from PBMCs using immobilized 4-1BBL and interleukin-21

“…However, it is difficult to obtain large-scale clinical-grade NK cells from donors; therefore, to overcome this limitation, many researchers have developed methods to amplify NK cells ex vivo (4). In the present study, we used solid phase cytokines of recombinant human IL-21 and 4-1BBL to proliferate the NK cells in PBMCs obtained from healthy donors.…”

“…Natural killer cells (NK cells), a subset of approximately 5-15% of the peripheral blood lymphocyte population, based on the expression levels of surface markers, are classified into two subpopulations with different functions, CD3 -CD56 dim CD16 + (90%) and CD3 -CD56 bright CD16 -(10%) (1)(2)(3)(4). NK cells typically lack antigen-specific cell surface receptors (5), consistent with the fact that NK cells do not require tumor-specific antigen recognition when killing tumor cells.…”