CD34+ cells cultured in stem cell factor and interleukin-2 generate CD56+ cells with antiproliferative effects on tumor cell lines

CAR-NK cells: a promising cellular immunotherapy in lymphoma

INTRODUCTION

New methods in cancer immunotherapy, such as chimeric antigen receptor (CAR)-T cells, have shown promising results in destroying malignant cells. However, limitations and side effects of CAR-T cell therapy, such as graft-versus-host disease (GVHD), neurotoxicity, and cytokine release syndrome, have motivated researchers to investigate safer alternative cells like natural killer (NK) cells.

AREA COVERED

NK cells can effectively recognize hematologic malignant cells and destroy them. Many clinical and preclinical studies investigate the efficacy of CAR-NK cells in treating lymphoma and other hematologic malignancies. The results of published clinical trials and preclinical studies have shown that CAR-NK cells could be an appropriate choice for treating lymphoma. In this review, we discuss the characteristics of CAR-NK cells, their role in treating B-cell and T-cell lymphoma, and the challenges faced by using them. We also highlight clinical trials using CAR-NK cells for treating lymphoma.

EXPERT OPINION

CAR-NK cells have shown promising results in cancer therapy, especially B-cell lymphoma, with a much lower risk for GVHD, cytokine release syndrome, and neurotoxicity than CAR-T cells. Further investigations are required to overcome the obstacles of CAR-NK cell therapy, both generally, and in cancers like T-cell lymphoma.

Bone marrow CD34 positive cells may be suitable for collection after death

Hematopoietic stem cells (HSCs) which are characterized with CD34+ phenotype, have a pivotal role in blood cell regeneration. They are located in lowest hypoxic areas in the bone marrow niches. This microenvironment protects them from DNA damage and excessive proliferation, whereas the oxygenated area driving cells out of quiescent state into proliferation. Given the resistance of HSCs to hypoxia, it is reasonable to imagine that they can survive for some time in the absence of oxygen. Here, we evaluated CD34, Bax, Bcl-2, Bcl-xl, and p53 genes expression after death. Moreover, we established the ex-vivo development of HSCs using SCF, FLT3, IL-2, and IL-15 cytokines in culture system. Our finding indicated that although the most of the dead person's mononuclear cells were alive and adequately expressed the CD34 on their surfaces at the first day of isolation, the viability and CD34+/Ki-67 expression declined significantly after culture process. Taken together, our finding indicated that the viability and CD34+ expression was acceptable on day 0 and could be used as a novel method for therapeutic purposes.

Enhancing a Natural Killer: Modification of NK Cells for Cancer Immunotherapy

Natural killer (NK) cells are potent innate immune system effector lymphocytes armed with multiple mechanisms for killing cancer cells. Given the dynamic roles of NK cells in tumor surveillance, they are fast becoming a next-generation tool for adoptive immunotherapy. Many strategies are being employed to increase their number and improve their ability to overcome cancer resistance and the immunosuppressive tumor microenvironment. These include the use of cytokines and synthetic compounds to bolster propagation and killing capacity, targeting immune-function checkpoints, addition of chimeric antigen receptors (CARs) to provide cancer specificity and genetic ablation of inhibitory molecules. The next generation of NK cell products will ideally be readily available as an “off-the-shelf” product and stem cell derived to enable potentially unlimited supply. However, several considerations regarding NK cell source, genetic modification and scale up first need addressing. Understanding NK cell biology and interaction within specific tumor contexts will help identify necessary NK cell modifications and relevant choice of NK cell source. Further enhancement of manufacturing processes will allow for off-the-shelf NK cell immunotherapies to become key components of multifaceted therapeutic strategies for cancer.

Directed Differentiation of Mobilized Hematopoietic Stem and Progenitor Cells into Functional NK cells with Enhanced Antitumor Activity

Obtaining sufficient numbers of functional natural killer (NK) cells is crucial for the success of NK-cell-based adoptive immunotherapies. While expansion from peripheral blood (PB) is the current method of choice, ex vivo generation of NK cells from hematopoietic stem and progenitor cells (HSCs) may constitute an attractive alternative. Thereby, HSCs mobilized into peripheral blood (PB-CD34⁺) represent a valuable starting material, but the rather poor and donor-dependent differentiation of isolated PB-CD34⁺ cells into NK cells observed in earlier studies still represents a major hurdle. Here, we report a refined approach based on ex vivo culture of PB-CD34⁺ cells with optimized cytokine cocktails that reliably generates functionally mature NK cells, as assessed by analyzing NK-cell-associated surface markers and cytotoxicity. To further enhance NK cell expansion, we generated K562 feeder cells co-expressing 4-1BB ligand and membrane-anchored IL-15 and IL-21. Co-culture of PB-derived NK cells and NK cells that were ex-vivo-differentiated from HSCs with these feeder cells dramatically improved NK cell expansion, and fully compensated for donor-to-donor variability observed during only cytokine-based propagation. Our findings suggest mobilized PB-CD34⁺ cells expanded and differentiated according to this two-step protocol as a promising source for the generation of allogeneic NK cells for adoptive cancer immunotherapy.

NK Cell Inflammation in the Clinical Outcome of Colorectal Carcinoma

The ability of natural killer (NK) cells to provide protection against myeloid leukemia has been demonstrated in clinical settings. However, whether NK cells play a role in the clinical course of solid tumors is debated. The controversy surrounding the role of NK cells is due, at least in part, to the limited extent of NK cell infiltration found in the tumor bed. Inactivation of NK cells may explain the shortage of NK cells in the microenvironment of colorectal cancer (CRC). Upon NK cell/tumor cell interaction, tumor cells may escape NK cells by creating an immunosuppressive microenvironment, which possibly affects T-cells as well. Such an immunosuppressive microenvironment would hamper the functions of NK and T-cell and reduce NK and T-cell interactions. CRC patients with levels of tumor NK cell infiltration suitable for statistical analysis have been identified. The infiltration of the CRC microenvironment by NK cells, in combination with CD8⁺ T-lymphocytes, has been shown to enhance the prognosis of CRC patients. Here, we discuss the clinicopathological role of NK cells in CRC, and present clinical data indicating a potential supporting role for NK cells in the anti-CRC effects of CD8⁺ T-cells.

Generation of natural killer cells from hematopoietic stem cells in vitro for immunotherapy

Natural killer (NK) cells are part of the innate immune system and are an alluring option for immunotherapy due to their ability to kill infected cells or cancer cells without prior sensitization. Throughout the past 20 years, different groups have been able to reproduce NK cell development in vitro, and NK cell ontogeny studies have provided the basis for the establishment of protocols to produce NK cells in vitro for immunotherapy. Here, we briefly discuss NK cell development and NK cell immunotherapy approaches. We review the factors needed for NK cell differentiation in vitro, which stem cell sources have been used, published protocols, challenges and future directions for Good Manufacturing Practice protocols.

Generation of natural killer cells from serum-free, expanded human umbilical cord blood CD34+ cells

Natural killer (NK) cells are important effectors of the innate immune system, which exhibits cytolytic activity against infectious agents and tumor cells. NK cells are derived from CD34(+) hematopoietic stem cells (HSCs). Human umbilical cord blood (UCB) has been recognized as a rich source of HSCs. Previously, we have reported an optimized serum-free medium for ex vivo expansion of CD34(+) cells from UCB. In this study, the serum-free, expanded CD34(+) cells were tested to differentiate into NK cells and their induction kinetics. After 5 weeks of induction, the induced NK cells were characterized by analysis of surface antigens, IFN-gamma secretion, and cytotoxicity against K562 cells. The results indicated that NK cells derived from the serum-free, expanded CD34(+) cells exhibited both characteristics and functions of NK cells. Furthermore, the serum-free, expanded CD34(+) cells showed a significantly higher NK cell differentiation potential than freshly isolated CD34(+) cells. NK cells induced from serum-free, expanded CD34(+) cells showed a higher concentration of IFN-gamma secretion and ability of cytotoxicity than those from freshly isolated CD34(+) cells. Therefore, ex vivo-expanded CD34(+) cells in optimized serum-free medium could differentiate into NK cells and provided a promising cell source for immunotherapeutic approaches.

Zinc improves the development of human CD34+ cell progenitors towards Natural Killer cells and induces the expression of GATA-3 transcription factor

The Natural Killer cell maturation from CD34(+) hematopoietic cell precursors is a complex process that requires the synergistic effect of different cytokines and growth factors. Although there have been a number of important advances in our understanding of the Natural Killer differentiation, the developmental step leading to mature Natural Killer cells is still poorly defined. We evaluated the effect of two zinc concentrations (10 and 20microM) on the kinetic of development of CD34(+) cell progenitors towards Natural Killer cells. CD34(+) cells were purified from peripheral blood and cultured in medium supplemented with interleukin-15, interleukin-7, Flt 3 ligand, and stem cell factor. CD34(+) cells underwent proliferation and progressively lost CD34 antigen and acquired a CD56(+) phenotype. These CD56(+) cells exerted cytotoxic activity and expressed the CD94 inhibitory receptor. The supplementation with zinc greatly increased both the number of cells in culture and the absolute number of CD56(+) cells. Zinc induced higher levels of cytotoxic activity and a higher number of perforin-producing and of CD94-bearing CD56(+) cells in comparison with zinc unsupplemented cultures in early stages of Natural Killer cell development. The zinc-induced changes in CD34-derived CD56(+) cells were associated with an increased expression of GATA-3, a zinc-finger transcription factor providing for maturation and activity of T and Natural Killer cells. The increase was related to a higher CD56(+) cell number (10microM zinc), or to an increased GATA-3 mRNA transcription in CD56(+) cells (20microM zinc). Our data demonstrate that zinc influences the proliferation and differentiation of CD34(+) progenitors.

Coordinated acquisition of inhibitory and activating receptors and functional properties by developing human natural killer cells

The stages of human natural killer (NK) cell differentiation are not well established. Culturing CD34(+) progenitors with interleukin 7 (IL-7), IL-15, stem cell factor (SCF), FLT-3L, and murine fetal liver cell line (EL08.1D2), we identified 2 nonoverlapping subsets of differentiating CD56(+) cells based on CD117 and CD94 (CD117(high)CD94(-) and CD117(low/-)CD94(+) cells). Both populations expressed CD161 and NKp44, but differed with respect to NKp30, NKp46, NKG2A, NKG2C, NKG2D, CD8, CD16, and KIR. Only the CD117(low/-) CD94(+) population displayed cytotoxicity and interferon-gamma production. Both populations arose from a single CD34(+)CD38(-) Lin(-) cell and their percentages changed over time in a reciprocal fashion, with CD117(high)CD94(-) cells predominating early and decreasing due to an increase of the CD117(low/-)CD94(+) population. These 2 subsets represent distinct stages of NKcell differentiation, since purified CD117(high) CD94(-) cells give rise to CD117(low/-)CD94(+) cells. The stromal cell line (EL08.1D2) facilitated the transition from CD117(high)CD94(-) to CD117(low/-)CD94(+) via an intermediate phenotype (CD117(low)CD94(low/-)). EL08.1D2 also maintained the mature phenotype, preventing the reversion of CD117(low/-)CD94(+) cells to the intermediate (CD117(low)CD94(low/-)) phenotype. An analogous population of CD56(+)CD117(high)CD94(-) cells was found in cord blood. The identified stages of NK-cell differentiation provide evidence for coordinated acquisition of HLA-specific inhibitory receptors (ie, CD94/NKG2A) and function in developing human NK cells.