Natural killer cell licensing during viral infection

CAR-NK Cells: A Chimeric Hope or a Promising Therapy?

Simple Summary

In recent years, innovative immunotherapy-based treatments have paved the way for a new approach to hematological malignancies. Instead of conventional chemotherapy, T cells have been genetically engineered to detect—and engage their cytotoxicity against—tumor cells, and their success story is astonishing. However, many setbacks—including insufficient efficacy, deficient autologous source, heavy side effects, and a hefty price—limit their use. A promising alternative could be chimeric antigen receptor NK cells, which possess interesting cytotoxicity and minimal graft-versus-host disease risk. In this article, we review the possible sources, the development techniques, the potential advantages, and the challenges faced in the field of chimeric antigen receptor NK cells.

Abstract

Immunotherapy with chimeric antigen receptor-engineered T cells (CAR-T) has revolutionized the treatment landscape of relapsed/refractory B-cell malignancies. Nonetheless, the use of autologous T cells has certain limitations, including the variable quality and quantity of collected effector T cells, extended time of cell processing, limited number of available CAR cells, toxicities, and a high cost. Thanks to their powerful cytotoxic capabilities, with proven antitumor effects in both haploidentical hematopoietic stem cell transplantation and adoptive cell therapy against solid tumors and hematological malignancies, Natural Killer cells could be a promising alternative. Different sources of NK cells can be used, including cellular lines, cord blood, peripheral blood, and induced pluripotent stem cells. Their biggest advantage is the possibility of using them in an allogeneic context without major toxic side effects. However, the majority of the reports on CAR-NK cells concern preclinical or early clinical trials. Indeed, NK cells might be more difficult to engineer, and the optimization and standardization of expansion and transfection protocols need to be defined. Furthermore, their short persistence after infusion is also a major setback. However, with recent advances in manufacturing engineered CAR-NK cells exploiting their cytolytic capacities, antibody-dependent cellular cytotoxicity (ADCC), and cytokine production, “off-the-shelf” allogeneic CAR-NK cells can provide a great potential in cancer treatments.

CD56+/CD16- Natural Killer cells expressing the inflammatory protease granzyme A are enriched in synovial fluid from patients with osteoarthritis

OBJECTIVE

Natural killer (NK) cells have been involved in the pathology of different inflammatory and autoimmune disorders. Inflammation is an important regulator of osteoarthritis (OA), but the molecular and cellular mechanisms regulating this process are not well defined.

DESIGN

To understand the role of NK cells in OA, we have compared the phenotype (CD56 subsets and perforin and granzyme expression) and cytotoxic function of NK cells in peripheral blood and synovial fluid from patients with OA undergoing total knee arthroplasty.

RESULTS

In contrast to peripheral blood lymphocytes (PBLs), the majority of NK cells from the synovial fluid were CD56^brightCD16(-) cells. As expected the expression of the cytolytic mediators perforin and granzyme B in CD56^brightCD16(-) cells was low and correlated with a poor cytotoxic potential against K562 sensitive target cells. Surprisingly, this low cytotoxic NK cell subset expressed high levels of granzyme A (a protease recently characterized as a key modulator of inflammation in mouse models) in synovial fluid but not in peripheral blood. The presence of the CD56(+)^brightCD16(-) cells expressing granzyme A correlated with increased levels of pro-inflammatory cytokines in synovial fluid from OA patients.

CONCLUSION

Our results indicate that NK cells from the synovium of patients with OA, which present an immunoregulatory non-cytotoxic phenotype, show different phenotype comparing with NK cells from peripheral blood, especially expressing granzyme A, a pro-inflammatory molecule which may contribute to the establishment of chronic articular inflammation in this type of patients.

Human Leukocyte Antigen (HLA) and Immune Regulation: How Do Classical and Non-Classical HLA Alleles Modulate Immune Response to Human Immunodeficiency Virus and Hepatitis C Virus Infections?

The genetic factors associated with susceptibility or resistance to viral infections are likely to involve a sophisticated array of immune response. These genetic elements may modulate other biological factors that account for significant influence on the gene expression and/or protein function in the host. Among them, the role of the major histocompatibility complex in viral pathogenesis in particular human immunodeficiency virus (HIV) and hepatitis C virus (HCV), is very well documented. We, recently, added a novel insight into the field by identifying the molecular mechanism associated with the protective role of human leukocyte antigen (HLA)-B27/B57 CD8⁺ T cells in the context of HIV-1 infection and why these alleles act as a double-edged sword protecting against viral infections but predisposing the host to autoimmune diseases. The focus of this review will be reexamining the role of classical and non-classical HLA alleles, including class Ia (HLA-A, -B, -C), class Ib (HLA-E, -F, -G, -H), and class II (HLA-DR, -DQ, -DM, and -DP) in immune regulation and viral pathogenesis (e.g., HIV and HCV). To our knowledge, this is the very first review of its kind to comprehensively analyze the role of these molecules in immune regulation associated with chronic viral infections.

NK cell education via nonclassical MHC and non-MHC ligands

Natural killer (NK) cell education, a process for achieving functional maturation and self-tolerance, has been previously defined by the interaction between self-major histocompatibility complex class I (MHC-I) molecules and their specific inhibitory receptors. Over the past several years, growing evidence has highlighted the important roles of nonclassical MHC-I and non-MHC-I molecules in NK cell education. Herein, we review the current knowledge of NK cell education, with a particular focus on nonclassical MHC-I- and non-MHC-I-dependent education, and compare them with the classical MHC-I-dependent education theory. In addition, we update and extend this theory by presenting the 'Confining Model', discussing cis and trans characteristics, reassessing quantity and quality control, and elucidating the redundancy of NK cell education in tumor and virus infection.

CEACAM1 on activated NK cells inhibits NKG2D-mediated cytolytic function and signaling

Carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) is expressed on activated natural killer (NK) cells wherein it inhibits lysis of CEACAM1-bearing tumor cell lines. The mechanism for this is unknown. Here, we show that interleukin-2-induced expression of CEACAM1 on both mouse and primary human NK cells impairs the ability of NK gene complex group 2 member D (NKG2D) to stimulate cytolysis of CEACAM1-bearing cells. This process requires the expression of CEACAM1 on the NK cells and on the tumor cells, which is consistent with the involvement of trans-homophilic interactions between CEACAM1. Mechanistically, co-engagement of NKG2D and CEACAM1 results in a biochemical association between these two surface receptors and the recruitment of Src homology phosphatase 1 by CEACAM1 that leads to dephosphorylation of the guanine nucleotide exchange factor Vav1 and blockade of downstream signaling that is associated with the initiation of cytolysis. Thus, CEACAM1 on activated NK cells functions as an inhibitory receptor for NKG2D-mediated cytolysis, which has important implications for understanding the means by which CEACAM1 expression adversely affects tumor immunity.

Structural insights into activation of antiviral NK cell responses

Natural killer (NK) cells are key components of innate immune responses, providing surveillance against cells undergoing tumorigenesis or infection, by viruses or internal pathogens. NK cells can directly eliminate compromised cells and regulate downstream responses of the innate and acquired immune systems through the release of immune modulators (cytokines, interferons). The importance of the role NK cells play in immune defense was demonstrated originally in herpes viral infections, usually mild or localized, which become severe and life threatening in NK-deficient patients . NK cell effector functions are governed by balancing opposing signals from a diverse array of activating and inhibitory receptors. Many NK receptors occur in paired activating and inhibitory isoforms and recognize major histocompatibility complex (MHC) class I proteins with varying degrees of peptide specificity. Structural studies have made considerable inroads into understanding the molecular mechanisms employed to broadly recognize multiple MHC ligands or specific pathogen-associated antigens and the strategies employed by viruses to thwart these defenses. Although many details of NK development, signaling, and integration remain mysterious, it is clear that NK receptors are key components of a system exquisitely tuned to sense any dysregulation in MHC class I expression, or the expression of certain viral antigens, resulting in the elimination of affected cells.

Frequent and strong antibody-mediated natural killer cell activation in response to HIV-1 Env in individuals with chronic HIV-1 infection

Natural killer (NK) cells play a critical role in the control of HIV-1 infection, and NK cells that respond to HIV-1 peptides have been recently described. However, the mechanisms by which NK cells recognize HIV-1 antigens are not fully understood. We investigated NK cell activation in response to HIV-1 peptides during early and chronic HIV-1 clade B infection using a whole-blood assay and multiparameter flow cytometry. Antibody-mediated NK cell activation in response to HIV-1 peptides was not detected in HIV-1-uninfected individuals. In contrast, 79% of individuals with chronic infection and 22% of individuals with early infection had detectable gamma interferon (IFN-γ) NK cell responses to HIV-1 antigens (P < 0.00001). IFN-γ- and tumor necrosis factor alpha (TNF-α)-producing NK cells most frequently targeted Env gp120 (median of 4% and range of 0 to 31% of all NK cells). NK cells rarely targeted other HIV-1 proteins such as Gag, Pol, and Nef. Antibody-mediated NK cell responses to peptides mapped predominantly to Env protein, required the presence of plasma or plasma IgG, and resulted in lower CD16 expression on NK cells, suggesting an antibody-mediated activation of NK cells. Further studies are needed to assess the consequences of these antibody-mediated NK cell responses for HIV-1 disease progression and vaccine-induced protection from infection.