Requirements for human natural killer cell development informed by primary immunodeficiency

A critical threshold of MCM10 is required to maintain genome stability during differentiation of induced pluripotent stem cells into natural killer cells

Natural killer (NK) cell deficiency (NKD) is a rare disease in which NK cell function is reduced, leaving affected individuals susceptible to repeated viral infections and cancer. Recently, a patient with NKD was identified carrying compound heterozygous variants of MCM10 (minichromosome maintenance protein 10), an essential gene required for DNA replication, that caused a significant decrease in the amount of functional MCM10. NKD in this patient presented as loss of functionally mature late-stage NK cells. To understand how MCM10 deficiency affects NK cell development, we generated MCM10 heterozygous (MCM10+/-) induced pluripotent stem cell (iPSC) lines. Analyses of these cell lines demonstrated that MCM10 was haploinsufficient, similar to results in other human cell lines. Reduced levels of MCM10 in mutant iPSCs was associated with impaired clonogenic survival and increased genomic instability, including micronuclei formation and telomere erosion. The severity of these phenotypes correlated with the extent of MCM10 depletion. Significantly, MCM10+/- iPSCs displayed defects in NK cell differentiation, exhibiting reduced yields of hematopoietic stem cells (HSCs). Although MCM10+/- HSCs were able to give rise to lymphoid progenitors, these did not generate mature NK cells. The lack of mature NK cells coincided with telomere erosion, suggesting that NKD caused by these MCM10 variants arose from the accumulation of genomic instability including degradation of chromosome ends.

Unbiased Screening Identifies Functional Differences in NK Cells After Early Life Psychosocial Stress

Early Life Adversity (ELA) is closely associated with the risk for developing diseases later in life, such as autoimmune diseases, type-2 diabetes and cardiovascular diseases. In humans, early parental separation, physical and sexual abuse or low social-economic status during childhood are known to have great impact on brain development, in the hormonal system and immune responses. Maternal deprivation (MD) is the closest animal model available to the human situation. This paradigm induces long lasting behavioral effects, causes changes in the HPA axis and affects the immune system. However, the mechanisms underlying changes in the immune response after ELA are still not fully understood. In this study we investigated how ELA changes the immune system, through an unbiased analysis, viSNE, and addressed specially the NK immune cell population and its functionality. We have demonstrated that maternal separation, in both humans and rats, significantly affects the sensitivity of the immune system in adulthood. Particularly, NK cells’ profile and response to target cell lines are significantly changed after ELA. These immune cells in rats are not only less cytotoxic towards YAC-1 cells, but also show a clear increase in the expression of maturation markers after 3h of maternal separation. Similarly, individuals who suffered from ELA display significant changes in the cytotoxic profile of NK cells together with decreased degranulation capacity. These results suggest that one of the key mechanisms by which the immune system becomes impaired after ELA might be due to a shift on the senescent state of the cells, specifically NK cells. Elucidation of such a mechanism highlights the importance of ELA prevention and how NK targeted immunotherapy might help attenuating ELA consequences.

Phenotypic and Functional Changes in Peripheral Blood Natural Killer Cells in Crohn Disease Patients

We investigated activation status, cytotoxic potential, and gut homing ability of the peripheral blood Natural Killer (NK) cells in Crohn disease (CD) patients. For this purpose, we compared the expression of different activating and inhibitory receptors (KIR and non-KIR) and integrins on NK cells as well as their recent degranulation history between the patients and age-matched healthy controls. The study was conducted using freshly obtained peripheral blood samples from the study participants. Multiple color flow cytometry was used for these determinations. Our results show that NK cells from treatment-naïve CD patients expressed higher levels of activating KIR as well as other non-KIR activating receptors vis-à-vis healthy controls. They also showed increased frequencies of the cells expressing these receptors. The expression of several KIR and non-KIR inhibitory receptors tended to decrease compared with the cells from healthy donors. NK cells from the patients also expressed increased levels of different gut-homing integrin molecules and showed a history of increased recent degranulation events both constitutively and in response to their in vitro stimulation. Furthermore, treatment of the patients tended to reverse these NK cell changes. Our results demonstrate unequivocally, for the first time, that peripheral blood NK cells in treatment-naïve CD patients are more activated and are more poised to migrate to the gut compared to their counterpart cells from healthy individuals. Moreover, they show that treatment of the patients tends to normalize their NK cells. The results suggest that NK cells are very likely to play a role in the immunopathogenesis of Crohn disease.

How I Manage Natural Killer Cell Deficiency

Natural killer (NK) cell deficiency (NKD) is a subset of primary immunodeficiency disorders (PID) in which an abnormality of NK cells represents a major immunological defect resulting in the patient’s clinical immunodeficiency. This is distinct from a much larger group of PIDs that include an NK cell abnormality as a minor component of the immunodeficiency. Patients with NKD most frequently have atypical consequences of herpesviral infections. There are now 6 genes that have been ascribed to causing NKD, some exclusively and others that also cause other known immunodeficiencies. This list has grown in recent years and as such the mechanistic and molecular clarity around what defines an NKD is an emerging and important field of research. Continued increased clarity will allow for more rational approaches to the patients themselves from a therapeutic standpoint. Having evaluated numerous individuals for NKD, I share my perspective on approaching the diagnosis and managing these patients.

CD137 (4-1BB) Engagement Fine-Tunes Synergistic IL-15- and IL-21-Driven NK Cell Proliferation

To understand and dissect the mechanisms driving human NK cell proliferation, we exploited the methodology used in cell therapy to numerically expand NK cells in the presence of K562-derived artificial APC (aAPCs) and cytokines. For four consecutive weeks, high expression of CD137L by a K562-derived aAPC cell line could sustain NK cell expansion by 3 × 10⁵-fold, whereas low expression of CD137L by the parental K562 cell line only supported the expansion by 2 × 10³-fold. The level of expression of CD137L, however, did not modulate the sensitivity of K562 cells to the intrinsic cytotoxicity of NK cells. Similarly, the low NK cell proliferation in the presence of the parental K562 cell line and cytokines was increased by adding agonistic anti-CD137 Abs to levels similar to CD137L-expressing K562-derived aAPCs. Finally, synergy between IL-15 and IL-21 was observed only upon CD137 engagement and the presence of aAPCs. Therefore, we conclude that NK cell proliferation requires cell-to-cell contact, activation of the CD137 axis, and presence of IL-15 (or its membranous form) and IL-21. By analogy with the three-signal model required to activate T cells, we speculate that the cell-to-cell contact represents "signal 1," CD137 represents "signal 2," and cytokines represent "signal 3." The precise nature of signal 1 remains to be defined.

Human CD56dimCD16dim Cells As an Individualized Natural Killer Cell Subset

Human natural killer (NK) cells can be subdivided in several subpopulations on the basis of the relative expression of the adhesion molecule CD56 and the activating receptor CD16. Whereas blood CD56^brightCD16^dim/− NK cells are classically viewed as immature precursors and cytokine producers, the larger CD56^dimCD16^bright subset is considered as the most cytotoxic one. In peripheral blood of healthy donors, we noticed the existence of a population of CD56^dimCD16^dim NK cells that was frequently higher in number than the CD56^bright subsets and even expanded in occasional control donors but also in transporter associated with antigen processing-deficient patients, two familial hemophagocytic lymphohistiocytosis type II patients, and several common variable immunodeficiency patients. This population was detected but globally reduced in a longitudinal cohort of 18 HIV-1-infected individuals. Phenotypically, the new subset contained a high percentage of relatively immature cells, as reflected by a significantly stronger representation of NKG2A⁺ and CD57⁻ cells compared to their CD56^dimCD16^bright counterparts. The phenotype of the CD56^dimCD16^dim population was differentially affected by HIV-1 infection as compared to the other NK cell subsets and only partly restored to normal by antiretroviral therapy. From the functional point of view, sorted CD56^dimCD16^dim cells degranulated more than CD56^dimCD16^bright cells but less than CD56^dimCD16⁻ NK cells. The population was also identified in various organs of immunodeficient mice with a human immune system (“humanized” mice) reconstituted from human cord blood stem cells. In conclusion, the CD56^dimCD16^dim NK cell subpopulation displays distinct phenotypic and functional features. It remains to be clarified if these cells are the immediate precursors of the CD56^dimCD16^bright subset or placed somewhere else in the NK cell differentiation and maturation pathway.