How I Manage Natural Killer Cell Deficiency

CAR-NK cell therapy: a potential antiviral platform

Viral infections persist as a significant cause of morbidity and mortality worldwide. Conventional therapeutic approaches often fall short in fully eliminating viral infections, primarily due to the emergence of drug resistance. Natural killer (NK) cells, one of the important members of the innate immune system, possess potent immunosurveillance and cytotoxic functions, thereby playing a crucial role in the host's defense against viral infections. Chimeric antigen receptor (CAR)-NK cell therapy has been developed to redirect the cytotoxic function of NK cells specifically towards virus-infected cells, further enhancing their cytotoxic efficacy. In this manuscript, we review the role of NK cells in antiviral infections and explore the mechanisms by which viruses evade immune detection. Subsequently, we focus on the optimization strategies for CAR-NK cell therapy to address existing limitations. Furthermore, we discuss significant advancements in CAR-NK cell therapy targeting viral infections, including those caused by severe acute respiratory syndrome coronavirus 2, human immunodeficiency virus, hepatitis B virus, human cytomegalovirus, and Epstein-Barr virus.

β-Actin G342D as a Cause of NK Cell Deficiency Impairing Lytic Synapse Termination

NK cell deficiency (NKD) occurs when an individual's major clinical immunodeficiency derives from abnormal NK cells and is associated with several genetic etiologies. Three categories of β-actin-related diseases with over 60 ACTB (β-actin) variants have previously been identified, none with a distinct NK cell phenotype. An individual with mild developmental delay, macrothrombocytopenia, and susceptibility to infections, molluscum contagiosum virus, and EBV-associated lymphoma had functional NKD for over a decade. A de novo ACTB variant encoding G342D β-actin was identified and was consistent with the individual's developmental and platelet phenotype. This novel variant also was found to have direct impact in NK cells because its expression in the human NK cell line YTS (YTS-NKD) caused increased cell spreading in lytic immune synapses created on activating surfaces. YTS-NKD cells were able to degranulate and perform cytotoxicity, but they demonstrated defective serial killing because of prolonged conjugation to the killed target cell and thus were effectively unable to terminate lytic synapses. G342D β-actin results in a novel, to our knowledge, mechanism of functional NKD via increased synaptic spreading and defective lytic synapse termination with resulting impaired serial killing, leading to overall reductions in NK cell cytotoxicity.

Metabolic regulation of NK cell antiviral functions during cytomegalovirus infection

Natural killer (NK) cells quickly mount cytotoxic responses, produce cytokines, and proliferate in response to infected or transformed cells. Moreover, they can develop memory, with enhanced effector responses following activation, in some cases with antigen specificity. To optimally execute these functions, NK cells undergo metabolic reprogramming. Here, we discuss the interplay between metabolism and NK cell function in the context of viral infections. We review findings supporting metabolic regulation of NK cell effector functions, with a focus on NK cell antiviral infection in the context of cytomegalovirus in the mouse (MCMV) and human (HCMV).

Inborn Errors of Immunity Causing Pediatric Susceptibility to Fungal Diseases

Inborn errors of immunity are a heterogeneous group of genetically determined disorders that compromise the immune system, predisposing patients to infections, autoinflammatory/autoimmunity syndromes, atopy/allergies, lymphoproliferative disorders, and/or malignancies. An emerging manifestation is susceptibility to fungal disease, caused by yeasts or moulds, in a superficial or invasive fashion. In this review, we describe recent advances in the field of inborn errors of immunity associated with increased susceptibility to fungal disease.

Azathioprine therapy induces selective NK cell depletion and IFN-γ deficiency predisposing to herpesvirus reactivation

BACKGROUND

Azathioprine is a widely prescribed drug for patients with chronic inflammatory diseases such as myasthenia gravis or organ transplant recipients. Azathioprine exerts immunosuppressive effects by inhibiting intracellular purine synthesis and reducing the numbers of circulating B and T lymphocytes. Case reports indicate increased risk for serious infections that can occur despite regular measurements of lymphocyte counts during azathioprine therapy.

OBJECTIVE

We sought to comprehensively investigate therapy-associated patient risks and the underlying immune dysfunction of azathioprine use.

METHODS

Peripheral blood leukocytes were analyzed using single-cell mass and spectral flow cytometry to detect specific effects of azathioprine use on the systemic immune signature. Therapy-associated clinical features were analyzed in 2 independent cohorts of myasthenia gravis patients.

RESULTS

Azathioprine therapy selectively induced pronounced CD56^dimCD16⁺ natural killer cell depletion and concomitant IFN-γ deficiency. Cytokine profiling revealed a specific contraction of classical T_H1 cells during azathioprine treatment. We further observed an increased occurrence of reactivation of endogenous latent herpesviruses in the azathioprine-treated group versus in patients with myasthenia gravis who were not receiving immunomodulatory treatment; this increased occurrence was validated in an independent cohort.

CONCLUSION

Our study highlights the risk of development of adverse events during azathioprine therapy and suggests that natural killer cell monitoring could be valuable in clinical practice.

Partial loss-of-function mutations in GINS4 lead to NK cell deficiency with neutropenia

Human NK cell deficiency (NKD) is a primary immunodeficiency in which the main clinically relevant immunological defect involves missing or dysfunctional NK cells. Here, we describe a familial NKD case in which 2 siblings had a substantive NKD and neutropenia in the absence of other immune system abnormalities. Exome sequencing identified compound heterozygous variants in Go-Ichi-Ni-San (GINS) complex subunit 4 (GINS4, also known as SLD5), an essential component of the human replicative helicase, which we demonstrate to have a damaging impact upon the expression and assembly of the GINS complex. Cells derived from affected individuals and a GINS4-knockdown cell line demonstrate delayed cell cycle progression, without signs of improper DNA synthesis or increased replication stress. By modeling partial GINS4 depletion in differentiating NK cells in vitro, we demonstrate the causal relationship between the genotype and the NK cell phenotype, as well as a cell-intrinsic defect in NK cell development. Thus, biallelic partial loss-of-function mutations in GINS4 define a potentially novel disease-causing gene underlying NKD with neutropenia. Together with the previously described mutations in other helicase genes causing NKD, and with the mild defects observed in other human cells, these variants underscore the importance of this pathway in NK cell biology.

NK Cells and Other Cytotoxic Innate Lymphocytes in Colorectal Cancer Progression and Metastasis

Colorectal cancer (CRC) is one of the most common malignancies and leading causes of cancer-related deaths worldwide. Despite its complex pathogenesis and progression, CRC represents a well-fitting example of how the immune contexture can dictate the disease outcome. The presence of cytotoxic lymphocytes, both CD8⁺ T cells and natural killer (NK) cells, represents a relevant prognostic factor in CRC and is associated with a better overall survival. Together with NK cells, other innate lymphocytes, namely, innate lymphoid cells (ILCs), have been found both in biopsies of CRC patients and in murine models of intestinal cancer, playing both pro- and anti-tumor activities. In particular, several type 1 innate lymphoid cells (ILC1) with cytotoxic functions have been recently described, and evidence in mice shows a role for both NK cells and ILC1 in controlling CRC metastasis. In this review, we provide an overview of the features of NK cells and the expanding spectrum of innate lymphocytes with cytotoxic functions. We also comment on both the described and the potential roles these innate lymphocytes can play during the progression of intestinal cancer leading to metastasis. Finally, we discuss recent advances in the molecular mechanisms underlying the functional regulation of cytotoxic innate lymphocytes in CRC.

Different Background: Natural Killer Cell Profiles in Secondary versus Primary Recurrent Pregnancy Loss

(1) Background: Prior studies suggested a significant impact of previous live births on peripheral natural killer cells (pNK) in patients with recurrent pregnancy loss (RPL). Patients with primary RPL (pRPL, no live birth) showed higher numbers of pNK than secondary RPL patients (sRPL, ≥ 1 live birth). (2) Methods: To further determine immunological differences between RPL patients and controls, we analysed pNK subpopulations and activation markers in pRPL (n = 47), sRPL (n = 24) and controls with previous live birth (sCtrl, n = 25) and nullipara (pCtrl, n = 60) within a prospective study. Percentages and numbers of CD56dimCD16bright cells, subpopulations and activation markers (CD57+, CD62L+, NKG2D+, NKp46+) were measured in non-pregnant RPL patients and n = 85 controls (n = 60 pCtrl, n = 25 sCtrl) in the mid-luteal phase by flow cytometry. (3) Results: Compared to sRPL patients, sCtrls showed higher CD56+ and CD56dimCD16bright numbers. Further, sRPL patients showed lower numbers of CD56dimCD16brightNKG2D+ and CD56dimCD16brightNKp46+ than sCtrls. (4) Conclusion: We suggest a chronic immune stimulation leading to a lower NK-cell count in sRPL patients with a lower NK cytotoxicity. This underlines the necessity to investigate pNK subpopulations as well as pRPL and sRPL separately to delineate the immune alterations in RPL.