The global pandemic of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2)–driven coronavirus disease 2019 (COVID-19) has caused unprecedented human death and has seriously threatened the global economy. Early data suggest a surge in proinflammatory cytokines in patients with severe COVID-19, which has been associated with poor outcomes. We recently postulated that the inflammatory response in patients with severe COVID-19 disease is not inhibited by natural killer (NK) cells, resulting in a “cytokine storm.” Here, we assessed the NK-cell functional activity and the associated cytokines and soluble mediators in hospitalized COVID-19 patients. Significantly impaired NK-cell counts and cytolytic activity were observed in COVID-19 patients when compared with healthy controls. Also, cytokines like interleukin 12 (IL12), IL15, and IL21 that are important for NK-cell activity were not detected systematically. Serum concentrations of soluble CD25 (sCD25)/soluble IL2 receptor α (sIL2-Rα) were significantly elevated and were inversely correlated with the percentage of NK cells. Impaired NK-cell cytolytic activity together with other laboratory trends including elevated sCD25 were consistent with a hyperinflammatory state in keeping with macrophage-activation syndrome. Our findings suggest that impaired counts and cytolytic activity of NK cells are important characteristics of severe COVID-19 and can potentially facilitate strategies for immunomodulatory therapies.

BACKGROUND Understanding of the immune events and mechanisms occurring at the feto–maternal interface is likely to help in understanding the ability of the fetus to survive within the maternal body. Evidence supporting extensive roles of natural killer cells during pregnancy gives rise to a possibility that these NK cells can be mis-regulated and involved in fetal allograft rejection. Killer immunoglobulin-like receptors (KIR) play an important role in regulating the NK cell activity through their activating and inhibiting isoforms. Since there exists a considerable, genetically determined variation in the repertoire of KIR receptors between different individuals, a particular maternal KIR repertoire may predispose to recurrent miscarriages (RMs).

Susceptibility to abacavir hypersensitivity (ABH) in HIV‐1‐positive patients is strongly linked to the carriage of HLA‐B*57:01 and the potential mechanism includes drug‐specific activation of cytokine producing CD8 T cells exclusively in individuals carrying HLA‐B*57:01. Here, we report a detailed characterization of abacavir‐induced functional response of CD8 T cells in HLA‐B*57:01^pos individuals. Peripheral blood mononuclear cells (PBMNCs) from HLA‐B*57:01^posABH^pos and HLA‐B*57:01^negABH^neg individuals were stimulated with abacavir. Multicolor flow cytometry was performed to assess the cytokine (IFNγ) production and degranulation (CD107a expression) after 6–18 hr culture and to enumerate proliferating CD4/CD8 T cells by culturing carboxyfluorescein diacetate succinimidyl ester‐loaded PBMNCs for 7 days. CD8 T cells from HLA‐B*57:01^posABH^pos individuals were multifunctional: proliferating, IFNγ producing, degranulating (CD107a^pos), and both degranulating and IFNγ producing (CD107a^posIFNγ^pos). Degranulating CD8 T cells in general and both degranulating and IFNγ producing CD8 T cells in particular dominated abacavir‐specific immune response. All functional responses were partially blocked by addition of HLA‐B*57:01‐reactive Bw4 mAb, but not by non‐HLA‐B*57:01‐reactive Bw6 mAb. In conclusion, the study demonstrates that abacavir‐specific CD8 T‐cell‐restricted immune response in HLA‐B*57:01^posABH^pos HIV‐1 patients has multiple effector and proliferating functions, where the primary effector response appears to be the release of cytolytic granules. The findings have implications for immunotherapy of HLA‐related drug hypersensitivities.

The persistence of graft-versus-host disease (GVHD) as the principal complication of allogeneic hematopoietic cell transplantation (HCT) demonstrates that HLA matching alone is insufficient to prevent alloreactivity. We performed molecular and functional characterization of 22 candidate cytokine genes for their potential to improve matching in 315 myeloablative, 10/10 HLA-matched donor–recipient pairs. Recipients of a graft carrying the -1082GG IL10 gene promoter region variant had a three-fold lower incidence of grade II–IV acute GVHD compared to IL10-1082AA graft recipients (SHR = 0.25, p = 0.005). This was most evident in matched unrelated donor (MUD) transplants, where the greatest alloreactivity is expected. IL10-1082GG transplants did not experience an increased incidence of relapse, and, consequently, overall survival was two-fold higher in IL10-1082GG MUD transplants (HR = 0.17, p = 0.023). Longitudinal post-transplant measurements demonstrated that -1082GG is a high-IL10-producing and -expressing genotype with attenuated CD8⁺ T-cell reconstitution. High post-transplant donor chimerism in T- and myeloid-cells (>95%) confirmed a predominant donor, rather than recipient, genotype effect on immune function and aGVHD. To date, this is the first study to report corroborating genome-to-cellular evidence for a non-HLA donor immunogenetic variant that appears to be protective against GVHD. The incorporation of IL10 variants in donor selection criteria and clinical-management decisions has the potential to improve patient outcomes.

Background: Cytomegalovirus (CMV) reactivation is a major complication after hematopoietic stem cell transplantation (HSCT). Natural killer (NK) cells help control CMV through killer-cell immunoglobulin-like receptors (KIRs) and their HLA ligands, but donor-derived CMV-specific T-cells may confound the interpretation of NK-mediated effects. Methods: We analyzed 276 HLA-matched (10/10) adults receiving ATG-based T-cell-depleted myeloablative HSCT with a known donor and recipient CMV serostatus. The donor and recipient KIR genotypes were scored by the Cooley B-content score (0–4; ≥2 = high). Clinically significant CMV reactivation (plasma viral load > 25,000 IU/mL, the institutional threshold for pre-emptive therapy) was analyzed with Fine–Gray competing-risks regression, stratified by the donor–recipient serostatus. Results: In seronegative-donor/seropositive-recipient (D−R+) pairs (n = 68), a high donor KIR B-content score was associated with a significantly lower reactivation risk (sub-hazard ratio, 0.46; 95% CI, 0.24–0.91; p = 0.024). No effect was seen in D+R+ pairs (n = 82; SHR, 0.65; p = 0.241); D+R− (n = 28) had too few events to model. A donor Tel-AA/recipient Tel-B+ mismatch was independently associated with a higher reactivation risk (adjusted HR, 2.41; 95% CI, 1.33–4.37; p = 0.004). The overall survival was unaffected in either stratum. Conclusions: A high donor KIR B-content score protects against CMV reactivation in D−R+, but not D+R+, HSCT recipients, consistent with NK dominance when CMV-specific donor T-cells are sparse. A specific donor–recipient telomeric mismatch independently modifies the risk. Donor KIR profiling warrants prospective evaluation in donor-selection algorithms.