NK cells modulate in vivo control of SARS-CoV-2 replication and suppression of lung damage.

Natural killer (NK) cells play a critical role in virus control. However, it has remained largely unclear whether NK cell mobilization in SARS-CoV-2 infections is beneficial or pathologic. To address this deficit, we employed a validated experimental NK cell depletion non-human primate (NHP) model with SARS-CoV-2 Delta variant B.1.617.2 challenge. Viral loads (VL), NK cell numbers, activation, proliferation, and functional measures were evaluated in blood and tissues. In non-depleted (control) animals, infection rapidly induced NK cell expansion, activation, and increased tissue trafficking associated with VL. Strikingly, we report that experimental NK cell depletion leads to higher VL, longer duration of viral shedding, significantly increased levels of pro-inflammatory cytokines in the lungs, and overt lung damage. Overall, we find the first significant and conclusive evidence for NK cell-mediated control of SARS-CoV-2 virus replication and disease pathology. These data indicate that adjunct therapies for infection could largely benefit from NK cell-targeted approaches.

Knockdowns of CD3zeta Chain in Primary NK Cells Illustrate Modulation of Antibody-Dependent Cellular Cytotoxicity Against Human Immunodeficiency Virus-1.

Multifaceted natural killer (NK) cell activities are indispensable for controlling human immunodeficiency virus (HIV)-1 transmission and pathogenesis. Among the diverse functions of NK cells, antibody-dependent cellular cytotoxicity (ADCC) has been shown to predict better HIV-1 protection. ADCC is initiated by the engagement of an Fc γ receptor CD16 with an Fc portion of the antibody, leading to phosphorylation of the CD3 ζ chain (CD3ζ) and Fc receptor γ chain (FcRγ) as well as downstream signaling activation. Though CD3ζ and FcRγ were thought to have overlapping roles in NK cell ADCC, several groups have reported that CD3ζ-mediated signals trigger a more robust ADCC. However, few studies have illustrated the direct contribution of CD3ζ in HIV-1-specific ADCC. To further understand the roles played by CD3ζ in HIV-1-specific ADCC, we developed a CD3ζ knockdown system in primary human NK cells. We observed that HIV-1-specific ADCC was inhibited by CD3ζ perturbation. In summary, we demonstrated that CD3ζ is important for eliciting HIV-1-specific ADCC, and this dynamic can be utilized for NK cell immunotherapeutics against HIV-1 infection and other diseases.

Natural killer-like B cells are a distinct but infrequent innate immune cell subset modulated by SIV infection of rhesus macaques.

Natural killer-like B (NKB) cells are unique innate immune cells expressing both natural killer (NK) and B cell receptors. As first responders to infection, they secrete IL-18 to induce a critical cascade of innate and adaptive immune cell infiltration and activation. However, limited research exists on the role of NKB cells in homeostasis and infection, largely due to incomplete and erroneous evaluations. To fill this knowledge gap, we investigated the expression of signaling and trafficking proteins, and the in situ localization and transcriptome of naïve NKB cells compared to conventionally-defined NK and B cells, as well as modulations of these cells in SIV infection. Intracellular signaling proteins and trafficking markers were expressed differentially on naïve NKB cells, with high expression of CD62L and Syk, and low expression of CD69, α4ß7, FcRg, Zap70, and CD3z, findings which were more similar to B cells than NK cells. CD20+NKG2a/c+ NKB cells were identified in spleen, mesenteric lymph nodes (MLN), colon, jejunum, and liver of naïve rhesus macaques (RM) via tissue imaging, with NKB cell counts concentrated in spleen and MLN. For the first time, single cell RNA sequencing (scRNAseq), including B cell receptor (BCR) sequencing, of sorted NKB cells confirmed that NKB cells are unique. Transcriptomic analysis of naïve splenic NKB cells by scRNAseq showed that NKB cells undergo somatic hypermutation and express Ig receptors, similar to B cells. While only 15% of sorted NKB cells showed transcript expression of both KLRC1 (NKG2A) and MS4A1 (CD20) genes, only 5% of cells expressed KLRC1, MS4A1, and IgH/IgL transcripts. We observed expanded NKB frequencies in RM gut and buccal mucosa as early as 14 and 35 days post-SIV infection, respectively. Further, mucosal and peripheral NKB cells were associated with colorectal cytokine milieu and oral microbiome changes, respectively. Our studies indicate that NKB cells gated on CD3-CD14-CD20+NKG2A/C+ cells were inclusive of transcriptomically conventional B and NK cells in addition to true NKB cells, confounding accurate phenotyping and frequency recordings that could only be resolved using genomic techniques. Although NKB cells were clearly elevated during SIV infection and associated with inflammatory changes during infection, further interrogation is necessary to acurately identify the true phenotype and significance of NKB cells in infection and inflammation.

The Climate Change Burden on Immune Health: Are Persons Living with HIV More at Risk?

Climate change poses one of the most significant modern threats to overall human health,especially for vulnerable populations including persons living with HIV (PLWH). In this perspective, we specifically explore the concept of immune resilience in human health and how climate change phenomena - including extreme weather events, food insecurity, pollution, and emerging diseases - may exacerbate immune dysfunction and comorbidities faced by PLWH and hinder access to HIV treatment and prevention services. Multidisciplinary, collaborative efforts are urgently needed to quantify these impacts, develop mitigation strategies, and strengthen policies and funding to bolster immune resilience for PLWH in the face of accelerating climate change.

FcαRI (CD89) is upregulated on subsets of mucosal and circulating NK cells and regulates IgA-class specific signaling and functions.

Immunoglobulin A (IgA) is the predominant mucosal antibody class with both anti- and pro-inflammatory roles1-3. However, the specific role of the IgA receptor cluster of differentiation (CD)89, expressed by a subset of natural killer (NK) cells, is poorly explored. We found that CD89 protein expression on circulating NK cells is infrequent in humans and rhesus macaques, but transcriptomic analysis showed ubiquitous CD89 expression, suggesting an inducible phenotype. Interestingly, CD89+ NK cells were more frequent in cord blood and mucosae, indicating a putative IgA-mediated NK cell function in the mucosae and infant immune system. CD89+ NK cells signaled through upregulated CD3 zeta chain (CD3ζ), spleen tyrosine kinase (Syk), zeta chain-associated protein kinase 70 (ZAP70), and signaling lymphocytic activation molecule family 1 (SLAMF1), but also showed high expression of inhibitory receptors such as killer cell lectin-like receptor subfamily G (KLRG1) and reduced activating NKp46 and NKp30. CD89-based activation or antibody-mediated cellular cytotoxicity with monomeric IgA1 reduced NK cell functions, while antibody-mediated cellular cytotoxicity with combinations of IgG and IgA2 was enhanced compared to IgG alone. These data suggest that functional CD89+ NK cells survey mucosal sites, but CD89 likely serves as regulatory receptor which can be further modulated depending on IgA and IgG subclass. Although the full functional niche of CD89+ NK cells remains unexplored, these intriguing data suggest the CD89 axis could represent a novel immunotherapeutic target in the mucosae or early life.