The role of adaptive NK cells in the control of SARS-CoV-2 infection

自然杀伤（NK）细胞是对抗急性病毒感染的第一道防线的一部分。最近，鉴定了一种新型的病毒特异性适应性NK细胞，其在急性巨细胞病毒（CMV）感染期间扩增，并且通常对IgG抗体的刺激超敏感，导致高效和快速的抗体介导的细胞毒性（ADCC）。这些适应性（也称为记忆性）NK细胞的标志是刺激性受体NKG 2C的表达，其对人类白细胞抗原E（HLA-E）具有特异性。我们最近发现，在30-40%的HCMV+病例中，适应性NKG 2C + NK细胞稳定维持为大克隆扩增。此外，我们已经表明，这些扩展的大小与KIR 2DL受体的共表达相关，KIR 2DL受体是HLA-C的抑制性受体，是高度多态性KIR家族的成员。由于其高ADCC潜力，适应性NK细胞在SARS-CoV-2感染中可能发挥关键作用，这通常与强IgG抗体应答相关。事实上，最近显示，患有严重疾病的患者在循环中表现出适应性NK细胞的存在增加。重要的是，与传统的NK细胞相比，适应性NK细胞可以持续多年，因此有可能有助于长期保护免受再感染。在这个项目中，我们希望了解适应性NKG 2C + NK细胞如何影响SARS-CoV-2感染的结果。我们将在恢复期COVID-19患者（MU）的样本以及COVID-19灵长类动物模型（LW）中解决这一问题。杜塞尔多夫团队已经收集了超过130例SARS-CoV-2病例的样本和临床数据，并希望通过流式细胞术将相关临床参数（如疾病严重程度、病毒载量、SARS-CoV-2特异性IgM和IgG滴度以及CMV状态）与适应性NK细胞的存在相关联。此外，基于最近观察到SARS-CoV-2刺突蛋白SP1导致肺上皮细胞中HLA-E的上调，我们将在体外探索该机制是否通过HLA-E/NKG 2C轴导致适应性NK细胞的刺激和扩增。德国灵长类动物中心（DPZ）的哥廷根团队已经可以在新开发的猕猴NKG 2C和KIR特异性mAb的基础上证明猕猴中存在类似的CMV相关扩增。因此，我们想研究适应性NK细胞在SARS-CoV-2感染的急性期的贡献，采用实验感染的恒河猴。血液样本以及组织切片的分析将为我们提供独特的机会来监测这种灵长类动物模型中适应性NK细胞的分布和功能作用。如果适应性NK细胞确实参与了SARS-CoV-2感染的控制，那么这种可以在体外容易地扩增的先天免疫细胞类型可以为COVID-19患者的同种异体细胞治疗提供非常有趣的新选择。

Natural killer (NK) cells are part of the first line of defense against acute viral infections. Recently, a novel type of virus-specific adaptive NK cell was identified that expands during acute cytomegalovirus (CMV) infection and is generally hypersensitive to stimulation by IgG antibodies leading to highly efficient and rapid antibody-mediated cellular cytotoxicity (ADCC). A hallmark of these adaptive (also known as memory) NK cells is the expression of the stimulatory receptor NKG2C, which is specific for the Human Leucocyte Antigen E (HLA-E). We have recently shown that adaptive NKG2C+ NK cells are stably maintained as large clonal expansions in 30-40% of HCMV+ cases. Furthermore, we have shown that the size of these expansions correlates with the coexpression of KIR2DL receptors, which are inhibitory receptors for HLA-C and members of the highly polymorphic KIR family. Due to their high ADCC potential, adaptive NK cells could play a critical role in SARS-CoV-2 infection, which is often associated with strong IgG antibody responses. Indeed, it was recently shown that patients with severe disease exhibited increased presence of adaptive NK cells in the circulation. Importantly, in contrast to conventional NK cells, adaptive NK cells can persist for many years and thus have the potential to contribute to long-term protection against re-infection. In this project, we would like to find out how adaptive NKG2C+ NK cells influence the outcome of SARS-CoV-2 infection. We will address this in samples from convalescent COVID-19 patients (MU) as well as in a primate model of Covid-19 (LW). The Düsseldorf team has already collected samples and clinical data on >130 SARS-CoV-2 cases and would like to correlate the relevant clinical parameters such as disease severity, virus load, SARS-CoV-2-specific IgM and IgG titer, and CMV status with the presence of adaptive NK cells by multicolor flow cytometry. Furthermore, based on the recent observation that the SARS-CoV-2 spike protein SP1 leads to upregulation of HLA-E in lung epithelial cells, we will explore in vitro if this mechanism leads to stimulation and expansion of adaptive NK cells via the HLA-E/NKG2C axis. The Göttingen team at the German Primate Center (DPZ) could already demonstrate the presence of similar CMV-associated expansions in macaques on the basis of newly-developed mAbs specific for macaque NKG2C and KIR. We would thus like to study the contribution of adaptive NK cells in the acute phase of SARS-CoV-2 infection, employing experimentally infected rhesus macaques. The analysis of blood samples as well as tissue sections will give us the unique opportunity to monitor the distribution and functional role of adaptive NK cells in this primate model. If adaptive NK cells are indeed involved in control of SARS-CoV-2 infection, this innate immune cell type, which can be easily expanded in vitro, could provide a highly interesting novel option for allogeneic cellular therapy of COVID-19 patients.