Table_2_Monocytic-Myeloid Derived Suppressor Cells Suppress T-Cell Responses in Recovered SARS CoV2-Infected Individuals.xls

Coronavirus disease 2019 (COVID-19) caused by SARS Coronavirus 2 (CoV2) is associated with massive immune activation and hyperinflammatory response. Acute and severe CoV2 infection is characterized by the expansion of myeloid derived suppressor cells (MDSC) because of cytokine storm, these MDSC suppress T cell functions. However, the presence of MDSC and its effect on CoV2 antigen specific T cell responses in individuals long after first detection of CoV2 and recovery from infection has not been studied. We and others have previously shown that CD11b+CD33+CD14+HLA-DR-/lo monocytic MDSC (M-MDSC) are present in individuals with clinical recovery from viral infection. In this study, we compared the frequency, functional and transcriptional signatures of M-MDSC isolated from CoV2 infected individuals after 5-months of the first detection of the virus (CoV2+) and who were not infected with CoV2 (CoV2-). Compared to CoV2- individuals, M-MDSC were present in CoV2+ individuals at a higher frequency, the level of M-MDSC correlated with the quantity of IL-6 in the plasma. Compared to CoV2-, increased frequency of PD1+, CD57+ and CX3CR1+ T effector memory (TEM) cell subsets was also present in CoV2+ individuals, but these did not correlate with M-MDSC levels. Furthermore, depleting M-MDSC from peripheral blood mononuclear cells (PBMC) increased T cell cytokine production when cultured with the peptide pools of immune dominant spike glycoprotein (S), membrane (M), and nucleocapsid (N) antigens of CoV2. M-MDSC suppressed CoV2 S- antigen-specific T cell in ROS, Arginase, and TGFβ dependent manner. Our gene expression, RNA-seq and pathway analysis studies further confirm that M-MDSC isolated from CoV2+ individuals are enriched in pathways that regulate both innate and adaptive immune responses, but the genes regulating these functions (HLA-DQA1, HLA-DQB1, HLA-B, NLRP3, IL1β, CXCL2, CXCL1) remained downregulated in M-MDSC isolated from CoV2+ individuals. These results demonstrate that M-MDSC suppresses recall responses to CoV2 antigens long after recovery from infection. Our findings suggest M-MDSC as novel regulators of CoV2 specific T cell responses, and should be considered as target to augment responses to vaccine.

由严重急性呼吸综合征冠状病毒2（SARS Coronavirus 2，CoV2）引发的2019冠状病毒病（Coronavirus disease 2019，COVID-19）与大规模免疫激活及过度炎症反应密切相关。急性重症CoV2感染的特征为细胞因子风暴介导的髓系来源抑制细胞（myeloid derived suppressor cells，MDSC）扩增，此类MDSC可抑制T细胞功能。然而，针对首次检测到CoV2并康复许久的个体，其体内MDSC的存在情况以及对CoV2抗原特异性T细胞应答的影响尚未被研究。
我们及其他研究团队此前已证实，病毒感染临床康复者体内存在CD11b+CD33+CD14+HLA-DR-/lo单核细胞型髓系来源抑制细胞（monocytic MDSC，M-MDSC）。本研究对比了首次检测病毒5个月后的CoV2感染者（CoV2+组）与未感染CoV2个体（CoV2-组）体内分离得到的M-MDSC的频率、功能及转录特征。
与CoV2-组相比，CoV2+组个体体内M-MDSC的频率更高，且M-MDSC水平与血浆IL-6含量呈正相关。相较于CoV2-组，CoV2+组个体体内PD1+、CD57+及CX3CR1+ T效应记忆（T effector memory，TEM）细胞亚群的频率也有所升高，但上述指标与M-MDSC水平无显著关联。此外，从外周血单个核细胞（peripheral blood mononuclear cells，PBMC）中清除M-MDSC后，在用CoV2免疫显性刺突糖蛋白（spike glycoprotein，S）、膜蛋白（membrane，M）及核衣壳蛋白（nucleocapsid，N）抗原的肽库进行体外培养时，T细胞的细胞因子产生量显著提升。M-MDSC可通过活性氧（reactive oxygen species，ROS）、精氨酸酶及转化生长因子β（transforming growth factor β，TGFβ）依赖的方式抑制CoV2 S抗原特异性T细胞应答。
我们的基因表达、RNA测序（RNA-seq）及通路分析研究进一步证实，从CoV2+组个体体内分离的M-MDSC富集了调控固有免疫与适应性免疫应答的通路，但调控此类功能的基因（HLA-DQA1、HLA-DQB1、HLA-B、NLRP3、IL1β、CXCL2、CXCL1）在CoV2+组的M-MDSC中仍呈低表达状态。
上述研究结果表明，在感染康复许久之后，M-MDSC仍可抑制针对CoV2抗原的免疫回忆应答。本研究提示M-MDSC是调控CoV2特异性T细胞应答的新型调节因子，有望作为增强疫苗应答的潜在靶点。