The CD38+ HLA-DR+ T Cells with Activation and Exhaustion Characteristics as Predictors of Severity and Mortality in COVID-19 patients

Qiuyue Long ^1,2 Shixu Song ^1,2 Jianbo Xue ³ Wenyi Yu ³ Yaolin Zheng ^1,2 Ji-Wei Li ⁴ Jing Wu ^1,2 Xiaoyi Hu ^2,3 Mingzheng Jiang ^1,2 Hongli Ye ^1,2 Binghan Zheng ^1,2 Minghui Wang ^1,2 Fangfang Wu ^1,2 Ke Li ⁵ Gao Zhancheng ^1,2,3* Yali Zheng ^1,2*

• ¹ Department of Respiratory, Critical Care and Sleep Medicine, Xiang'an Hospital of Xiamen University, School of Medicine, Xiamen University, Xiamen, Fujian Province, China
• ² Institute of Chest and Lung Diseases, Xiang'an Hospital of Xiamen University, Xiamen, Fujian Province, China
• ³ Department of Respiratory and Critical Care Medicine, Peking University People’s Hospital, Beijing, Beijing Municipality, China
• ⁴ Department of Thoracic Surgery and Oncology, the First Affiliated Hospital of Guangzhou Medical University, State Key Laboratory of Respiratory Disease, Guangzhou, China
• ⁵ Department of Critical Care Medicine, Xiang’an Hospital of Xiamen University, School of Medicine, Xiamen University, Xiamen, China

Background: The COVID-19 pandemic remains a global health challenge. Severe cases often respond poorly to standard treatments, highlighting the necessity for novel therapeutic targets and early predictive biomarkers.Methods: We utilized flow cytometry to analyze peripheral immune cells from healthy, bacterial pneumonia patients, and COVID-19 patients. The expansion of activated T cells (CD38+HLA-DR+), monocytes, and myeloid-derived suppressor cells (MDSCs) were detected and correlated with clinical outcomes to evaluate prognostic potential. The single-cell RNA sequencing (scRNA-seq) was applied to characterize the critical cell subset associated with prognosis and elucidate its phenotype in COVID-19.Results: We revealed a significant increase in CD38+HLA-DR+ T cells in non-survivor COVID-19 patients, establishing them as an independent risk factor for 28-day mortality. The scRNA-seq analysis identified the CD38+HLA-DR+ T cell as a terminally differentiated, Treg-like subset exhibiting both activation and exhaustion characteristics. This subset presented the highest IL-6 and IL-10 mRNA levels among all T-cell subsets. Further functional analysis demonstrated its enhanced major histocompatibility complex class II (MHC-II) cross-signaling and correspondingly enriched cytoskeletal rearrangement processes. In addition, there was dysregulated NAD+ metabolism in CD38+HLA-DR+ T cells via scRNA-seq, accompanied by elevated adenosine and decreased NAD+ levels in serums from COVID-19 patients.Conclusions: We identified the selective expansion of CD38+HLA-DR+ T cells as a novel prognostic indicator for COVID-19 outcomes. These cells' unique activated-exhausted phenotype, along with their impact on NAD+ metabolism, provides new insights into COVID-19 immunopathogenesis.