Min-Seok Rha^1,12, Hye Won Jeong^2,12, Jae-Hoon Ko^3,12, Seong Jin Choi¹, In-Ho Seo¹, Jeong Seok Lee¹⁴, Moa Sa^1,5, A Reum Kim¹, Eun-Jeong Joo⁶, Jin Young Ahn⁷, Jung Ho Kim⁷, Kyoung-Ho Song⁸, Eu Suk Kim⁸, Dong Hyun Oh⁹, Mi Young Ahn⁹, Hee Kyoung Choi¹⁰, Ji Hoon Jeon¹⁰, Jae-Phil Choi⁹, Hong Bin Kim⁸, Young Keun Kim¹¹, Su-Hyung Park¹⁵, Won Suk Choi^10,*, Jun Yong Choi^7,*, Kyong Ran Peck^3,*, Eui-Cheol Shin^1,5,13,*

¹Graduate School of Medical Science and Engineering, Korea Advanced Institute of Science and Technology (KAIST), Daejeon 34141, Republic of Korea
²Department of Internal Medicine, Chungbuk National University College of Medicine, Cheongju 28644, Republic of Korea
³Division of Infectious Diseases, Department of Medicine, Samsung Medical Center, Sungkyunkwan University School of Medicine, Seoul 06351, Republic of Korea
⁴GENOME INSIGHT Inc., Daejeon 34051, Republic of Korea
⁵The Center for Epidemic Preparedness, KAIST Institute, Daejeon 34141, Republic of Korea
⁶Division of Infectious Diseases, Department of Internal Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul 03181, Republic of Korea
⁷Department of Internal Medicine, Severance Hospital, Yonsei University College of Medicine, Seoul 03722, Republic of Korea
⁸Department of Internal Medicine, Seoul National University Bundang Hospital, Seoul National University College of Medicine, Seongnam 13620, Republic of Korea
⁹Department of Internal Medicine, Seoul Medical Center, Seoul 02053, Republic of Korea
¹⁰Division of Infectious Diseases, Department of Internal Medicine, Korea University College of Medicine, Ansan Hospital, Ansan 15355, Republic of Korea
¹¹Department of Internal Medicine, Wonju Severance Christian Hospital, Yonsei University Wonju College of Medicine, Wonju 26426, Republic of Korea

¹²These authors contributed equally.

¹³Lead contact

^*Corresponding author

Memory T cell responses have been demonstrated in COVID-19 convalescents, but ex vivo phenotypes of SARS-CoV-2-specific T cells have been unclear. We detected SARS-CoV-2-specific CD8⁺ T cells by MHC-I multimer staining and examined their phenotypes and functions in acute and convalescent COVID-19. Multimer⁺ cells exhibited early differentiated effector-memory phenotypes in the early convalescent phase. The frequency of stem-like memory cells was increased among multimer⁺ cells in the late convalescent phase. Cytokine secretion assays combined with MHC-I multimer staining revealed that the proportion of interferon-γ (IFN-γ)-producing cells was significantly lower among SARS-CoV-2-specific CD8⁺ T cells than those specific to influenza A virus. Importantly, the proportion of IFN-γ-producing cells was higher in PD-1⁺ cells than PD-1^- cells among multimer⁺ cells, indicating that PD-1-expressing, SARS-CoV-2-specific CD8⁺ T cells are not exhausted, but functional. Our current findings provide information for understanding of SARS-CoV-2-specific CD8⁺ T cells elicited by infection or vaccination.