T cell phenotypes in COVID-19 - a living review
Authors: Hanna Stephanie J , Codd Amy S , Gea-Mallorqui Ester , Scourfield D Oliver , Richter Felix C , Ladell Kristin , Borsa Mariana , Compeer Ewoud B , Moon Owen R , Galloway Sarah A E , Dimonte Sandra , Capitani Lorenzo , Shepherd Freya R , Wilson Joseph D , Uhl Lion F K ,   The Oxford-Cardiff COVID-19 Literature Consortium, Ahern David J , Almuttaqi Hannah , Alonzi Dominic S , Alrubayyi Aljawharah , Alsaleh Ghada , Bart Valentina M T , Batchelor Vicky , Bayliss Rebecca , Berthold Dorothée L , Bezbradica Jelena S , Bharuchq Tehmina , Borrmann Helene , Borsa Mariana , Borst Rowie , Brun Juliane , Burnell Stephanie , Capitani Lorenzo , Cavounidis Athena , Chapman Lucy , Chauveau Anne , Cifuentes Liliana , Codd Amy Susan , Compeer Ewoud Bernardus , Coveney Clarissa , Cross Amy , Danielli Sara , Davies Luke C , Dendrou Calliope A , Dimonte Sandra , Peter Durairaj Ruban Rex , Dustin Lynn B , Dyer Arthur , Fielding Ceri , Fischer Fabian , Gallimore Awen , Galloway Sarah , Gammage Anís , Gea-Mallorquí Ester , Godkin Andrew , Hanna Stephanie J , Heuberger Cornelia , Hulin-Curtis Sarah , Issa Fadi , Jones Emma , Jones Ruth , Ladell Kristin , Lauder Sarah N , Liddiard Kate , Ligoxygakis Petros , Lu Fangfang , MacLachlan Bruce , Maleki-Toyserkani Shayda , Mann Elizabeth H , Marzeda Anna M , Matthews Reginald James , Mazet Julie M , Milicic Anita , Mitchell Emma , Moon Owen , Nguyen Van Dien , O'Hanlon Miriam , Eléonore Pavillet Clara , Peppa Dimitra , Pires Ana , Pring Eleanor , Quastel Max , Reed Sophie , Rehwinkel Jan , Richmond Niamh , Richter Felix Clemens , Robinson Alice J B , Rodrigues Patrícia R S , Sabberwal Pragati , Sami Arvind , Peres Raphael Sanches , Sattentau Quentin , Schonfeldova Barbora , Scourfield David Oliver , Selvakumar Tharini A , Shepherd Freya R , Shorten Cariad , Simon Anna Katharina , Smith Adrian L , Crespo Alicia Teijeira , Tellier Michael , Thornton Emily , Uhl Lion F K , van Grinsven Erinke , Wann Angus K T , Williams Richard , Wilson Joseph D , Zhou Dingxi , Zhu Zihan , Gallimore Awen M , Milicic Anita 
Published: December 2020

Abstract
COVID-19 is characterized by profound lymphopenia in the peripheral blood, and the remaining T cells display altered phenotypes, characterized by a spectrum of activation and exhaustion. However, antigen-specific T cell responses are emerging as a crucial mechanism for both clearance of the virus and as the most likely route to long-lasting immune memory that would protect against re-infection. Therefore, T cell responses are also of considerable interest in vaccine development. Furthermore, persistent alterations in T cell subset composition and function post-infection have important implications for patients’ long-term immune function. In this review, we examine T cell phenotypes, including those of innate T cells, in both peripheral blood and lungs, and consider how key markers of activation and exhaustion correlate with, and may be able to predict, disease severity. We focus on SARS-CoV-2-specific T cells to elucidate markers that may indicate formation of antigen-specific T cell memory. We also examine peripheral T cell phenotypes in recovery and the likelihood of long-lasting immune disruption. Finally, we discuss T cell phenotypes in the lung as important drivers of both virus clearance and tissue damage. As our knowledge of the adaptive immune response to COVID-19 rapidly evolves, it has become clear that while some areas of the T cell response have been investigated in some detail, others, such as the T cell response in children remain largely unexplored. Therefore, this review will also highlight areas where T cell phenotypes require urgent characterisation.