Johan K. Sandberg(1#), Jean-Baptiste Gorin(1*), Tiphaine Parrot(1*), Yu Gao(1), Tobias Kammann(1), Hans-Gustaf Ljunggren(1), Soo Aleman(2,3), Marcus Buggert(1), Kristoffer Strålin(2,3), for the Karolinska COVID-19 Study Group

Affiliates

(1) Center for Infectious Medicine, Department of Medicine Huddinge, Karolinska Institutet, Karolinska University Hospital, Stockholm, Sweden (2) Department of Infectious Diseases, Karolinska University Hospital, Stockholm, Sweden (3) Division of Infectious Diseases and Dermatology, Department of Medicine Huddinge, Karolinska Institutet, Stockholm, Sweden

Abstract

Severe COVID-19 is associated with strong activation of mucosa-associated invariant T (MAIT) cells and loss of these cells from circulation. However, MAIT cells play important roles in immune defence against microbial infections, and we therefore investigated the capacity of the MAIT cell compartment to rebound in patients recovering from COVID-19. In longitudinal paired analysis, the MAIT cell compartment initially rebounded numerically and phenotypically in most patients at three months post release from hospital. Furthermore, while MAIT cell function restored in most patients, a subgroup displayed predominantly PD-1high functionally impaired MAIT cells. Finally, expression of CD56 and PD-1 in the recovering MAIT cell compartment correlated with levels at the acute disease stage, indicative that qualitative characteristics remain imprinted. Unexpectedly, the normalization of the MAIT cell compartment failed at nine months’ follow-up, with falling MAIT cell counts and accumulation of the CD4-CD8- MAIT cell subset. Together, these results indicate an initial transient period of inconsistent recovery of the MAIT cell compartment that is not sustained and eventually fails. Given the emerging role of MAIT cells in antimicrobial immunity and inflammation, the impairment of these cells may play a role in persisting health problems experienced by previously hospitalized COVID-19 patients.