Impaired ICOS signaling between Tfh and B cells distinguishes hospitalized from ambulatory CoViD-19 patients

Emerging evidence suggests that SARS-CoV-2 infections are characterized by systemic immune responses that appear to be dysregulated with more severe CoViD-19 disease. Lymphopenia and delayed antibody responses are commonly identified in CoViD-19 subjects, and recent reports have demonstrated abrogation of germinal centers in severe CoViD-19. This work assessed a potential mechanistic basis for impaired humoral responses, focusing on the T follicular helper (Tfh) and B cell interface that is critical for germinal center reactions. Here we demonstrated that Tfh activity is impaired in hospitalized relative to ambulatory CoViD-19 subjects, potentially due to decreased expression of the costimulatory molecule ICOS-L on B cells. Functional impairment manifested as a diminished ability to stimulated Tfh derived IFNγ and IL-21, the latter of which is critical for B cell proliferation and differentiation. Activation of Tfh cells by agonism of the ICOS receptor ex vivo by an agonistic antibody stimulated the generation of IFNγ/IL-21 double positive cells from hospitalized CoViD-19 subjects. This report establishes an immunological defect that differentiates ambulatory from hospitalized CoViD and suggests that agents that could restore impaired mechanisms at the Tfh–B cell interface may be of therapeutic value. ### Competing Interest Statement All authors are employees or contractors of Jounce Therapeutics, Inc. ### Funding Statement This work was sponsored and funded by Jounce Therapeutics, Inc. ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study was approved through the New England IRB (Needham, MA). All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data necessary to support the conclusions of the manuscript are contained within the manuscript or supplemental materials.