CD96 as a target to reverse aryl hydrocarbon receptor mediated immune suppression in aged individuals

Introduction/Rationale: Influenza virus is a major source of morbidity and mortality throughout the world. The majority of deaths and hospitalizations from seasonal influenza infection occur in older individuals. Even with high dose or adjuvanted vaccines, influenza vaccine responsiveness is lower in older individuals.

Methods: We collected plasma and peripheral blood mononuclear cells from 96 individuals over the age of 65 and 14 under the age of 40 prior to and 7,14, and 30 days after receipt of the seasonal influenza vaccine. We assessed antibody responses to the hemagglutinin and neuraminidase components of the vaccine as well as hemagglutination inhibition titers as an established correlate of protection. We further assessed the B cell compartment of each donor using spectral flow cytometry, and selected donors by single cell RNA sequencing.

Results: Transcripts and protein of CD96 were upregulated in naïve B cells of aged individuals. CD96 is a known inhibitory receptor in T and NK cells but its function in B cells is largely unknown. CD96 interaction with its ligand CD155 inhibited B cell receptor (BCR) crosslinking-mediated calcium flux. We developed a panel of human anti-CD96 antibodies by phage display and found that these antibodies could block CD96-mediated BCR signaling suppression. Metabolomic and transcriptomic data indicated alterations in tryptophan metabolism toward the kynurenine pathway in older individuals, and kynurenine, an aryl hydrocarbon receptor (AHR) agonist, induced CD96 expression in B cells. Kynurenine suppressed antibody production and class switching in a B-T follicular helper cell coculture model, and CD96 blockade reversed the suppressive effect of kynurenine in this model.

Conclusion: Accumulation of kynurenine and related AHR agonist metabolites may play a role in age-related immune suppression and vaccine hyporesponsiveness in part via upregulation of CD96 on B cells. Blocking CD96 signaling represents a potential avenue to restore vaccine responsiveness in older individuals.