Chronic infection control relies on T cells with lower foreign antigen binding strength generated by N-nucleotide diversity

The pathogens to which T cells respond is determined by the T cell receptors (TCRs) present in an individuals repertoire. Although more than 90% of the TCR repertoire is generated by terminal deoxynucleotidyl transferase (TdT)-mediated N-nucleotide addition during V(D)J recombination, the benefit of TdT-modified TCRs remains unclear. Here, we computationally and experimentally investigated whether TdT systematically modifies the affinity distribution of a TCR repertoire in ways that impacts acute or chronic infection. Our computational model predicts a shift toward low-affinity T cells over time during chronic, but not acute, infections. Elimination of low-affinity T cells in silico substantially delayed chronic infection clearance. Corroborating an affinity-centric benefit for TCR diversity, we showed that infection of TdT-deficient mice delayed the clearance of a chronic viral pathogen, while acute viral control was unaffected. Our data thus suggest that TdT-mediated TCR diversity is of particular benefit in the control of prolonged pathogen replication.