Numerous studies in murine models and humans have gathered evidence that CD8+ T cells of higher functional avidity are more efficient in clearing viral infection.42, 43, 44 For CD4+ T cells in particular, fewer conclusive data regarding TCR affinity are available, and it has been suggested that MHC II-restricted TCRs generally display weaker binding affinities in comparison with MHC I-restricted TCRs.45 This evidence concerns the gene CD4 and viral infectious disease.