Furthermore, while lack of routine B and T cell immunophenotyping prohibited an accurate assessment of combined immunodeficiency frequency in both cohorts, the overlapping reduction in naïve CD4+ T cell counts and response to mitogen challenge in patients with ≤2% class-switched memory B cells in the Partners cohort was consistent with the identification of a late-onset combined immunodeficiency phenotype. This evidence concerns the gene CD4 and Immunodeficiency.