X-linked moesin-associated immune deficiency (X-MAID), a human genetic disorder caused by the missense mutation R171W in the moesin gene, is characterized by extensive lymphopenia, resembling the phenotype observed in moesin-knockout mice, with low proliferation of T lymphocyte in which the proportion of naïve CD4+ and senescent and exhausted CD8+ T cell subtypes is unusually high [82,140,141]. This evidence concerns the gene MSN and lymphopenia.