PDCD1 and obesity due to melanocortin 4 receptor deficiency: We discovered that diet-induced obesity reduced the frequency of CD44lo CD62Lhi naïve CD4+ T cells and increased the frequency of both CD44hi CD62Llo memory phenotype CD4+ T cells in VAT and a unique population of CD44hi CD62Llo CD4+ T cells that constitutively express PD-1 and CD153 exhibit cellular senescence [25].