Although naïve lymphocytes are rare in the healthy colonic mucosa, we have previously shown that an unusually high frequency of naïve (CD45RA+) CD4 T cells resides in the colonic lamina propria of IBD patients, particularly in the setting of inflammation.20,21 A smaller fraction of CD4 T cells were naive in the colon biopsies of vedolizumab recipients than in their control individuals (Figure 1A), although by paired analyses, the difference was significant for both the nonresponder (P = .003) and responder (P = .01) cohorts. This evidence concerns the gene CD4 and inflammatory bowel disease.