Letter to the Editor on "CD4+ T cells persist for years in the human small intestine and display a TH1 cytokine profile"

We read and appreciated the recent study by Bartolome’-Casado R et al.1: the authors examined the turnover of CD4+ T cells in human transplanted duodenum, showing that the majority of CD4+ T cells were still donor-derived 1 year after transplantation and suggesting that immune-surveillance in non-lymphoid tissues is dominated by CD4+ T cell-resident populations. In their opinion most CD4+ T cells in human small intestine under normal conditions are non-circulating, resident cells that most likely perpetuate for years and tissue residency represents a major mechanism for CD4+ memory T cell immune-surveillance in human small bowel. In their study transplanted patients with episodes of acute cellular rejection (ACR) or with donor-specific antibodies (DSA) were excluded. Notwithstanding, there was a large variation in persisting donorderived CD4+ T cells among human duodenal grafts after 1 year: the Authors explained the phenomenon with the probability of undiagnosed intermittent rejection episodes (or other clinical problems) among patients between 6 and 52 weeks after transplantation. Rejection episodes dramatically increase the replacement kinetics of immune cells and microchimerism.