The Holy Grail: operational tolerance in intestinal transplantation

A: To achieve operational tolerance is the holy grail of transplantation immunology. However, due to the immunogenicity of intestinal transplant (ITx), to date no case of operational tolerance has been described. The purpose of this study is to report on the first case of ITx operational tolerance and his immunocharacterization. B: An immunophenotype of ITx patients was created utilizing peripheral blood and allograft samples, which were then analyzed with polychromatic flow cytometry (PFC) and rtPCR. A demographic matched control cohort, a stable ITx cohort and a rejection cohort were investigated in parallel. C: Our operational tolerant patient is a 20-year-old male with prior isolated ITx who, due to non-compliance, has been off all immunosuppressive medication for 2.5 years. He received his transplant in 2010 for pseudo-obstruction from a 17 year-old male donor with 5/6 mismatched antigens. His course was complicated by GvHD at 6 months, thus prompting us to hypothesize that his tolerance could be secondary to chimerism. Therefore, his peripheral blood was genotyped which showed no evidence of chimerism on 2 samples over several years, suggesting rather a mechanism of peripheral tolerance. In order to test this theory, his allograft lymphocytes were isolated and analyzed via PFC revealing 7.6% CD3+ T cells in the lamina propria, which is lower than the stable cohort who had 12.3% and the rejection cohort with 27.8%. He also had lower pro-inflammatory CCR6+ Th17 cells (20%) than the stable and rejection cohort (24% and 48%, respectively), revealing an anti-inflammatory immunophenotype in his allograft. In peripheral blood, he had 70% CD3+ T cells which was similar to his matched control cohort. Importantly, further subset analysis revealed a high 54% naïve CD4+ T cell population, which is higher from his control cohort at 34.8%. Moreover, we found a comparable T regulatory cell population (6.7% vs. 5.7%), signifying a functionally balanced T cell compartment in our patient. On the innate side, we noted 18.3% NK cells in his peripheral blood, a stark increase compared to his controls with 7.7%. Importantly, the majority were CD56dim NK cells, who have been shown to play a role in immunotolerance in liver transplantation. D: This study details the proven possibility of operational tolerance following isolated intestinal transplantation and warrants further immunomonitoring and tolerance studies on ITx patients.