Introduction: It is more urgent to achieve immune tolerance in children than in adults due to the longer survival after liver transplantation (LT). However, there is a lack of data on inflammatory cells distribution in graft histology following the withdrawal of immunosuppressants. Our objective is to summarize the characteristics of CD4+ T lymphocyte subsets, including Treg cells, in pediatric recipients following immune tolerance.
Methods: The recipients were divided into a successful tolerance group (n=13) and a failed tolerance group (n=9), and compared with an acute rejection group (n=10), a subclinical rejection group (n=9), and a stable graft function group (n=10). Repeated liver biopsies were performed, and all specimens were formalin-fixed and paraffin-embedded. CD4+ T lymphocyte subsets were detected by multiple immunohistochemistry (mIHC). Foxp3 and CTLA-4 were doubly stained by fluorescence in situ hybridization (FISH).
Results: The recipients in the successful tolerance group, who were at 48.8±21.3 months post-LT and followed up for 41.6±17.2 months after complete withdrawal of immunosuppressants, were primarily living donor liver transplantation recipients (12/13), with no fibrosis progression and achieving tolerance. The proportion of Treg cells (CD4+Foxp3+ T cells) in the grafts of the successful tolerance group decreased at 0, 12, and 24 months after enrollment, while there was no difference in Th1 (CD4+T-Bet+ T cells), Th2 (CD4+GATA3+ T cells), and Th17 (CD4+IL-17+ T cells) subsets. At enrollment, the proportion of memory Treg cells (CD4+Foxp3+CD45RO+ T cells) in the successful tolerance group was higher than that in the failed tolerance group, but there were no differences at 12 and 24 months between the two groups after enrollment. However, there were no differences in Foxp3 or CTLA-4 between the successful and failed tolerance groups at any time points after enrollment. The positive rate and cell positive density of Foxp3 in the successful tolerance group were lower than those in the rejection group and subclinical rejection group.
Conclusions: Through the examination of pediatric recipients in different immune states post-LT, it was confirmed that the successful induction of immune tolerance was closely related to Treg cells in the graft tissue, especially memory Treg cells, rather than other subsets of CD4+ T cells. Graft fibrosis in tolerant recipients did not progress, but longer observation is needed in the future.