Reconstitution of the uterine immune milieu after uterus or hematopoietic stem cell transplantation.

Maintenance of tissue-specific immunity is important for immunological fitness, but its establishment has been difficult to assess in humans. Here, we investigated reconstitution of the human uterine immune system by studying women who underwent uterus solid organ transplantation or hematopoietic stem cell transplantation (HSCT). Through single-cell identification based on single-nucleotide polymorphisms and disparate human leukocyte antigen expression using single-cell RNA sequencing or high-parameter flow cytometry, donor versus recipient cell origin was determined, and we examined the gene expression states, surface marker profiles, and spatial organization of these cells in the endometrium. Endometrial immune cell reconstitution occurred after both uterus transplant and HSCT at the transcriptomic, phenotypic, and spatial levels. Reconstitution involved restoration of all major immune lineages with frequencies comparable to those of healthy controls, with preservation of canonical endometrial immune architecture. Recipient-derived immune cells replaced donor immune cells after uterus transplant, whereas HSCT resulted in near-complete donor-derived immune reconstitution, including formation of tissue-resident lymphocytes. This occurred despite tacrolimus-induced, calcineurin-mediated inhibition of the nuclear factor of activated T cells (NFAT) pathway, which affected de novo induction of tissue-residency features in vitro. In one patient, immune cells of male origin reconstituted the endometrium after HSCT. Collectively, these data provide insights into tissue immune system persistence and reconstitution capabilities in the uterus, an organ that undergoes continuous regeneration.