Donor and recipient hematopoietic stem and progenitor cells mobilization in liver transplantation patients.

BACKGROUND: Hematopoietic stem and progenitor cells (HSPCs) mobilize from bone marrow to peripheral blood in response to stress. The impact of alloresponse-induced stress on HSPCs mobilization in human liver transplantation (LTx) recipients remains under-investigated. METHODS: Peripheral blood mononuclear cell (PBMC) samples were longitudinally collected from pre- to post-LTx for one year from 36 recipients with acute rejection (AR), 74 recipients without rejection (NR), and 5 recipients with graft-versus-host disease (GVHD). 28 PBMC samples from age-matched healthy donors were collected as healthy control (HC). Multi-color flow cytometry (MCFC) was used to immunophenotype HSPCs and their subpopulations. Donor recipient-distinguishable major histocompatibility complex (MHC) antibodies determined cell origin. RESULTS: Before LTx, patients who developed AR after transplant contained more HSPCs in PBMC samples than HC, while the NR group patients contained fewer HSPCs than HC. After LTx, the HSPC ratio in the AR group sharply decreased and became less than HC within six months, and dropped to a comparable NR level afterward. During the one-year follow-up period, myeloid progenitors (MPs) biased differentiation was observed in all LTx recipients who were under tacrolimus-based immunosuppressive treatment. During both AR and GVHD episodes, the recipient-derived and donor-derived HSPCs mobilized into the recipient's blood-circulation and migrated to the target tissue, respectively. The HSPCs percentage in blood reduced after the disease was cured. CONCLUSIONS: A preoperative high HSPC ratio in blood characterizes recipients who developed AR after LTx. Recipients exhibited a decline in blood-circulating HSPCs after transplant, the cells mobilized into the blood and migrated to target tissue during alloresponse.

Alloreactive T cells temporarily increased in peripheral blood of patients before liver allograft rejection.

T cells are key mediators of alloresponse during liver transplantation (LTx). However, the dynamics of donor-reactive T cell clones in peripheral blood during a clinical T-cell-mediated rejection (TCMR) episode remain unknown. Here, we collected serial peripheral blood mononuclear cells (PBMCs) samples spanning from pre-LTx to one-year post-LTx and available biopsies during the TCMR episodes from 26 rejecting patients, and serial PBMC samples were collected from 96 non-rejectors. Immunophenotypic and repertoire analyses were integrated on T cells from rejectors and longitudinally compared them to non-rejected patients. Donor-reactive T cell clone was identified and tracked by cross-matching with mappable donor-reactive TCR repertoire of each donor-recipient pair in 9 rejectors and 5 non-rejectors. Before transplantation, the naive T cell percentage and TCR repertoire diversity of rejectors was comparable to healthy control, it was reduced in non-rejectors. After transplantation, the naïve T cell percentages decreased and TCR repertoires were skewed in rejectors, the phenomenon was not observed in non-rejectors. Alloreactive clones increased in proportion in peripheral blood of rejectors before TCMR for weeks. The increase was accompanied by the naïve T cell decline and memory T cell increase and acquired an activated phenotype. Intragraft alloreactive clone tracking in pre- and post-LTx PBMC samples revealed that the pre-transplant naïve T cells were significant contributors to the donor-reactive clones, and they temporarily increased in proportion and subsequently reduced in blood at the beginning of TCMR. Together, our findings offer an insight into the dynamic and origin of alloreactive T cells in clinical LTx TCMR cases, and may facilitate disease prediction and management.

Dynamic establishment of recipient resident memory T cell repertoire after human intestinal transplantation.

BACKGROUND: Understanding formation of the human tissue resident memory T cell (TRM) repertoire requires longitudinal access to human non-lymphoid tissues. METHODS: By applying flow cytometry and next generation sequencing to serial blood, lymphoid tissue, and gut samples from 16 intestinal transplantation (ITx) patients, we assessed the origin, distribution, and specificity of human TRMs at phenotypic and clonal levels. FINDINGS: Donor age ≥1 year and blood T cell macrochimerism (peak level ≥4%) were associated with delayed establishment of stable recipient TRM repertoires in the transplanted ileum. T cell receptor (TCR) overlap between paired gut and blood repertoires from ITx patients was significantly greater than that in healthy controls, demonstrating increased gut-blood crosstalk after ITx. Crosstalk with the circulating pool remained high for years of follow-up. TCR sequences identifiable in pre-Tx recipient gut but not those in lymphoid tissues alone were more likely to populate post-Tx ileal allografts. Clones detected in both pre-Tx gut and lymphoid tissue had distinct transcriptional profiles from those identifiable in only one tissue. Recipient T cells were distributed widely throughout the gut, including allograft and native colon, which had substantial repertoire overlap. Both alloreactive and microbe-reactive recipient T cells persisted in transplanted ileum, contributing to the TRM repertoire. INTERPRETATION: Our studies reveal human intestinal TRM repertoire establishment from the circulation, preferentially involving lymphoid tissue counterparts of recipient intestinal T cell clones, including TRMs. We have described the temporal and spatial dynamics of this active crosstalk between the circulating pool and the intestinal TRM pool. FUNDING: This study was funded by the National Institute of Allergy and Infectious Diseases (NIAID) P01 grant AI106697.