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.

Plasticity of intragraft alloreactive T cell clones in human gut correlates with transplant outcomes.

The site of transition between tissue-resident memory (TRM) and circulating phenotypes of T cells is unknown. We integrated clonotype, alloreactivity, and gene expression profiles of graft-repopulating recipient T cells in the intestinal mucosa at the single-cell level after human intestinal transplantation. Host-versus-graft (HvG)-reactive T cells were mainly distributed to TRM, effector T (Teff)/TRM, and T follicular helper compartments. RNA velocity analysis demonstrated a trajectory from TRM to Teff/TRM clusters in association with rejection. By integrating pre- and post-transplantation (Tx) mixed lymphocyte reaction-determined alloreactive repertoires, we observed that pre-existing HvG-reactive T cells that demonstrated tolerance in the circulation were dominated by TRM profiles in quiescent allografts. Putative de novo HvG-reactive clones showed a transcriptional profile skewed to cytotoxic effectors in rejecting grafts. Inferred protein regulon network analysis revealed upstream regulators that accounted for the effector and tolerant T cell states. We demonstrate Teff/TRM interchangeability for individual T cell clones with known (allo)recognition in the human gut, providing novel insight into TRM biology.

Dynamic establishment and maintenance of the human intestinal B cell population and repertoire following transplantation.

It is unknown how intestinal B cell populations and B cell receptor (BCR) repertoires are established and maintained over time in humans. Following intestinal transplantation (ITx), surveillance ileal mucosal biopsies provide a unique opportunity to map the dynamic establishment of gut lymphocyte populations. Using polychromatic flow cytometry that includes HLA allele group-specific mAbs distinguishing donor from recipient cells along with high throughput BCR sequencing, we tracked the establishment of recipient B cell populations and BCR repertoire in the allograft mucosa of ITx recipients. We confirm the early presence of naïve donor B cells in the circulation and, for the first time, document the establishment of recipient B cell populations, including B resident memory cells, in the intestinal allograft mucosa. Recipient B cell repopulation of the allograft was most rapid in infant (<1 year old)-derived allografts and, unlike T cell repopulation, did not correlate with rejection rates. While recipient memory B cell populations were increased in graft mucosa compared to circulation, naïve recipient B cells remained detectable in the graft mucosa for years. Comparisons of peripheral and intra-mucosal B cell repertoires in the absence of rejection revealed increased BCR mutation rates and clonal expansion in graft mucosa compared to circulating B cells, but these parameters did not increase markedly after the first year post-transplant. Furthermore, clonal mixing between the allograft mucosa and the circulation was significantly greater in ITx recipients, even years after transplantation, than in healthy control adults. Collectively, our data demonstrate intestinal mucosal B cell repertoire establishment from a circulating pool, a process that continues for years without evidence of establishment of a stable mucosal B cell repertoire.

Mixed xenogeneic porcine chimerism tolerizes human anti-pig natural antibody-producing cells in a humanized mouse model.

BACKGROUND: A major obstacle to the success of organ transplantation from pigs to humans, necessitated by the shortage of human organs, is robust humoral immune rejection by pig-reactive human antibodies. Mixed xenogeneic hematopoietic chimerism induces xenoreactive B cell tolerance in rodents, but whether mixed pig/human chimerism could induce tolerance of human B cells to pig xenoantigens is unknown. METHODS: We investigated this question using a humanized mouse model in which durable mixed (pig-human) xenogeneic chimerism can be established. RESULTS: Human natural anti-pig cytotoxic antibodies, predominantly IgM, are detectable in non-chimeric humanized mouse serum, and pig-reactive antibodies were reduced in mixed chimeric versus non-chimeric humanized mice. This difference required persistent mixed chimerism and was not due to the adsorption of antibodies on pig cells in vivo. Furthermore, human B cells from spleens of mixed chimeric mice produced lower levels of anti-pig antibodies when stimulated in vitro compared with those from non-chimeric mice. CONCLUSIONS: Our findings demonstrate that mixed chimerism reduces human natural antibodies to pig xenoantigens, providing the first in vivo evidence of human B cell tolerance induction by mixed xenogeneic chimerism and supporting further evaluation of this approach for inducing human B cell tolerance to xenografts.

Lymphohematopoietic graft-versus-host responses promote mixed chimerism in patients receiving intestinal transplantation.

In humans receiving intestinal transplantation (ITx), long-term multilineage blood chimerism often develops. Donor T cell macrochimerism (≥4%) frequently occurs without graft-versus-host disease (GVHD) and is associated with reduced rejection. Here we demonstrate that patients with macrochimerism had high graft-versus-host (GvH) to host-versus-graft (HvG) T cell clonal ratios in their allografts. These GvH clones entered the circulation, where their peak levels were associated with declines in HvG clones early after transplant, suggesting that GvH reactions may contribute to chimerism and control HvG responses without causing GVHD. Consistently, donor-derived T cells, including GvH clones, and CD34+ hematopoietic stem and progenitor cells (HSPCs) were simultaneously detected in the recipients' BM more than 100 days after transplant. Individual GvH clones appeared in ileal mucosa or PBMCs before detection in recipient BM, consistent with an intestinal mucosal origin, where donor GvH-reactive T cells expanded early upon entry of recipient APCs into the graft. These results, combined with cytotoxic single-cell transcriptional profiles of donor T cells in recipient BM, suggest that tissue-resident GvH-reactive donor T cells migrated into the recipient circulation and BM, where they destroyed recipient hematopoietic cells through cytolytic effector functions and promoted engraftment of graft-derived HSPCs that maintain chimerism. These mechanisms suggest an approach to achieving intestinal allograft tolerance.

Human Intestinal Allografts Contain Functional Hematopoietic Stem and Progenitor Cells that Are Maintained by a Circulating Pool.

Human intestinal transplantation often results in long-term mixed chimerism of donor and recipient blood in transplant patients. We followed the phenotypes of chimeric peripheral blood cells in 21 patients receiving intestinal allografts over 5 years. Donor lymphocyte phenotypes suggested a contribution of hematopoietic stem and progenitor cells (HSPCs) from the graft. Surprisingly, we detected donor-derived HSPCs in intestinal mucosa, Peyer's patches, mesenteric lymph nodes, and liver. Human gut HSPCs are phenotypically similar to bone marrow HSPCs and have multilineage differentiation potential in vitro and in vivo. Analysis of circulating post-transplant donor T cells suggests that they undergo selection in recipient lymphoid organs to acquire immune tolerance. Our longitudinal study of human HSPCs carried in intestinal allografts demonstrates their turnover kinetics and gradual replacement of donor-derived HSPCs from a circulating pool. Thus, we have demonstrated the existence of functioning HSPCs in human intestines with implications for promoting tolerance in transplant recipients.

Quantification of somatic mutation flow across individual cell division events by lineage sequencing.

Mutation data reveal the dynamic equilibrium between DNA damage and repair processes in cells and are indispensable to the understanding of age-related diseases, tumor evolution, and the acquisition of drug resistance. However, available genome-wide methods have a limited ability to resolve rare somatic variants and the relationships between these variants. Here, we present lineage sequencing, a new genome sequencing approach that enables somatic event reconstruction by providing quality somatic mutation call sets with resolution as high as the single-cell level in subject lineages. Lineage sequencing entails sampling single cells from a population and sequencing subclonal sample sets derived from these cells such that knowledge of relationships among the cells can be used to jointly call variants across the sample set. This approach integrates data from multiple sequence libraries to support each variant and precisely assigns mutations to lineage segments. We applied lineage sequencing to a human colon cancer cell line with a DNA polymerase epsilon (POLE) proofreading deficiency (HT115) and a human retinal epithelial cell line immortalized by constitutive telomerase expression (RPE1). Cells were cultured under continuous observation to link observed single-cell phenotypes with single-cell mutation data. The high sensitivity, specificity, and resolution of the data provide a unique opportunity for quantitative analysis of variation in mutation rate, spectrum, and correlations among variants. Our data show that mutations arrive with nonuniform probability across sublineages and that DNA lesion dynamics may cause strong correlations between certain mutations.