Intragraft distribution of lymphocytes expressing β7 integrins after small bowel transplantation in mice

Immune cell profiling in intestinal transplantation

Since the first published case study of human intestinal transplantation in 1967, there have been significant studies of intestinal transplant immunology in both animal models and humans. An improved understanding of the profiles of different immune cell subsets is critical for understanding their contributions to graft outcomes. While different studies have focused on the contribution of one or a few subsets to intestinal transplant, no study has integrated these data for a comprehensive overview of immune dynamics after intestinal transplant. Here, we provide a systematic review of the literature on different immune subsets and discuss their roles in intestinal transplant outcomes on multiple levels, focusing on chimerism and graft immune reconstitution, clonal alloreactivity, and cell phenotype. In Sections 1, 2 and 3, we lay out a shared framework for understanding intestinal transplant, focusing on the mechanisms of rejection or tolerance in the context of mucosal immunology and illustrate the unique role of the bidirectional graft-versus-host (GvH) and host-versus-graft (HvG) alloresponse. In Sections 4, 5 and 6, we further expand upon these concepts as we discuss the contribution of different cell subsets to intestinal transplant. An improved understanding of intestinal transplantation immunology will bring us closer to maximizing the potential of this important treatment.

Low percentages of circulating CD8(+)/CD45RA(+) human T lymphocytes expressing beta7 integrin correlate with the occurrence of intestinal acute graft-versus-host disease after allogeneic hematopoietic stem cell transplantation

OBJECTIVE

Effector phase of acute graft-versus-host disease (a-GVHD) is mainly mediated by donor-derived, anti-host cytotoxic T cells. T-cell homing into gut-associated lymphoid tissues is ascribed to the alpha4beta7 integrin. We reasoned that development of intestinal a-GVHD might be triggered by recruitment in the intestinal mucosa of circulating, alloreactive, alpha4beta7(+) donor T cells. Therefore, we evaluated the correlation existing between circulating beta7(+) T-lymphocyte subsets early after allogeneic hematopoietic stem cell transplantation (allo-HSCT) and occurrence of a-GVHD.

PATIENTS AND METHODS

Surface expression of beta7 integrin on T cells was evaluated by means of direct immunofluorescence, in three-color analysis. Sixty-five patients given allo-HSCT were evaluated: 13 of them experienced intestinal a-GVHD, 14 developed a-GVHD without intestinal involvement, and 38 did not develop a-GVHD. Patients were studied early after initial signs of hematologic reconstitution and before occurrence of a-GVHD.

RESULTS

We found a significantly higher absolute number of CD8(+) and a significantly lower percentage of CD8(+)CD45RA(+)beta7(+) T cells in patients with intestinal a-GVHD than in patients with a-GVHD without intestinal involvement (p = 0.003 and p = 0.003, respectively) or not experiencing a-GVHD (p = 0.02 and p = 0.002, respectively). In particular, we found that intestinal a-GVHD occurred in over 70% of patients showing an absolute number of CD8(+) T cells > or = 60 x 10(6)/L and a percentage of circulating CD8(+)CD45RA(+)beta7(+) T cells < 35%.

CONCLUSION

Measuring the absolute number of CD8(+) T cells and percentage of CD8(+)CD45RA(+)beta7(+) T cells at time of hematologic reconstitution may help identify patients at risk of developing intestinal a-GVHD who could benefit from strategies aimed at hampering alloreactive T-cell homing to intestinal mucosa.

Donor lymphoid organs are a major site of alloreactive T-cell priming following intestinal transplantation

We hypothesized that lymphoid organs within intestinal allografts contribute to their immunogenicity. Consistent with this hypothesis recipient T cells rapidly migrated to the lymph nodes and Peyer's patches of syngeneic and allogeneic intestinal grafts such that at 24 h approximately 50% of the lymphocytes isolated from donor lymphoid organs were of recipient origin. However, only in the lymphoid organs of allografts did recipient T cells display an activated phenotype, proliferate and produce IFNgamma. Rejection of allogeneic intestines lacking lymphoid organs was dramatically impaired in splenectomized, lymph node-deficient recipients compared to lymph node bearing, wild-type allogeneic intestines. This demonstrates the important role of donor lymphoid organs in the rejection process. Furthermore, recipient T cells proliferated more extensively and produced more IFNgamma in donor lymphoid organs than in recipient lymphoid organs, indicating that donor lymphoid organs play a dominant role in initiating the recipient anti-donor immune response following intestinal transplantation.

Angiotensin II Receptor Expression Following Intestinal Transplantation in Mice

BACKGROUND

To further improve the success rate of intestinal transplantation there is a need to find early appearing indicators of rejection. The specific aim of this study was to compare Angiotensin (Ang) II type 1 receptor and Ang II type 2 receptor expression in relation to histological signs of rejection.

METHODS

Mice of the C57BL6 strain with syngeneic intestinal grafts were compared to mice subjected to allogeneic intestinal transplantation with BalbC strain as donors. Local expression of Ang II type 1 and 2 receptor was evaluated using rt-PCR and Western blot and compared to histological picture in grafts and native intestine.

RESULTS

The Ang II type 2 receptor protein expression was markedly up-regulated in the allogeneically transplanted graft from day 1 postoperatively. Histological signs of rejection were not seen until day 6.

CONCLUSION

Intestinal allograft transplantation in mice is associated with a marked up-regulation of the Ang II type 2 receptor. However, the detailed role of the renin-angiotensin system in the immune rejection following intestinal transplantation remains to be clarified.