Small Intestinal Allografts Research Articles

Endoscopic ultrasound in the monitoring of the intestinal allograft

ObjectiveChronic rejection (CR) of the small intestinal allograft includes mucosal fibrosis, bowel thickening and arteriopathy in the outer wall layers and the mesentery. CR lacks non-invasive markers and reliable diagnostic...

Utility of colon allograft biopsies in surveillance of patients with small intestinal transplantation – A systematic study of 129 biopsies

Abstract Introduction/Objective A segment of right colon is sometimes included with small intestinal allografts to preserve the ileocecal valve and maintain water reabsorption. We correlated pathological findings of colon allograft biopsies obtained during surveillance colonoscopies with clinical, endoscopic, and microbiologic findings. Methods/Case Report All colon allograft biopsies from surveillance colonoscopies over a 3-year period were reviewed for crypt apoptotic activity, cryptitis, lamina propria inflammation, ulceration, and crypt architectural distortion. Clinical and endoscopic findings, and positive cultures a week before and after the biopsies were recorded. Results (if a Case Study enter NA) There were 129 colon biopsies from 29 patients; 98 were histologically normal, whereas 28 showed rare apoptoses (n=14), focal cryptitis (n=8), increased intraepithelial lymphocytes (n=2), moderate acute rejection (n=1), and crypt architectural distortion (n=2). Of these 29 patients, 8 had abnormal endoscopic findings, 21 were normal. Out of 8 patients with abnormal endoscopic exams, 50% had normal histology on biopsy. Twenty-one biopsies were associated with positive cultures in the blood (n=5), urine (n=16) or wound, peritoneal, stool (n=6); 3 had abnormal endoscopies, and 4, abnormal histology. One patient with C.difficle toxin had normal endoscopy and focal cryptitis, whereas another with CMV DNA in blood showed endoscopically congested mucosa and rare apoptoses on biopsy. Of 12 biopsies (7 patients) with abnormal endoscopic findings, (erythema, congestion, ulceration), 4 biopsies had no pathologic findings, 8 had rare apoptosis, and one each had focal cryptitis and chronic colitis. Paired small intestinal biopsies were present with 59 biopsies; 10 showed rare apoptosis and 2, focal cryptitis. Of 70 without paired small intestinal biopsies, there were 5 with rare apoptotic bodies, 5 with focal cryptitis, and 2 with crypt architectural distortion. Conclusion The correlation of histologic, endoscopic, and microbiologic findings in colonic allograft surveillance biopsies is inconsistent. Colon allograft biopsies have limited utility in the follow-up of patients, particularly in absence of paired small intestinal biopsies.

Allograft Duodenal Cuff Biopsy as Surrogate in Evaluation of Pancreatic Transplant Rejection – A Multicenter Data Effort

Introduction Accurate diagnosis of pancreas rejection is required for early, targeted treatment and function preservation. Pancreas biopsy considered the gold standard presents with sampling issues and perceived procedural risks that limit its widespread use. Evaluation of the graft duodenal cuff, through upper endoscopy in intestine drained pancreas transplants has been proposed as a surrogate of pancreas biopsy but the utility of this approach has not been tested. In this multicenter effort we retrospectively evaluated pancreas and duodenal tissues collected simultaneously to correlate findings of acute cell-mediated rejection (ACR) in these two organs and offer interpretation of duodenal cuff biopsies as a potential diagnostic surrogate for its corresponding pancreas allograft. Materials and Methods A total of 88 cases were evaluated retrospectively from allograft pancreas performed between 1995 and 2015, with incidentally or intentionally obtained duodenal cuff mucosa from 11 reference tranplant centers in the North and South Americas, E.U. and U.K. These cases were re-analyzed and graded for ACR. Sixteen cases were excluded due to inadequate pancreas or duodenal sample, possible non-rejection biopsy findings or samples that were not simultaneously obtained. Of the remaining 72 cases, 50 were biopsies and 22 were explant cases. The cases were graded according to the Banff schema for grading pancreas allograft rejection (Drachenberg et al 2008) and from the schema for histologic grading of small intestine allografts (Wu et al 2008). Results Of the 72 cases, 20 cases showed a diagnosis of rejection. All 20 (100%) cases showed rejection in both pancreas and duodenal tissue. Fifty eight cases (80.5%) showed results that were concordant for a final diagnosis of rejection/suspicious for rejection or no evidence of rejection. Of the 14 (19.5%) cases that showed complete discordance (either suspected or diagnostic for rejection in pancreas but not duodenum or suspected or diagnostic for rejection in duodenum but not pancreas) 2 cases (2.7%) showed findings of rejection in the duodenum but not pancreas and 12 cases (16.6%) showed findings of rejection in pancreas but not in duodenum. Discussion In this cohort with simultaneous histological evaluation of pancreas parenchyma and graft duodenal cuff, a diagnosis of ACR in the duodenum showed a positive predictive value of 100% for pancreas ACR. Therefore evaluation of the duodenal cuff appears to be a useful surrogate in the absence of pancreas parenchyma in this setting. On the other hand, absence of rejection in the duodenum did not totally exclude rejecion in the pancreas, with a negative predictive value of 83%. Results that were graded as indeterminate (suspicious for) rejection in duodenum were not reliable and had both low PPV and NPV for pancreas rejection. Our results are encouraging and indicate the potential value of duodenal cuff evaluation, as well as the need for additional studies.

Effects of Adoptive Transfer of Tolerogenic Dendritic Cells on Allograft Survival in Organ Transplantation Models: An Overview of Systematic Reviews.

Objective. To dissect the efficacy of Tol-DC therapy with or without IS in multiple animal models of transplantation. Methods and Results. PubMed, Medline, Embase, and the Cochrane Library were searched for reviews published up to April 2015. Six systematic reviews and a total of 61 articles were finally included. Data were grouped by organ transplantation models and applied to meta-analysis. Our meta-analysis shows that Tol-DC therapy successfully prolonged allograft survival to varying extents in all except the islet transplantation models and with IS drugs further prolonged the survival of heart, skin, and islet allografts in mice, but not of heart allografts in rats. Compared with IS drugs alone, Tol-DC therapy with IS extended islet allograft survival in rats but failed to influence the survival of skin, small intestine, and heart allografts in rats or of heart and skin allografts in mice. Conclusion. Tol-DC therapy significantly prolonged multiple allograft survival and further prolonged survival with IS. However, standardized protocols for modification of Tol-DC should be established before its application in clinic.

Adoptive infusion of tolerance dendritic cells prolongs survival of small intestine allografts in rats: systematic review and meta-analysis

Postoperative infections and rejection are the main limiting factors of small intestine allograft survival. In this study, we performed a systematic review and meta-analysis to review rat small intestine allograft survival following infusion of tolerance dendritic cells (Tol-DCs) induced by different methods. Relevant publications were searched from PubMed database and EMbase database. Meta-analysis was performed using RevMan 5.0 software. We chose allograft survival, mixed leukocyte reaction, Th1/Th2 differentiation, Treg induction, and cytotoxic T lymphocyte activity as the outcomes by which to examine possible mechanisms that promote survival. Eleven suitable articles were identified and assessed. Tol-DCs induced by four methods all prolonged allograft survival. The difference in survival time between the Tol-DC group and the control group was indicated by SMD as follows: drug intervention (SMD = 3.02, 95% CI 1.16 to 4.88, P = 0.001), gene modification (SMD = 2.43, 95% CI 1.77 to 3.10, P < 0.00001), imDC (SMD = 1.76, 95% CI 0.90 to 2.62, P < 0.0001), cytokine induction (SMD = 1.68, 95% CI 0.40 to 2.96, P = 0.01). Tol-DCs were also synergistic with immunosuppressive drugs or costimulation inhibitors, but no immune tolerance was observed. A single-dose intravenous injection of 5×10(6) to 6×10(6) Tol-DCs showed the highest allograft survival. Possible mechanisms included donor-specific T-cell hyporesponsiveness and Th2 differentiation. Our results demonstrated that Tol-DCs induced by four methods prolong rat small intestine allograft survival. Intravenous infusion of 5×10(6) to 6×10(6) Tol-DCs was the optimum dose in rat small intestine transplantation. Immunosuppressive or costimulatory blockade was synergistic with Tol-DC on graft survival. Additional high-quality studies with larger sample sizes are needed to better investigate small intestinal graft longer term survival.

Innate immunity in the small intestine

This article reviews the most recent publications on innate immunity in the small intestine. We will go over the innate immune receptors that act as sensors of microbial presence or cell injury, Paneth cells as the main epithelial cell type that secrete antimicrobial peptides, and mucosal production of immunoglobulin A (IgA). In addition, we will give an update on examples of imbalance of the innate immune response resulting in clinical disease with the most relevant example being Crohn's disease. Toll-like receptors (TLRs) are involved in B-cell homing to the intestine, rejection of small intestinal allografts, and recruitment of mast cells. The TLR adaptor Toll/interleukin-1 receptor domain-containing adapter-inducing interferon-β is necessary to activate innate immunity after Yersinia enterocolitica infection. Moreover, MyD88 is required to keep the intestinal microbiota under control and physically separated from the epithelium, and RegIIIγ is responsible for the bacterial segregation from the lining epithelial cells. In Crohn's disease, ATG16L1 T300A variant promotes a proinflammatory response; and miR-196 downregulates a protective immunity-related GTPase family M protein (IRGM) polymorphism leading to impaired clearance of adherent Escherichia coli in the intestine. The intestine is continuously exposed to dietary and microbial antigens. The host has to maintain intestinal homeostasis to keep the commensal and pathogenic bacteria under control. Some of the mechanisms to do so are by expression of innate immune receptors, production of antimicrobial peptides, secretion of IgA, or autophagy of intracellular bacteria. Unfortunately, in some cases the innate immune response fails to protect the host and chronic inflammation, transplant rejection, or other disorders may occur.

Use of canine small intestinal submucosa allograft for treating perineal hernias in two dogs

Here, we describe two dogs in which canine small intestinal submucosa (SIS) was implanted as a biomaterial scaffold during perineal herniorrhaphy. Both dogs had developed severe muscle weakness, unilaterally herniated rectal protrusions, and heart problems with potential anesthetic risks. Areas affected by the perineal hernia (PH) located between the internal obturator and external anal sphincter muscles were reconstructed with naïve canine SIS sheets. In 12 months, post-operative complications such as wound infections, sciatic paralysis, rectal prolapse, or recurrence of the hernia were not observed. Symptoms of defecatory tenesmus also improved. Neither case showed any signs of rejection or specific immune responses as determined by complete and differential cell counts. Our findings demonstrate that canine SIS can be used as a biomaterial scaffold for PH repair in dogs.

Quantification of Intraepithelial Lymphocytes in Normal Pediatric Small Intestinal Allograft and Native Ilea

Background The small bowel acts as one of the first lines of defense against intraluminal infections and antigenic stimuli. Pediatric small bowel transplant patients are at particular risk from such agents, especially viral enteridities. Quantification of intraepithelial lymphocytes (IEL) in architecturally normal small intestinal mucosal biopsies plays an important role in the diagnosis of conditions such as celiac disease and some viral infections. No studies to date have been done to quantify IEL numbers in pediatric small bowel allografts and in native pediatric ilea. Our study investigated the IEL:enterocyte (EC) ratio in pediatric allograft and native ilea. Methods Hematoxylin and eosin slides from 50 surveillance endoscopic biopsies of small bowel allografts taken from patients <8 years of age and 50 terminal ileal biopsies from aged-matched control populations were reviewed. IEL:EC ratios were averaged from five well-oriented villi in each case. IEC numbers were compared between biopsies from proximal (afferent) and distal (efferent) limbs of double-barrel allograft stomas, as well as native terminal ilea. Results Within small bowel allografts, the average number of villus tip IELs was 1.3/20 ECs (standard deviation [SD] 0.6) in the proximal limb and 1.0/20 ECs in the distal (SD 0.6 P < .01). This value was significantly lower than in the control ilea (2.1/20 EC [SD 0.6]; P < .01, each). The overall distribution of lymphocytes was in a similar pattern throughout the villus with IEL:EC ratios on villus sides from proximal allografts, distal allografts, and native ilea being 1:20, 0.8:20, and 2:20, respectively. Conclusions The results suggest that approximately one to two IEL per 20 ECs at villus tips may represent a “normal” intraepithelial inflammatory cell population in small bowel allografts. The value is lower than that seen in age-matched native ileal biopsies. IEL numbers are significantly higher in the proximal limb compared to the distal limb of double-barrel stomas.

Allograft survival is prolonged in the absence of NKG2D (169.19)

Abstract NKG2D is expressed by Natural Killer (NK cells) and subsets of T cells. On NK cells, NKG2D functions as a stimulatory receptor that induces effector functions. We have demonstrated increased expression of NKG2D ligands on rejecting grafts and enhanced infiltration of NKG2D-expressing cells in allografts during rejection. To further examine the role of NKG2D in graft survival we utilized Klrk1 mice that are deficient for NKG2D as recipients of cardiac or small intestine allografts. Groups (n=4-6) of C57BL/6 (H-2b) or NKG2D deficient Klrk1 mice (H-2b) received heterotopic donor hearts or vascularized, orthotopic small intestine grafts from BALB/c (H-2d) or BALB/c x C57BL/6 F1 mice (H-2d/b). Some groups of mice also received 200μg (heart) or 500μg (intestine) anti-CD40L mAb (MR1) at transplant. Cardiac allograft survival was similar in wild-type and Klrk1 mice although intestinal allograft survival was prolonged in Klrk1 mice. Treatment with MR1 prolonged cardiac allograft survival that was further enhanced in the absence of NKG2D. Treatment with MR1 did not prolong survival of intestine allografts in wild-type recipients. Quite dramatically, however, treatment with MR1, significantly (p=0.007) prolonged intestinal allograft survival in Klrk1 mice. Prolongation of intestinal graft survival in the absence of NKG2D and CD40-CD40L interactions suggest that the addition of therapeutics to block NKG2D has great potential for improving costimulation blockade based therapies

Acute Rejection of Small Intestine Allografts Is Associated With Increased Expression of Toll-like Receptors

Although outcomes after intestinal transplantation have steadily improved owing to advances in immunosuppressive therapy, operative techniques, and postoperative medical management, rejection of the intestinal allograft continues to be a major clinical problem and constitutes the primary reason for graft loss. Although the adaptive immune system has been the major focus of investigation regarding regulation of rejection of the intestinal allograft, the role of the innate immune system has recently become of increased interest. We hypothesized that microbial products of the microflora associated with the intestinal allograft may engage the Toll-like receptor pathway of the innate immune system to potentiate alloimmune responses and rejection of the allograft. To investigate this, we established a murine model for orthotopic intestinal transplantation and allograft rejection. Using this model, we show that the expression of Toll-like receptor 2 is increased 50-fold and the expression of Toll-like receptor 4 is increased 200-fold during rejection of the allograft. We then performed survival studies that showed increased survival of mice, which had the Toll-like receptor knocked out. These preliminary studies suggest an important role for in innate immune system in acute rejection of the small intestinal allografts, and as such represents an emerging and promising area of investigation.

Gene Expression Profiling of MicroRNAs in Small-Bowel Transplantation Paraffin-Embedded Mucosal Biopsy Tissue

Background The molecular mechanisms and regulation of immune-mediated rejection of organ allografts remains unclear. Recent studies have reported that small non-coding RNAs, microRNAs (miRNAs) play a critical role in the immune system via modulation of transcription and translation. Purpose We hypothesized that particular miRNAs provide regulation of an ensuing intragraft immune effector response. The aim of our study was to detect miRNAs involved in acute cellular rejection (AR) in human small intestinal allografts. Materials We examined 12 small intestinal mucosal biopsies (AR, 7 cases, all grade 2 or 3) and non-rejecting (NR) allografts (5 cases, all grade 0) obtained from recipients after small bowel or multivisceral transplantation. RNA was isolated from the formalin-fixed paraffin-embedded (FFPE) biopsy samples and transcribed to cDNA. After preamplification we utilized a PCR based TaqMan Low Density Array (TLDA) containing 365 mature human miRNAs. Relative quantification was done based on pooled normal intestine using a comparative Ct method. Results We identified 62 miRNA upregulated genes in small bowels with ACR, and 35 were downregulated. Forty-two miRNA genes were upregulated in non-ACR small bowel biopsy samples (grade IND), and 45 were downregulated. The relative fold change ratio of ACR to non-ACR was calculated, and 50 upregulated and 8 downregulated miRNAs were detected as significant. Several interesting miRNAs will be evaluated further from this preliminary study. Our data suggests that intragraft miRNAs are potentially involved in the activation of a host alloimmune response to donor. These miRNAs may serve as targets for appropriate intervention and may be useful to monitor the allograft status.

Rejection Reversibly Alters Enteroendocrine Cell Renewal in the Transplanted Small Intestine

Acute small intestinal allograft rejection presents clinically as an abrupt increase in ileal fluid output in the absence of extensive inflammation. We questioned whether acute intestinal rejection might be accompanied by a disturbance of normal intestinal stem cell differentiation. We examined the intestinal epithelial secretory cell lineage among patients experiencing early rejection before and during rejection as well as following corrective therapy. Lineage-specific progenitors were identified by their expression of stage-specific transcription factors. Progenitors of the enteroendocrine cell (EEC) expressing neurogenin-3 (NEUROG3) were found to be disproportionately reduced in numbers, along with their more mature EEC derivatives expressing neuro D; the enteric hormone PYY was the most profoundly depleted of all the EEC products evaluated. No change in the numbers of goblet or Paneth cells was observed. Steroid treatment resulted in resolution of clinical symptoms, restoration of normal patterns of EEC differentiation and recovery of normal levels of enteric hormones. Acute intestinal rejection is associated with a loss of certain subtypes of EEC, most profoundly, those expressing PYY. Deficiency of the mature EECs appears to occur as a consequence of a mechanism that depletes NEUROG3 EEC progenitors. Our study highlights the dynamics of the EEC lineage during acute intestinal rejection.

Analysis of Acute and Chronic Rejection in Multiple Organ Allografts From Retransplantation and Autopsy Cases of Multivisceral Transplantation

Small intestinal allografts in multivisceral transplantation are felt to be more susceptible to acute cellular rejection (ACR) and chronic rejection (CR) when compared with other allografts although there is little direct evidence for this impression. A total of 48 cases of multiple allograft specimens (37 autopsy and 11 explanted allograft cases) from 41 patients were evaluated in this study. Histopathologic assessments were performed with special concern to ACR and CR in allografts. The numbers of allografts available for evaluation were liver 37, small intestine 47, stomach 41, pancreas 45, and large intestine 25. Among 48 cases, 15 cases showed ACR (ACR case) and 12 showed CR (CR case) in at least one organ. In ACR cases, there was a statistically significant difference of organ-specific susceptibility to ACR among multivisceral allografts with the small intestinal allograft being the most susceptible (P<0.05). Severe ACR were observed only in small and large intestinal allografts. In CR cases, there was no statistically significant difference of organ-specific susceptibility to CR among multivisceral allografts with a tendency for the pancreas allograft to be the most susceptible (P=0.35). Our study clearly indicated variation in organ susceptibility to ACR and CR. Small intestinal allografts were the most susceptible organ to ACR in frequency and severity. Pancreatic allografts may be more susceptible to CR in comparison with ACR.

Evaluation of C4d Staining in Liver and Small Intestine Allografts

Antibody-mediated humoral rejection in kidney and heart allografts is well recognized and is often associated with poor outcome. C4d deposition in allograft biopsy specimens occurs at sites of antibody-mediated complement activation and has become one of the histopathologic criteria for diagnosis of humoral rejection in the kidney and the heart. To study immunohistochemical C4d staining as a potential diagnostic marker in liver and small intestine allograft biopsy specimens. Thirty-six small intestine and 71 liver specimens, including native specimens, allografts with and without histologic features of acute cellular rejection, and explants, were stained with antisera to C4d using an immunohistochemical method on formalin-fixed, paraffin-embedded tissue. In small intestine, C4d labeled capillaries in 27% of cases with no evidence of rejection, 36% of cases with evidence of acute rejection, and 2 (28%) of 7 specimens of native normal small intestine. In liver allograft biopsy specimens, C4d stained endothelium of veins, arteries, and/or sinusoids in 2 (8%) of 25 cases of acute rejection with central vein involvement; C4d staining was negative in biopsy specimens with no evidence of rejection. C4d stained the endothelium in a subset of explanted liver allografts with ductopenic rejection or chronic vascular rejection and strongly stained 1 explant with features of hyperacute rejection. The clinical utility of C4d staining in solid organ transplantation may vary by organ. Our data show C4d is unlikely to have utility in small intestine allograft biopsy specimens; however, further study in liver allografts, in conjunction with donor-specific antibody testing, is warranted.

Early and Frequent Histological Recurrence of Crohn's Disease in Small Intestinal Allografts

Recurrence of Crohn's disease in small intestinal allografts, although rarely described, can cause serious morbidity and jeopardize graft survival among transplant recipients with Crohn's disease. However, systematic studies to determine the frequency, predictors, and clinical implications of recurrent Crohn's disease have not been reported We analyzed our transplant program's experience with small intestinal allografts in patients with Crohn's disease based on retrospective review of clinical and pathological records and corresponding pathology slides. Of 67 patients undergoing 70 transplantations between 1998 and 2004, six adults (three males, three females; mean age 48.1 years) had Crohn's disease complicated by short gut syndrome and total parenteral nutrition failure. Four survivors surveyed endoscopically for a mean 29 (range, 20-40) months and underwent a mean 37 endoscopic examinations with biopsies (range, 31-44) while on maintenance immunosuppression. Despite absence of any endoscopic or clinical manifestations of Crohn's disease throughout this period, two patients had granulomatous enteritis characteristic of Crohn's disease in multiple biopsies, one patient in 8/44 examinations (18%) ranging from 34 days to 20 months postoperatively and the other in 6/32 examinations (19%) ranging from 20 days to 22 months postoperatively. No comparable changes occurred in 57 other patients without Crohn's disease followed endoscopically under the same protocol Histological recurrence of Crohn's disease may occur in small intestinal allografts despite the absence of endoscopic and clinical disease manifestations. Such recurrences are probably not rare, may occur as early as 3 weeks after transplantation, and do not necessarily portend early clinical recurrence or mandate aggressive therapy to prevent allograft loss.

Prolonged survival of donor-specific rat intestinal allograft by administration of bone-marrow-derived immature dendritic cells

It has been reported that intraportal administration of donor antigens induced donor-specific hyporesponsiveness. We studied here the effects of transplantation of BM-derived immature dendritic cells (imDCs) and mature DCs (mDCs) via portal vein on rat small intestinal allograft survival. This study comprised four treatment groups: 1) untreated controls; 2) FK506 alone; 3) intraportal donor-specific BM-derived imDCs transplantation+FK506; 4) mDCs/Tx+FK506. Allograft survival was minimal in control group (5.2±0.8 days) and maximal in imDC+FK506 group (28.4±3.0 days). The rats in mDC+FK506 group showed systemic inflammatory reaction due to GVHR, and died within 10 days after transplantation. The in vitro MLR reaction using imDCs was also strongly inhibited both in direct and indirect recognition pathways. The impact of imDCs for the specific induction of transplant tolerance may suggest that immunization with donor-specific imDCs has therapeutic potential in organ transplantation.

Gene expression profile in rat small intestinal allografts after cold preservation/reperfusion

To determine the changes of gene expression profile in small intestinal allografts in rats after cold preservation/reperfusion, and to identify the genes relevant to cold preservation/reperfusion injury. Heterotopic segmental small bowel transplantation was performed in six rats with a sham operation and they were used as controls. Total RNA was extracted from the allografts (experimental group) and normal intestines (control group) 1 h after cold preservation/reperfusion, and then purified to mRNA, which was then reversely transcribed to cDNA, and labeled with fluorescent Cy5-dUTP and Cy3-dUTP to prepare hybridization probes. The mixed probes were hybridized to the cDNA microarray. After high-stringent washing, the fluorescent signals on cDNA microarray chip were scanned and analyzed. Among the 4 096 target genes, 82 differentially expressed genes were identified between the two groups. There were 18 novel genes, 33 expression sequence tags, and 31 previously reported genes. The selected genes may be divided into four classes: genes modulating cellular adhesion, genes regulating cellular energy, glucose and protein metabolism, early response genes and other genes. A total of 82 genes that may be relevant to cold preservation/reperfusion injury in small intestinal allografts are identified. Abnormal adhesion between polymorphonuclears and endothelia and failure in energy, glucose and protein metabolism of the grafts may contribute to preservation/reperfusion injury. The functions of the novel genes identified in our study need to be clarified further.

Minimal Evidence of Transdifferentiation from Recipient Bone Marrow to Parenchymal Cells in Regenerating and Long‐Surviving Human Allografts

Liver, small intestine, and heart allografts in residence for 4 days to 16 years were analyzed by simultaneous XY fluorescent in situ hybridization to search for evidence of the recently described process of transdifferentiation of recipient bone marrow stem cells to allograft parenchymal cells. These studies were carried out in an effort to find conditions associated with maximal levels of engraftment or expansion of the recipient parenchymal cells. Despite prolonged survival up to 16 years, regeneration after severe preservation injury or use of split livers, only rare, isolated and tentatively identified recipient hepatocytes were detected in liver allografts. In intestinal allografts, despite survival of up to 8 years and extensive mucosal regeneration because of severe damage from acute rejection, there was no crypt replacement by recipient epithelial cells. In cardiac allografts, no recipient myocytes were detected despite recipient survival for 2–3 days and 3–4 weeks after myocardial infarcts at 5 and 8 years after transplantation.Parenchymal cell transdifferentiation from recipient bone marrow stem cells was rare to nonexistent in severely injured, regenerating, and long‐surviving allografts. The rare isolated recipient parenchymal cells tentatively identified did not appear to behave as stem cells: they did not form clusters and did not increase with time after transplantation. Because of the extremely low frequency, interpretation was difficult. Regardless of these results, a more vigorous search for conditions that promote transdifferentiation is warranted.

Impaired rejection and mucosal injury of small intestinal allografts lacking the interferon-gamma receptor.

Small intestinal mucosal T cell activation results in villous atrophy and crypt hyperplasia. There is conflicting evidence as to whether a Th1 IFN-gamma response may be involved. Using a murine intestinal transplant model of T cell-mediated enteropathy we aimed to study the role of IFN-gamma on the development of villous atrophy and crypt hyperplasia. Isografts or allografts of foetal small intestine from 129SV-/- IFN-gamma receptor knockout mice or wild type mice were implanted under the kidney capsule of Balb/c recipient mice. Grafts were examined histologically at intervals from 2 to 9 days post implantation for signs of rejection. Quantitative rtPCR for IFN-gamma, TNFalpha and IL-4 was conducted on grafts at 5 and 9 days post implantation. In allografts, rejection accompanied by the development of villous atrophy and crypt hyperplasia, occurred in a time-dependent manner. However this process was markedly slower in the IFN-gamma receptor knockout grafts compared to the wild type grafts at 5 days (chi2 = 10.08, P = 0.007) and 9 days post implantation (chi2 = 13.25, P = 0.004). There were also significantly fewer TNFalpha transcripts in allografts of IFN-gamma-/- intestine than in wild type allografts (P = 0.02). IFN-gamma has a partial, but not obligatory, role in the development of villous atrophy and crypt hyperplasia during T cell mediated rejection of intestinal allografts.

Temporal relationships between acute cellular rejection features and increased mucosal fibrosis in the early posttransplant period of human small intestinal allografts.

Intestinal allograft biopsies limit histopathological analysis to the superficial layers of the bowel. These biopsies allow a reasonable assessment of the histological features of acute rejection, but characteristics of chronic injury in mucosal layers remain poorly defined because of the limitations posed by endoscopic sampling. Experimental work has inferred that intestinal mucosal fibrosis may be indicative of chronic rejection; however, a temporal, graded study of mucosal fibrosis has not been performed. A total of 79 endoscopic intestinal allograft biopsies from 12 patients obtained at 3 to 120 days posttransplantation were evaluated. Fibrosis and individual parameters of acute cellular rejection were graded according to a semiquantitative scoring system and were evaluated for potential relationships with each other. We found that while acute rejection tends to occur early in the posttransplant period, fibrosis of the lamina propria increases at a later time, particularly in the third and fourth month. Several individual graded parameters of acute rejection had an association with fibrosis at the same time points. Fibrous replacement of the lamina propria in human endoscopic allograft biopsies occurs with advancing time after transplantation. Acute rejection precedes and may have some eventual impact upon the amount of fibrosis present. A measurement of the connective tissue component of bowel transplant tissue may serve as a harbinger of long-term enteral allograft dysfunction.