Utility of an immune cell function assay to differentiate rejection from infectious enteritis in pediatric intestinal transplant recipients

Grant monitoring after intestinal transplantation

PURPOSE OF REVIEW

The current review aims to describe in detail the most common practices utilized to monitor graft function in intestinal transplant (ITx) recipients. In addition, to discussing the role of endoscopy and stool studies it will examine the use of other potential biomarkers which have been utilized. Data will be discussed from contemporary publications in the field, the Intestinal Transplant Registry as well as detailed data from a large, ITx single-center.

RECENT FINDINGS

Significant improvements have been made in early outcomes following ITx, yet long-term survival remains challenged by infection and rejection, both of which can present with diarrhea. While endoscopy and stool studies are the gold-standard for graft monitoring, calprotectin, citrulline, measurements of immunoreactivity and donor-specific antibodies have been investigated in the field and are herein reviewed.

SUMMARY

Despite a number of tests which are currently available for monitoring ITx recipients, a strong need exists for improved noninvasive, timely and accurate biomarkers to help improve ITx graft and patient survival.

Characterization of T cell immunophenotypes in intestinal transplantation: A pilot study

Immunophenotyping of peripheral blood mononuclear cells has been shown to be a useful, non-invasive method of predicting acute cellular rejection (ACR) following intestinal transplantation (ITx). Our objectives were to characterize differences in the T cell immunophenotype of ITx recipients in peripheral blood samples (1) collected late versus early after ITx and (1) associated with episodes of ACR and infectious enteritis. An IRB-approved, cross-sectional study of ITx recipients was performed. Peripheral blood samples were collected during normal visits and episodes of allograft dysfunction. A total of 38 patients were included in the analysis: 31 ITx recipients (87% liver-inclusive allografts) and 7 intestinal failure control patients. Of the ITx patients, 26 patients were pediatric patients (<21 years). A total of 70 samples were analyzed from ITx recipients, including 51 during normal visits and 19 during episodes of allograft dysfunction (median of 2 samples per patient; range of 1-6 samples per patient). In the late (n = 32) versus early post-ITx (n = 19) normal samples, there was a significantly higher percentage of central memory CD4 T cells (p = .001). In the ACR (n = 5) versus infectious enteritis (n = 14) samples, there was a higher percentage of CD8 T cells expressing HLA-DR (p = .002), CD57 (p < .001), and KLRG1 (p < .001) and a higher percentage of CD4 T cells expressing CD57 (p = .03). Additional studies are needed with larger cohorts to validate these changes in the T cell immunophenotype. Further elucidating T cell immunophenotypes in ITx will lead to a better understanding of immune mechanisms of allograft dysfunction, identification of potential biomarkers in ITx, and optimized selection of immunosuppressive therapies.

Immune function monitoring in lung transplantation using adenosine triphosphate production: time trends and relationship to postoperative infection

PURPOSE

The ImmuKnow (IK) assay is a comprehensive immune function test that involves measuring adenosine triphosphate produced by the cluster of differentiation 4+ T lymphocytes in peripheral blood. The aim of this study was to analyze the time trends of IK values and assess the relationship between IK values and infections in lung transplants.

METHODS

We prospectively collected 178 blood samples from 22 deceased-donor lung transplant (DDLT) recipients and 17 living-donor lobar lung transplant (LDLLT) recipients. A surveillance IK assay was performed postoperatively, then after 1 week and 1, 3, 6, and 12 months.

RESULTS

Time trends of IK values in stable recipients peaked 1 week after DDLT (477 ± 247 ATP ng/ml), and 1 month after LDLLT (433 ± 134 ng/ml), followed by a gradual decline over 1 year. The mean IK values in infections were significantly lower than those in the stable state (119 vs 312 ATP ng/ml, p = 0.0002).

CONCLUSIONS

IK values increased sharply after lung transplantation and then decreased gradually over time in the first year, suggesting a natural history of immune function. IK values were also significantly reduced during infections. These results may provide new insights into the utility of immune monitoring after lung transplantation.

Profile of the Pleximmune blood test for transplant rejection risk prediction

The Pleximmune™ test (Plexision Inc., Pittsburgh, PA, USA) is the first cell-based test approved by the US FDA, which predicts acute cellular rejection in children with liver- or intestine transplantation. The test addresses an unmet need to improve management of immunosuppression, which incurs greater risks of opportunistic infections and Epstein-Barr virus-induced malignancy during childhood. High-dose immunosuppression and recurrent rejection after intestine transplantation also result in a 5-year graft loss rate of up to 50%. Such outcomes seem increasingly unacceptable because children can experience rejection-free survival with reduced immunosuppression. Pleximmune test sensitivity and specificity for predicting acute cellular rejection is 84% and 80% respectively in training set-validation set testing of 214 children. Among existing gold standards, the biopsy detects but cannot predict rejection. Anti-donor antibodies, which presage antibody-mediated injury, reflect late-stage allosensitization as a downstream effect of engagement between recipient and donor cells. Therefore, durable graft and patient outcomes also require accurate management of cellular immune responses in clinical practice.

Pediatric small bowel transplantation

PURPOSE OF REVIEW

Intestine has become a transplantable organ due to the improvement in immunosuppressive drugs. The early referral to a reference unit is crucial in prognosis. There are still some pending issues like chronic rejection, the knowledge of the role of DSA development or early noninvasive detection of acute rejection.

RECENT FINDINGS

The appearance of tacrolimus and mTOR, and the use of induction therapy have marked a turning point with better graft and patient survival rates. The inclusion of the liver in the graft seems to have a protective effect. Surveillance of opportunistic infections has also contributed to improved results. Infection, post-transplant lymphoproliferative disease, rejection and GVHD have still a major role in survival; however, antibody-mediated rejection has gained increased attention.

SUMMARY

Parenteral nutrition remains the main therapeutic resource in the management of intestinal failure, but intestinal transplant is a therapeutic option when this therapy has failed. Finding the balanced immunosuppression that minimizes risk of rejection while preventing occurrence of complications like post-transplant lymphoproliferative disease or GVHD is an ongoing challenge. The current survival rates of intestinal transplantation are similar to other solid organ transplant.

Endoscopy Following Pediatric Intestinal Transplant

OBJECTIVES

Biopsies remain the criterion standard in the diagnosis of intestinal transplant (ITx) rejection, and gastrointestinal endoscopy plays a pivotal role in patient management. Herein, we describe a single-center 23-year endoscopic experience in pediatric ITx recipients.

METHODS

A retrospective review of endoscopy and pathology reports of all ITx recipients <18 years old transplanted between 1991 and 2013 was performed with the aim of describing the procedural indications, findings, and complications.

RESULTS

A total of 1770 endoscopic procedures within 1014 sessions were performed. A combination of esophagogastroduodenoscopy and ileoscopy was the most common procedure (36%). Increased stool output (35%) and surveillance endoscopy (32%) were the most common indications. A total of 162 episodes of biopsy-proven rejection were diagnosed. The first episode of rejection occurred at a median of 1 month after ITx. Of histology-proven rejections, 45% had normal-appearing endoscopies. The rate of procedural complications, including but not limited to bleeding and perforation, was 1.8%.

CONCLUSIONS

Endoscopy with biopsy plays a significant role in the care of ITx recipients. Multiple procedures are required for graft surveillance, diagnosis of rejection, subsequent treatment, and follow-up of therapy. The gross endoscopic appearance, particularly in mild to moderate acute cellular rejection, does not correlate well with histology. Complex anatomy, complication rates that are higher than patients with non-ITx pediatric endoscopy, and timely histologic interpretation by experienced pathologists are reasons that these procedures should be performed at centers accustomed to caring for ITx recipients. The field would benefit from the development of a noninvasive biomarker to reliably and efficiently detect rejection.