Noninvasive Biomarkers for Allograft Monitoring After Intestinal Transplantation: Promising Early Results from a Novel Peptide, REG3a

Background: The field of intestinal transplantation (ITx) lacks a specific biomarker for diagnosing acute allograft rejection. Currently, calprotectin and citrulline, biomarkers used classically in monitoring disease activity in inflammatory bowel disease (IBD) and short-bowel syndrome, are employed for detection of allograft rejection, but neither are specific in distinguishing rejection from other non-specific causes of intestinal inflammation. The regenerating islet-derived (REG) proteins, a family of anti-inflammatory/anti-bacterial proteins expressed in Paneth cells within the epithelium of the small intestine, are emerging as a potential biomarker for intestinal pathology. REG proteins are known to be highly expressed in several human intestinal pathologies related to epithelial injury and inflammation. REG3α specifically has been correlated with disease severity in IBD and intestinal graft vs host disease and has potential as a biomarker for intestinal allograft pathology but has not been extensively studied in ITx. Methods: Our center has maintained a detailed prospective database on all ITx recipients since 1991. A protocol of weekly allograft monitoring with stool calprotectin, serum citrulline and endoscopy and biopsy is followed. In 2015, the novel peptide REG3α was added to this protocol. Biopsy-confirmed acute rejection (BCAR) is graded according to international standards. Markers are correlated to BCAR by post-operative week (POW). Analysis compared markers by severity of rejection (grade 0-2 vs 3-4) using standard statistical tests. Results: Five adults underwent isolated ITx and one child underwent multivisceral transplantation. Median time to first BCAR was 3 weeks; all experienced at least 1 episode of BCAR. One-year patient and graft survival was 100%. Calprotectin, citrulline and REG3A were significantly associated with grade 3-4 BCAR (p=0.00). The median REG3α level was 5.5 times the upper limit of normal during grade 3-4 BCAR. Calprotectin had the highest positive predictive value (PPV) (76%); REG3A had the highest negative predictive value (NPV) (89%). Together, they demonstrate a high PPV and NPV (100% and 93%, respectively). Conclusions: This is the first case series to describe a protocol of allograft monitoring after ITx using invasive and noninvasive testing including REG3A. Calprotectin, citrulline and REG3A are individually associated with moderate-severe BCAR and together demonstrate a high PPV and NPV. REG3A demonstrated a superior NPV for the presence of rejection. This preliminary experience indicates that REG3A may be useful for monitoring allograft function. Future work includes a prospective multicenter investigation to determine the association of REG3A with BCAR, and to determine the relationship of REG3A with calprotectin and citrulline in association with allograft pathology.