1₈ F-FLT PET and Blood-based Biomarkers for Identifying Gastrointestinal Graft versus Host Disease after Allogeneic Cell Transplantation

Purpose: To determine whether fluorine 18 (¹⁸F) fluorothymidine (FLT) PET imaging alone or combined with Mount Sinai Acute GVHD International Consortium (MAGIC) biomarkers could help identify subclinical gastrointestinal graft versus host disease (GI-GVHD) by day 100 following hematopoietic stem cell transplantation (HSCT). 1₈ Materials and Methods: F-FLT PET imaging was analyzed in a prospective pilot study (ClinicalTrials.gov identifier no. NCT01338987) with a primary end point of engraftment for a planned secondary end point identifying GI-GVHD. Regions of interest (ROIs) in the colon (1 cm³), jejunum (1 cm³), and ileum (1 cm³) were drawn in the area of greatest signal intensity within each segment of the GI tract by using software. Standardized uptake values (SUVs) were captured on day 28 following transplantation, along with MAGIC serum biomarkers and MAGIC algorithm probability (MAP) scores using MAGIC serum biomarkers collected at days 28–35. Results: Among 20 participants (median age, 33.85 years [IQR: 28.65–39.25 years]; 11 female, nine male), seven presented with clinically diagnosed GI-GVHD by 100 days. Increased SUV was observed throughout the GI tract, most predominantly in the jejunum. Maximum and mean SUV by day 100 were significantly elevated in those with GI-GVHD (maximum SUV, 4.81; mean SUV, 3.73; n = 7) compared with those without (maximum SUV, 3.99; mean SUV, 2.56). MAP score (P =.02) was associated with acute GVHD on day 28 but not on day 100. Spearman correlation between maximum SUV in the jejunum and MAP score was r = 0.65 (P =.002). Conclusion: These data suggest that¹⁸F-FLT PET may help identify acute GI-GVHD after HSCT and could inform location in areas difficult to biopsy.