Donor tissue-specific exosome profiling enables noninvasive monitoring of acute rejection in mouse allogeneic heart transplantation

Objective: In heart transplantation, there is a critical need for development of bio-markers to noninvasively monitor cardiac allografts for immunologic rejection or injury. Exosomes are tissue-specific nanovesicles released into circulation by many cell types. Their profiles are dynamic, reflecting conditional changes imposed on their tissue counterparts. We proposed that a transplanted heart releases donor-specific exosomes into the recipient's circulation that are conditionally altered during immunologic rejection. We investigated this novel concept in a rodent heterotopic heart transplantation model. Materials and Methods: Full major histocompatibility mismatch (BALB/c [H2-K-d] into C57BL/6 [H2-K-b]) heterotopic heart transplantation was performed in 2 study arms: Rejection (n = 64) and Maintenance (n = 28). In the Rejection arm, immunocompetent recipients fully rejected the donor heart, whereas in the Maintenance arm, immunodeficient recipients (C57BL/6 Prkdc(SCID)) accepted the allograft. Recipient plasma exosomes were isolated and a donor heart-specific exosome signal was characterized on the nanoparticle detector for time-specific profile changes using anti-H2-K-d antibody quantum dot. Results: In the Maintenance arm, allografts were viable throughout follow-up of 30 days, with histology confirming absence of rejection or injury. Time course analysis (days 1, 2, 3, 4, 5, 7, 9, 11, 15, and 30) showed that total plasma exosome concentration (P = .157) and donor heart exosome signal (P = .538) was similar between time points. In the Rejection arm, allografts were universally rejected (median, day 11). Total plasma exosome quantity and size distribution were similar between follow-up time points (P = .278). Donor heart exosome signals peaked on day 1, but significantly decreased by day 2 (P = 2 x 10(-4)) and day 3 (P = 3.3 x 10(-6)), when histology showed grade 0R rejection. The receiver operating characteristic curve for a binary separation of the 2 study arms (Maintenance vs Rejection) demonstrated that a donor heart exosome signal threshold < 0.3146 was 91.4% sensitive and 95.8% specific for diagnosis of early acute rejection. Conclusions: Transplant heart exosome profiling enables noninvasive monitoring of early acute rejection with high accuracy. Translation of this concept to clinical settings might enable development of a novel biomarker platform for allograft monitoring in transplantation diagnostics.