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 biomarkers 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 × 10 −4 ) and day 3 ( P = 3.3 × 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 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.