Identifying patients who are at risk for complications after thoracic transplantation assists in better defining outcomes and promoting discovery of new mechanisms that can be targeted to mitigate these complications. The gold-standard for diagnosing rejection, a major cause of morbidity and mortality after transplantation, is biopsy, which (1) is not risk-free, (2) may not be practical in critically ill patients and (3) may result in false-negative findings.1 Exosomes had been described as far back as in 1981 as membrane fragments from reticulocytes detected in body fluids.