Regulatory T cell (Treg) is a subset of T cells that negatively regulates immunity and has the function of inhibiting rejection. The specific modification of Treg by chimeric antigen receptor (CAR) technology can successfully chime donor-specific antigen onto the surface of Treg, thus regulating the immune function of the body in a real-time manner. It provides a novel and promising therapeutic option for inducing immune tolerance. In this article, research progresses on Treg in immune related diseases, main difficulties in the realization of CAR-Treg technology and its role in inducing transplantation immune tolerance were reviewed, and the opportunities and challenges of CAR-Treg application in the field of organ transplantation are prospected.

BK polyomavirus-associated nephropathy (BKPyVAN) is a common cause of allograft failure. However, differentiation between BKPyVAN and type I T cell-mediated rejection (TCMR) is challenging when simian virus 40 (SV40) staining is negative, because of the similarities in histopathology. This study investigated whether donor-derived cell-free DNA (ddcfDNA) can be used to differentiate BKPyVAN. Target region capture sequencing was applied to detect the ddcfDNAs of 12 recipients with stable graft function, 22 with type I TCMR, 21 with proven BKPyVAN, and 5 with possible PyVAN. We found that urinary ddcfDNA levels were upregulated in recipients with graft injury, whereas plasma ddcfDNA levels were comparable for all groups. The median urinary concentrations and fractions of ddcfDNA in proven BKPyVAN recipients were significantly higher than those in type I TCMR recipients (10.4 vs. 6.1 ng/mL,