Table 1.

Overview of the main safety and efficacy outcomes of the major cell types studied in clinical trials in transplant patients.

Cell type	Safety aspects	Efficacy outcomes
Mesenchymal stromal cells	No adverse effects in majority of patients Engraftment syndrome reported in 2 patients after MSC infusion 7 days post‐transplantation Possible formation of antibodies against allogeneic MSC	Indication for regulatory T‐cell expansion Indication that MSC treatment allows weaning of immunosuppressive drugs No increase or reduced incidence of opportunistic infections
Regulatory T cells	Evidence for safety, with report of lymphopenia and mild liver graft dysfunction in one patient	Hints for reduced requirement for induction immunosuppression in renal transplantation and reduced maintenance immunosuppression in liver transplantation
Regulatory myeloid cells	No evidence of adverse effects in studies published so far	Hints for regulatory T‐cell expansion after regulatory macrophage administration Potentially allowing weaning of immunosuppressive drugs
Extracellular vesicles	No safety data yet	No clinical trials yet, but indication for reparative effects on isolated organs