Dendritic cell (DC)- derived exosomes spread donor allo-antigen between recipient's DC following cardiac transplantation (141.11)

Exosomes are nanovesicles generated in multivesicular endosomes that are released to the extracellular space by different cell types. Since DC-derived exosomes (dexosomes) express MHC-peptide and costimulatory molecules, we investigated the role of dexosomes in elicitation of the anti-donor response in transplantation. Dexosomes were generated from bone marrow-derived DC and labeled with PKH67 for traffic studies. CD4+ TCRtg T cells (Thy1.1+) specific for the IEα52-68 (BALB/c)-IAb (B10) complex were CFSE-labeled and transferred i.v. to host Thy1.2+ B6 mice. Graft infiltrating DC were isolated from BALB/c (CD45.2+) cardiac grafts 3 days after transplantation in B6 (CD45.2+) recipients and genetically-engineered ex vivo to release exosomes expressing the reporter marker eGFP, and then transferred i.v. into host CD45.1+ B6 mice. We demonstrated that although graft-infiltrating leukocytes release exosomes ex vivo, they do not secrete enough exosomes in circulation to stimulate donor-reactive T-cells in lymphoid organs. Instead, migrating DCs (generated in vitro or isolated from allografts), once they home in the spleen, they transfer exosomes expressing eGFP to spleen-resident DCs. Thus, exchange of exosomes between DCs in lymphoid organs constitutes a mechanism by which passenger leukocytes transfer alloAg to recipient's APC and amplify generation of donor-reactive T-cells.