Di-Chimeric Cell Therapy Derived From Hematopoietic and Mesenchymal Stem Cells Promotes Immune Tolerance and Extends Vascularized Composite Allograft Survival.

Chimerism-based strategies remain promising for tolerance induction in solid organ and vascularized composite allograft (VCA) transplantation. This study aimed to develop a novel, less toxic chimeric cell therapy to prolong allograft survival and reduce the need for lifelong immunosuppression. Di-chimeric cells (DCC) were created via polyethylene glycol (PEG)-mediated ex vivo fusion of allogeneic hematopoietic stem cells (HSC) and mesenchymal stem cells (MSC) derived from August Copenhagen Irish (ACI) and Lewis rats. Twenty-four fully major histocompatibility complex (MHC)-mismatched groin flap VCAs were transplanted from ACI rat major histocompatibility complex (rat MHC) (RT1a) donors to Lewis (RT11) recipients under a 7-day immunosuppressive protocol of anti-αβTCR antibody and tacrolimus, combined with four different cell therapies of n = 6/group: Group 1, saline control; Group 2, MSC; Group 3, HSC/HSC DCC; and Group 4, HSC/MSC DCC. DCC were delivered via the intraosseous injection. DCC phenotype was confirmed by flow cytometry (FC). Graft rejection was evaluated macroscopically. A single DCC dose significantly prolonged VCA survival, with the best results in Group 4 (94 ± 1.65 days), followed by Group 3 (66 ± 1.24 days), Group 2 (45.5 ± 4.08 days), and Group 1 (38 ± 4.29 days). This study confirmed immunomodulatory and tolerogenic properties of DCC, supporting VCA transplantation.