Pediatric cardiac xenograft growth in a rhesus monkey-to-baboon transplantation model

It is unclear that organs from other species could grow successfully in the environment of another species. We evaluated the growth capacity of a cardiac xenograft in a rhesus monkey-to-juvenile baboon orthotopic heart transplantation model where there exists a discrepancy of the organ size and its growth rate between donor and recipient species. Eight recipient baboons who survived over 60 days were followed for body weight (BW) and the size of xenografts (left ventricular end-diastolic volume, LVEDV; left ventricular mass, LVM; and left ventricular posterior wall thickness, LVPWT) by echocardiography at 1 week and monthly after xenotransplantation. One baboon is growing along the normal growth curve. The other three baboons gained BW in parallel with normal growth curve except for a few months after surgery. LVEDV, LVM, and LVPWT increased constantly in these four baboons. In one baboon, BW increased over 1 year to 5.5 kg (which was almost the same as BW of adult rhesus monkey) and then plateaued. LVEDV, LVM, and LVPWT increased until 1 year posttransplantation, but then stopped when BW plateaued. In the other four baboons who did not gain BW because of infectious complications or side effects by immunosuppressive therapy, LVEDV, LVM, and LVPWT did not change significantly. We conclude that a cardiac xenograft from a rhesus monkey can successfully grow and support normal growth of a juvenile baboon, but whether a recipient can grow beyond the donor size is yet unknown.