Kaposi sarcoma is a slow-growing vascular tumor localized to skin, but which spreads to internal viscera in 40% of immunosuppressed post-transplant patients. Kaposi sarcoma results from either primary infection or reactivation of human herpesvirus-8 (HHV-8), a gammaherpesvirus associated with Kaposi sarcoma. It is not known, however, if the transplanted organ itself can transmit Kaposi sarcoma from the donor. In the April 7 advance online Nature Medicine, Patrizia Barozzi from University of Modena and Reggio Emilia, Italy, and colleagues from elsewhere in Italy, Israel, and Germany, show that post-transplant Kaposi sarcoma can originate from the seeding of donor-derived progenitors.