American Journal of Transplantation: Volume 16, Number 7, July 2016

On the cover this month: Transplantation chimerism refers to the coexistence of cells or tissues from two individuals within one recipient. All transplant patients are chimeras of sorts, with the allograft being of donor origin, but this degree of chimerism clearly does not lead to allograft tolerance. However, numerous studies have shown that augmenting the degree of chimerism (e.g. creating a state of mixed bone marrow chimerism) can lead to a state of tolerance, albeit with substantial risks related to donor bone marrow infusion. This month, we report two articles (Hu et al, page 2055, and Cameron et al, page 2066) showing that mobilization of recipient stem cells using a CXCR4 antagonist facilitates their engraftment within the donor organ, and in doing so creates a chimeric organ that can be maintained without immunosuppression. This novel take on the chimerism model of tolerance is intriguing for its simplicity and potential broad applicability, and is certainly worthy of attention. Cover design by Lauren Halligan, Duke University Department of Surgery.