Minimum conditions of major histocompatibility complex compatibility and recipient immune compromise required to establish donor white blood cell persistence in a murine transfusion model

BACKGROUND: In some patients multiply transfused to treat severe trauma, white blood cells (WBCs) from a single blood donor can persist for years, constituting up to 5 percent of all circulating WBCs. The immunologic mechanisms responsible for this are not known but, if understood, might allow manipulation of the human immune system to induce microchimerism for a variety of therapeutic purposes. To better characterize these mechanisms, a murine transfusion model was developed with a panel of immunologic knockouts as transfusion recipients. By conducting a systematic series of transfusion experiments, the purpose was to determine which recipient immune cell population, when abrogated, could lead to prolonged survival of donor cells (microchimerism). STUDY DESIGN AND METHODS: Blood was transfused from normal donors to knockout recipients in syngeneic, allogeneic, and xenogeneic settings. Donor WBC survival was evaluated by quantitative polymerase chain reaction, and recipient lymphocyte subsets by fluorescence‐activated cell sorting. RESULTS: In the syngeneic setting, donor WBCs persisted in C2ta , RAG‐1, and TCR knockout recipients. Allogeneic donor WBCs persisted in RAG‐2 and RAG‐2/Common gamma knockout recipients. Xenogeneic donor WBCs required RAG‐2/Common gamma and RAG‐2/Pfp double knockouts to persist. CONCLUSION: It is concluded that donor‐recipient major histocompatibility complex (MHC) concordance alone is not sufficient to achieve microchimerism. Further, the degree of recipient immune compromise necessary to achieve persistent microchimerism is directly proportional to the degree of donor‐recipient MHC disparity.