Cross-species compatibility of intercellular adhesion molecule-1 (CD54) with its ligands

The molecular interactions of intercellular adhesion molecule-1 (ICAM-1; CD54) are potentially important in several situations in the context of pig-to-human xenotransplantation. If porcine bone marrow is to be used for the induction of xenograft tolerance in humans, the role that has been suggested for ICAM-1 in the interactions of haematopoietic stem cells makes its cross-species compatibility important. Similarly, the potential role of ICAM-1 interactions in graft rejection makes it an important molecule to study. An in vitro static cell-to-cell adhesion study was used to look at the successful interaction of ICAM-1 with its ligands across the pig-human species barrier in both directions. A second in vitro system, the standard long-term bone marrow culture (LT-BMC), was used to study the functional role of ICAM-1 in haematopoiesis. Human ICAM-1 was able to adhere to ligands on porcine cells, including one or more ligand that contains CD18. Conversely, human CD18-containing ligands mediated adherence to porcine cells. Using the long-term bone marrow culture system, there was no evidence that blocking the interactions of ICAM-1 inhibited hematopoiesis, either in the human-human or pig-human combinations of precursor cells and marrow stroma. ICAM-1 is able to interact with at least some of its ligands across the species barrier, in both pig-human and human-pig combinations. However, the interactions of ICAM-1 do not appear to be central to hematopoiesis, at least in the model system used.