Purpose of review: To consolidate our basic scientific and technological appreciation of human regulatory macrophages (M reg) as a cell-based medicinal product for use as an adjunct immunosuppressive therapy in organ transplantation.
Recent findings: Building on the original observation that crude preparations of IFN-γ-stimulated allogeneic macrophages prolong allograft survival in experimental animals, we have arrived at a detailed understanding of the derivation, phenotype and T-cell-suppressive potential of a population of in-vitro-derived human macrophages, which have been designated M regs. This basic scientific knowledge has inspired methodological advances in M reg manufacture, leading to a purer and more homogeneous cell product. In turn, cells produced by these improved protocols have been applied in the clinic, so completing a cycle of technological development. Studying the migration and physiological impact of M reg administration in patients provides a measure of reassurance that the procedure is well tolerated. Cutting-edge strategies to assess the immunological status of solid organ transplant recipients allow the biological effects of M reg treatment to be monitored.
Summary: A view of the human M reg as a novel, stringently defined medicinal product is presented, opening exciting possibilities for its future investigation as a therapy in solid organ transplantation and beyond.