| Citation | He is distinguished for his pioneering work on lymphocyte development in the vertebrate immune system. He showed that T and B lymphocytes derive from stem cells that migrate into the embryonic thymus and avian bursa of Fabricius, respectively. He showed that B cells are initially produced in the mouse foetal liver, thereby identifying the haemopoietic tissues as the mammalian bursa-equivalent. By micromanipulating single thymus stem cells into explants of thymus epithelium, he demonstrated that all of the major subclasses of T cells derive from a common precursor cell. By the transplantation of chimeric embryonic thymus lobes constructed in vitro, he showed that major histocompatibility complex (MHC) antigens expressed on thymus dendritic cells, rather than on thymus epithelial cells, are responsible for tolerance induction. |