 An immunologist, he was the co-discoverer with Peter Medawar and Rupert Billingham of acquired immunological tolerance.They injected cells from donor mice into fetal mice, and later neonatal mice, which would as adults receive donor skin grafts without rejection.Brent was born Lothar Baruch, in Köslin, Germany (now Koszalin, Poland), to German Jewish parents, Charlotte (Rosenthal) and Arthur Baruch.