The Major Histocompatibility Complex (MHC) was discovered as a con-
sequence of the chronic problem encountered by cancer biologists in the
early years of this century: the failure to maintain tumor lines by
serial passage in outbred mice. A number of observations pointed to
genetic similarity being a prerequisite for successful transplantation
and they were incorporated into a genetic theory of transplantation by
C.C. Little. This prompted scientists like Little to initiate breeding
experiments designed to test his hypothesis and produce genetically
identical mice which would permit the growth of trans- planted tumors.
Most inbred strains of mice commonly used in immunology derive from
those efforts. Transplantation of normal tissues obeyed the same rules
found for malignant tissues and rejection was shown to be an
immunological phenomenon. G.D. Snell showed that a single genetic locus
determined rapid rejection of skin grafts. This was initially called the
Major Histocompatibility Locus but was subsequently shown to include
many functionally related genes and renamed the Major Histocompatibility
Complex (MHC). In mouse this is the H-2 complex and man the HLA complex.
During this same period P.A.