The researchers then did tests for so-called transplantation antigens, a standard method of determining the makeup of part of an individual's immune system.

From a more modern perspective, HLA gene products (i.e., antigen-presenting, cell-surface receptors) did not evolve to be transplantation antigens, nor to interfere with transplantation, organ transplantation being unknown until 1960.

The findings were that the NK cells are inhibited by a transplantation antigen, the major histocompatibility complex (MHC) class I, which prevents NK cells from killing their target cells.

The name 'HLA-DP' originally describes a transplantation antigen of MHC class II category of the major histocompatibility complex of humans, however this antigen is an artifact of the era of organ transplantation.

Dausset's further work in 1965 examining the effects of Hu-1 antigen injection on skin graft rejection further confirmed the conclusion that this Hu-1 complex was indeed a transplantation antigen, a conclusion which would in time have profound effects on the transplantation process.