The prefix histo- means tissue. The term histocompatible is literally tissue compatible. If a donor and recipient are histocompatible (like identical twins), a transplant will be easily accepted. ... (12 Dec 1998) ... 
Histocompatible: Literally, tissue compatible. If a donor and recipient are histocompatible, a transplant is expected to be easily accepted.
histocompatible Marked by histocompatibility; not likely to induce an immune response lading to rejection; said especially of a tissue graft or organ transplant.