HLA stands for “human leu­ko­cy­te antigen(s).” It enab­les the immu­ne sys­tem to dis­tin­guish bet­ween its own and for­eign tis­sue. It hel­ps the immu­ne sys­tem not only to reco­gni­ze patho­gens but also to dis­tin­guish bet­ween its own and for­eign tis­sue. HLA cha­rac­te­ris­tics should be deter­mi­ned as com­ple­te­ly as pos­si­ble when trans­plan­ting stem cells. They are also fre­quent­ly refer­red to as tis­sue characteristics.