The trans­fer of human stem cells from a donor to a pati­ent. Stem cells are a rege­ne­ra­ti­ve tis­sue in the body which are taken from a spe­ci­fi­cal­ly selec­ted donor – usual­ly an adult. As a com­ple­te immu­ne sys­tem is trans­plan­ted rather than nor­mal body cells only, the requi­re­ments for an HLA match are much hig­her and the medi­cal con­di­ti­ons far more com­plex (allo­gen­eic trans­plan­ta­ti­on, auto­lo­gous transplantation).