Photopheresis is a technique in which peripheral blood mononuclear cel
ls, in the presence of a photoactivatable compound, are exposed extrac
orporeally to ultraviolet A light and reinfused, inducing a host autor
egulatory immune response. Experimental work and ongoing clinical stud
ies are helping to define the role of this novel, safe, and non-toxic
immunomodulating technology in the field of transplantation.