Extracorporeal photopheresis: Buffy coat is collected from patient, 8-MOP added to the collected cells, then treated with UVA. Monocytes shift to DCs with immature, tolerogenic phenotype; all treated cells infused back to patient. Activated lymphocytes undergo apoptosis over 24 to 48 hours. Donor and residual host APCs take up apoptotic bodies, resulting in favorable changes in cytokine milieu. Tolerogenic DCs are unable to stimulate effector T cells; T-regulatory cell population promoted. DC, dendritic cell; APC, antigen presenting cell. (Cell image credits Blausen Medical, US National Library of Medicine; figure design Mia Zierk.)