- Leukapheresis (on two occasions). This is a method of collecting large numbers of white blood cells. The cells obtained in the first leukapheresis procedure are grown in the laboratory, and the anti-gp100 protein is inserted into the cells using an inactivated (harmless) virus in a process called retroviral transduction. Cells collected in the second leukapheresis procedure are used to evaluate the effectiveness of the study treatment.