 These effects - sensitization and immunosuppression - are thought to be due largely to white blood cells present in the transfusion product. Doctors order specially pretreated blood transfusions that have been depleted of white blood cells with the aim of minimizing risks in an immunocompromised patient. Leukofiltration and gamma-irradiation are the special treatments that deplete white blood cells. A combination of leukofiltration and gamma-irradiation pretreatment of donor blood is thought to deplete the white blood cells most effectively. Therefore, blood is pretreated both ways before it is given to patients who need a stem cell transplant or others who are immunosuppressed. 