Does one unit really matter? Immunological effects of transfusion after universal leucodepletion

Patients with cancer who receive allogeneic red blood cell transfusions are at risk of adverse reactions of varying severity. One of these reactions is immunomodulation, also known as transfusion-related immunomodulation. With the exact mechanism of transfusion related immunomodulation being unclear, storage lesions (both the cellular and cytokine component) are considered a major contributor. Leucocytes are believed to be implicated in storage lesions and immunomodulation. However, the efficacy of leucodepletion in reducing immunomodulation is controversial. The theoretical link between these three interconnected events - storage lesions, immunomodulation and cancer progression remain controversial and poorly understood. This article summarizes the available evidence on efficacy of leucodepletion, storage lesions and transfusion related immunomodulation, while rationalizing the possible association between an immunomodulation triggering transfusion 'dose' in cancer patients and subsequent cancer recurrence.