Passive transfusion of JCV antibodies in blood products

Multiple sclerosis (MS) is an immune-mediated disease causing inflammatory demyelination and axonal loss of the central nervous system. The overarching goal of treatment for MS is to become free from disease activity. Natalizumab is the first monoclonal antibody approved to treat MS and is a highly efficacious treatment, particularly in active or rapidly evolving relapsing remitting MS. Its use, however, is influenced by the occurrence of progressive multifocal leukoencephalopathy, a potentially fatal brain infection caused by the John Cunningham virus (JCV) in patients on natalizumab who are JCV antibody positive. The presence of the JCV antibody often results in discontinuation of treatment. The authors would like to report a case of passive transfusion of JCV antibody following administration of blood products and highlight how lack of awareness of this phenomenon could negatively influence treatment choice in patients with highly active disease.