Preexisting Antiviral Immunity and Allogeneic T-Cell Transfer: Redefining the Therapeutic Landscape of Progressive Multifocal Leukoencephalopathy

The Demyelinating Dilemma: Progressive Multifocal Leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) has long remained one of the most daunting challenges in clinical neurology and infectious disease. Caused by the reactivation of the JC polyomavirus (JCV) in the setting of severe cellular immunodeficiency, this opportunistic infection leads to the lytic destruction of oligodendrocytes, resulting in rapidly progressive demyelination of the central nervous system. Historically, PML carried a dismal prognosis, particularly in patients with HIV/AIDS, hematologic malignancies, or those receiving potent immunosuppressive therapies like natalizumab for multiple sclerosis.

Until recently, the therapeutic cornerstone for PML was the restoration of the host’s immune system—either through antiretroviral therapy in HIV patients or the cessation of immunosuppressants. However, for many patients, these strategies are either insufficient or impossible. The emergence of immune checkpoint inhibitors (ICIs), such as those targeting the PD-1/PD-L1 axis, offered a glimmer of hope, theoretically ‘releasing the brakes’ on exhausted antiviral T-cells. Yet, clinical responses to ICIs have been notoriously heterogeneous. Two landmark studies published in JAMA Neurology by Möhn and colleagues now provide critical insights into why some patients respond while others do not, and how allogeneic cell therapy might fill the gap for the most vulnerable.