The role of the immune system in progressive multifocal leukoencephalopathy: a comparative analysis of two cases following autologous and allogeneic hematopoietic stem cell transplantation.

Progressive multifocal leukoencephalopathy (PML) is a rare, subacute demyelinating disorder of the central nervous system (CNS) caused by the JCV. In immunosuppressed hosts, PML is caused by reactivation of a latent infection rather than primary exposure. Hematological patients, particularly post-transplant, presenting with worsening neurological symptoms should promptly consider PML in the differential diagnosis. The rarity of PML after autologous or allogeneic hematopoietic stem cell transplantation (HSCT) and the absence of a universally effective therapy represents a clinical challenge. Here, we present two cases of PML developed after autologous and allogeneic HSCT, with completely different outcomes dependent on the patients' clinical backgrounds and the level of immune system competence which is the key factor in determining either the onset or viral clearance of the infection.