A New Therapeutic Option for Progressive Multifocal Leukoencephalopathy after Allogeneic Hematopoietic Cell Transplantation

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease of central nervous system caused by human polyoma virus, JC virus, which can occur in the patients with severe immune compromised condition. PML is a rare disease, seen in hematologic malignancies, organ transplantation, and HIV infected patients. PML is often fatal, because of the lack of effective anti-viral drug for JC virus. Clinical observations of survival improvement in HIV-positive patients after the introduction of combination antiretroviral therapy (cART) could suggest the importance of restoration of immune response. In the setting of PML after allogeneic hematopoietic cell transplantation (HCT), it is very difficult to reduce or stop immunosuppressants to restore immune response, because of graft versus host disease (GVHD) and so on. Therefore, new anti-viral drugs against JC virus should be needed. Recently, mirtazapine (antagonists of 5-HT2 serotonergic receptor) and mefloquine (anti-malarial drug), have been shown to have anti-viral activities against JC virus even in the clinical setting as well as in vitro experiments. Several case reports using each drug have been found in recent years. A controlled study for PML patients treated with or without mirtazapine has shown superior survival rate at 1-year in the patients treated with mirtazapine, although statistical significance was not observed. Concomitant usage of both mirtazapine and mefloquine could be expected to induce more effective anti-viral activities, because the mechanism of each drug to inhibit JC virus proliferation is independent. Indeed, some case reports have shown the efficacies of these drugs for the treatment of the patients with PML including after allogenic HCT patients. Controlled study should be required to identify the efficacies of the combinational treatment of both mirtazapine and mefloquine for the treatment of PML patients after allogenic HCT.