Infectious issues of therapeutic monoclonal antibodies in multiple sclerosis and neuromyelitis optica spectrum disorders

Various effective monoclonal antibodies (mAbs) have been approved for both multiple sclerosis (MS) and anti-aquaporin-4-seropositive neuromyelitis optica spectrum disorders worldwide, including in Japan. As these newer mAbs have distinct modes of action that effectively suppress the recurrence of inflammation and slow disability progression, they can modulate and interfere with the protective immune response against pathogens, resulting in various infectious complications. Among various mAbs, natalizumab (NTZ) has the highest risk of causing progressive multifocal leukoencephalopathy (PML), a rare but fatal opportunistic brain infection caused by John Cunningham polyomavirus. Switching from NTZ to B-cell-depleting mAbs, such as ocrelizumab, is also a possible risk factor for PML development. Alemtuzumab carries the risk of reactivation of varicella-zoster virus (VZV); therefore, prophylactic acyclovir treatment is required. NTZ has also been associated with VZV reactivation. Eculizumab can cause severe meningococcal infection due to Neisseria meningitis, and vaccination prior to treatment induction is required. Attention to the reactivation of hepatitis B or Mycobacterium tuberculosis is also needed during mAb therapy. Additionally, in the era of severe acute respiratory syndrome coronavirus 2 infection (COVID-19), the risk for of developing severe COVID-19 may be associated with some mAbs, such as B-cell-depleting agents. Thorough understanding and mitigation strategies for infectious risks are essential.