Lymphocytosis as a biomarker for natalizumab treatment response in multiple sclerosis: The link with anti-drug antibodies

Background

Natalizumab is a high-efficacy therapy drug for multiple sclerosis that inhibits lymphocyte migration into the central nervous system, increasing lymphocyte counts in the peripheral blood. Anti-drug antibody responses may limit drug efficacy, but current guidance recommends anti-drug antibody testing only after evidence of ‘reduced efficacy’.