Natalizumab treatment shows no clinically meaningful effects on immunization responses in patients with relapsing-remitting multiple sclerosis.

Abstract Natalizumab is an immunomodulatory drug approved for the treatment of multiple sclerosis. This randomized, multicenter, open-label study evaluated natalizumab's effects on immunization responses to a recall antigen (tetanus toxoid [TT]) and a neoantigen (keyhole limpet hemocyanin [KLH]) in patients with relapsing forms of multiple sclerosis (MS). Natalizumab-naive relapsing MS patients were randomized (1:1; n = 30 per group) to receive TT and KLH immunizations either without natalizumab treatment (control) or after 6 months of natalizumab treatment (natalizumab group). An adequate response to immunization was defined as an increase to at least twofold in specific serum immunoglobulin G (IgG) 28 days after the first immunization. All evaluable patients achieved protective levels of anti-TT IgG antibodies, and the proportion of responders to this recall antigen, as well as to primary immunization with KLH, was similar in the presence and absence of natalizumab. This indicates that natalizumab treatment does not appear to affect responses to primary or secondary immunization in a clinically meaningful way.