[Open use of natalizumab. Neutralising antibodies and clinical data]

Since June 2006 natalizumab has been available for use as monotherapy in relapsing-remitting MS with high disease activity. The AFFIRM study showed the occurrence of persisting and neutralising antinatalizumab antibodies (nAb) in 6% of the patients. We present data revealing the number of nAb-positive patients assessed in our independent laboratory. Additionally we provide retrospective clinical data on the efficacy of natalizumab as escalating immunotherapy.

Blood samples of patients treated with natalizumab in Germany were tested for nAb using an enzyme-linked immunosorbent assay. If nAb were detectable at a single time point, the according patients were categorised as transiently positive. They were diagnosed as persistently positive if they had nAb at two or more time points which were at least 6 weeks apart. The treating neurologists sending the serum samples were asked to provide clinical data of their patients.

Forty-seven of 593 samples (9.1%) were nAb-positive, 19 of them (3.7%) persistently positive and two (0.3%) transiently. Twenty-six patients (5%) were not retested for nAb, as we did not receive material for confirmatory analysis. Infusion-related adverse events were reported for 53 patients (10.3%). Averages of 2.6 relapses per year were reported previous to natalizumab therapy and 0.3 per year during natalizumab therapy.

During natalizumab therapy, testing for nAb should be strongly considered for further therapy decisions and in cases of suspected allergic reaction. Basically the obtained data compare with those of the AFFIRM study. Natalizumab is applied as escalating therapy in MS according to the recommendations of the MSTKG, and it seems to match the expectations in open-label use.