the invention relates to methods and products for the identification of a clinically significant immune response in subjects treated with a therapeutic protein . aspects of the invention relate to methods and compositions for identifying a clinically significant immune response in patients treated with therapeutic amounts of a vla4 binding antibody . a second aspect of the invention concerns the chronological details of sample collection for determining the titre of antibodies against the therapeutic protein , e . g . the collection of at least two samples at two different time points . a third aspect of the invention relates to the selection of the critical threshold level , which corresponds to the antibody titre of untreated patients increased by the double of the standard deviation of this control antibody titre .