Inclusion criteria: moderate to severe AS, prior radiographic evidence according to the Modified NY Criteria (1984), inadequate response to NSAIDs. -- Exclusion criteria: pregnancy or lactation, on-going infectious or malignant process on a chest X-ray or MRI, previous exposure to IL-17 or IL-17R targeting therapies, previous exposure to any biological immunomodulating agent excluding TNF antagonists, previous cell depleting therapy. -- Other protocol-defined inclusion/exclusion criteria do apply.