By Rosy Guerra
Senior editor

While investors have been focused on the coming rivalry in rheumatoid arthritis treatment between anti-tumor necrosis factor therapies being developed by Immunex Corp. and Centocor Inc., dark horse Cypress Bioscience Inc. has been taking a completely different approach with its Prosorba immunoadsorption column. Assuming all three ultimately are approved, the issue will be which therapy proves more attractive to patients and physicians, as well as the marketing clout the three can bring to bear on buyers.