While most of the attention on Xoma Corp. is focused on its E5septic shock therapeutic, the company's CD5 Plus product maybe leading the way to Xoma's future.

Xoma's president, Dr. Pat Scannon, said that the company'scurrent clinical work and research programs have been heavilyinfluenced by findings from clinical studies of CD5 Plus fortreatment of graft-vs.-host (GVHD) disease following bonemarrow transplants. This product is up for review this monthby a Food and Drug Administration advisory committee.

GVHD is a potentially fatal disease in which T cells within thedonor marrow recognize the recipient's tissues as "foreign" andmount an immune system attack.

CD5 Plus uses a monoclonal antibody conjugated with the planttoxin ricin. The MAb binds to mature T cells, killing them withthe toxin.

CD5 Plus is used to pre-treat the bone marrow prior to injectioninto the recipient. For reasons that aren't understood, T cellsthat subsequently grow out of the treated marrow don't reactagainst the patient's tissues.

Xoma has applied that observation to immune system diseases,such as rheumatoid arthritis (RA) and Type I diabetes, in whichinappropriate T cell activation causes damage. The Berkeley,Calif., company (NASDAQ:XOMA) this spring began Phase IIItrials in patients with severe RA for whom conventionaltreatment has failed.

Even more exciting to Xoma is the potential use of CD5 Plus totreat Type I diabetes, in which the body mounts an immuneattack on the islet cells that produce insulin. Xoma decided tosee if wiping out the T cells, which are required to initiate theattack, could stop progression of the disease.

Patients in Phase I/II trials treated within five months ofdiagnosis maintained stable levels of insulin over a 12-monthperiod after receiving one five-to-10-day course of CD5 Plus.Untreated patients tended to show a drop in insulin productionto near zero within a year of diagnosis. Xoma will begin PhaseIII studies within the next few months.

Xoma is about to launch a Phase II study of CD5 Plus inpatients with psoriatic arthritis. It is also looking at CD5 Plus inpilot clinical studies to treat systemic lupuserythematosus,scleroderma and hematological cancers, including mycosisfungoides and chronic lymphocytic leukemia.

-- Cynthia Robbins-Roth, Ph.D. BioVenture View

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