Idec Pharmaceuticals Corp. and partner SmithKline Beecham have chosen a new product candidate in their anti-CD4 program for rheumatoid arthritis. But as a reminder of the role of serendipity in drug development, the failed first candidate may find new application in other diseases based on the very characteristics that caused problems in RA.

The first compound IDEC-CE9.1 failed in clinical trials for RA because it depletes the CD4 cells it targets, a detrimental effect in arthritis. Yet this is precisely the action sought