Restoration of p21 in p21(-/-) fibroblast-like synoviocytes (FLS) significantly reduces excessive migration to rheumatoid arthritis (RA) synovial fluid (SF). Cells were infected as described and used for chemotaxis the following day, when nearly all FLS were estimated to express their recipient transgene. Three high powered fields (HPFs) of migrated cells were counted and their sum was determined for each well. Bars represent the mean of quadruplicate wells ± standard error (SE) and an asterisk indicates a statistically significant difference. These data are representative of three independent assays. AdlacZ, adenovirus expressing β-galactosidase; Adp21, adenovirus expressing p21; WT, wild type.