We show that predicted epitopes can bind to HLA class II on dendritic cells and demonstrate that CD4 T cell reactivity against variable epitopes of adalimumab occurs both in adalimumab-treated RA patients and in healthy donors, with a significant overlap between the two groups, adding to the evidence that anti-drug reactivity can be associated with pre-existing T cell repertoires. The gene discussed is CD4; the disease is rheumatoid arthritis.