APL-1, an altered peptide ligand derived from human heat-shock protein 60, selectively induces apoptosis in activated CD4 + CD25 + T cells from peripheral blood of rheumatoid arthritis patients

• Activated CD4 + T cells were identified as targets of APL-1 induced apoptosis.
• APL-1 induces CD4 + CD25highFoxp3 + Tregs independently of RA patients' clinical stage.
• CD4 + T − cell responses to APL-1 are HLA-DR restricted.
• Bioinformatics approach predicts two potential T cell epitopes in APL-1 sequence.

Rheumatoid arthritis (RA) is a chronic T-cell mediated autoimmune disease that affects primarily the joints. The induction of immune tolerance through antigen-specific therapies for the blockade of pathogenic CD4 + T cells constitutes a current focus of research. In this focus it is attempted to simultaneously activate multiple regulatory mechanisms, such as: apoptosis and regulatory T cells (Tregs). APL-1 is an altered peptide ligand derived from a novel CD4 + T-cell epitope of human heat-shock protein of 60 kDa, an autoantigen involved in the pathogenesis of RA. Previously, we have reported that APL-1 induces CD4 + CD25highFoxp3 + Tregs in several systems. Here, we investigated the ability of APL-1 in inducing apoptosis in PBMCs from RA patients, who were classified as active or inactive according to their DAS28 score. APL-1 decreased the viability of PBMCs from active but not from inactive patients. DNA fragmentation assays and typical morphological features clearly demonstrated that APL-1 induced apoptosis in these cells. Activated CD4 + CD25 + T cells but not resting CD4 + CD25 − T cells were identified as targets of APL-1. Furthermore, CD4 + T-cell responses to APL-1 were found to be dependent on antigen presentation via the HLA-DR molecule. Thus, APL-1 is a regulatory CD4 + T cell epitope which might modulate inflammatory immune responses in PBMCs from RA patients by inducing CD4 + CD25highFoxp3 + Tregs and apoptosis in activated CD4 + T cells. These results support further investigation of this candidate drug for the treatment of RA.