Phosphopeptide P140 (Lupuzor) is an inhibitor of autophagy currently being evaluated in late-stage clinical trials for the treatment of lupus. This study was undertaken to investigate the effect of P140 ex vivo on human T and B cells.
Human B cells, T cells, and dendritic cells were analyzed by flow cytometry and cellular assays. The expression of autophagy markers was evaluated by immunoblotting and flow cytometry. The levels of B cell receptor (BCR) signaling markers and HLA molecules were assessed by flow cytometry. Toll-like receptor ligands were screened using an assay with transfected HEK 293 cells. P140 cell entry and trafficking were measured by immunofluorescence in the presence of various inhibitors of endosomal pathways.
As was previously observed after intravenous injection of the peptide in a mouse model of lupus, P140 entered human B cells by a clathrin coat-dependent endocytosis process and homed into lysosomes. The peptide displayed no direct effect on BCR signaling of memory, naive mature, transitional, and B1 cells. However, it strongly reduced the overexpression of HLA class II molecules on lupus B cells that were acting as antigen-presenting cells, down-regulated the maturation and differentiation of B cells into plasma cells, and decreased IgG secretion.
These findings show that P140 down-regulates HLA class II overexpression in human lupus B cells, and also that P140 hampers the differentiation of B cells into autoantibody-secreting plasma cells, likely due to the resulting lack of T cell signaling and activation. This mechanism appears to switch off the downstream events leading to secretion of pathogenic autoantibodies, thus explaining the highly promising results obtained in clinical trials of P140 (Lupuzor) for the treatment of lupus.