The present invention relates to gene therapy delivery and expression systems comprising at least one helper-dependent adenoviral vector containing a nucleic acid sequence encoding for proteoglycan 4 (PRG4) or a biologically active fragment thereof. The invention further relates to a pharmaceutical composition comprising a therapeutically effective amount of at least one helper-dependent adenoviral vector containing said nucleic acid sequence encoding for proteoglycan 4 (PRG4), or a homolog thereof from any other species, or a biologically active fragment thereof. The invention also relates to the use of the novel gene therapy delivery and expression system according to the invention for use in the prevention and/or treatment of camptodactyly-arthropathy-coxa vara-pericarditis (CACP), or a musculoskeletal disorder such as a joint disorder or joint disease.