Methods for improving transgene expression in chloroplasts are disclosed along with improved transgenes so produced and methods of use thereof for the treatment of disease. Specifically, the methods comprising analyzing the native sequence of a nucleic acid encoding a protein of interest and replacing codons in said sequence with those preferentially used in psbA genes in chloroplasts in higher plants.Linvention concerne des procédés permettant daméliorer lexpression transgénique dans des chloroplastes, ainsi que les transgènes améliorés ainsi produits et leurs méthodes dutilisation pour le traitement dune maladie.