Transgenic plants expressing human glutamic acid decarboxylase (GAD65), a major autoantigen in insulin-dependent diabetes mellitus

Parenteral and oral administration of autoantigens can induce immune tolera nce in autoimmune diseases. Prophylactic therapy based on oral administrati on of human autoantigens is not, however, feasible when sufficient quantiti es of candidate autoantigens are not available. Transgenic plants that expr ess high levels of recombinant proteins would allow large quantities of aut oantigens to be produced at relatively low costs. In addition, transgenic f ood would provide a simple and direct method of delivering autoantigens. Th e production and the characterization of transgenic tobacco and carrot plan ts expressing human GAD65, a major autoantigen in human insulin-dependent d iabetes mellitus (IDDM), is reported. Immunogold labeling and electron micr oscopy of transgenic tobacco tissue shows the selective targeting of human GAD65 to chloroplast tylacoids and mitochondria. In planta expressed GAD65 has a correct immunoreactivity with IDDM-associated autoantibodies and reta ins enzymatic activity, a finding that suggests a correct protein folding. In transgenic tobacco and carrot the expression levels of human GAD65 varie s between 0.01% and 0.04% of total soluble proteins. Transgenic edible plan t organs are now available to study the feasibility of inducing immune tole rance in IDDM animals by oral administration of GAD65.