So although Agracetus must ensure that its plantibodies are free from pesticides and other kinds of contaminants, it can forgo expensive screening for viruses and bacterial toxins. Corn is not the only crop that can mimic human cells. Agracetus is also cultivating soybeans that contain human antibodies against herpes simplex virus 2, a culprit in venereal disease, in the hope of producing a drug cheap enough to add to contraceptives. CropTech in Blacksburg, Va., has modified tobacco to manufacture an enzyme called glucocerebrosidase in its leaves. But, she cautions, there are important differences as well.
Human cells adorn some antibodies with special carbohydrate molecules.
Plant cells can stick the wrong carbohydrates onto a human antibody. If that happens, says Douglas A. Russell, a molecular biologist at Agracetus, the maladjusted antibodies cannot stimulate the body into producing its own immune response, and they are rapidly filtered from the bloodstream. Until that discrepancy is solved, Russell says, Agracetus will focus on plantibodies that don't need the carbohydrates. Next spring the company's clinical trial results may reveal other differences as well.