The gene containing DNA coated metal particles are fired at the plant cells using a gene gun. The plants take up the DNA, grow into new plants, then are cloned to produce large numbers of genetically identical crops. The gene transfer is independent, and it can express antigens through nuclear and chloroplast transformation. There are a few other techniques that have been tested, however, the three techniques describe above are more common and practical. One of the alternative methods is nuclear transformation. This is when the desired gene is inserted into the plant nucleus through non-homologous recombination. Furthermore, electroporation has been considered, but it is not common because the cell wall has to be weakened before the pulses and DNA insertion can occur. Lastly, it is thought that molecular farming can be used so that the plants can be used as protein factories. After the vaccine is orally ingested, it reaches the digestive tract mucosa and stimulates the mucosal immune system. These provide the first-line of defense against attacking pathogens. The M-cells (found in Peyer’s patches) in the mucous membranes of the lymphoid tissues push the antigens to the antigen presenting cells in the underlying tissues. The antigenic epitopes are then shown on the antigen presenting cells’ surface and the T-cells activate the B-cells. The activated B-cells then move to the mesenteric lymph nodes where they become plasma cells and move to the mucous membrane to produce immunoglobulin A (IgA) (a type of antibody). Then the M-cells channel the antigen. As the cells go toward the lumen, the IgA combine with secretary components to make secretory IgA (sIgA). Then, the sIgA and the specific antigenic epitopes work together to eliminate the unwanted pathogen. Current research has focused on a variety of different types of plants in order to determine which is the most eligible and efficient. The plant has to be robust, nutritious, appetizing, transformable, and ideally domestic. Some examples of crops that are being tested include: corn, tomato, rice, carrots, soybeans, alfalfa, papaya, quinoa, peas, apples, algae, wheat, lettuce, potatoes, bananas, and tobacco; with the last four being the most common. When looking at which plants are the best, there are many factors that must be taken into account. From the research, scientists have started to pair crops with diseases. They believe that edible vaccines can be made for many diseases; such as, rotavirus, cholera, gastroenteritis, autoimmune disease, malaria and rabies For example, they think that booster shots can be distributed through lettuce.