Future vaccines are likely to contain more than one type of cargo being pulled into cells by the Toxin Freight Lines. We're also attempting to design vaccines against viruses. One project uses diphtheria toxin as a delivery system. Another involves immunizing mice against a virus that causes meningitis in humans. Other possible targets include HIV, papillomavirus, and cytomegalovirus.
Viruses invade cells, then take over the cell's resources to reproduce more of themselves.
As this happens, they make abnormal bits of protein that work their way to the cell surface. That's the signal for killer T-cells, stimulated by a vaccine, to recognize and attack the invaders. Another possible application, already under pursuit, would be to custom-tailor vaccines against cancer tumors. Tumor cells produce abnormal proteins as they grow and fragments of these proteins find their way to the cell surface. Researchers have identified such markers for breast, bowel, lung, and bladder cancer.