Ebola vaccine. Various approaches are being used to develop an ebola vaccine. On the left is an ebola virus attaching itself to a NPC1 receptor on the surface of a cell. The virus will then penetrate the cell membrane and begin the process of replication. Vaccines are designed to keep this from happening, either by alerting the immune system to kill the virus directly or by blocking the viral receptor. At top left, an inactive adenovirus has been genetically engineered with ebola GP1 surface proteins to provide immunity. In the center an engineered antibody (blue) blocks a toll receptor on the cell surface. Farther to the right is a group of antibodies developed in tobacco leaves which also utilize GP1 proteins to offer immunity.