It is not vital in that if something goes wrong with it and it is severely damaged in auto accidents, it can be removed. As a matter of fact the spleen when severely injured can cause extreme blood loss.
But, the tissue within the spleen known as "white pulp" is comprised of lymphatic tissue, hence, it's affiliation with the body's defense mechanisms. It has stored within it immune cells known as macrophages, T lymphocytes, and B lymphocytes.
The spleen of mice is the first place cells were collected to produce Z-Mapp's monoclonal antibodies.
The mice antibodies are then introduced to cancer/viral cells called hybridomas.
The hydridomas are then introduced to a HAT medium which is made with all kinds of human enzymes. It is here the mice characteristics are converted to human genetic characteristics. The positive cells are then harvested as monoclonal antibodies.
This is an expensive procedure because of all the necessary parts of the process. But, basically ZMapp is a genetically engineered treatment classified as passive immunity. It is a transfusion of antibodies the human immune system was unable to produce for whatever reason.
Just a little food for thought. Ebola comes from mammals. The earlier outbreak was believed to be contracted by hunters of primates in Africa, but, his outbreak is believed to be contracted by bats. Bats are the only flying mammals known. Ebola likes the internal body environment of mammals probably because of the constant body temperature.
For those wondering why isn't this used for HIV; it is most likely because it is unsuccessful against a virus that attacks T lymphocytes. Ebola is a hemorrhagic virus. It is different than HIV. I am sure this technique was already investigated for HIV.
