I was wondering how the body "remembers" viruses after having once overcome them, and while reading this article on the immune system (page 14, Vaccinations), I read:
There are many diseases that, if you catch them once, you will never catch again. Measles is a good example, as is chicken pox. What happens with these diseases is that they make it into your body and start reproducing. The immune system gears up to eliminate them. In your body you already have B cells that can recognize the virus and produce antibodies for it. However, there are only a few of these cells for each antibody. Once a particular disease is recognized by these few specific B cells, the B cells turn into plasma cells, clone themselves and start pumping out antibodies. This process takes time, but the disease runs it course and is eventually eliminated. However, while it is being eliminated, other B cells for the disease clone themselves but do not generate antibodies. This second set of B cells remains in your body for years, so if the disease reappears your body is able to eliminate it immediately before it can do anything to you.
Which made me wonder, instead of vaccinating people with weakened forms of the disease, getting their B cells to activate as described, what would be wrong with growing large colonies of B cells for a given virus and injecting them into someone who has never had the disease so that one can go straight to the last sentence of that paragraph, having many of those B cells in place before the virus is ever experienced?