That takes a while, much much longer then how long it takes a mouse to react to a virus injected directly into its bloodstream. Human cells don't really enjoy g

That takes a while, much much longer then how long it takes a mouse to react to a virus injected directly into its bloodstream. Human cells don't really enjoy growing outside the body. Genetic alteration involves infecting a cell with a virus that cuts DNA and splices in its own (along with the correct antibody). You have the slight possibility that the virus cuts randomly, turning off some cancer-inhibitory pathways. B cells also have this really interesting maturation pathway where they splice their own DNA randomly in the process of becoming an antibody-producing cell. Edit, to add: The B-cell maturation pathway is called V(D)J recombination. Cool stuff. It's how the immune system can create cells that respond to things it's never seen before. http://en.wikipedia.org/wiki/V(D)J_recombination http://en.wikipedia.org/wiki/V(D)J_recombination