in wikipedia Immunotherapy article it talks about how they treat some cancers with "T-cell adoptive transfer" involving cloning patient's white blood cells, sometimes modifying / improving them and then injecting them back into the patient. It says that research started in the 80s and seems to still go on, mostly with cancers. So I am wondering, why isn't this general approach a generic panacea for all bacterial and viral diseases? E.g. if flu vaccine in vivo makes immune system eventually suppress the current flu strain (and in fact young people do it themselves without vaccine) why can't vaccine be replaced with massive infusion of these cloned T-cells with "vaccine" / response to the strain inserted in the lab? Likewise, why can't HIV be eliminated by using cloned T-cells whose membranes are modified to eliminate whatever feature involved in allowing the virus enter and attack them? I guess the main gist of this question is, I understand that if the above isn't happening, there are major limitations to the procedure that are not elaborated in the brief description in wikipedia. So, anybody knows what they are? What makes this procedure so limited that it remains experimental cancer treatment instead of a panacea for everything under the sun?