The immune system operates more or less as a limited capacity system. It has low levels of replacement of immune cells in old age. For reasons that may have to

The immune system operates more or less as a limited capacity system. It has low levels of replacement of immune cells in old age. For reasons that may have to do with exposure to persistent herpesviruses there is an expansion of memory cells and related types at the expense of the naive T cells needed to deal with new threats. So the quick and dirty solution to this, which has some support from animal studies in the past few years, is to selectively kill off the undesirable excess memory cells. Perhaps via one of the targeted cell killing technologies developed in the cancer research community. This should free up capacity and spur the generation of more naive T cells to replace the lost numbers. It isn't a reality yet, but all the pieces are more or less in place. Someone just needs to do it. A similar thing was demonstrated for B cell destruction in mice (innate immunity, not adaptive immunity): the bad cells were stripped out, and fresh new cells were generated as a result, and the innate immune response improved.