Senescent cells accumulate with age because they are produced too rapidly for the immune system to clear, the immune system becomes less efficient, or senescent cells evade immune clearance.

“So we're considering several possibilities. So one is maybe you're just making them too fast, the immune system can't keep up. The other is that although the innate immune system doesn't decline with age per se, it does change and it could change in a way that it becomes less efficient at clearing senescent cells. So that's a big open question, we don't know the answer to that. And the third possibility is that some senescent cells may develop mechanisms to protect themselves from immune clearance and we're sort of still studying that now. And we think maybe all possibilities are still open.”