“…Importantly, the fact that cellular attributes that characterize aging (including epigenetic alterations) are highly signal-responsive and regulated by their extracellular environment provides clear evidence that biological age is modifiable. For the past 70 years, it has been known that exposing older cells and animals to a "younger" blood-based secretome (heterochronic parabiosis) has a profound effect on reversing ageassociated gene expression and cellular hallmarks of aging [5] .…”