Paper: https://www.cell.com/immunity/fulltext/S1074-7613(26)00440-1

Granzyme K is the protein.

From the abstract of the paper, significantly more nuance.

> Despite persistent immune aging phenotypes, GzmK deficiency markedly attenuated organ aging, effectively uncoupling immune and tissue aging... These findings identify GzmK as a tissue-specific driver of organismal aging but not immune aging or systemic inflammaging.

Paywall

Thank God! Finally, mice that don't age!

In mice.