Importantly, we also found that the strong increase in intracellular GrK expression was selective for the CD103–CD8+ Trm cell population (86% of which produced GrK) when compared to the CD103+ population (Fig. 3n, o), suggesting the production of GrK is a key pathological mechanism of CD103–CD8+ Trm cells in the brains of 3xTg-AD mice. This evidence concerns the gene CD8A and Alzheimer disease.