SUMMARY To date nine hallmarks of the aging process have been described, which can be grouped into three major categories: primary hallmarks or cause of damage (genomic instability, telomere attrition, epigenetic alterations and loss of proteostasis), antagonist hallmarks or responses to damage (cellular senescence, mitochondrial dysfunction and deregulated nutrient sensing) and integrative hallmarks or manifestations of the aging phenotype (stem cell exhaustion and altered intercellular communication). Despite intensive research on each individual hallmark, little is known about their interconnectivity and the hierarchies governing those interactions. A limiting factor in these studies is the time and resources needed for developing, breeding and aging mouse models that would allow to untangle the interactions as well as the lack of highly selective small molecules that would enable somatic approaches. In this regard, our recent work showed for the first time the feasibility of employing cellular therapy to eliminate cells that have entered a specific cellular program such as cellular senescence. In a proof- of-concept study we identified uPAR as a surface molecule upregulated in cellular senescence and developed CAR T cells able to eliminate senescent cells with high potency and specificity. CAR T cells have the advantage that they can be administered somatically and are highly effective at exclusively targeting cells expressing a specific antigen. In addition, they offer the possibility of spatial and temporal control making them highly versatile tools. Herein we leverage our team’s expertise in senescence biology and cell engineering technology to shed light into the interactions among the hallmarks of aging. Our goals are to characterize in depth the impact of senolytic CAR T cells on the antagonistic and integrative hallmarks of aging; develop tissue specific senolytic CAR T cells that would allow us to untangle hierarchies among the hallmarks across physiological lifespan and study the therapeutic potential of modulating the interactions for the treatment of age-related pathologies. Preliminary data strongly supports the feasibility of the proposed work: we have successfully and safely employed senolytic CAR T cells in naturally aged mice and showed their high potency at eliminating target positive cells in the tissues over long periods of time. Importantly, treatment with senolytic CAR T cells results in significant improvements in healthspan. In our application, we continue to characterize in a systematic way the effects across hallmarks and harness the flexibility of cellular therapy to untangle the hierarchies governing the interactions. Overall, we expect our studies will lead to versatile tools to interrogate aging biology as well as to the development of new therapies for a range of age-related pathologies.