Impact of human CD8+ T cell senescence on 89Zr radiolabelling and PET imaging

The ability of CD8+ T cells to protect against infection and malignant transformation diminishes with age. Novel means to assess cellular functional deficits in vivo are being made available such as total-body positron emission tomography (PET) and radiotracers with long half-lives. Here, we determined radiolabeled human CD8+ T cells isolated from young and old individuals with zirconium-89 (89Zr) and assessed their biological status in vitro and distribution in vivo. MethodsFresh and cryopreserved CD8+ T cells from young and old individuals were labelled with varying activities of [89Zr]Zr-oxine and assessed for DNA damage and survival, subsequent to in vitro culture in the presence or absence of antioxidants. 89Zr-labelled CD8+ T cells were injected intravenously in NSG mice and whole-body cell migration assessed using PET imaging. ResultsFresh and cryopreserved CD8+ T cells showed no difference in ability to be labelled with 89Zr, radionuclide retention, or CD8+ T cell phenotype. 89Zr induced partial cell death and DNA damage, which was no longer detectable visible after four days. The level of DNA repair observed in old samples was highly variable. 89Zr efflux from cells, seen in vitro, did not occur in vivo. Longitudinal PET imaging indicated that CD8+ T cells from old individuals accumulated in tissues at a slower rate than those isolated from young individuals. ConclusionWe have established a strategy to label and track the biodistribution of cryopreserved CD8+T cells. Further study is required to understand differences in migratory behaviour of CD8+ T cells isolated from old and young individuals.