Post-doctoral researcher Harvard Med. Sch. Boston, Massachusetts, United States
Disclosure(s):
Olga Barreiro: No financial relationships to disclose
Introduction/Rationale: T cell function is tightly regulated to ensure effective immunity during acute viral infections. In this regard, we recently identified CX3CR1^hi CD8⁺ effector T cells that reside within the intravascular compartment and perform endothelial immune surveillance. How endothelial interactions shape the fate and function of patrolling effectors, and how they communicate with antigen-presenting endothelial cells (ECs) to control infection remain unclear, as both subsets are difficult to distinguish from other cells with overlapping phenotypes.
Methods: To overcome this limitation, we developed two complementary in vivo labeling strategies: (i) in situ photoconversion using Kaede, and (ii) exosome-based tagging using the Rosa26 CAG-CD63emGFP reporter crossed with either an endothelial or a CD8+ T cell-specific Cre strain. Photoconversion enables precise characterization of the number and phenotype of CD8+ T cells interacting with the endothelium at a given time point but cannot distinguish cells engaging for different durations, resulting in a heterogeneous population. In contrast, the exosome tagging allows for the isolation of a substantial and more synchronized pool of crawling effectors and ECs, facilitating comprehensive transcriptional profiling.
Results: Bulk and scRNASeq analyses of labeled patrolling T cells revealed a unique differentiation program induced during endothelial surveillance that redirects their transcriptional trajectory away from terminal effector fate and toward KLRG1+ CX3CR1^hi long-lived effector memory differentiation. The transcriptional profiling of ECs presenting viral antigens to patrolling T cells uncovered the elicitation of a coordinated antiviral program encompassing regulatory mechanisms that restrain T cell cytotoxicity.
Conclusion: Together, these methodologies have provided unprecedented insight into the reciprocal crosstalk between effector CD8⁺ T cells and blood ECs, thereby greatly expanding our understanding of vascular antiviral immunity.
