Defining early CD8+ T cell responses during acute and chronic viral infection using single-cell RNA-seq analysis

CD8+ T cells are key in mediating immune responses to viral infections. Viral infections can be acute, in which the infection is resolved, or chronic, when antigen persists. Several studies have illustrated that CD8+ T cells adopt distinct functional states in each infection type. In acute infections, naïve CD8+T cells differentiate into cytotoxic CD8+ T cells and memory CD8+ T cells. In chronic infections, activated CD8+ T cells adopt an altered state known as exhaustion. Exhausted CD8+ T cells lose effector functions and show high expression of inhibitory receptors such as PD-1. Several studies have characterized CD8+ T cell exhaustion at late time-points after a persistent infection has already been established. Recent studies demonstrate that CD8+ T cell exhaustion may be specified during earlier phases of a developing chronic infection. However, these studies do not address the effect of biological sex on early CD8+ T cell responses to chronic infection. Sex differences in susceptibility and outcomes of viral infectious diseases are well-appreciated. Still, the role of sex in the development of CD8+ T cell exhaustion and in the molecular programs underlying CD8+ T cell responses to acute and chronic viral infections remains undefined. This study, therefore, set out to investigate early and sex-based differences in the transcriptional profiles of CD8+ T cells that underlie their responses to acute versus chronic viral infection. The mouse model of acute and chronic lymphocytic choriomeningitis virus infection was used to comparatively analyze transcriptional signatures of single antigen-specific CD8+ T cells during acute versus chronic infection at multiple time-points post-infection. Next sequencing coupled with bioinformatics-based approaches were used to analyze our single-cell RNA sequencing data. Our results reveal an early transcriptional divergence of CD8+ T cells responding to acute versus chronic viral infection. We show that there are sex-specific diff