Spatial transcriptomics demonstrates the role of CD4 Tcells in effector CD8 Tcell differentiation during chronic viral infection.

Abstract

CD4 Tcell help is critical to sustain effector CD8 Tcell responses during chronic infection, notably via T follicular helper (Tfh)-derived interleukin-21 (IL-21). Conversely, CD4 depletion results in severe CD8 Tcell dysfunction and lifelong viremia despite CD4 Tcell reemergence following transient depletion. These observations suggest that repopulating CD4 subsets are functionally or numerically insufficient to orchestrate a robust CD8 response. We utilize spatial transcriptomics and single-cell RNA sequencing (scRNA-seq) to investigate CD4 Tcell heterogeneity under CD4-replete and -deplete conditions and explore cellular interactions during chronic infection. Although IL-21-producing Tfh cells repopulate following transient CD4 depletion, they are outnumbered by immunomodulatory CD4 Tcells. Moreover, the splenic architecture appears perturbed, with decreases in white pulp regions, coinciding with germinal center losses. These disruptions in splenic architecture are associated with diminished Tfh and progenitor CD8 Tcell colocalization, providing a potential mechanism for impaired progenitor-to-effector CD8 Tcell differentiation during "un-helped" conditions.