CD4+ T cell calibration of antigen-presenting cells optimizes antiviral CD8+ T cell immunity

Bedoui and colleagues describe a sequential process of integration of innate and CD40-delivered signals in APCs, which optimizes their capacity to drive antiviral CD8(+) T cell responses. Antiviral CD8(+) T cell immunity depends on the integration of various contextual cues, but how antigen-presenting cells (APCs) consolidate these signals for decoding by T cells remains unclear. Here, we describe gradual interferon-alpha/interferon-beta (IFN alpha/beta)-induced transcriptional adaptations that endow APCs with the capacity to rapidly activate the transcriptional regulators p65, IRF1 and FOS after CD4(+) T cell-mediated CD40 stimulation. While these responses operate through broadly used signaling components, they induce a unique set of co-stimulatory molecules and soluble mediators that cannot be elicited by IFN alpha/beta or CD40 alone. These responses are critical for the acquisition of antiviral CD8(+) T cell effector function, and their activity in APCs from individuals infected with severe acute respiratory syndrome coronavirus 2 correlates with milder disease. These observations uncover a sequential integration process whereby APCs rely on CD4(+) T cells to select the innate circuits that guide antiviral CD8(+) T cell responses.