A CD40-OX40 co-stimulatory circuit orchestrates protective CD4T cell immunity in tuberculosis.

Abstract

Effective CD4T cell responses are essential for controlling Mycobacterium tuberculosis (Mtb), but they fail to achieve sterilizing immunity in infected lungs. In mouse models of Mtb infection, single-cell transcriptomic profiling identified a dominant population of OX40CD4T cells that emerged during Mtb infection yet exhibited impaired effector differentiation. This dysfunction was linked to defective co-stimulatory signaling, corresponding to persistently low OX40 ligand (OX40L) expression on antigen-presenting cells. Therapeutic activation of OX40 restored CD4T cell functionality, expanded protective clonotypes, and reduced pulmonary bacterial burden in vivo. These effects required intact CD40-CD40L interactions to sustain OX40 expression and promote T cell differentiation, and were critically dependent on interferon (IFN)-γ signaling for antimicrobial activity. CD40L blockade abolished the immunotherapeutic benefits of OX40 stimulation, revealing a cooperative CD40-OX40 axis that orchestrates protective immunity in tuberculosis. These findings identify impaired co-stimulatory signaling as a central mechanism of CD4T cell dysfunction during chronic infection and highlight this axis as a target for host-directed immunotherapy in tuberculosis.