CD40 ligand and IFN-γ induce proinflammatory activity and microglia-mediated neurodegeneration in human stem cell models

The cluster of differentiation 40 (CD40)/CD40 ligand (CD40L) co-stimulatory pathway plays a critical role in the activation and regulation of immune networks involving both adaptive and innate immune cells. Dysregulation of this pathway has been implicated in multiple autoimmune diseases, including multiple sclerosis (MS). MS is characterized by progressive neurodegeneration driven by compartmentalized neuroinflammation within the central nervous system (CNS), sustained low-grade T cell infiltration at the blood-brain barrier, and T cell reactivation at CNS border tissues. CD40L-expressing T cells can activate CD40-expressing microglia, which are a critical effector cell that contribute to neurodegeneration in MS. However, the consequence of this functional interaction in the brain remains poorly understood. Here, we demonstrate that the combination of CD40L and interferon-gamma (IFN-γ), a cytokine produced by activated T cells, induces a robust inflammatory response and cell death in human induced pluripotent stem cells (hiPSC)-derived microglia. Stimulation with CD40L elicited microglial clustering, morphological transformation, and robust release of proinflammatory cytokines including interleukin-12 (IL-12), tumor necrosis factor-alpha (TNF-α), and IL-6. Anti-CD40L antibody treatment reversed both cell death and inflammatory response and partially normalized the associated transcriptional changes. Furthermore, using an hiPSC-derived tri-culture system comprising neurons, astrocytes, and microglia, we demonstrated that CD40L and IFN-γ trigger microglia-dependent neuronal dysregulation and death. Anti-CD40L treatment substantially attenuated neuronal injury. Finally, transcriptomic enrichment analysis identified CD40L-mediated microglial gene expression signatures that correlated with CD40 expression in primary progressive MS brain tissue but not in the normal-appearing white matter of healthy controls. Collectively, these findings support a role for the microglial CD40/T cell CD40L axis in MS pathology and suggest CD40L blockade as a potential therapeutic strategy warranting further investigation.