CD4 and viral infectious disease: CD40L plays a critical role in the generation of primary effector T cell responses in acute viral infection.50 CD8+ T cells can be accompanied by CD4+ T cells through CD40L/CD40 interactions, which is fundamental for CD8+ T cell memory generation.51 Harcourt et al. have previously shown that CD40L improved the durability of respiratory syncytial virus DNA vaccination in BALB/C mice.52 Interestingly, our results showed that CD40L‐positive CD4+ T cell EVs‐treated HBsAg‐vaccinated mice had a greater proportion of Th1 cells compared to PBS‐treated mice.