CD4+ T Cells Are Key to Shaping a Protective Humoral Immunity in Primary Dengue 2 Virus Infection: Implications for Rational Vaccine Design

<b>Background:</b> Understanding the immune mechanisms that differentiate protective from pathogenic responses during dengue virus (DENV) infection is critical for effective vaccine development. <b>Objective:</b> To investigate how CD4⁺ T cell depletion alters viral control and the humoral immune response during primary DENV2 infection in a non-human primate (NHP) model. <b>Methods:</b> Rhesus macaques were depleted of CD4⁺ T cells prior to DENV2 infection. Viral kinetics, B cell activation, antibody specificity, and functional outcomes were evaluated longitudinally, including cross-reactivity and antibody-dependent enhancement (ADE) potential. <b>Results:</b> CD4⁺ T cells were essential for early viral clearance and the generation of robust, type-specific neutralizing antibodies. In their absence, animals exhibited early non-specific polyclonal B cell activation, delayed isotype switching, and an expanded repertoire of cross-reactive antibodies to DENV and Zika virus (ZIKV), with diminished neutralizing capacity. CD4-depleted macaques also showed increased ADE potential, particularly against ZIKV, and elevated anti-NS1 IgG titers that persisted one-year post-infection. <b>Conclusion:</b> CD4⁺ T cells play a critical role in orchestrating effective, durable, and type-specific antibody responses during primary DENV infection. Their absence leads to delayed antibody maturation, greater cross-reactivity, and higher ADE potential. These findings emphasize the need for DENV and ZIKV vaccines to include CD4⁺ T cell epitopes that promote high-quality, type-specific antibody responses and minimize ADE risk.