Langerin negative dendritic cells promote potent CD8⁺ T-cell priming by skin delivery of live adenovirus vaccine microneedle arrays

Stabilization of virus protein structure and nucleic acid integrity is challenging yet essential to preserve the transcriptional competence of live recombinant viral vaccine vectors in the absence of a cold chain. When coupled with needle-free skin delivery, such a platform would address an unmet need in global vaccine coverage against HIV and other global pathogens. Herein, we show that a simple dissolvable microneedle array (MA) delivery system preserves the immunogenicity of vaccines encoded by live recombinant human adenovirus type 5 (rAdHu5). Specifically, dried rAdHu5MAimmunizationinduced CD8⁺ T-cell expansion and multifunctional cytokine responses equipotent with conventional injectable routes of immunization. Intravital imagingdemonstratedMAcargodistributed both in the epidermis and dermis, with acquisition by CD11c⁺ dendritic cells (DCs) in the dermis. The MA immunizing properties were attributable to CD11c⁺ MHCIIhi CD8α^neg epithelial cell adhesion molecule (EpCAM^neg) CD11b⁺ langerin (Lang; CD207)^neg DCs, but neither Langerhans cells nor Lang⁺ DCswere required for CD8⁺ T-cell priming. This study demonstrates an important technical advance for viral vaccine vectors progressing to the clinic and provides insights into the mechanism of CD8⁺ T-cell priming by live rAdHu5 MAs.