Adenovirus-based vaccines transduce and activate human Langerhans cells

Langerhans cells (LCs) are specialized antigen-presenting cells (APCs) located in the epidermis and mucosal tissues and play a critical role in host immune surveillance. The role of LCs in antiviral responses is well established, but their involvement in vaccine-induced immunity, particularly with human adenovirus (HAdV) vectors, remains poorly understood. Here, we investigated how human LCs respond to HAdV vectors commonly used in vaccine development. We used CD34+ hematopoietic stem cells differentiated into LCs (CD34-LCs) to evaluate their ability to internalize replication-defective HAdV types C5, D26, and B35 vectors. CD34-LCs took up all three vectors, which induced an antiviral and pro-inflammatory cytokine response and morphological changes indicative of activation. To address the role of LCs in a more physiologically relevant setting, we injected human skin explants with the HAdV vectors. Epidermal LCs were recruited to the injection site and took up the vectors. Moreover, we show that the presence of lactoferrin (Lf), an antimicrobial protein, enhances HAdV uptake. Overall, our findings highlight a key role for LCs in the initiation of immune responses to HAdV-based vaccines. This work lays a foundation for strategies aiming to enhance vaccine efficacy by modulating LC activation and targeting. IMPORTANCEHAdV vectors are widely used in vaccine development, but the role of LCs, the epidermal immune sentinels, remains poorly defined. Here, we show using in vitro and ex vivo human systems that LCs efficiently detect, internalize and express transgenes delivered by three HAdV species. Because LCs link innate and adaptive immunity, the direct and indirect uptake of HAdVs may contribute to vaccine efficacy.