Nanofiber Length Shapes Vaccine Immunity: Mechanistic Insights from M13 Bacteriophage

Self-assembled nanofibers have emerged as attractive vaccine platforms, but their inherent polydispersity makes controlled-length studies challenging. Here, we use the M13 bacteriophage, a biological nanofiber with near-monodisperse length, as a model system to study the effect of nanofiber length on immune activation. Our results demonstrated that short (100 nm) and long (800 nm) nanofibers displaying similar antigen density elicited comparable CD8⁺ T cell responses, despite short nanofibers exhibiting higher antigen-presenting cell (APC) uptake and lymph node drainage. Mechanistic studies revealed that long nanofibers induced higher pro-inflammatory cytokine production and APC activation, which could compensate for the lower APC uptake and lymph node drainage. These findings establish nanofiber length as an independent design parameter that shapes immune outcomes through mechanisms beyond simple biodistribution, offering insights for engineering nanovaccines with optimized immunogenicity.