Sustained exposure of lymphoid tissues to vaccine antigens promotes humoral immunity， but traditional bolus immunizations lead to rapid antigen clearance. We describe a technology to tailor vaccine kinetics in a needle-free platform translatable to human immunization. Solid pyramidal microneedle (MN) arrays were fabricated with silk fibroin protein tips encapsulating a stabilized HIV envelope trimer immunogen and adjuvant， supported on a dissolving polymer base. Upon brief skin application， vaccine-loaded silk tips are implanted in the epidermis/upper dermis where they release vaccine over a time period determined by the crystallinity of the silk matrix. Following MN immunization in mice， Env trimer was released over 2 wk in the skin， correlating with increased germinal center (GC) B cell responses， a ～1，300-fold increase in serum IgG titers and a 16-fold increase in bone marrow (BM) plasma cells compared with bolus immunization. Thus， implantable MNs provide a practical means to substantially enhance humoral immunity to subunit vaccines.