Epidermal powder immunization induces both cytotoxic T-lymphocyte and antibody responses to protein antigens of influenza and hepatitis B viruses

Cytotoxic T lymphocytes (CTL) play a vital role in host defense against vir al and intracellular bacterial infections. However, nonreplicating vaccines administered by intramuscular injection using a syringe and needle elicit predominantly humoral responses and not CTL responses. Here we report that epidermal powder immunization (EPI), a technology that delivers antigens on 1.5- to 2.5-mum gold particles to the epidermis using a needle-free powder delivery system, elicits CTL responses to nonreplicating antigens. Followi ng EPI, a majority of the antigen-coated gold particles were found in the v iable epidermis in the histological sections of the target skin. Further st udies using transmission electron microscopy revealed the intracellular loc alization of the gold particles. Many Langerhans cells (LCs) at the vaccina tion site contained antigen-coated particles, as revealed by two-color immu nofluorescence microscopy, and these cells were found in the draining lymph nodes 20 h later. Immune responses to several viral protein antigens after EPI were studied in mice. EPI with hepatitis B surface antigen (HBsAg) and a synthetic peptide of influenza virus nucleoprotein (NP peptide) elicited antigen-specific CTL responses as well as antibody responses. In an in vit ro cell depletion experiment, we demonstrated that the CTL activity against HBsAg elicited by EPI was attributed to CD8(+), not CD4(+), T cells. As co ntrols, needle injections of HBsAg or the NP peptide into deeper tissues el icited solely antibody, not CTL, responses. We further demonstrated that EP I with inactivated A/Aichi/68 (H3N2) or A/Sydney/97 (H3N2) influenza virus elicited complete protection against a mouse-adapted A/Aichi/68 virus. In s ummary, EPI directly delivers protein antigens to the cytosol of the LCs in the skin and elicits both cellular and antibody responses.