Particle-based vaccination through direct targeting of antigen presenting cells

Particle-based delivery of antigen has great potential for generating improved vaccines. During the course of an immune response, a pathogen may trigger multiple pattern- recognition receptors, instilling a strong proinflammatory immune response. Highly successful vaccines, such yellow fever vaccine and Dryvax® (smallpox), also induce immune responses by utilizing multiple pathogen-sensing signaling pathways, yielding long-lasting B and T cell responses. Subunit vaccines generally require an external adjuvant to boost immune responses; however, recent data has shown that targeting multiple immune activation pathways generates a more potent immune response, similar to native infection or immunization with live vaccines (Kasturi et al., 2011; Ahonen et al., 2004, 2008). To determine the effects of presenting targeting and/or activating moieties in a multivalent form, we generated two different particle -based vaccines. The first, an antigen-loaded, pH- sensitive hydrogel microparticle, was found to be taken up and presented by bone marrow-derived dendritic cells (BMDCs) in vitro and targeted to dendritic cells (DCs) and monocytes in vivo. Addition of targeting antibodies to the particle surface did not influence its uptake. DCs also upregulated activation markers when treated with microparticles, even when no agonistic anti-CD40 was conjugated to the microparticles. Furthermore, these particles induced increased percentages of interferon- [gamma]-producing CD8 T cells in response to challenge with a pathogen expressing the same antigen, in both an accelerated vaccination strategy using pre-loaded BMDCs and a traditional mouse immunization setting. The second particle, a luminescent porous silicon nanoparticle, displayed the same targeting and/or activating antibodies. This particle used antigen that was encoded in the 3' end of the targeting antibody instead of encapsulating it in the particle. Nanoparticles displaying agonistic anti-CD40 (with no antigen), produced a multivalent effect in B cells in vitro, in which the stimulatory effects of the CD40 nanoparticle were observed at 30-40-fold lower dose of antibody versus free anti-CD40. In vitro and in vivo, nanoparticles displaying targeting antibodies induced CD8 T cell proliferation better than those displaying control antibodies; however, this effect could not be consistently observed long-term in vivo, even with both targeting antibody and anti-CD40. In fact antigen-specific cells were most often deleted at memory time point