Immune Engineering Via Differential Antigen Carriers and Co-Stimulatory Molecules

There is an increasing clinical need for vaccines capable of enhancing antigen-specific immune responses and treatments that can induce immunological tolerance toward a single antigen. Here we explore two platforms to enhance either immunization or tolerization depending upon the secondary signals involved. First, a poly(ethylene glycol)-bl-poly(propylene sulfide) (PEG-bl-PPS)-based micelle platform capable of conjugating antigen to its surface was developed. Biodistribution studies showed that these micelles (MC) traffic to lymph nodes where they preferentially interact with antigen presenting cells (APC) for over 24 hr. When ovalbumin (Ova)-conjugated micelles (MC-Ova) were delivered intradermally with the adjuvant CpG, they enhanced cytotoxic T cell responses against Ova as well as anti-Ova IgG1 production compared to free Ova with CpG. To change the signals from the MCs to encourage tolerization, hydrophobic corticosteroids capable of preventing APC maturation were incorporated into the PPS core and were shown to be released over the course of 2 days. These vehicles were able to prevent dendritic cell (DC) activation in response to adjuvant both in vitro and in vivo. Ova-conjugated drug-loaded MCs were able to prevent antigen-specific T cell activation in vitro and in vivo as well, but caused an anti-Ova humoral response that was enhanced upon subsequent Ova challenge. Thus, PEG-bl-PPS micelles are valuable tools for enhancing immunization but not tolerization toward exogenous antigens. Second, erythrocytes were labeled in situ for use as apoptotic cell carriers. To enhance immunogenicity, the necrotic signal calreticulin (CRT) was decorated with the erythrocyte- binding peptide ERY (ERY-CRT) and delivered intravenously with ERY-Ova. When combined with chloroquine, this signaling caused production of anti-Ova IgG1 to a level similar to that seen with intradermal MC-Ova + CpG, but showed no cytotoxic T cell response. Because apoptotic cells can be tolerogenic, the Ter119 erythrocyte-binding single- chain antibody fragment (scFv) was used in a fusion with Ova peptides to determine if this technique could delete Ova-recognizing T cells within an immunized repertoire. After immunization with Ova + lipopolysaccharide (LPS), these constructs deleted CD4+ and CD8+ T cell clones specific for Ova without causing adverse reactions from anti-Ova antibodies in circulation. Erythrocytes are therefore encouraging protein-delivery vehicles for induction of both tolerance and humoral immunity.