(526h) Oncofetal Antigen Peptide Nanoclusters for Cancer Vaccines

Oncofetal antigen (OFA) is a protein found on many cancer cell surfaces including myeloma, lymphoma, myeloid leukemia, and some solid tumor cells, yet it is expressed in much lower levels on normal cells. OFA has been shown to have multiple immunogenic epitopes. Similarly to how bacterial or viral vaccines are made, proteins unique to cancer cell surface markers can be used as antigens in cancer vaccines to enhance the immune system’s ability to kill cancer cells. A unique 9-mer peptide epitope on OFA, known as OFA 2, has been investigated in clinical trials as a vaccine along with soluble adjuvants. The goal in this work is to improve the delivery and immunogenicity of OFA 2 by packaging it as a peptide nanocluster. The nanoclusters developed in this work provide the conventional nanoparticle benefits to vaccines by increasing stability and retention in tissue as well as higher cellular uptake and adjuvant-like behavior. Nanoclusters, however, are made entirely of the peptide epitope and small amounts of crosslinker to keep the peptides in a stable structure. This characteristic eliminates the delivery of non-essential portions of a subunit vaccine, reducing the potential for off target or over-reactive immune responses. It also provides enhanced benefits of much more delivered antigen for every particle internalized.

To enable optimal particle fabrication from OFA 2, it was modified with the addition of one cysteine onto the C-terminus, making OFA 2C. Desolvation was used to make nanoclusters ~200 nm in diameter, consisting of OFA 2C crosslinked with a thiol crosslinker. Peptide concentration, solvent:desolvent pairings and volume ratio, crosslinker type and concentration were among the parameters optimized in nanocluster synthesis to achieve a target size to maximize dendritic cell antigen recognition and uptake as well as to minimize passive diffusion away from the injection site prior to uptake. A reversible thiol crosslinker was used to maintain the immunogenic epitope sequence after intracellular processing and breakdown of the nanocluster. OFA 2C nanoclusters demonstrated comparable dendritic cell (DC) uptake in vitro in comparison to OFA 2C peptide administered in soluble form. DC activation and surface presentation of internalized peptide nanoclusters, however, has shown to be enhanced compared to soluble peptide. In an in vivo mouse model, the nanoclusters were retained 2.7-fold more in an intradermal injection site (an area high in localized immune cell uptake and trafficking) than the injected soluble peptide. Ongoing work is assessing any benefits in nanocluster presentation and activation of T-cells by DCs compared to soluble peptides. The peptide nanocluster formation of immunogenic peptide OFA 2C holds potential to increase the efficacy of OFA cancer vaccines.