Purpose: We developed a complex of tumor antigen protein with a novel nanoparticle antigen delivery system of cholesteryl pullulan (CHP). To target HER2 antigen, we prepared truncated HER2 protein 1-146 (146HER2) complexed with CHP, the CHP-HER2 vaccine. We designed a clinical study to assess the safety of the vaccine and HER2-specific T-cell immune responses measured by the newly developed enzyme-linked immunospot assay with mRNA-transduced phytohemagglutinin-stimulated CD4⁺ T cells in HLA-A2402-positive patients with therapy-refractory HER2-expressing cancers.

Experimental Design: Nine patients with various types of solid tumors were enrolled. Each patient was s.c. vaccinated biweekly with 300 μg of CHP-HER2 vaccine for three times followed by booster doses. HER2-specific T-cell responses were evaluated by enzyme-linked immunospot assay by targeting autologous phytohemagglutinin-stimulated CD4⁺ T cells transduced with 146HER2-encoding mRNA to cover both identified peptides and unknown epitopes for MHC class I and class II that might exist in the sequence of the vaccine protein.

Results: CHP-HER2 vaccine was well tolerated; the only adverse effect was grade 1 transient skin reaction at the sites of vaccination. HER2-specific CD8⁺ and/or CD4⁺ T-cell immune responses were detected in five patients who received four to eight vaccinations, among whom both T-cell responses were detected in these patients. In four patients with CD8⁺ T-cell responses, two patients reacted to previously identified HER2_63-71 peptide and the other two reacted only to 146HER2 mRNA-transduced cells.

Conclusions: CHP-HER2 vaccine was safe and induced HER2-specific CD8⁺ and/or CD4⁺ T-cell immune responses.