Background Glioblastoma (GMB), advanced prostate cancer (PCa) and triple negative breast cancer (TNBC) are hard-to-treat cancers with 5-year survival rates of 5%, 12% and 30% respectively in their metastatic stage. With surgery, chemotherapy, and radiotherapy (and hormone therapy for PCa) being the only feasible treatment options, novel therapies are urgently required. Adjuvanted peptide vaccines based on tumour antigens hold promise in prophylactic and therapeutic settings, especially when there is residual disease following treatment. Research suggests that the cancer/testis antigens HAGE and NY-ESO-1 as well as the tumour associated antigen WT1 (antigens of interest) are good candidates for peptide vaccine development, being expressed at various levels in GBM, PCa and TNBC tissues. Additionally, the expression of these antigens can be upregulated by treatment with low-dose DNA methyltransferase inhibitors like decitabine (DAC), offering the possibility to maximise the detection and destruction of residual cancer cells by vaccine-induced T cells.

Materials and Methods A panel of GBM, PCa and TNBC cell lines was treated with 1μM, 5μM and 10μM DAC and tested for antigens of interest using qPCR and western blot, aiming to validate them as immunotherapeutic targets. Peptide sequences derived from these antigens, including a mutated NY-ESO-1-derived sequence, were selected for vaccine development using in silico prediction algorithms (SYFPEITHI and IEDB databases), combined with the novel adjuvant CAF09b and used for the immunisation of HHDII/DR1 and HHDII/DP4 mice. Following splenocyte extraction, peptides-derived vaccines were tested for immunogenicity using IFNγ ELISpot assays and killing of target cells was assessed using the same assay, co-culturing isolated CD3⁺ T cells with antigen-expressing cancer cells.

Results Antigen expression of TNBC cell lines as revealed by qPCR suggested that treatment with 5μM DAC induced optimal upregulation, with 10μM usually leading to a plateau. These observations were confirmed by western blotting. Splenocytes derived from CAF09b-adjuvanted NY-ESO-1/HAGE/WT1 vaccine-immunised mice showed strong IFNγresponses, and the isolated CD3⁺ T cells from these splenocytes could specifically recognise TNBC cells expressing all three antigens in a HLA-A2 restricted manner.

Conclusions We propose the use of mutated NY-ESO-1/HAGE/WT1-derived peptides in combination with CAF09b for the treatment of GBM, PCa and TNBC at a stage where no tumour cells can be detected to prevent or delay relapse in these malignancies.

Disclosure Information C. Puig Saenz: None. D. Christensen: A. Employment (full or part-time); Significant; Croda Pharmaceuticals. S.E.B. McArdle: None.