Conclusion
We propose that citrullinated GRP78 is a candidate tumour antigen and vaccination against citrullinated GRP78 may provide a promising tumour therapy approach.
Methods
A citrullinated GRP78 specific antibody was used to assess citrullinated GRP78 expression in murine and human tumour cells by flow cytometry. Five peptides were selected and used to vaccinate HLA transgenic mice and immune responses were characterised by ex vivo cytokine ELISpot assay. T cell repertoire in humans was assessed through proliferation assays and cytokine ELISpot assay. Citrullinated peptide was identified in murine B16 melanoma by mass spectrometry and the peptide vaccine was assessed for tumour therapy in a mouse melanoma model.
Results
We show the identification CD4 T cell responses to one citrullinated GRP78 epitope that are restricted through HLA DP*0401 and HLA-DR*0101 alleles. This peptide is detected by mass spectrometry in B16 melanoma grown in vivo and citrulline specific CD4 responses to two peptides spanning this epitope mediate efficient therapy of established B16 melanoma tumours in HHDII/DP4 (p<0.0001) transgenic mouse model. Finally, we demonstrate the existence of a repertoire of responses to the citrullinated GRP78 peptide in healthy individuals (p=0.0023) with 13/17 (76%) individuals showing a response to this peptide.