The invention relates to a HLA-B27 Fc open conformer or a HLA-B27 Fc fusion protein for use in the treatment or prevention of cancer. The Fc open conformer comprises or consists of a first and a second monomer, and each monomer comprises a HLA-B27 chain. The Fc fusion protein further comprises a protein stabilizing polypeptide sequence and optionally an amino acid linker. Further aspects of the invention provide combination medicaments comprising the HLA-B27 Fc open conformer and immune checkpoint inhibitors.