HSPPC-96: a personalised cancer vaccine

HSPPC-96 is a protein peptide complex consisting of a 96 kDa heat shock protein (Hsp), gp96, and an array of gp96-associated cellular peptides. Immunisation with HSPPC-96 induces T-cell specific immunity against these peptides; gp96 is not immunogenic per se. The non-covalent binding of gp96 to peptides is neither selective nor restricted to cell types. Thus, the collection of gp96-associated peptides represents the antigenic peptide pool of a cell; this is the basis of the peptide-specific immunogenicity elicited by HSPPC-96. Since the repertoire of antigenic peptides in the cell is different between normal and tumour cells and is also distinct among tumours of the same histology due to the randomness of tumour-specific mutations, a purified sample of HSPPC-96 can only effectively immunise against the tumour from which it originates. The immunisation effect is, therefore, specific to both the individual patient and the tumour type. This true custom-based vaccine has been shown to induce protective T-cell immunity against a variety of tumours in animal models. The major mechanism of action is thought to be the ability of HSPPC-96 to prime peptide-specific MHC class I-restricted CD8+ T-cells by interacting with antigen-presenting cells in a receptor-dependent manner. HSPPC-96 is now being widely tested against human malignancies for which effective therapies do not exist. The major challenges of the human studies are immunological monitoring and the determination of optimal dosing, scheduling and route of administration. HSPPC-96 has been well tolerated at all dose levels. Clinical applications are being addressed by numerous studies including an international, multi-centre, double-blind Phase III trial for the treatment of stage III renal cell carcinoma in the adjuvant setting.