Early investigations into the immune surveillance of chemically-induced sarcomas 
led to two important concepts in tumour immunobiology: one, tumour rejection can 
be elicited by immune recognition of tumour antigens; and two, tumours express 
unique sets of antigens, which are known as tumour-specific antigens. The 
pioneering studies of Srivastava and colleagues led to the proposal that 
heat-shock proteins (HSPs) function as ubiquitous tumour-specific antigens, with 
the specificity residing in a population of bound peptides that identify the 
tissue of origin of the HSP. However, recent findings, including new data on the 
cell biology of peptide generation and trafficking, have called into question 
the specificity of tumour rejection that is induced by HSPs.