Malignancy associated papillomaviruses and morphology of human bladder cancer.
Animal studies in rabbit and cattle have clearly demonstrated the contribution of host genetics, chemical carcinogens and immunosuppression to the conversion of papillomavirus induced benign regressing warts into malignant cancers. More significant is the role of vaccination both with whole tumour cell suspensions with whole virus and viral proteins, particularly L2 molecules, in causing progressing warts to regress. Early results in small scale studies of HPV16 E6/E7 vaccine in patients with cervical cancer have provided evidence that tumour regression can be induced in human papillomavirus induced tumours. These observations provided added impetus for more research to firm up the increasing, but still principally anecdotal, evidence that papillomaviruses may be involved in the pathogenesis of bladder cancer. Studies of carcinomas arising in cattle after BBV 4 infection show absence of fully infectious virus in the majority of tumours, though the tumours have persistent E7, E8 and LCR sequences. As this is all that is required for transformation, it may require in vitro molecular studies in human bladder cancer screening for such elements before final proof of involvement is confirmed. However, even before this is achieved, given the success in animal models of whole tumour cell vaccines, serious thought should be given to how to develop protocols for study of crude tumour cell vaccines in vivo. Such studies would need in vitro assays to seek evidence for specific antitumour immunity, focusing on studies of tumour infiltrating lymphocytes and their T cell receptor polymorphisms.