Tumour vaccines

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Hepatitis B virus (HBV) vaccine is a widely used, very effective vaccine against hepatocellular carcinoma, while studies are in progress to develop vaccines against Epstein-Barr virus, which is closely linked to the development of:

♦ Burkitt's lymphoma

♦ Nasopharyngeal carcinoma

♦ Non-Hodgkin's lymphomas

Other obvious candidates for development of an anti-tumour vaccine are the human papilloma virus (HPV) and the human retrovirus, HTLV, which are causative agents for several human malignancies.

While the development of a vaccine is obvious in a virally-induced tumour, in non-virally-induced tumours, the concept of a vaccine is more complicated. In this case, tumour cells or tumour cell extracts are used as cancer vaccines intending to enhance a humoral or cellmediated immune response to relevant tumour antigens, rather than to induce prophylactic immunity. The antibodies produced may kill the tumour cells by complement fixation or antibody-dependent cellular cytotoxicity, while the activation of cytotoxic T cells that recognize antigens on the tumour cell surface may induce specific cytolysis. This approach was expected to reduce tumour-induced immuno-suppression and selectively augment long-lasting humoral and cellular anti-tumour immunity but, in general, it seems to have only minimal clinical significance.

More promising is the vaccination with anti-idiotype antibodies, directed against determinants expressed on the variable regions of anti-tumour antibodies. However, this strategy is limited by the fact that anti-idiotypic antibodies have to be produced individually and are thus expensive and labour-intensive.

Several vaccines for melanoma, colorectal, breast, prostate, and lung cancers are currently under clinical evaluation. Preliminary data support the concept that active immunization will be effective to patients with high-risk recurrent disease, after surgical removal of the tumour, when the tumour burden is small. Unfortunately, most of the clinical trials have been in patients with advanced, extensive disease, refractory to conventional therapies and probably already immunosuppressed.

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