“…The last two viruses are of particular significance to our study since they have been reported to occur in both normal and malignant tissue of the oral cavity (Maitland et al, 1987;1989, Yeudall & Campo, 1991. In addition, transfection of these viruses in vitro into human keratinocytes from both the epidermis (Pirisi et al, 1987;Kaur & McDougall, 1988) and the oral cavity (Park et al, 1991) leads to their immortalisation, and both the E6 and E7 proteins are important for this process (Hawley-Nelson et al, 1989;Munger et al, 1989).…”