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High-risk mucosal human papillomaviruses (HPVs) are major aetiological agents for the development of cervical cancer. Thus, the current goal of cervical cancer treatment is to develop vaccines against HPV s. Such vaccines would either prevent cervical cancer by eliminating HPV infection or be useful for treating established lesions by the destruction of cells displaying HPV proteins. The aim of this thesis was to characterise immune responses to the E5 protein of HPV -16, one of several antigens with possible use in vaccination. To determine whether immune responses to HPV -16 E5 existed and whether they could be correlated with disease severity or with the presence of HPV -16 DNA, both cell mediated (Chapter Two) and humoral (Chapter Three) immunity was investigated in women with and without cervical disease. Cellular responses in a minority of women were inversely correlated with disease severity. However, E5 specific antibodies were negatively correlated with the absence of HPV -16 DNA. Thus, although some immune responses were evident, these were generally limited to a small number of subjects and were not associated with the detection of HPV-16 E5 mRNA or DNA sequence variants. Due to the immune responses in women, E5 was further investigated to determine if the absence of HPV -16 E5 specific immune responses was due to the poor antigenicity of HPV -16. Mice were immunised with synthetic peptides corresponding to full length HPV -16 E5 (Chapter Four). As with the human data, cellular responses and weak antibody responses were detected in mice. Some mice also exhibited cytotoxic T -lymphocyte responses and when E5/major histocompatibility class I (MHC-I) interactions were investigated, a number of peptides showed a high percentage of binding. The E5/MHC-I interactions were further investigated (Chapter Five). The surface expression of MHC-I on cells containing HPV-16 or -18 DNA was found to be lower than on HPV DNA negative cell lines even after stimulation with interferon-gamma. Stimulation with E5 synthetic peptides increased expression of cell surface MHC-I molecules on cell lines negative for HPV DNA. Furthermore, the presence of the E5 gene reduced the expression of the ovalbumin gene in normal human keratinocytes. In conclusion, the data contained within this thesis indicate that HPV-16 E5 CMI is inversely correlated with disease status. It is possible to induce cell mediated responses to HPV -16 E5 and low-titre antibody responses. The presence of HPV16 E5 DNA may impair normal cellular function.