Improving the immunogenicity of HIV-1 DNA vaccines

Abstract: Nearly 30 years have passed since the start of the global HIV epidemic and we are still unable to control the spread of the virus. HIV predominately infects cells crucial for the function of the immune system, integrates into the host genome and demonstrates a huge genetic variability, and the use of therapeutic antiretroviral drugs can restrain but not clear the infection. Therefore a protective vaccine is considered the best approach to counteract HIV. The failure of HIV vaccine candidates based on classical vaccine strategies have paved the way for novel vaccine modalities, such as genetic vaccines. These vaccines have induced broad and robust immune responses in animals but need to be optimized to ultimately induce protection against HIV infection. Furthermore, no definite correlates of protection against HIV infection are yet identified and this severely complicates the vaccine development. Nevertheless, the licensure of several DNA vaccines for veterinary use and the induction of protection against SIV infection/disease in non‐human primate models raise hope for the possibility to induce protection against HIV‐1/AIDS by DNA vaccination also in humans. This thesis describes both the effect of optimizing the gene insert and the use of adjuvants to augment the immune responses after immunization with HIV‐1 plasmids. A HIV‐1 protease gene was genetically optimized by changing the amino acid composition. By altering the enzymatic active site, rendering the protein inactive, it was possible to greatly increase the in vitro protein expression and significantly increase the immunogenicity of the gene in various mouse strains, including mice transgenic for the human HLA‐A0201 molecule. We thus identified a rather simple strategy to drastically increase the immunogenicity of HIV‐1 protease and induce strong immune responses against wild type protease as well as against protease carrying drug resistance mutations. The optimized protease construct will be integrated into the clinically evaluated multigene vaccine, HIVIS, and initial results have shown that the immunogenicity of the protease construct, as well as the immunogenicity of the other constructs in the vaccine, is not negatively affected by the addition of the new plasmid. Also, by administering our multigene vaccine formulated in a lipid‐based adjuvant intranasally to young mice we could increase both the systemic cellular and humoral immune responses. In addition, antibody responses could be detected at mucosal sites distant from the intranasal mucosa, demonstrating the ability of DNA vaccines to induce broad immune responses in different compartments of the body. The induction of these mucosal anti‐HIV antibodies presents a possible means to prevent infection at the mucosal surface where the majority of HIV transmissions take place. These and other ways to augment the induction of strong immune responses by DNA vaccination will hopefully provide clues on how to construct and deliver the next generation of potent DNA vaccines against HIV as well as against other infectious diseases and cancers.