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Principal Investigator: George N. Pavlakis
Organization: DIVISION OF BASIC SCIENCES - NCI
Fiscal Year: 2022
Award: $884,441
Funding agency: National Cancer Institute
An important goal of this project continues to be the generation and testing of maximally efficient expression vectors for specific antigens. Our hypothesis is that the DNA vaccine dose is suboptimal for many human applications; therefore, increased efficiency is necessary for practical human DNA vaccines. We have generated a set of optimized expression vectors for HIV and SIV. HIV vectors are developed for eventual human clinical trials. These vectors are studied in macaques for immunogenicity and ability to protect against challenge with Simian/Human Immunodeficiency Virus hybrid viruses (SHIV). Several of our vectors have been used in clinical trials sponsored by our previous CRADA collaborator (Wyeth) and more recently by us through the support of NIAID. In parallel, SIV expression vectors are developed and studied in the most faithful model system for human AIDS, i.e., challenge of Rhesus macaques by SIV, a virus closely related to HIV, which causes very similar pathology to human AIDS. Our results have shown that optimized DNA expression vectors in the absence of any other form of vaccine boosting are able to protect rhesus macaques from high viremia after challenge with a highly pathogenic SIVmac251 challenge. In addition, we have developed powerful new DNA and protein co-immunization protocols that increase the magnitude, rapidity and longevity of immune responses. These vaccines were shown to protect macaques from infection in several studies. In this reporting period, we have shown 67% per challenge protection of macaques from SHIV pathogenic challenge using an optimized DNA and protein vaccination. These results suggest novel avenues for clinical development, especially to advance the concept of co-immunization with DNA and protein at the same site and time. To further improve vaccine efficiency, we study the intrinsic properties of the different candidate antigens. We take advantage of the ability to manipulate the form of expressed antigen by recombinant DNA technology. We have shown that modulating the form, stability and cellular fate of the DNA-produced antigens has profound effects on their immunogenicity and the type of response generated. We perform comparative studies to develop optimal forms of several antigens. Results in rhesus macaques verified that the form of expressed antigen affects the type and magnitude of immune response. We study several different antigen forms to achieve optimal immune response and to address the variability of HIV strains circulating worldwide. We compare the immune response generated by either mixes of native antigens, mosaics, centralized and consensus candidates, and also antigens containing only conserved elements of HIV proteins. Such comparisons may lead to further optimization of a protective immune response. We have recently shown, in collaboration with the Human Retrovirus Pathogenesis Section (Dr. Barbara Felber), that vaccination with conserved elements vaccine constructs has the ability to alter the hierarchy of immune response and to direct it towards conserved elements, which are found in all HIV clades. On the basis of these data, we have completed a clinical trial (HVTN 119) to test the ability of Conserved Element vectors to provide broader immune response in humans. The methodology and vectors used for DNA vaccination of macaques have shown that we produce a strong, broad, and long-lasting immunity, which is able to contain virus replication and prevent disease development. We also showed that DNA in combination with an adjuvanted protein delays or prevents infection after repeated low dose virus challenge. This DNA and protein combination vaccine does not use live recombinant vectors (usually employed by other AIDS vaccine programs) and may provide practical advantages. DNA vaccination is emerging as a strong and most effective vaccination procedure for the development of cellular immunity in humans, based on clinical trials using the same methods and vectors we co-developed for macaques. These results strongly suggest that DNA vaccination will have many practical clinical applications. In addition to prophylactic vaccination against AIDS, the same methodologies were used in therapeutic vaccination protocols. A strong boost of cellular immune responses and subsequent control of viremia was observed in therapeutically immunized macaques, suggesting that therapeutic vaccination may contribute to long-term virus control. These results have also implications for the development of methods to apply DNA vaccine methodology to therapeutic cancer vaccines. We wish to combine therapeutic vaccination with additional methods to boost immune response and specific cell killing by cytotoxic cells. We therefore have used hetIL-15 to further boost cytotoxic cell responses based on our completion of studies demonstrating the safety of hetIL-15 in infected macaques. We have shown that inclusion of hetIL-15 in therapeutic vaccination results in high levels of cytotoxic cells. We also developed vaccine formulations that greatly enhance Antibody Dependent Cellular Cytotoxicity (ADCC) as an additional mechanism to eliminate virus-infected cells. We apply these new tools to identify optimal therapeutic protocols able to suppress or eliminate virus in infected subjects. We have further expanded the CE vaccine regimen in collaboration with CureVac, Inc. as an mRNA/lipid nanoparticle (LNP) formulation in the macaque model (Valentin, Frontiers in Immunol. 2022). The mRNA/LNP formulation induced robust, durable antibody responses but low adaptive T-cell responses, a feature also shared with the current COVID-19 mRNA vaccine. On the other hand, the mRNA/LNP vaccine was able to strongly boost pre-existing cellular response suggesting that it could be useful in heterologous prime/boost modality and in immune therapeutic interventions against HIV infection or other chronic human diseases. Our studies have provided useful information about different nucleic acid vaccine platforms and guide further clinical development. We have therefore provided on of the first comparisons of the same immunogen delivered as DNA or as mRNA vaccine under state-of-the-art conditions. These provides a stronger cellular immune response compared to RNA. It is becoming a rather general conclusion that the current formulations of RNA vaccines in humans provide good humoral immunity, whereas the cellular immunity is rather low. We therefore asked whether the combination of DNA and RNA could alter the immune response. Our published results show that a DNA prime is excellent in helping a subsequent RNA boost to cause a strong cellular immune response. This specific heterologous prime/boost modality may provide methods for further optimization of vaccine effectiveness. It could be useful as a prophylactic vaccine and in immune therapeutic interventions against HIV infection or other human diseases.
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