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 were used in clinical trials sponsored by our CRADA collaborator (Wyeth). 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 show 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. 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 that vaccination with conserved elements vaccine constructs have 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 proposed a clinical trial 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 very strong, broad and long-lasting immunity, which is able to contain virus replication and prevent disease development. More recently, we showed that DNA in combination with an adjuvanted protein is able to delay or prevent infection after repeated low dose virus challenge. DNA vaccination is emerging as the strongest and most effective vaccination procedure 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. We have used our understanding of gene regulation to develop non-pathogenic strains of SIV, which are maintained in macaques for more than 10 years, yet they do not cause any disease. These animals develop a strong protective immune response and are able to resist high viremia and disease development even after challenge with wild-type SIV. We showed that these animals develop neutralizing antibodies against difficult-to-neutralize SIVmac239, and that CD8 cells contribute to the protective effect. We have also shown that these animals develop high levels of cytotoxic CD4 cells, which contribute to viral control. This macaque model is important for the further understanding of the pathogenic mechanisms leading to AIDS, the virus interactions in different tissues and the components of the immune system contributing to protection from disease development. 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 macaque studies, 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.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Investigator-Initiated Intramural Research Projects (ZIA)
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National Cancer Institute Division of Basic Sciences
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Kulkarni, Viraj; Valentin, Antonio; Rosati, Margherita et al. (2014) Altered response hierarchy and increased T-cell breadth upon HIV-1 conserved element DNA vaccination in macaques. PLoS One 9:e86254
Kulkarni, Viraj; Rosati, Margherita; Jalah, Rashmi et al. (2014) DNA vaccination by intradermal electroporation induces long-lasting immune responses in rhesus macaques. J Med Primatol 43:329-40
Jalah, Rashmi; Kulkarni, Viraj; Patel, Vainav et al. (2014) DNA and protein co-immunization improves the magnitude and longevity of humoral immune responses in macaques. PLoS One 9:e91550
Rosati, Margherita; Bergamaschi, Cristina; Valentin, Antonio et al. (2009) DNA vaccination in rhesus macaques induces potent immune responses and decreases acute and chronic viremia after SIVmac251 challenge. Proc Natl Acad Sci U S A 106:15831-6
Valentin, Antonio; Chikhlikar, Priya; Patel, Vainav et al. (2009) Comparison of DNA vaccines producing HIV-1 Gag and LAMP/Gag chimera in rhesus macaques reveals antigen-specific T-cell responses with distinct phenotypes. Vaccine 27:4840-9
Halwani, Rabih; Boyer, Jean D; Yassine-Diab, Bader et al. (2008) Therapeutic vaccination with simian immunodeficiency virus (SIV)-DNA + IL-12 or IL-15 induces distinct CD8 memory subsets in SIV-infected macaques. J Immunol 180:7969-79
Vaccari, M; Boasso, A; Ma, Z-M et al. (2008) CD4+ T-cell loss and delayed expression of modulators of immune responses at mucosal sites of vaccinated macaques following SIV(mac251) infection. Mucosal Immunol 1:497-507
Xu, Rong; Megati, Shakuntala; Roopchand, Vidia et al. (2008) Comparative ability of various plasmid-based cytokines and chemokines to adjuvant the activity of HIV plasmid DNA vaccines. Vaccine 26:4819-29
Rosati, Margherita; Valentin, Antonio; Jalah, Rashmi et al. (2008) Increased immune responses in rhesus macaques by DNA vaccination combined with electroporation. Vaccine 26:5223-9