George N. Pavlakis, M.D., Ph.D.

Senior Investigator

Vaccine Branch

NCI/CCR

Building 535, Room 210
Frederick, MD 21702-1201

301-846-1474

george.pavlakis@nih.gov

Research Topics

New Vaccine Approaches, DNA Vaccine Optimization

Our overall goal is to improve DNA and nucleic acid vaccination  technologies so that they becomes rapid, safe, and effective vaccine platforms for AIDS, cancer and other indications. DNA vaccination has distinct advantages, including that it provides a broad priming of the immune system that may result in a robust and effective immune response. The strong and effective cellular immunity achieved by optimized DNA is an important consideration for the expanding field of cancer vaccines.

Rapid advances in the efficiency of DNA vaccination make this approach very promising for the development of safe and effective vaccines with distinct advantages for many indications including AIDS and cancer. Yet, further research and development is needed for the DNA vaccine field to fulfill this promise. Our goal is to further improve this technology and contribute to its translation to the clinic. We use molecular biology and animal models to test new vectors, new technologies and new combinations for DNA vaccination. We have successfully applied the increased understanding in basic knowledge of gene expression regulation to the improvement of DNA vaccines. We have shown in the past that DNA vaccine expression in the tissues is a major limiting step for meaningful immunogenicity and we developed general methods for efficient plasmid expression. The methods (RNA or codon optimization to increase mRNA stability transport and expression) have applications in both DNA and viral vaccine vectors and also gene therapy protocols. These patented technologies have contributed to overcoming a critical barrier for clinical application of DNA vaccines. An additional advancement in DNA vaccines is the development of more efficient delivery methods such as in vivo DNA electroporation. These advancements form the basis for the accelerated development of DNA vaccines for AIDS, other infectious diseases and also cancer. We are presently optimizing the formulations and delivery of DNA vaccines using molecular adjuvants, liposomes, nanoparticle formulations and electroporation. A novel potential application for cancer is DNA-delivered immunotherapies, based on the development of efficient expression vectors for cytokines and other immunomodulators. We are testing the hypothesis that DNA-delivered immunotherapies are beneficial in cancer models.

We have used different DNA vaccine delivery procedures to discover optimal methods of DNA vaccination. This work has led to the conclusion that both the form and the method of delivery of specific antigens affect strongly the produced immune response. We have tested different adjuvants for their compatibility with DNA vaccine protocols and have developed shortened protocols able to produce strong humoral immune response. We have compared the humoral and cellular immune responses obtained after DNA vaccination to other vaccine modalities. These studies are important in understanding strengths and weaknesses of different vectors and protocols and provide guidance for further development of improved vaccine protocols.

A new type of DNA vaccine comprising Conserved Elements of HIV Gag protein is currently developed for a clinical trial on the basis of mouse and macaque immunogenicity. Inclusion of a Conserved Element immunogen provides a novel and effective strategy to broaden responses against highly diverse pathogens by avoiding decoy epitopes, while focusing responses to critical viral elements for which few escape pathways exist.

Cytokines and Immunomodulatory Molecules in Immunotherapy and Vaccines
The overall goal of this project is to study gene expression and function of selected cytokines and other immunomodulatory molecules relevant for cancer and AIDS immunotherapy. This goal is important for the development of more efficient interventions to alleviate, delay or prevent disease through immunotherapy, gene therapy and DNA vaccine technologies. Such novel interventions require a more thorough understanding of all aspects of cellular processes. One goal is to develop efficient expression vectors by identifying key elements and factors associated with the pathways of posttranscriptional control of gene expression used by many genes, including cytokines. The validity of this approach is demonstrated by the development of efficient vectors for the expression of important cytokines, especially IL-15 and IL-12..

In the case of IL-15, the understanding of the cellular mechanisms controlling expression has led to methods of preparation and purification of the heterodimeric form of this cytokine and the demonstration that the heterodimer is the bioactive form circulating in human blood. This has now being recognized as an important development in our understanding of IL-15 function. Pharmacokinetic studies in animals show that the heterodimeric IL-15 has favorable properties for clinical applications.

Rapid progress in the IL-15 clinical development project has led to the production of a GMP lot of heterodimeric IL-15, which we named hetIL-15 for clinical trials projected to start in 2015. Our hypothesis is that IL-15 will activate Natural Killer cells and tumor infiltrating T cells. As a result, hetIL-15 may find important applications in cancer immunotherapy.

This project complements our efforts to improve DNA vaccines (see above) and DNA-delivered immunotherapies. An additional goal of this project is to explore function of key cytokine genes in order to establish their role in normal homeostasis and disease processes.

Our collaborators include Genoveffa Franchini, Marjorie Robert-Guroff, David J. Venzon, Jay A. Berzofsky, Thomas Waldmann, Steven A. Rosenberg (NCI); Barbara K. Felber (NCI-Frederick); Jeffrey D. Lifson, Elena N. Chertova (Leidos Biomedical Research, Inc./FNLCR); James I. Mullins (Univ. of Wash.); Georgia D. Tomaras, David C. Montefiori (Duke Human Vaccine Institute); Timothy Fouts (Profectus BioSciences); Niranjan Y. Sardesai (Inovio); George K. Lewis (Institute of Human Virology/Univ. of MD); and David B. Weiner (Univ. of Penn.).

Biography

Dr. Pavlakis received his M.D. from the University of Athens, Greece, and his Ph.D. from Syracuse University. He has been associated with the National Cancer Institute since 1980 and is currently Chief of the Human Retrovirus Section. He has directed both basic research and clinical development projects based on his pioneering research achievements. Dr. Pavlakis has extensive research and development experience in molecular biology, virology, and immunology. He is credited with the first production of mature human hormones in mammalian cells by recombinant DNA technologies. This methodology is still in commercial production (human Growth Hormone). He continues this work by the development of new production methods and clinical application of heterodimeric IL-15 (hetIL-15), a cytokine essential for NK and T lymphocyte development and function.

Dr. Pavlakis co-developed codon/RNA optimization methods that have found wide applications in biotechnology, gene therapy protocols and DNA vaccines. He developed DNA vaccines for HIV and showed they provide strong and long lasting immunity. He developed strong fluorescent GFP mutants that are in wide use in biology. He studied the molecular biology, genetic organization and expression strategy of HIV and discovered important functions of its regulatory factors Tat and Rev. He described the first transcriptional activator on oncoretroviruses, the Tax protein of HTLV-I and the first posttranscriptional regulatory factor controlling mRNA export from the nucleus, the Rev protein of HIV-1. His studies have provided new insights on the biology of several viruses, and have aided the development of diagnostic and therapeutic procedures. His work has also led to the development of innovative biotechnology drugs and gene therapy procedures.

Dr. Pavlakis is member of several professional societies, including the American Society for Clinical Investigation and the American Association of Physicians. He is a highly cited researcher, has authored more than 200 publications and is inventor of more than 50 US and International patents.

Selected Publications

  1. Ng SSM, Nagy BA, Jensen SM, Hu X, Alicea C, Fox BA, Felber BK, Bergamaschi C, Pavlakis GN. Heterodimeric IL15 Treatment Enhances Tumor Infiltration, Persistence, and Effector Functions of Adoptively Transferred Tumor-specific T Cells in the Absence of Lymphodepletion. Clin Cancer Res. 2017;23(11):2817-2830.

  2. Thaysen-Andersen M, Chertova E, Bergamaschi C, Moh ES, Chertov O, Roser J, Sowder R, Bear J, Lifson J, Packer NH, Felber BK, Pavlakis GN. Recombinant human heterodimeric IL-15 complex displays extensive and reproducible N- and O-linked glycosylation. Glycoconj J. 2016;33(3):417-33.

  3. Watson DC, Bayik D, Srivatsan A, Bergamaschi C, Valentin A, Niu G, Bear J, Monninger M, Sun M, Morales-Kastresana A, Jones JC, Felber BK, Chen X, Gursel I, Pavlakis GN. Efficient production and enhanced tumor delivery of engineered extracellular vesicles. Biomaterials. 2016;105:195-205.

  4. Hu X, Valentin A, Dayton F, Kulkarni V, Alicea C, Rosati M, Chowdhury B, Gautam R, Broderick KE, Sardesai NY, Martin MA, Mullins JI, Pavlakis GN, Felber BK. DNA Prime-Boost Vaccine Regimen To Increase Breadth, Magnitude, and Cytotoxicity of the Cellular Immune Responses to Subdominant Gag Epitopes of Simian Immunodeficiency Virus and HIV. J Immunol. 2016;197(10):3999-4013.

  5. Li J, Valentin A, Ng S, Beach RK, Alicea C, Bergamaschi C, Felber BK, Pavlakis GN. Differential effects of IL-15 on the generation, maintenance and cytotoxic potential of adaptive cellular responses induced by DNA vaccination. Vaccine. 2015;33(9):1188-96.


This page was last updated on June 15th, 2017