The Immune Properties of Natural and Synthetic DNA
Wednesday, November 12, 2014
12:30 p.m.-1:30 p.m.
FDA-White Oak Bldg. 2 Room 2031
301 405 0285
David S. Pisetsky, MD, Ph.D.
Professor of Medicine and Immunology, Duke University Medical Center
Dr. Pisetsky received his BA from Harvard College magna cum laude in 1967 and his Ph.D. and M.D. degrees from the Albert Einstein College of Medicine in 1972 and 1973. He was then an intern and resident in Internal Medicine at the Yale-New Haven Hospital from 1973-1975. From 1975-1978, he was a clinical associate at the National Cancer Institute, studying the immune response to protein antigens. He joined the faculty of the Duke University Medical Center in 1978 as Chief of Rheumatology at the Durham VA Hospital where he has remained since. He served as Chief of Rheumatology at Duke from 1996-2007.
Dr. Pisetsky has conducted basic and translational research on the pathogenesis of systemic lupus erythematosus (SLE), focusing on the generation of antinuclear antibodies and the immunological properties of nuclear macromolecules. His studies were among the first to establish the antigenic and mitogenic activity of bacterial DNA, the antigenicity of oligonucleotides and the ability of synthetic oligonucleotides to modulate immune responses. More recently, he has investigated the release of DNA and HMGB1, a prototype alarmin, during cell death. He is also studying the immunological properties of cellular microparticles and their role in immune complex formation in SLE. Other studies relate to the immunological properties of synthetic oligonucleotides.
Dr. Pisetsky has had grant funding from the NIH, Veterans Administration and various foundations. He has published over 350 articles and chapters and has edited several textbooks and volumes. From 2000-2005, he served as Editor of Arthritis and Rheumatism and was the first Physician Editor of The Rheumatologist from 2006-2011. He is currently on the editorial board of Annals of Rheumatic Disease, International Journal of Rheumatic Diseases and Arthritis Research and Therapy. He continues to see patients at the Durham VA Hospital.
DNA is a large polymeric macromolecule whose immunological properties depend on structural features that include sequence, base methylation, strandedness and backbone modification. These features affect immunogenicity (including immune cell activation) as well as antigenicity. Thus, while mammalian DNA is unable to stimulate B cells, macrophages or dendritic cells, bacterial DNA can potently stimulate these cells by interaction with toll-like receptor 9 (TLR9). This stimulation results from the presence of CpG motifs in bacterial DNA. The immune properties of DNA are mutable, however, and depending on mechanisms of entry of DNA into the cells, both mammalian and bacterial DNA can stimulate other internal receptors that do not require CpG motifs. Similarly, antigenicity depends on structure and varies in normal and autoimmunity settings. Thus, sera of normal human subjects contain antibodies highly specific for DNA from certain bacteria, binding non-conserved sequences that differ from CpG motifs. In contrast, sera from patients with systemic lupus erythematosus (SLE) bind to conserved sequences on the DNA backbone, most likely phosphate groups. The binding of lupus DNA, however, requires an extended polynucleotide structure since the interaction of each Fab site with DNA is relatively weak. This type of binding is termed monogamous or bivalent and indicates the need for simultaneous binding of both Fab sites to the same molecular structure. In contrast, lupus anti-DNA can bind to phosphorothioate oligonucleotides even with compounds as short as 20 bases; the phosphorothioate (Ps) backbone has a sulfur modification for one of the non-bridging oxygens. This chemistry has been used for the design of antisense compounds. The difference in the size requirement for binding of phosphodiesters and phosphorothioates relates to the greater protein binding capacity of Ps compounds. Since antisense compounds are now being used therapeutically, understanding the immune properties of DNA is important in terms of both efficacy and potential toxicity, including immunogenicity.