Contact Information:

Dept. of Microbiology and
Molecular Genetics

Harvard Medical School

200 Longwood Ave.

Boston, MA 02115

phone: 617-432-5415

fax: 617-738-7664

priscilla_yang@hms.harvard.edu

Yang Lab Web Site

Research Summary

Our research group uses a combination of chemical and biological techniques to investigate how viruses use host cell machinery to replicate themselves, how the interaction between virus and host leads to disease, and how the host combats infection by viruses. We focus on hepatitis B virus (HBV), hepatitis C virus (HCV), and dengue virus (DEN) because they are scientifically interesting but, more importantly, because they are significant causes of human morbidity and mortality. HBV and HCV are the most common blood-borne infections in the world, chronically infecting 6.3% and 2.2% of all people and causing more than a million deaths annually. DEN infection, in contrast, is usually acute but causes a broad range of disease, ranging from generic, "flu-like" symptoms to the uncontrolled bleeding and pulmonary shock characteristic of dengue hemorrhagic fever (DHF). Common to all three viruses is a tropism for the human liver. HBV and HCV are exclusively hepatotropic while DEN infects many different cell types. Recently, a growing body of evidence suggests that replication of DEN in the liver is associated with progression to DHF. Our goal is to understand the molecular mechanisms underlying the basic biology of HBV, HCV, and DEN infection and the diseases that result from it.

First, we are very much interested in the identification of small molecules inhibitors (or enhancers) of dengue virus replication that can be used as tools to dissect mechanism and validate possible therapeutic targets. Compounds are initially identified using high throughput cellular assays and optimized and characterized using a combination of medicinal chemical (SAR studies), biochemical (yeast two-hybrid screens, affinity chromatography), and immunological (intrahepatic lymphocyte analysis, FACS, immunofluorescence microscopy) methods.

The study of HBV is challenging because it is only infectious in humans and chimpanzees; there are no tissue culture or small animal models of HBV infection. Using the method of hydrodynamic transfection to introduce a supergenomic HBV transgene to mouse hepatocytes in vivo, we have found that mice thus transfected replicate virus, mount virus-specific humoral and cellular immune responses, and clear the virus. We are using the model to study, for the first time, the entire host immune response to acute HBV infection. This may be important in identifying defects or deficits in the immune responses mounted by chronically infected patients. We are also using this model to examine host-pathogen interactions in a very precise manner 1) by mutating the viral genome in vitro and then examining the phenotype of those mutations in vivo; 2) by using knockout and transgenic mice to manipulate the host background at a single gene level; and 3) by analyzing viral variants isolated from patients and correlating viral genotypes with the disease outcomes of the patients from whom they were derived. Collectively these experiments are aimed at identifying the host and pathogen determinants of viral persistence and disease.

Since the absence of suitable small animal models has severely impaired study of HBV, HCV, and DEN pathogenesis as well as study of the determinants of disease outcome during infection with these viruses, we maintain a strong interest in developing new mouse models that enable us to examine these issues. We plan to use diversification strategies such as PCR mutagenesis and DNA shuffling to generate libraries of HBV and HCV genomes that can then be introduced into the murine liver via hydrodynamic transfection and selected to isolate and amplify variants with expanded tropism.

Selected Publications

Yang, P.L., Althage, A., Chung, J., and Chisari, F.V. Hydrodynamic injection of viral DNA: a mouse model of acute hepatitis B virus infection. Proc Natl Acad Sci USA 99:13825-30 (2002).

Yin, J., Mundorff, E.C., Yang, P.L., Wendt, K.U., Hanway, D., Stevens, R.C., and Schultz, P.G. A comparative analysis of the immunological evolution of antibody 28B4. Biochemistry 40:10764-73 (2001).

Yang, P.L. and Schultz, P.G. Mutational analysis of the affinity maturation of antibody 48G7. J Mol Biol 294:1191-201 (1999).

Patten, P.A., Gray, N.S., Yang, P.L., Marks, C.B., Wedemayer, G.J., Boniface, J.J., Stevens, R.C., Schultz, P.G. The immunological evolution of catalysis. Science 271:1086-91 (1996).