Molecular Virology and Experimental Therapeutics laboratory

Research aims include:

• Understand virus replication, particle assembly, and cell escape
• Characterize receptor attachment, membrane fusion, and cell entry
• Understand tropism, and the mechanisms of virulence and immunosuppression
• Re-target tropism, and develop vectors for oncolytic therapy (lymphoma)
• Produce measles virus-based vaccines with added specificities and graded attenuation

Approach

Virus tropism is the predilection of a virus to invade, and replicate in, a particular cell or type of tissue. We have disclosed mechanisms by which viruses enter specific cells, corrupt host defense mechanisms, and appropriate cellular functions without destroying the infrastructure until they are ready to escape. We now envisage coercing viral tropism for selective elimination of cancer cells.

We focus on a virus that occasionally causes lymphoma regression in humans: measles virus (MV). MV and the related morbilliviruses have six structural and two host control evasion proteins, and a negative strand RNA genome. We characterize viral replication and transcription, protein synthesis and transport, particle assembly and release, and mechanisms of membrane fusion and entry into cells through the two known receptors, the immune cell specific protein SLAM and the ubiquitous protein CD46. We use molecular modeling to predict how the viral attachment protein interacts with the receptors. We verify these predictions by measuring the binding kinetics of mutant proteins, and their membrane fusion function. We also seek to identify the unknown epithelial cell receptor.

Measles is the disease with which virus-induced immunosuppression was discovered in 1908. We are characterizing how the viral P and V proteins control innate immunity by interacting with the signal transducer and activator of transcription protein STAT1, and with the RNA helicase mda-5. We generate viruses unable to interact with these proteins, and infect genetically modified mice expressing the MV receptors, and then macaques, to document spread and study virulence/attenuation.

Based on the safe and effective live attenuated MV vaccine strain we develop divalent vaccines to protect humans against measles and additional pathogens like the hepatitis B or the hepatitis C viruses. These vectored MV would deliver an additional immunization safely and without additional costs. We have shown that a vectored MV expressing the hepatitis B surface antigen induces protective levels of antibodies while protecting rhesus macaques against measles challenge. We are generating vectors with the potential of inducing strong hepatitis C virus humoral and cellular immune responses. We are also exploring the concept of producing a panel of viruses with graded attenuation to allow vaccination of immunocompromized individuals.

To transform the MV vaccine strain into a cytoreductive vector specific for cancer cells we have developed a three-layer targeting strategy. We have generated MVs that are activated intra-tumorally by matrix-metalloproteases, viruses retargeted to receptors expressed preferentially or exclusively in cancer cells, and viruses with modified innate immunity control proteins. Moreover we have armed viruses with prodrug convertases or cytokines. To address the issue of neutralizing antibodies, frequently available in cancer patients, we recoat MV with the envelopes of non-cross reacting related viruses. To assess efficacy we operate with human tumors set in immunodeficient mice, and also with fully immunocompetent tumor models. Oncolysis projects include lymphoma and colon carcinoma models.