My overall research goals aim to detail the fundamental mechanisms of host-pathogen interactions that influence and facilitate the induction of protective humoral immune responses during natural infection and vaccination. By using my multidisciplinary expertise, that I have successfully applied to infectious disease research, my future research activities will be focused on deciphering the structural and immunological basis of infectious diseases, and the development of effective vaccines and immune-therapeutics against various pathogenic agents including HIV-1 (AIDS) and other viruses by innovative structural vaccinology approaches.
Infectious Disease Research
My research in infectious diseases research has been focused on understanding mechanism of pathogen-host interaction and protective humoral immune response during natural infection and vaccination, then translating knowledge to design of vaccines and drugs. My research pioneers in the field of structure-based protein engineering and vaccine development. I have led the following projects with teams of multidisciplinary research expertise and oversaw the collaborative research as a project leader.
Revealed HIV immune recognition mechanism and designed revolutionary HIV vaccine
AIDS caused by HIV-1 infection is a global epidemic affecting approximately 37 million people. HIV vaccine has been considered as a necessary and effective way to control HIV spread. The central goal of HIV vaccine design is to create immunogens that are capable of inducing broadly neutralizing antibody (bnAb) against majority circulating HIV strains. It is a challenging task to develop effective HIV vaccine due to HIV’s immune-evasion mechanism, including sequence variation, surface glycan mask and conformational instability on HIV Env protein. BnAbs isolated from AIDS patients provide templates for vaccine research. However, none of the previous developed vaccine candidates can elicited bnAbs. Through structural and functional characterization of a bnAb VRC34, I identified the fusion peptide (FP) as a new site of HIV vulnerability (Science2016). Conventionally, the hydrophobic FP of HIV Envelope protein was predicted to be occluded inside the protein, instead of exposed on protein surface. Moreover, multiple prior attempts to systemically assess the potential of HIV Env peptide-based vaccine (including FP) did not yield positive result. Therefore, FP has never been considered to be a valid HIV vaccine target. My research revealed that the first eight resides (FP8), but not the entire length, of FP is accessible to immune recognition, and the mechanism of FP-directed HIV neutralization is through preventing CD4-triggered Env protein transformation from prefusion to post-fusion state. HIV FP is a conserved and functional essential site on HIV. Based on my initial discovery, I hypothesized that bnAb can be induced by focusing humoral immune response on FP8. Through structure vaccinology and structure-based protein engineering approach, I invented the FP-based HIV vaccine by grafting HIV FP site on to scaffold proteins, nanoparticles, carrier proteins and various Env trimer immunogens, and by designing a prime-boost vaccination regimen (Nature Med. 2018). I designed and conducted animal studies to demonstrate that by focusing immune response to the FP8, bnAb response can be induced in all tested animals, including mouse, rabbit, guinea pig and non-human primates (NHP). This has been the long-sought goal in the HIV vaccine field which has not been reached by any other HIV vaccine candidates. Using a combination of techniques including structural determination, B cell analysis, virological examination, next generation sequencing, bioinformatic analysis, biochemical and biophysical assessment I delineated the development pathways of multiple bnAbs from FP-vaccinated NHP, which can neutralize up to 59% circulating HIV strains (Cell 2019). The development of FP-directed bnAbs initiate from weak affinity to FP8, then mature by focusing on Env trimer FP region hotspot to reach high affinity to both FP8 and Env trimer. This study sheds light on FP-directed bnAb neutralization mechanism and ontogeny, as well as future design and optimization of FP-based HIV vaccine.
Structure-guided rational design of highly effective parainfluenza virus vaccine
Human parainfluenza viruses type 1-4 (hPIV1-4) are responsible for frequently occurring severe respiratory illness in newborns, elderly, and immunocompromised individuals. hPIV vaccines have high market demand but technically difficulties to develop. The PIV fusion proteins are highly conserved and functionally necessary for viral entry, which are suitable as vaccine targets. However, native conformation of hPIV fusion proteins, through which antibodies can recognize hPIV virions, are in metastable state. Conventional vaccine creation methods cannot preserve the native conformation of hPIV fusion protein, therefore generated little effect. Through structure-based design and high-throughput screening, I jointly led the project to develop subunit vaccine candidates for hPIV1-4. We demonstrated that by stabilizing the prefusion conformation, hPIVs fusion (F) glycoproteins subunit vaccine can induce potent neutralizing immune responses in both mice and NHPs. (PNAS. 2018). The hPIV vaccines have been recently licensed by Moderna.
Uncovered henipavirus entry mechanism and designed Nipah virus vaccine with a structural approach
Henipavirus, known by Nipah and Hendra viruses, is a member of paramyxovirus family. It poses constant threat to global public health and economy with repeated outbreak and spill over in recent years. Two surface glycoproteins of henipavirus, the attachment G protein and the fusion F protein, mediate viral entry and are major targets of vaccine and therapeutic design. Through structural study, I delineated the fundamental mechanism underlying the G and F protein-mediated henipavirus entry process and the protective immune recognition against G protein. (PNAS 2019, 2008, PLoS Pathogens 2015, 2013). Furthermore, through structure-guided rational vaccine design, I stabilized the metastable F protein in its prefusion conformation through engineering a trimeric GCN4 motif at the C-terminus of F protein and demonstrated its vaccine efficacy (PLoS Pathogens 2015, PLoS One 2012).
Development of soluble HIV Env trimer immunogens stabilized in prefusion closed state
Soluble Env trimer immunogen derived from specific HIV-1 strains when stabilized in native conformation may be a component of an effective HIV vaccine. The clade C strain CH505, a transmitted founder (T/F) virus whose co-evolution ultimately led to the development of several broadly neutralizing antibodies is one such strain. I used structure-based design and ELISA-based antigenicity screening method to develop an optimal CH505 Env trimer immunogen and verified its immunogenicity in animal studies (Cell Rep. 2017, AIDS RES & HUMAN RETROV. 2016). The optimal CH505 Env immunogen is comprised of gp120 from T/F CH505 strain and gp41 from T/F BG505 strain. The immunogen was stabilized by structure-based mutation of gp120-gp41 interface residues, two additional pair of disulfide bonds located in the gp120-gp41 interface and V3 loop region, and an Isoleucine to Proline mutation in the gp41 HR1 region. This CH505 immunogen has been selected as a vaccine boost component for upcoming clinical trials conducted by Duke Human Vaccine Institute.
Neuronal Development and Neurodegenerative Diseases Research
My research in this area aimed at understanding the ligand-receptor interaction and signal activation mechanism in the process of neuronal development and neuronal diseases.
Explored the attractive and repulsive axon guidance signaling mechanism
By structural and functional analysis of Netrin1 in complex with Neogenin/DCC, I discovered that the attractive axon guidance signal is activated by ligand-induced receptor cross-linking (Science 2014). Through structural characterization and functional analysis with structure-based mutagenesis of ephrinA5- EphA4 interaction, I found that the repulsive axon guidance signal is triggered by ligand-induced receptor dimerization, and pre-associated EphA4 receptor cluster facilitates the activation process (PNAS 2013).
Gained insight into the mechanism of Wnt signaling modulation
Wnt signaling is critical in development. Leucine-rich repeat-containing G-protein coupled receptor (LGR) and R-spondin (Rspo) are the key modulators of Wnt signaling. I solved the crystal structure of LGR4/Rspo1 that provided insight into the mechanism of signal modulation (Structure 2013).
Discovered the physiological function of the proteins associated with Alzheimer disease
Amyloid precursor protein (APP) has been tightly associated to the pathogenesis of Alzheimer disease (AD). Understanding the physiological function of APP will help to facilitate AD research and therapeutic design. A physiological role of APP in the neuronal pruning was recently identified. I determined the structure of APP in complex with its functional receptor DR6 that revealed a ligand-induced activation of neuronal pruning signal (Genes Dev. 2015).