My research focus has been on the design and characterization of polymeric biomaterials for modulating the immune responses. It has also been devoted to studies on development of novel nanoparticle delivery system such as viral vectors and functional liposomes for translational medicine.
(1) Polymeric Biomaterials Containing Cytokines for Modulating Dendritic Cell-Derived Immune Responses
Development of an effective vaccine and immunotherapy technology for cancer involves eliciting a potent tumor antigen-specific immune response by introduction of tumor antigens and generating systemic immunity against the tumors. Dendritic cells (DCs) are the most powerful antigen-presenting cells, capable of initiating immune response by stimulating both T cells and B cells, and much effort has therefore been devoted to methods for delivering appropriate antigens to DCs to develop effective vaccines. Immunization by adoptive transfer of autologous DCs that are loaded with antigens in vitro is, however, labor-intensive and requires significant regulatory concerns. In addition, most transplanted DCs remain non-functional, and few home to the lymph nodes where the subsequent activation of T-cell immunity is induced. More cost-effective and efficient protocols involve delivering antigen to host DCs in vivo by direct injection of vaccine vectors to program DCs in situ. Thus, the ability to deliver antigens to host DCs in vivo is a key step towards generating a potent antitumor immunity.
In this study, we demonstrate a general strategy to enhance antigen-uptake by DCs in vivo. It depends on recruiting and housing host DCs at the immunization injection site using functionalized biomaterials incorporating inflammatory cytokines. This approach offers the sustained and localized release of the cytokine granulocyte-macrophage colony-stimulating factor (GM-CSF), which has been identified as a potent stimulator of DC recruitment and proliferation, from the subcutaneously injected hydrogels / implanted PLGA scaffold. The engineered biomaterials provide a controllable subcutaneous microenvironment where host DCs could be recruited and further educated in situ by following injection of immunogens (antigens) at the recruited site. The porous PLGA scaffold & Thermo-sensitive mPEG-PLGA hydrogels capable of solution-gel transition through changes in temperature enable greater efficiency of drug/cytokine loading and also exhibit a sustained and localized release of GM-CSF in the target site. The enhanced antigen-specific immune response was observed when viral vector-based vaccine carriers were administered at the site implanted with these engineered hydrogel biomaterials.
(2) Targeted Gene Delivery with Viral Vectors
One of the most challenging problems in virus-mediated gene therapy is how the gene can be specifically delivered into the target tissues or cells. Our lab has developed a novel and efficient strategy that allows the retro/lentiviral vectors to enter specifically into the target cell. This innovative design is based on engineering retro/lentiviral vectors by altering the viral envelope glycoprotein (Env), the protein that is responsible for binding the virus to cell surface receptors and for mediating entry. Compared with conventional methods that manipulate the delicate coupling interactions of the binding and fusion domains of Env glycoprotein, which usually causes decreased viral infectivity, our engineering approach involved the incorporation of a targeting antibody and pH-dependent fusogenic protein as two distinct molecules on the viral surface. A major advantage of this scheme over others where the viral protein is engineered with a foreign binding component is that the fusion protein maintains its full biological activity so that viral titer is not killed for increased specificity. This targeting methodology is flexible and can be extended to other forms of cell type-speciﬁc recognition with the different targeting antibody (or other cell-binding protein) to mediate targeting. The flexibility and broadness of this method will facilitate the application of targeted gene delivery for therapy and research.
Adeno-associated virus (AAV) vectors have attracted considerable interest because of its great premise as a vector for human gene therapy. However, their applicability is limited due to the restricted range of cells that they can efficiently transduce. Therefore, it is desirable to redirect AAV vector tropism that specifically transduces selected target cells in vivo. In this study, we have developed a new method for site-specific modification of AAV2 in order to generate a targeted AAV2 vector. This approach involves the insertion of a genetically encoded aldehyde tag onto AAV2 capsids, which can be metabolically modified to generate an aldehyde group as a unique chemical handle for further site-specific introduction of targeting ligands without causing a significant loss of viral titer. We demonstrated that this aldehyde tag enables covalent attachment of hydrazide-functionalized molecules including antibodies and peptides to AAV2 vector in a site-specific manner. It showed that antibody conjugation to AAV2 could significantly enhance viral transduction in both permissive and non-permissive cell lines expressing alternative cell-surface receptors. In addition, RGD-peptide conjugated AAV2 exhibited tumor targeting in vitro. These results demonstrated a general and efficient means for targeting AAV vectors.