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Department of Laboratory Medicine and Pathology
University of North Carolina at Chapel Hill, 1984, Ph.D.
Tumor immunology and immunotherapy, molecular immunology
The major goal of my research is to devise novel immune-based strategies for cancer therapy. Currently we are focusing on two approaches. One is to develop plasmid DNA-based cancer vaccines. The second is to introduce chimeric antigen receptors into primary T cells to redirect their cytotoxicity to tumor targets.
Plasmid DNA (pDNA) is an attractive platform for gene delivery in vivo because it is a non-viral, non-integrating vector that is safe, inexpensive, stable and easily manipulated. However, clinical trials of plasmid DNA therapeutics reveal they have two major disadvantages. The first is poor transfection in vivo while the second is transient expression of their encoded genes. The latter is primarily due to the spread of transcriptionally repressive chromatin initially deposited on plasmid bacterial backbone sequences. To overcome transient expression, we have explored using minicircle DNA to deliver genes encoding antigens of interest.
Minicircle DNA lacks plasmid backbone sequences and correspondingly confers higher levels of sustained transgene expression upon delivery, accounting for its success in preclinical gene therapy models. Due to its smaller size, it also transfects cells more efficiently than larger plasmids. We showed for the first time that minicircle DNA also functions as a vaccine platform and is superior to full length plasmid DNA in eliciting protective immune responses in a model of Listeria monocytes infection. We are now extending these studies to mouse models of cancer to understand how these vaccines work at the molecular and cellular levels. Our long-term goal is to develop minicircle-based DNA vaccines to treat human diseases such as breast cancer, melanoma, and glioblastoma.
Our second approach involves chimeric antigen receptors or CARs. As their name implies, CARs have several disparate components that are combined genetically. The goal of a CAR is to redirect a T cell’s effector function (e.g. cytotoxicity) to a cell bearing an antigen of interest, regardless of the T cell’s inherent specificity. In a typical CAR, the antigen-binding portions of an antibody of a desired specificity (e.g. for a cell surface-expressed tumor antigen) are linked via a spacer and transmembrane region to intracellular signaling domains derived from proteins required for T cell activation and costimulation (e.g. CD3zeta and CD28/41BB). When the antibody-derived portion of the CAR binds the tumor-associated antigen, activating signals are delivered to the T cell via the T cell-derived portions of the CAR. These signals stimulate the CAR T cell to differentiate into an effector cell capable of eliminating the tumor to which it is bound. We employ mouse models of CAR therapy for hematopoietic malignancies to inform planned clinical trials.
Dietz, W.M., Skinner, N.E.B., Hamilton, S.E., Jund, M.D., Heitfeld, S.M., Litterman, A.J., Hwu, P., Chen, Z.-Y., Salazar, A.M., John Ohlfest, J.R., Blazar, B.R., Pennell, C.A.*^ and Osborn, M.J.* 2013. Minicircle DNA is Superior to Plasmic DNA in Eliciting Antigen-Specific CD8+ T Cell Responses. Mol Ther. 21(8):1526-35. *Co-senior authors. ^Corresponding author.
Ohlfest, J.R., Andersen, B.M., Litterman, A.J., Pennell, C.A., Swier, L.E., Salazar, A.M., and Olin, M.R. 2013. Vaccine Injection Site Matters: Qualitative and Quantitative Defects in CD8 T Cells Primed as a Function of Proximity to the Tumor in a Murine Glioma Model. J. Immunol. 190(2):613-20.
Philpott, N., Bakken, T., Pennell, C., Chen, L., Wu, J. and Cannon, M., 2011. The KSHV G Protein-Coupled Receptor Contains an Immunoreceptor Tyrosine-Based Inhibitory Motif that Activates Shp2 J Virol. 85(2):1140-4.
Wu, K., Peng, G., Zhou, W., Pennell, C.A., Mansky, L.M., Geraghty, R.J. and Fang, L. 2011. A Virus-binding Hotspot on Human Angiotensin-converting Enzyme 2 is Critical for the Binding of Two Different Coronaviruses. J. Virol. 85(11):5331-7.