BIOMED PhD Thesis Defense

Title:
Type V Collagen Orchestrates the Initial Matrix Templating in Developing Articular Cartilage and Meniscus

Speaker:
Bryan Kwok, PhD Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University
 
Advisor:
Lin Han, PhD
Professor
School of Biomedical Engineering, Science and Health Systems
Drexel University

Details:
The articular cartilage and meniscus in the knee joint are critical for painless movement, but these tissues’ have low regeneration capacities, rendering them vulnerable to injury and osteoarthritis (OA), the most prevalent musculoskeletal disease that afflicts more than 27 million people in the US. Successful regeneration in articular cartilage and meniscus is challenged by the limited understanding of how these two tissues and their extracellular matrices (ECMs) initially form. This thesis queries the early molecular events that govern the assembly of the initial primitive matrix in the embryonic cartilage and meniscus. Using wild-type embryonic murine knee joint as the model system, we found that the primitive matrix of cartilage and meniscus initiates with a pericellular matrix (PCM)-like template that matures into the specialized PCM and bulk ECM regions. In this early phase, articular cartilage and meniscus developed molecular characteristics signifying distinct matrix templating during initial formation. Also, from embryonic to neonatal development, the micromodulus of cartilage and meniscus matrices stiffen exponentially, with a daily modulus increase rate of ≈ 36% and ≈ 20%, respectively. These results together highlighted the rapid and distinct development traits of the primitive matrices for these two tissues, providing the foundation for determining the molecular mechanisms governing the early matrix templating, and for developing novel tissue engineering strategies to recapitulate the native ECM formation.

Building on these findings, we examined the role of type V collagen, a minor fibril-forming collagen, in regulating the initial matrix templating of both tissues. Although collagen V is usually considered as a co-initiator of collagen I fibrillogenesis, we found pronounced expression in both collagen I-based meniscus and collagen II-rich articular cartilage at embryonic stage. In the joint-specific Col5a1 knockout model (Col5a1f/f/Gdf5Cre, or Col5a1cKO), we found substantial matrix defects in newborn tissues, including reduced meniscus size, flattened cartilage, thickened collagen fibrils and reduced tissue modulus.

Despite these changes, single-cell RNA-sequencing did not yield clear phenotype in cell phenotype or signaling, supporting a direct role of collagen V in initial matrix templating. Such impaired matrix templating results in disrupted postnatal growth. In 1-month-old Col5a1cKO joints, we found decreased meniscus size, an absent meniscus inner zone with much reduced Col2a1 expression, and reduced proteoglycan content in cartilage. These changes further progressed to marked signs of OA-like cartilage and meniscus degeneration by 3 months of age, as well as aberrant formation of osteophytes and subchondral bone remodeling, which are signs of advanced OA, by 8 months of age. Together, these results show that collagen V is an essential constituent of the initial matrix templating of both articular cartilage and meniscus. Targeting molecular activities of collagen V could hold the potential of improving the regeneration of these two structurally distinct tissues to treat OA and joint injury.

BIOMED Master's Thesis Defense

Title:
Developing Mutant KRAS Targeted Vaccines for Pancreatic Cancer Interception

Speaker:
Ben Barrett, Master's Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University
 
Advisors:
Neeha Zaidi, MD
Assistant Professor of Oncology
Sidney Kimmel Comprehensive Cancer Center
Johns Hopkins Medicine
 
Adrian Shieh, PhD
Teaching Professor
School of Biomedical Engineering, Science and Health Systems
Drexel University

Details:
Pancreatic Ductal Adenocarcinoma (PDAC) remains one of the most lethal cancers to date, with a 5-year survival rate of only 12%. The poor survival rate can largely be attributed to an immunosuppressive tumor microenvironment (TME) that is largely devoid of anti-tumor T cells. Approximately 90% of PDACs are driven by mutations in KRAS (mKRAS), with the most common being KRASG12D (~40%). mKRAS serves as an ideal set of candidates for targeting due to their role as a driver mutation and high specificity to precancerous lesions. These shared driver mutations, along with the near decade-long timeframe from pre-cancer to PDAC development, allows for a window-of-opportunity to develop vaccines to activate T cells before cancer develops and immunosuppression evolves. Several considerations are key to vaccine performance including the platform and immunomodulatory adjuvants admixed with neoantigens. Within this thesis, we explore two promising vaccine platforms: a pooled neoantigen peptide vaccine and a bicistronic mRNA vaccine. Each platform contains distinct benefits with peptide vaccines consistently demonstrating immune responses to neoantigens, while mRNA offers the possibility of directly encoding immunomodulatory adjuvants often required to be admixed with peptide vaccines for acceptable responses. The stimulator of interferon genes (STING) pathway offers an increasingly attractive target for optimizing T cell response due to the upregulation of type I interferons.

We thus designed and verified the in vitro functionality of an mRNA vaccine encoding both a KRASG12D vaccine and immunomodulatory adjuvant STINGV155M, a constitutively active STING (caSTING) protein, on the same vector mediated by an EMCV IRES linker. We set 3 requirements that were paramount to design success: 1) Antigenic translation (KRASG12D), 2) Adjuvant Translation (STINGV155M), and 3) Constitutive STINGV155M Activation. Two constructs were tested that alternated the ordering of the cistrons, and thus modified the nature of translation. It was determined that while both encoded proteins were translated from the same vector using Western Blot, there was insufficient caSTING functionality when caSTING was subject to cap-independent translation as measured by a STING reporter cell line. However, STING signaling was rescued when the caSTING was translated via cap-dependent initiation, indicating that bicistronic translation requires improvement before it can be deemed that single construct met all requirements.

In parallel, we characterized the immunogenicity of a pool of mutant KRAS synthetic long peptides (SLPs) (G12C, G12V, G12R, G12A, G12D and G13D) via anti-IFNγ ELISpot and flow cytometry T cell phenotyping in C57BL/6 mice. We demonstrated robust antigen-specific responses when the SLPs were admixed with a STING adjuvant. We also found an increase in mKRAS-specific T cell responses when increasing the number of doses in the vaccination protocol. Interestingly, we found cross-reactive T cell responses in both CD4+ and CD8+ T cells, dependent on the epitopes included in the peptide mixture.

Finally, we characterized the pre-malignant and tumor microenvironment (TME) of an inducible, conditional mouse model of PDAC, commercially available from the Jackson Laboratory, Pdx1-CreERTg/Tg;Trp53fl/fl;KrasG12D/+. This mouse model expands on the Cre-Lox recombination of the traditional KPC mouse model, through the association of an estrogen receptor with the Cre protein. Thus, the estrogen-analog, Tamoxifen, is required for Cre to enter the nucleus and carry out recombination, allowing for the induction of the KRASG12D-driven tumorigenesis. We developed a method of inducing mKRAS, isolating and maintaining tissue, and studying tissue histology. We confirmed the expression of KRASG12D localized to precancerous lesions (PanINs) and PDAC tumors through in situ hybridization (ISH). We further observed a migration of CD3+ and CD68+ cells to sites of PanIN and PDAC via immunohistochemistry (IHC) staining, specifically noting a clear integration of immune cells within PanIN lesions and a clear restriction of CD3+ cells to the border of tumors. Based on the data collected, the tiKPC model serves an ideal candidate for future immunotherapy interception studies using the vaccine formulations outlined above. Throughout the course of this thesis, we demonstrated the potential for mKRAS-targeted vaccine platforms with the intention of intercepting pancreatic cancer, as well as the ideal model to characterize the efficacy of an interception strategy.

BIOMED PhD Research Proposal

Title:
Development and Characterization of Folic Acid Delivery Systems for Spinal Cord Repair

Speaker:
Mengxi Yang, PhD candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University

Advisor:
Yinghui Zhong, PhD
Associate Professor
School of Biomedical Engineering, Science and Health Systems
Drexel University
 
Details:
Traumatic spinal cord injury (SCI) causes partial or complete loss of sensory, motor, and autonomic functions below the site of injury. Patients suffering from SCI may experience severe morbidity and permanent disability. Clinically, there is no effective treatment for SCI. Thus, novel interventions are required to facilitate spinal cord repair. Following SCI, the secondary injury cascade can cause the lesion site to expand over time, frequently leading to the development of a cavity surrounded by an astroglial-fibrotic scar. This inhibitory extrinsic environment, presented by the astroglial-fibrotic scar, combined with diminished intrinsic CNS axon regenerative capability, further limits and impedes axon growth after SCI. Therefore, secondary injury and axon regeneration are crucial therapeutic targets for spinal cord repair.

Folic acid (FA), a small molecule, is an essential vitamin source for normal cellular metabolic function and also plays a pivotal role in the development, regeneration, and repair of neural cells in the CNS. It has been reported to have anti-inflammatory and neuroprotective effects and shown to promote axon regeneration via DNA methylation after SCI. In this study, we aim to develop a biomaterial-based approach to locally deliver FA with sufficient dose and duration for effective treatment of SCI and study its efficacy in promoting spinal cord repair.

BIOMED PhD Thesis Defense

Title:
Understanding and Tuning Macrophage Phenotype in Volumetric Muscle Loss (VML) Injury

Speaker:
Ricardo Checchia Whitaker, PhD Candidate
School of Biomedical Engineering, Science and Health Systems
Drexel University

Advisor:
Kara Spiller, PhD
URBN Professor of Biomedical Innovation
School of Biomedical Engineering, Science and Health Systems
Drexel University

Details:
Volumetric Muscle Loss (VML) is defined as the sudden loss of 20% or more of muscle mass, leading to tissue impairment. The current standard of care, consisting of rehabilitation, surgery, or amputation, is clearly ineffective. The sole therapy in clinical trials attempts to promote tissue regeneration via implantation of a decellularized matrix scaffold, nonetheless this approach also falls short of entirely reestablishing tissue function. The existing gap in knowledge behind the underpinning mechanisms driving VML pathology hinders the development of better therapeutics.

Recent studies uncovered the presence of dysfunctional macrophages following critical size VML injuries. Macrophages have been shown in vitro and in other models of muscle repair to be crucial for muscle regeneration due to its vital influence on supporting cells, such as stem cells, endothelial cells, and fibroblasts. Nonetheless, the mechanism(s) driving macrophages dysfunction following VML remain elusive. The goals of this thesis are to establish these mechanisms driving immune dysregulation, particularly on macrophages following VML, and make strides on the development of better therapeutics.

In this work, we have established a full timeline of macrophage dysfunction, both in the protein and gene level, from injury onset to the establishment of fibrosis. Next, we have uncovered previously unknown systemic changes in immune response, such as immune cell presence in the bone marrow, changes in splenic macrophage phenotype and blood serum cytokine levels, derived from this localized injury. In addition, we identified neutrophils as potential mediator of macrophage dysfunction. Lastly, we identified potential drugs and biomaterials to leverage a novel macrophage cell therapy approach for the treatment of VML.

The results from this thesis deepen our knowledge on some of the previously unknown mechanisms driving immune dysfunction and therefore tissue impairment after VML. It also lays down groundbreaking advances in possible treatments for VML patients.

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