Dissertation
Immunomodulatory effects of mesenchymal stem/stromal cell efferocytosis by monocytes
University of Iowa
Doctor of Philosophy (PhD), University of Iowa
Autumn 2023
DOI: 10.25820/etd.006855
Abstract
The immunosuppressive capability of mesenchymal stem/stromal cells (MSCs) demonstrated over the past two decades has fueled an eagerness to develop therapies using MSCs to treat a myriad of immune-mediated diseases. MSCs can alleviate inflammation and promote immune tolerance in several disease models, largely through an array of trophic factor signaling pathways. However, due to the diversity of MSC mechanisms of action and differences in diseases treated with MSCs, developing effective MSC therapies for clinical use has been slow and challenging. While MSC therapies have exhibited promising data in clinical trials, clinical approval for a MSC therapy remains elusive. The diverse nature of MSC mechanism of action is further muddied by paradoxical observations: MSCs exhibit limited persistence in vivo, yet they promote durable and robust immunomodulatory responses. A novel mechanism of action has emerged based on observations that host monocytes and macrophages are associated with the clearance of MSCs: efferocytosis. Efferocytosis is a natural mechanism the body employs to clear dead and dying cells while minimizing inflammatory responses. Evidence has accumulated to support this hypothesis, but isolating the effects of MSC-mediated efferocytosis from trophic factor signaling has not been fully studied. To realize the full potential of MSC therapies, it is critical to understand the various ways MSCs can exert their immunomodulatory capabilities, including via efferocytosis.
The aim of this thesis is to evaluate how MSC viability affects monocyte immunomodulatory efficacy through efferocytosis. To accomplish this, it is important to understand why MSCs are actively being explored as immunomodulatory therapeutics for treating immune diseases and how efferocytosis has emerged as a potential mechanism of action in this regard. In Chapter 1, I provide detailed background information of MSC immunomodulatory capability and mechanisms of action that culminates with the current gaps in knowledge regarding the effects of MSC efferocytosis on the human immune system.
The study of MSC efferocytosis explored in this thesis required extensive use of flow cytometry, specifically spectral flow cytometry, and, therefore, Chapter 2 is provides a thorough discussion of how flow cytometry works as well as the methods incorporated for biological inquiry. The purpose of the chapter is to be a comprehensive yet approachable reference for anyone who could benefit from flow cytometry in their research. Chapter 3 highlights how MSC viability affects monocyte phenotype and function via efferocytosis and, ultimately, the impact that efferocytosis of MSC material can have on immune-mediated diseases.
The results presented within this dissertation demonstrate the importance of MSC viability in promoting immunosuppression via monocyte efferocytosis in different disease contexts. Therefore, MSC efferocytosis should be considered as a potential mechanism of action that could have a significant impact when developing MSC therapies for different disease indications. Additionally, the viability status of the MSC product should be considered for potency testing of MSC therapies to ensure the best product is utilized for a given indication. Lastly, this research demonstrates the need to explore the efficacy of MSC therapies in conditions with significant monocyte depletion or adverse monocyte health. Evaluating the monocyte health of potential candidates for MSC therapies could identify individuals who may not benefit from a specific product.
Details
- Title: Subtitle
- Immunomodulatory effects of mesenchymal stem/stromal cell efferocytosis by monocytes
- Creators
- Michael Verle Schrodt
- Contributors
- James A Ankrum (Advisor)Edward A Sander (Committee Member)Kristan S Worthington (Committee Member)Donna A Santillan (Committee Member)
- Resource Type
- Dissertation
- Degree Awarded
- Doctor of Philosophy (PhD), University of Iowa
- Degree in
- Biomedical Engineering
- Date degree season
- Autumn 2023
- DOI
- 10.25820/etd.006855
- Publisher
- University of Iowa
- Number of pages
- xv, 171 pages
- Copyright
- Copyright 2023 Michael Verle Schrodt
- Grant note
- This work was funded primarily with support from the Straub Foundation and the Diabetes Action Research and Education Foundation to JAA. Additional support came from NIH P42 ES013661 (JAA). RBB and L.B. were supported in part by the University of Iowa MSTP Grant, NIH T32 GM139776. JL was supported by a Carver Biomedical Engineering PhD Fellowship from the Roy J. Carver Trust. (135) M.S. was supported through and L.B. was supported in part by NIH training grant #5T32GM007337. Support from the Straub Foundation, Diabetes Action Research and Education Foundation, and the Fraternal Order of Eagles Diabetes Research Foundation awarded to J.A.A. were used to complete the project. Several of the chemical/media reagents used for this work were provided through a BD Immunology Grant and a Biological Industries USA Research Award to J.A.A.. (160) M.V.S. was supported through an NIH training grant #5T32GM007337. Support from the Straub Foundation, Diabetes Action Research and Education Foundation, and the Fraternal Order of Eagles Diabetes Research Foundation awarded to J.A.A. were used to complete the project. Several of the chemical/media reagents used for this work were provided through a BD Immunology Grant and a Biological Industries USA Research Award to J.A.A.. (166)
- Language
- English
- Date submitted
- 12/04/2023
- Description illustrations
- illustrations, tables. graphs
- Description bibliographic
- Includes bibliographical references (pages 137-154).
- Public Abstract (ETD)
- Mesenchymal stem/stromal cells (MSCs) have known therapeutic potential in reducing or resolving inflammation of immune diseases; therefore, MSCs are actively being explored as cell-based therapies to treat diseases of the immune system. Considerable interest exists in diseases with poor prognosis and/or limited or challenging therapeutic options, such as graft-vs-host disease, Crohn’s, multiple sclerosis, cancer, diabetes, and inflammatory lung diseases. To date, no FDA-approved MSC therapy exists for any indication despite promising clinical trial data. To develop robust MSC therapies, it is crucial to understand MSC mechanisms of action, and research has uncovered several mechanisms employed in different diseases; however, evidence shows MSCs do not persist for long in the host body after administration. Despite their limited persistence, long-lasting effects from MSC treatments are observed. Recent work suggests a novel mechanism could explain this paradox. Evidence suggests MSCs are cleared by specialized host immune cells that engulf dead and dying cells in a non-inflammatory manner. This further suggests that variations in MSC viability could impact immune response; however, isolating the effects of this mechanism has remained elusive because residual effects from non-engulfed MSCs persist. Using cleverly designed cell separation techniques to remove non-engulfed MSCs, I isolated and determined the effects of MSC engulfment by host immune cells. Furthermore, I discovered MSC viability prior to engulfment influences the resultant immune response. This work advances understanding of MSC immunomodulation so that more effective cell therapies can be developed.
- Academic Unit
- Roy J. Carver Department of Biomedical Engineering; Craniofacial Anomalies Research Center
- Record Identifier
- 9984546749402771
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