Structure-guided engineering of CD47 and stem cell factor for immunotherapeutic applications
Abstract/Contents
- Abstract
- Protein biologics have revolutionized the clinical landscape in recent decades. In particular, abundant attention and momentum has been generated in the immunotherapy space, which directs one's immune system to combat diseases. Protein immunotherapeutics are currently evolving at a rapid pace as a result of growing efforts into applying protein-engineering strategies to improve their therapeutic index. In this dissertation, two independent immunoregulatory ligands, CD47 and stem cell factor (SCF), were engineered using structure-guided approaches for immunotherapeutic applications. CD47/SIRPα (Signal regulatory protein α) immunoregulatory pathway is a key inhibitor of macrophage effector function (i.e. phagocytosis) in homeostatic cell clearance and in immune evasion by cancer cells. Due to ubiquitous CD47 expression, current CD47-targeted cancer therapies are handicapped by large antigen sinks in vivo that could reduce bioavailability and increase the risk of toxicity. We engineered a high-affinity variant of human CD47 (Velcro-CD47) as a competitive antagonist of SIRPα, which has restricted tissue expression compared to CD47. To do so, we developed a novel approach that we termed 'Velcro' engineering, which enhances protein-protein interaction by a 'molecular velcro'. Specifically targeting a subset of myeloid cells in human blood ex vivo, Velcro-CD47 enhances tumor-specific antibody mediated antibody-dependent cellular phagocytosis (ADCP) of tumor cells in vitro, demonstrating its potential therapeutic use as an adjuvant to antibody therapy for cancer. On the other hand, SCF is a homodimeric growth factor that dimerizes c-Kit receptors to elicit therapeutic expansion of hematopoietic progenitors, but is toxic in vivo because it concurrently activates mast cells. We modified the SCF ligand in order to 'cripple' c-Kit dimerization efficiency and truncate downstream signaling as a strategy to decouple SCF efficacy and toxicity. We engineered a high-affinity monomeric SCF variant that behaves as a partial agonist of c-Kit and shows selectivity for hematopoietic progenitors over mast cells in vitro. Tests in pre-clinical mouse models of SCF-mediated anaphylaxis, radioprotection, and cancer therapy revealed that our SCF variant exhibits therapeutic efficacy in vivo with virtually no anaphylactic effects, thus unlocking SCF's clinical potential. This approach has broad applications in dimeric receptor-ligand systems. Collectively, the work presented in this dissertation has generated two potential immunotherapeutic leads that encourage further preclinical and clinical investigations. In addition, it has expanded the repertoire of protein-engineering strategies to create novel protein biologics with potentially improved therapeutic value.
Description
| Type of resource | text |
|---|---|
| Form | electronic; electronic resource; remote |
| Extent | 1 online resource. |
| Publication date | 2015 |
| Issuance | monographic |
| Language | English |
Creators/Contributors
| Associated with | Ho, Chia Chi Michelle |
|---|---|
| Associated with | Stanford University, Department of Bioengineering. |
| Primary advisor | Garcia, K. Christopher |
| Primary advisor | Weissman, Irving, 1905- |
| Thesis advisor | Garcia, K. Christopher |
| Thesis advisor | Weissman, Irving, 1905- |
| Thesis advisor | Cochran, Jennifer R |
| Thesis advisor | Shizuru, Judith Anne |
| Advisor | Cochran, Jennifer R |
| Advisor | Shizuru, Judith Anne |
Subjects
| Genre | Theses |
|---|
Bibliographic information
| Statement of responsibility | Chia Chi Michelle Ho. |
|---|---|
| Note | Submitted to the Department of Bioengineering. |
| Thesis | Thesis (Ph.D.)--Stanford University, 2015. |
| Location | electronic resource |
Access conditions
- Copyright
- © 2015 by Chia Chi Ho
- License
- This work is licensed under a Creative Commons Attribution Non Commercial 3.0 Unported license (CC BY-NC).
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