(4gc) Macrophage Engineering: From Enhancing Phagocytosis By Disrupting “Self” Signals to Cellular Immunotherapies and Tissue Patterning

Immunotherapy, Phagocytosis, Protein-based Materials, Mechanobiology

Phagocytosis (“cell eating”) is the evolutionarily conserved process by which cells engulf large particulate matter including other cells. Clearance of pathogens and dead cells by macrophages (“large eaters”) is critical for host defense and homeostasis. At the same time, engulfment of healthy “self” cells must be avoided in most situations. One example of how proper cell engulfment is achieved – as illustrated by my postdoctoral research – is by manipulating the balance between activating phagocytic signals (e.g., IgG antibodies) and inhibitory signals (e.g., CD47, the ubiquitous “marker of self” protein). With sufficient understanding of this and other pathways, I envision that we can engineer phagocytic macrophages to achieve desired therapeutic and engineering outcomes including engulfment of tumor cells, shielding of materials from immune recognition, and programmed cell removal from engineered tissues. This concept forms the basis for my proposed directions as an independent investigator to develop a research program that spans (i) fundamental immunobiology studies of macrophages and phagocytosis and (2) immunoengineering of macrophages for cancer therapy and regenerative engineering.

(1) Engineering better macrophages for cellular therapies My postdoctoral work demonstrates that macrophage phagocytose cancer cells, but it remains unclear how they integrate diverse and potentially conflicting self and non-self signals downstream of this process. Therefore, I propose to study signaling during and after tumor cell engulfment leading to antigen presentation and cytokine production. These studies will inform parallel efforts to engineer monocyte/macrophage-based cellular immunotherapies using primary immune cells and induced pluripotent stem cells together with gene editing technologies. In particular, cell engineering efforts will be aimed at overcoming current barriers to macrophage-based therapies including systemic delivery with accumulation in tumors and scaling production of cell types with limited capacity for ex vivo expansion.

(2) Tissue engineering and patterning via phagocytosis Macrophages are among the earliest hematopoietic cells observed in embryonic development, which reflects their requirement for shaping tissues via phagocytosis. Inspired by such developmental process – for example, the sculpting of limb digits – and motivated by my current work to understand phagocytosis of solid tumor targets, I propose to use engineered phagocytotic cells as a tool for tissue patterning toward applications in regenerative medicine.

(3) Role of CD47 on tumor-derived extracellular vesicles (EVs) and development of tools for isolating cell-type specific EVs Extracellular vesicles released by cells mediate intercellular communication and have also attracted considerable attention for drug delivery applications. I propose to investigate how CD47 influences the uptake and immune signaling capacity of EVs, especially those derived from tumor cells. As a component of this project, I will develop new technologies enabling isolation of EVs originating from specific cell types in vitro and in vivo with the specific goal of tracking EVs and their cargo trafficking from tumors to lymph nodes.

Postdoctoral Research: Macrophage Checkpoint Disruption for Cancer Immunotherapy (Adviser: Dennis E. Discher, University of Pennsylvania)

In my postdoctoral research, I am developing new approaches to cancer immunotherapy using phagocytic macrophages as effector cells. I have shown that disruption of CD47 signaling from cancer cells, which eliminates the inhibitory CD47:SIRPα immune checkpoint, enhances phagocytosis in vitro and tumor clearance in vivo when combined with an opsonizing anti-tumor IgG monoclonal antibody. Successful therapy not only eliminates tumor but also initiates an endogenous anti-tumor IgG antibody response suggesting that adaptive immunity feeds back in a manner that can enhance the effects of macrophage checkpoint disruption. We refer to this process ‘phagocytic feedback’. As a translatable approach that overcomes depletion of healthy cells seen with injection with anti-CD47 monoclonal antibodies being pursued clinically, I am also developing a cellular immunotherapy using adoptive transfer of bone marrow-derived phagocytic cells that are treated ex vivo with anti-SIRPα. In parallel, I have developed in vitro tumorosphere assays to address how macrophages engulf cancer cells in solid tumor-like microenvironments. The findings of these experiments indicate that macrophages might work cooperatively to engulf target cells that adhere to one another.

Ph.D. Thesis: “Programming Molecular Association and Viscoelastic Behavior in Protein Hydrogels” (Adviser: David A. Tirrell, California Institute of Technology)

In my Ph.D. research, I designed, fabricated, and characterized protein-based hydrogels with the goal of developing programmable materials in which the primary protein sequence encodes macroscopic viscoelastic properties. This work combined substantial elements of materials science, molecular biology, and protein engineering. These hydrogels have applications as matrices for studying the effects of ECM viscoelasticity on cellular fate, as model systems for studying biomolecular condensates, and for developing tougher hydrogels using reversible, energy dissipating cross-links. I envision using similar protein and materials engineering to investigate the mechanobiology of macrophage and phagocytosis.

Teaching Interests

Biomaterials, Immunology, Biomolecular Engineering, Nanomedicine and Drug Delivery, Core Chemical Engineering Curriculum

My undergraduate and graduate training were both in Chemical Engineering, and I would be comfortable teaching the core undergraduate courses in transport phenomena, kinetics, and thermodynamics. My graduate and postdoctoral research and previous teaching experience has prepared me to teach courses in biotechnology and biomolecular engineering at the graduate and undergraduate levels. I envision designing graduate or advanced undergraduate level courses at the interface of immunology and chemical and biological engineering with a strong basis in recent literature. The course(s) would be a hybrid of immunological fundamentals (e.g. immune cells and tissues, immunological biomolecules and macromolecular assemblies, immune signaling) and biomedical applications (development and biomanufacturing of antibodies, vaccines, and cellular therapies, immunological assays and methods, immunological responses to biomaterials).

In addition to core and elective engineering courses, I am interested in developing or coordinating a course focusing on basic research skills for graduate students and upper level undergraduates. Topics would be tailored to the specific needs of the students and potentially include data presentation and scientific illustration, library and digital resources, proposal writing and overviews of research funding organizations, responsible conduct of research, and others. I would seek to leverage existing resources at the university (e.g., librarians, graphic artists) or within department to cover these topics.

Teaching Experience
My teaching experience includes teaching assistantships for a graduate level cell engineering course and an undergraduate (junior/senior) level biomolecular engineering laboratory. I have guest lectured (2-5 classes per semester) for Nanoscale Systems Biology and Biological Soft Matter Fundamentals courses. I view mentoring as an important component to teaching and have mentored researchers across multiple levels including undergraduates and master’s thesis students. I also supervised high students and teachers as part of summer research outreach program.