Jeff Karp

Extracellular vesicles (EVs) are emerging as a potential alternative to some stem-cell–derived therapeutics (1, 2). Sometimes called exosomes, they are small, secreted vesicles that can possess similar therapeutic mechanisms to whole cells, possibly representing the active pharmaceutical ingredient. In the past 15 years, academic and industry interest in EVs has exponentially increased as mounting evidence demonstrates their role in physiology and pathology as well as their therapeutic… Show more

Extracellular vesicles (EVs) are emerging as a potential alternative to some stem-cell–derived therapeutics (1, 2). Sometimes called exosomes, they are small, secreted vesicles that can possess similar therapeutic mechanisms to whole cells, possibly representing the active pharmaceutical ingredient. In the past 15 years, academic and industry interest in EVs has exponentially increased as mounting evidence demonstrates their role in physiology and pathology as well as their therapeutic potential.

In light of growing efforts in using EVs for research and therapy, optimizing EV manufacturing is important. However, many challenges come with their characterization, scalable manufacture, and regulatory status. Here, we briefly review the biology and therapeutic application of EVs, discuss associated challenges, and suggest how the biotechnology industry could play an important role in overcoming those challenges. Many cell manufacturing companies currently produce EVs but discard them as waste, thereby losing a potentially valuable resource with multiple purposes in a market that’s otherwise rich with an exorbitant cost of goods. Show less

Poor homing of systemically infused cells to disease sites may limit the success of exogenous cell-based therapy. In this study, we screened 9,000 signal-transduction modulators to identify hits that increase mesenchymal stromal cell (MSC) surface expression of homing ligands that bind to intercellular adhesion molecule 1 (ICAM-1), such as CD11a. Pretreatment of MSCs with Ro-31-8425, an identified hit from this screen, increased MSC firm adhesion to an ICAM-1-coated substrate in vitro and… Show more

Poor homing of systemically infused cells to disease sites may limit the success of exogenous cell-based therapy. In this study, we screened 9,000 signal-transduction modulators to identify hits that increase mesenchymal stromal cell (MSC) surface expression of homing ligands that bind to intercellular adhesion molecule 1 (ICAM-1), such as CD11a. Pretreatment of MSCs with Ro-31-8425, an identified hit from this screen, increased MSC firm adhesion to an ICAM-1-coated substrate in vitro and enabled targeted delivery of systemically administered MSCs to inflamed sites in vivo in a CD11a- (and other ICAM-1-binding domains)-dependent manner. This resulted in a heightened anti-inflammatory response. This represents a new strategy for engineering cell homing to enhance therapeutic efficacy and validates CD11a and ICAM-1 as potential targets. Altogether, this multi-step screening process may significantly improve clinical outcomes of cell-based therapies. Show less

The diverse immunomodulatory properties of mesenchymal stem/stromal cells (MSCs) may be exploited for treatment of a multitude of inflammatory conditions. MSCs have long been reported to be hypoimmunogenic or 'immune privileged'; this property is thought to enable MSC transplantation across major histocompatibility barriers and the creation of off-the-shelf therapies consisting of MSCs grown in culture. However, recent studies describing generation of antibodies against and immune rejection of… Show more

The diverse immunomodulatory properties of mesenchymal stem/stromal cells (MSCs) may be exploited for treatment of a multitude of inflammatory conditions. MSCs have long been reported to be hypoimmunogenic or 'immune privileged'; this property is thought to enable MSC transplantation across major histocompatibility barriers and the creation of off-the-shelf therapies consisting of MSCs grown in culture. However, recent studies describing generation of antibodies against and immune rejection of allogeneic donor MSCs suggest that MSCs may not actually be immune privileged. Nevertheless, whether rejection of donor MSCs influences the efficacy of allogeneic MSC therapies is not known, and no definitive clinical advantage of autologous MSCs over allogeneic MSCs has been demonstrated to date. Although MSCs may exert therapeutic function through a brief 'hit and run' mechanism, protecting MSCs from immune detection and prolonging their persistence in vivo may improve clinical outcomes and prevent patient sensitization toward donor antigens. Show less

Yin X, Farin HF, van Es JH, Clevers H, Langer R, Karp JM.

Although Lgr5+ intestinal stem cells have been expanded in vitro as organoids, homogeneous culture of these cells has not been possible thus far. Here we show that two small molecules, CHIR99021 and valproic acid, synergistically maintain self-renewal of mouse Lgr5+ intestinal stem cells, resulting in nearly homogeneous cultures. The colony-forming efficiency of cells from these cultures is ∼100-fold greater than that of cells… Show more

Yin X, Farin HF, van Es JH, Clevers H, Langer R, Karp JM.

Although Lgr5+ intestinal stem cells have been expanded in vitro as organoids, homogeneous culture of these cells has not been possible thus far. Here we show that two small molecules, CHIR99021 and valproic acid, synergistically maintain self-renewal of mouse Lgr5+ intestinal stem cells, resulting in nearly homogeneous cultures. The colony-forming efficiency of cells from these cultures is ∼100-fold greater than that of cells cultured in the absence of CHIR99021 and valproic acid, and multilineage differentiation ability is preserved. We made use of these homogeneous cultures to identify conditions employing simultaneous modulation of Wnt and Notch signaling to direct lineage differentiation into mature enterocytes, goblet cells and Paneth cells. Expansion in these culture conditions may be feasible for Lgr5+ cells from the mouse stomach and colon and from the human small intestine. These methods provide new tools for the study and application of multiple intestinal epithelial cell types. Show less

Prodrug-based self-assembled hydrogels represent a new class of active biomaterials that can be harnessed for medical applications, in particular the design of stimuli responsive drug delivery devices. In this approach, a promoiety is chemically conjugated to a known-drug to generate an amphiphilic prodrug that is capable of forming self-assembled hydrogels. Prodrug-based self-assembled hydrogels are advantageous as they alter the solubility of the drug, enhance drug loading, and eliminate the… Show more

Prodrug-based self-assembled hydrogels represent a new class of active biomaterials that can be harnessed for medical applications, in particular the design of stimuli responsive drug delivery devices. In this approach, a promoiety is chemically conjugated to a known-drug to generate an amphiphilic prodrug that is capable of forming self-assembled hydrogels. Prodrug-based self-assembled hydrogels are advantageous as they alter the solubility of the drug, enhance drug loading, and eliminate the use of harmful excipients. In addition, self-assembled prodrug hydrogels can be designed to undergo controlled drug release or tailored degradation in response to biological cues. Herein we review the development of prodrug-based self-assembled hydrogels as an emerging class of biomaterials that overcome several common limitations encountered in conventional drug delivery. Show less

Prodrug-based self-assembled hydrogels represent a new class of active biomaterials that can be harnessed for medical applications, in particular the design of stimuli responsive drug delivery devices. In this approach, a promoiety is chemically conjugated to a known-drug to generate an amphiphilic prodrug that is capable of forming self-assembled hydrogels. Prodrug-based self-assembled hydrogels are advantageous as they alter the solubility of the drug, enhance drug loading, and eliminate the… Show more

Prodrug-based self-assembled hydrogels represent a new class of active biomaterials that can be harnessed for medical applications, in particular the design of stimuli responsive drug delivery devices. In this approach, a promoiety is chemically conjugated to a known-drug to generate an amphiphilic prodrug that is capable of forming self-assembled hydrogels. Prodrug-based self-assembled hydrogels are advantageous as they alter the solubility of the drug, enhance drug loading, and eliminate the use of harmful excipients. In addition, self-assembled prodrug hydrogels can be designed to undergo controlled drug release or tailored degradation in response to biological cues. Herein we review the development of prodrug-based self-assembled hydrogels as an emerging class of biomaterials that overcome several common limitations encountered in conventional drug delivery. Show less

W. K. Cho, J. A. Ankrum, D. Guo, S. A. Chester, S. Y. Yang, A. Kashyap, G. A. Campbell, R. J. Wood, R. K. Rijal, R. Karnik, R. Langer, J. M. Karp

North American porcupines are well known for their specialized hairs, or quills that feature microscopic backward-facing deployable barbs that are used in self-defense. Herein we show that the natural quill’s geometry enables easy penetration and high tissue adhesion where the barbs specifically contribute to adhesion and unexpectedly… Show more

W. K. Cho, J. A. Ankrum, D. Guo, S. A. Chester, S. Y. Yang, A. Kashyap, G. A. Campbell, R. J. Wood, R. K. Rijal, R. Karnik, R. Langer, J. M. Karp

North American porcupines are well known for their specialized hairs, or quills that feature microscopic backward-facing deployable barbs that are used in self-defense. Herein we show that the natural quill’s geometry enables easy penetration and high tissue adhesion where the barbs specifically contribute to adhesion and unexpectedly, dramatically reduce the force required to penetrate tissue. Reduced penetration force is achieved by topography that appears to create stress concentrations along regions of the quill where the cross sectional diameter grows rapidly, facilitating cutting of the tissue. Barbs located near the first geometrical transition zone exhibit the most substantial impact on minimizing the force required for penetration. Barbs at the tip of the quill independently exhibit the greatest impact on tissue adhesion force and the cooperation between barbs in the 0–2 mm and 2–4 mm regions appears critical to enhance tissue adhesion force. The dual functions of barbs were reproduced with replica molded synthetic polyurethane quills. These findings should serve as the basis for the development of bio-inspired devices such as tissue adhesives or needles, trocars, and vascular tunnelers where minimizing the penetration force is important to prevent collateral damage. Show less

The broad repertoire of secreted trophic and immunomodulatory cytokines produced by mesenchymal stem cells (MSCs), generally referred to as the MSC secretome, has considerable potential for the treatment of cardiovascular disease. However, harnessing this MSC secretome towards meaningful therapeutic outcomes is challenging due to limited control on cytokine production following transplantation. This review outlines current understanding of the MSC secretome as a therapeutic for treatment of… Show more

The broad repertoire of secreted trophic and immunomodulatory cytokines produced by mesenchymal stem cells (MSCs), generally referred to as the MSC secretome, has considerable potential for the treatment of cardiovascular disease. However, harnessing this MSC secretome towards meaningful therapeutic outcomes is challenging due to limited control on cytokine production following transplantation. This review outlines current understanding of the MSC secretome as a therapeutic for treatment of ischemic heart disease. We discuss ongoing investigative directions aimed at improving cellular activity and characterizing the secretome and its regulation in greater detail. Finally, we provide insights and perspectives for future development of the MSC secretome as a therapeutic tool. Show less

Teo GS, Ankrum JA, Martinelli R, Boetto SE, Simms K, Sciuto TE, Dvorak AM, Karp JM, Carman CV.
Systemically administered adult mesenchymal stem cells (MSC), which are being explored in clinical trials to treat inflammatory disease, exhibit the critical ability to extravasate at sites of inflammation. We aimed to characterize the basic cellular processes mediating this extravasation and compare them to those involved in leukocyte transmigration. Using high-resolution confocal and dynamic… Show more

Teo GS, Ankrum JA, Martinelli R, Boetto SE, Simms K, Sciuto TE, Dvorak AM, Karp JM, Carman CV.
Systemically administered adult mesenchymal stem cells (MSC), which are being explored in clinical trials to treat inflammatory disease, exhibit the critical ability to extravasate at sites of inflammation. We aimed to characterize the basic cellular processes mediating this extravasation and compare them to those involved in leukocyte transmigration. Using high-resolution confocal and dynamic microscopy, we show that, like leukocytes, human bone marrow-derived MSC preferentially adhere to and migrate across TNF-α activated endothelium in a vascular cell adhesion molecule-1 (VCAM-1) and G-protein coupled receptor (GPCR) signaling-dependent manner. As several studies have suggested, we observed that a fraction of MSC integrated into endothelium. In addition, we observed two modes of transmigration not previously observed for MSC: Para (between endothelial cells)- and trans (directly through individual endothelial cells)-cellular diapedesis through discrete pores and gaps in the endothelial monolayer, in association with VCAM-1-enriched 'transmigratory cups'. Contrasting leukocytes, MSC transmigration was not preceded by significant lateral migration and occurred on the time scale of hours rather than minutes. Interestingly, rather than lamellipodia and invadosomes, MSC exhibited non apoptotic membrane blebbing activity, that was similar to activities previously described for metastatic tumor and embryonic germ cells. Our studies suggest that low avidity binding between endothelium and MSC may grant a permissive environment for MSC blebbing. MSC blebbing was associated with early stages of transmigration, in which blebs could exert forces on underlying endothelial cells indicating potential functioning in breaching the endothelium. Collectively, our data suggest that MSC transmigrate actively into inflamed tissues via both leukocyte-like and novel mechanisms. Show less

Xu C, Miranda-Nieves D, Ankrum JA, Matthiesen ME, Phillips JA, Roes I, Wojtkiewicz GR, Juneja V, Kultima JR, Zhao W, Vemula PK, Lin CP, Nahrendorf M, Karp JM.
Monitoring the location, distribution and long-term engraftment of administered cells is critical for
demonstrating the success of a cell therapy. Among available imaging-based cell tracking tools, magnetic resonance imaging (MRI) is advantageous due to its noninvasiveness, deep penetration, and high spatial resolution. While… Show more

Xu C, Miranda-Nieves D, Ankrum JA, Matthiesen ME, Phillips JA, Roes I, Wojtkiewicz GR, Juneja V, Kultima JR, Zhao W, Vemula PK, Lin CP, Nahrendorf M, Karp JM.
Monitoring the location, distribution and long-term engraftment of administered cells is critical for
demonstrating the success of a cell therapy. Among available imaging-based cell tracking tools, magnetic resonance imaging (MRI) is advantageous due to its noninvasiveness, deep penetration, and high spatial resolution. While tracking cells in preclinical models via internalized MRI contrast agents (iron oxide nanoparticles, IO-NPs) is a widely used method, IO-NPs suffer from low iron content per particle, low uptake in nonphagocytotic cell types (e.g., mesenchymal stem cells, MSCs), weak negative contrast, and decreased MRI signal due to cell proliferation and cellular exocytosis. Herein, we demonstrate that internalization of IO-NP (10 nm) loaded biodegradable poly(lactide-co-glycolide) microparticles (IO/ PLGA-MPs, 0.4−3 μm) in MSCs enhances MR parameters such as the r2 relaxivity (5-fold), residence time inside the cells (3- fold) and R2 signal (2-fold) compared to IO-NPs alone. Intriguingly, in vitro and in vivo experiments demonstrate that internalization of IO/PLGA-MPs in MSCs does not compromise inherent cell properties such as viability, proliferation, migration and their ability to home to sites of inflammation. Show less

Weian Zhao, Sebastian Schafer, Jonghoon Choi, Yvonne J. Yamanaka, Maria L. Lombardi, Suman Bose, Alicia L. Carlson, Joseph A. Phillips, Weisuong Teo, Ilia A. Droujinine, Cheryl H. Cui, Rakesh K. Jain, Jan Lammerding, J. Christopher Love, Charles P. Lin, Debanjan Sarkar, Rohit Karnik & Jeffrey M. Karp Cell-surface sensors for real-time probing of cellular environments
The ability to explore cell signalling and cell-to-cell communication is essential for understanding cell… Show more

Weian Zhao, Sebastian Schafer, Jonghoon Choi, Yvonne J. Yamanaka, Maria L. Lombardi, Suman Bose, Alicia L. Carlson, Joseph A. Phillips, Weisuong Teo, Ilia A. Droujinine, Cheryl H. Cui, Rakesh K. Jain, Jan Lammerding, J. Christopher Love, Charles P. Lin, Debanjan Sarkar, Rohit Karnik & Jeffrey M. Karp Cell-surface sensors for real-time probing of cellular environments
The ability to explore cell signalling and cell-to-cell communication is essential for understanding cell biology and developing effective therapeutics. However, it is not yet possible to monitor the interaction of cells with their environments in real time. Here, we show that a fluorescent sensor attached to a cell membrane can detect signalling molecules in the cellular environment. The sensor is an aptamer (a short length of single-stranded DNA) that binds to platelet-derived growth factor (PDGF) and contains a pair of fluorescent dyes. When bound to PDGF, the aptamer changes conformation and the dyes come closer to each other, producing a signal. The sensor, which is covalently attached to the membranes of mesenchymal stem cells, can quantitatively detect with high spatial and temporal resolution PDGF that is added in cell culture medium or secreted by neighbouring cells. The engineered stem cells retain their ability to find their way to the bone marrow and can be monitored in vivo at the single-cell level using intravital microscopy. Show less

Sarkar D, Ankrum JA, Teo GS, Carman CV, Karp JM.
A cell's fate is tightly controlled by its microenvironment. Key factors contributing to this microenvironment include physical contacts with the extracellular matrix and neighboring cells, in addition to soluble factors produced locally or distally. Alterations to these cues can drive homeostatic processes, such as tissue regeneration/wound healing, or may lead to pathologic tissue dysfunction. In vitro models of cell and tissue… Show more

Sarkar D, Ankrum JA, Teo GS, Carman CV, Karp JM.
A cell's fate is tightly controlled by its microenvironment. Key factors contributing to this microenvironment include physical contacts with the extracellular matrix and neighboring cells, in addition to soluble factors produced locally or distally. Alterations to these cues can drive homeostatic processes, such as tissue regeneration/wound healing, or may lead to pathologic tissue dysfunction. In vitro models of cell and tissue microenvironments are desirable for enhanced understanding of the biology and ultimately for improved treatment. However, mechanisms to exert specific control over cellular microenvironments remains a significant challenge. Genetic modification has been used but is limited to products that can be manufactured by cells and release kinetics of therapeutics cannot easily be controlled. Herein we describe a non-genetic approach to engineer cells with an intracellular depot of phenotype altering agent/s that can be used for altering cell fate via intracrine-, paracrine-, and endocrine-like mechanisms. Specifically, we show that human mesenchymal stem cells (MSCs) can be engineered with poly lactide-co-glycolic acid (PLGA) particles containing dexamethasone, which acts on cytoplasmic receptors. The controlled release properties of these particles allowed for sustained intracellular and extracellular delivery of agent to promote differentiation of particle-carrying cells, as well as neighboring cells and distant cells that do not contain particles. Show less

Ankrum J, Karp JM.
Mesenchymal stem cell (MSC) therapy is poised to establish a new clinical paradigm; however, recent trials have produced mixed results. Although MSC were originally considered to treat connective tissue defects, preclinical studies revealed potent immunomodulatory properties that prompted the use of MSC to treat numerous inflammatory conditions. Unfortunately, although clinical trials have met safety endpoints, efficacy has not been demonstrated. We believe the challenge… Show more

Ankrum J, Karp JM.
Mesenchymal stem cell (MSC) therapy is poised to establish a new clinical paradigm; however, recent trials have produced mixed results. Although MSC were originally considered to treat connective tissue defects, preclinical studies revealed potent immunomodulatory properties that prompted the use of MSC to treat numerous inflammatory conditions. Unfortunately, although clinical trials have met safety endpoints, efficacy has not been demonstrated. We believe the challenge to demonstrate efficacy can be attributed in part to an incomplete understanding of the fate of MSC following infusion. Here, we highlight the clinical status of MSC therapy and discuss the importance of cell-tracking techniques, which have advanced our understanding of the fate and function of systemically infused MSC and might improve clinical application. Show less

The study of MSC trafficking is clinically relevant for minimally invasive cell therapy to promote regeneration of damaged tissue, to treat inflammation, and to promote angiogenesis. However, these studies are complicated by the diverse methods used to culture, characterize, and deliver MSCs and by the variety of methods used to assess homing events. This review provides a critical analysis of the methods used to track homing of exogenously infused MSCs and discusses strategies for enhancing… Show more

The study of MSC trafficking is clinically relevant for minimally invasive cell therapy to promote regeneration of damaged tissue, to treat inflammation, and to promote angiogenesis. However, these studies are complicated by the diverse methods used to culture, characterize, and deliver MSCs and by the variety of methods used to assess homing events. This review provides a critical analysis of the methods used to track homing of exogenously infused MSCs and discusses strategies for enhancing their trafficking to particular tissues. Show less