(4bv) Biomaterials and Stem Cells for Tissue Regeneration

Authors: 
Lei, Y., University of California, Berkeley


Research Overview: Human pluripotent stem cells (hPSCs) have the capacities for indefinite in vitro expansion and differentiation into presumably all cell types of the human body.  They therefore represent highly promising cell sources for numerous biomedical applications, such as cell replacement therapy, tissue engineering, and pharmacology and toxicology screens.  However, before achieving their potential, we have to solve many technical challenges including: a) produce large number of various progenitor/mature cells from hPSCs and b) make these cells survive, mature, integrate with the host tissue and function after implanting in vivo.  My researches focus on designing and using biomaterials to solve these problems.  In this poster, three current projects and the future research will be presented. 1) A scalable, GMP compliant 3D culture system for the production of hPSCs and their progeny:  The above mentioned applications require large numbers of cells of high quality.  For instance, ~105 surviving dopaminergic neurons, ~109 cardiomyocytes, or ~109 β cells are required to treat a patient with Parkinson’s disease (PD), myocardial infarction (MI), or type I diabetes respectively.  Analogously, ~1010 hepatocytes are need for an artificial human liver, and ~1010 cells may be required to screen a million compound library.  Considering the large patient populations with degenerative diseases or organ failure as well as the millions of chemical/peptide/nucleotide compounds that can be screened against thousands of molecular targets, massive numbers of hPSCs or their progeny are needed.  It is becoming clear that the current 2D-based cell culture systems are incapable of producing sufficient cells and are becoming a bottleneck.  Using biomaterials, we developed a simple, defined, scalable, GMP compliant 3D culture system for the production of hPSCs and their progeny.  With this system, we have achieved long-term, serial expansion (> 60 passages) of multiple hPSC lines with a high replication rate (20-fold over 5-day per passage), yield (2.0 x107 cells/ml), and purity (95% Oct4+), all of which offer considerable improvements over the current approaches.  After long term culture in 3D, hPSCs remained pluripotent as shown by their ability to form all the 3 germ layers during the in vitro EB assay and in vivo teratoma assay.  More importantly, directed differentiation of hPSCs into their progeny (e.g. dopaminergic neuron progenitors) could be conducted efficiently within the system following expansion, enabling us to produce large numbers of cells with direct therapeutic relevance.  This system will be of broad interest from the laboratory to the biotechnology scale.  2) Scalable production of dopaminergic neuron progenitors and their application in treating Parkinson’s Disease: Implanting fetal ventral mesencephalic tissue containing dopaminergic (DA) neuron progenitors into the putamen of Parkinson’s (PD) patients are effective to relief the motor symptoms.  However, this treatment hasn’t been widely used partially due to the ethic problem and limited cell source.  hPSCs are promising to overcome these problems with recent breakthrough on efficient differentiating them into DA progenitors or neurons.  However, a GMP compliant and cost effective culture system is required to produce these cells at various scales before they can be reached in clinic.  In this project, we used our 3D culture system along with a small molecule cocktail to produce DA progenitors.  We then used these cells to treat PD with rodent model.  Research on improving the treating efficiency through combining protein delivery with cell implantation is also undergoing. 3) Synthetic ECM hydrogel for stem cell therapy: In vivo, stem cells reside in complex 3D niches with well-regulated biochemical & biophysical cues that control cell maintenance, self-renew and differentiation.  We developed synthetic hydrogels to mimic these niches for 3D stem cell culture and delivery.  Polyethylene glycols or hyaluronic acids are cross-linked with protease degradable peptides.  Peptides derived from ECM proteins are introduced as adhesion points for cells.  Protein factors can be incorporated through physical or chemical immobilization.  With these hydrogels, we built a 3D model for studying the calcification of vascular stem cells.  We also cultured mesenchymal stem cells in these gels and found the 3D environments including the mechanics, adhesion peptide identity, concentration and presentation significantly affected their proliferation, spreading and migration. Currently, we are using these hydrogels to deliver stem cells with the objective to improve the cell survival rate and integration in vivo.  Future research will focus on combining stem cells, protein factors and biomaterials to treat degenerative diseases including: Parkinson’s, stroke, spinal cord injury, Type I diabetes and myocardial infarction

Education:

  • UCLA, Chemical and Biomolecular Engineering, PhD, 2010
  • UCLA, School of Medicine, M.S., 2006

Research Experience:

  • UC Berkeley, 2010- (Postdoc, David Schaffer Lab)
  • UCLA, 2006-2010 (Tatiana Segura Lab)
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