A cell delivery vehicle is a matrix (made from natural or synthetic materials or a combination of
the two) which can be combined with cells to be transplanted into a human or animal host.
A wide variety of cells at different stages of differentiation from a range of adult and embryonic sources is being investigated for therapeutic use in the human body. However, transplanted cells face a harsh environment and in general, most cells die shortly after implantation 1-5, 7. This can be attributed to ischemia due to absence of vascularization, the absence of cell attachment sites resulting in cell death (anoikis), the host immune response 6, 7, and low cell density 8. In the end, few cells engraft and many may veer down undesired differentiation pathways 9.
Cell delivery vehicles are designed to provide cell attachment sites to overcome anoikis7, protect from host immune cells, and localize the cells to maintain appropriate cell densities. The vehicle must also be non-immunogenic, biodegrade at a
ppropriate rates, and have a physiological pH and temperature to avoid pH shock and hypothermia 10-12. Ideally, it is desirable for its formulation to be customizable so that appropriate signals can be added (e.g. growth factors, extracellular matrix proteins) to provide boundaries against continued cellular differentiation. With the growing recognition of the benefits of minimally invasive surgical procedures, injectability of the vehicle also becomes an increasingly important attribute.
Different Types of Vehicles
Several hydrogels are currently used as vehicles in some cases for both preclinical and clinical research. They are differentiated by their origin (natural, synthetic, and semi-synthetic), microstructure (fibrous network), stiffness, degradation time, and potential toxicities. The following table lists some of the more commonly used vehicles*:
(*while a basement membrane preparation from EHS mouse sarcoma (Matrigel) is used widely for in vivo animal research, its rodent origin present large challenges for obtaining FDA approval for human implantation. It will not be considered in this discussion).
Comparison of the vehicles listed here is shown below. The primary differentiation occurs in their microstructure (i.e. self-organization into a fibrous network), stiffness (i.e. elastic, tensile, or shear modulus measured in kPa), gelation time
(from initial preparation as a liquid to final gel), and the pH, temperature, and salt content when the matrix is still a liquid.
The HyStem Advantage
Hyaluronate (HA) is a key component of the cell extracellular matrix and has been used for a variety of medical applications13. HyStem is thiol-modified HA which is chemically crosslinked in the presence of PEGDA (HyStem).Thiol-modified gelatin can also be included for providing cellular attachment sites (HyStem-C) as can thiol-modified heparin for providing slow growth factor release (HyStem-HP).
In general, HyStem differentiates itself from its competitors in its user-friendly customizability and gentleness to cells when mixed in liquid form.HyStem allows the user to adjust not only its stiffness but also gelation time by varying concentrations of crosslinker and HA. HyStem is at physiological pH and temperature in its liquid form and hence provides a gentle microenvironment for encapsulated cells during transplantation.In contrast, Collagen I and Puramatrix are pH 2 in liquid form whereas fibrin and alginate gel only in the presence of calcium which may adversely affect neuronal cell signal transduction15.PEGDA requires UV l
ight for crosslinking in the presence of free radical photocrosslinkers19.UV light is a known genotoxic agent can have deleterious effects on the cell cycle23.
- Contreras, J.L. et al. Cytoprotection of pancreatic islets before and early after transplantation using gene therapy. Kidney Int. 2002; 61: 79–84.
- Nakano, M. et al. Caspase-3 inhibitor prevents apoptosis of human islets immediately after isolation and improves islet graft function. Pancreas 2004; 29: 104–109.
- Schierle, G.S. et al. Caspase inhibition reduces apoptosis and increases survival of nigral transplants. Nat. Med. 1999; 5: 97–100.
- Emgard, M. et al. Both apoptosis and necrosis occur early after intracerebral grafting of ventral mesencephalic tissue: a role for protease activation. J. Neurochem. 2003; 86: 1223–1232.
- Guerette, B. et al. Prevention by anti-LFA-1 of acute myoblast death following transplantation. J. Immunol. 1997; 159: 2522–2531.
- Neural stem cell transplant survival in brains of mice: assessing the effect of immunity and ischemia by using real-time bioluminescent imaging.
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- Laflamme MA et al, Cardiomyocytes derived from human embryonic stem cells in pro-survival factors enhance function of infarcted rat hearts. Nat Biotechnol. 2007; 25:1015-24.
- Ohga Y. et al, Cell density increases Bcl-2 and Bcl-x expression in addition to survival of cultured cerebellar granule neurons. Neuroscience. 1996; 73:913-7.
- Mooney DJ and Vandenburgh H, Cell delivery mechanisms for tissue repair. Cell Stem Cell 2008; 2:205-13.
- Wuertz K et al, MSC response to pH levels found in degenerating intervertebral discs. Biochem Biophys Res. Comm 2009; 379: 824-829.
- Temenoff JS et al, In vitro cytotoxicity of redox radical initiators for cross-linking of oligo(poly(ethylene glycol) fumarate) maromers. Biomacromolecules 2003; 4: 1605-1613.
- Rauen U, Mammalian cell injury induced by hypothermia-the emerging role for reactive oxygen species. Biol Chem 2002; 383:477-88.
- Encyclopedia of Biomaterials and Biomedical Engineering. GE Wnek and GL Bowlin (editors) 2nd edition. 2008 Informa Healthcare.
- Weisel JW, The mechanical properties of fibrin for basic scientists and clinicians. Biophysical Chemistry 2004; 112:267-276.
- Bezprozvanny I and Mattson MP, Neuronal calcium mishandling and the pathogenesis of Alzheimer’s disease. Trends Neurosci. 2008; 31:454-63.
- Velegol D and Lanni F, Cell Traction Forces on Soft Biomaterials. I. Microrheology of Type I Collagen Gels. Biophysical Journal 2001; 81: 1786-1792.
- Boontheekul T, Kong HJ, and Mooney DJ, Controlling alginate gel degradation utilizing partial oxidation and bimodal molecular weight distribution. Biomaterials 2005; 26:2455-65.
- Vanderhooft JL, Alcoutlabi M, Magda JJ, and Prestwich GD, Rheological properties of cross-linked hyaluronan-gelatin hydrogels for tissue engineering. Macromol Biosci. 2009; 9:20-8.
- Patel PN, Smith CK, Patrick CW Jr, Rheological and recovery properties of poly(ethylene glycol) diacrylate hydrogels and human adipose tissue. J Biomed Mater Res A. 2005; 73:313-9.
- Scaffolding in Tissue Engineering PX Ma and J. Elisseeff (editors) 2005 CRC Press; Chapter 15: PuraMatrix: Self-Assembling Peptide Nanofiber Scaffolds (S. Zhang et al)
- BD® PuraMatrix® Peptide Hydrogel Guidelines for Use. SPC-354250-G rev 4.0.
- Spencer NJ, Cotanche DA, Klapperich CM, Peptide- and collagen-based hydrogel substrates for in vitro culture of chick cochleae. Biomaterials 2008; 29:1028-42.
- Hopkins KM et al, Deletion of mouse rad9 causes abnormal cellular responses to DAN damage, genomic instability, and embryonic lethality. Mol Cell. Biol2004; 24:7235-7248.