BOSTON—Scientists at nanotechnology, cancer and stem cell development company Minerva Biotechnologies have discovered that a single, new growth factor enables embryonic stem cell (hESCs) growth without using fibroblast "feeder cells." According to the researchers, the findings could be used to propagate large numbers of pluripotent stem cells for therapeutic interventions.
Earlier this year, Minerva reported that MUC1, a cell surface protein aberrantly expressed on more than 75 percent of cancer tumors, contains a small membrane receptor called MUC1* that is expressed to much higher levels than MUC1 in a variety of human tumor tissues (see "A midnight discovery," DDN June 2008). Using its proprietary nanoparticle technology, Minerva discovered that once cleaved, MUC1* dimerizes with itself and other growth factor receptors through binding of a newly discovered ligand for MUC1*, called NM23. Binding and dimerization then activates the tumor to unregulated cell growth, invasion and metastasis. Blocking MUC1* dimerization and NM23 binding leads to cancer cell death, Minerva found.
In this most recent study, Minerva, collaborating with researchers at the University of California at Santa Barbara, found that MUC1* acts as a growth factor receptor on undifferentiated hESCs. In fact, the team found that under conditions including the addition of conditioned media from fibroblast feeder cells, antibody-induced dimerization of the extracellular domain of MUC1* doubled the growth of hESCs compared with current methods and without requiring the addition of exogenous basic fibroblast growth factor (bFGF).
Further, the researchers found the addition of MUC1* dimerizing ligands, Anti-MUC1* or NM23, enabled the growth of pluripotent stem cells in feeder-cell-free and bFGF-free minimal growth media.
"In fact, stem cell growth supported by the addition of MUC1* ligands to minimal media resisted spontaneous differentiation and produced more pluripotent cells than any other growth condition that we tested," the researchers wrote. "In contrast, neither minimal stem cell growth media nor media plus bFGF produced any undifferentiated stem cells. Stem cells that were cultured in conditioned media from fibroblasts plus bFGF generated a mixture of undifferentiated and differentiated colonies and the colonies were smaller than those produced by MUC1* stimulation."
The finding suggests this receptor may be a pivotal switch in the process of differentiation, according to the research team.
"The data presented strongly suggest that MUC1* is a critical marker for the identification and isolation of pluripotent embryonic stem cells as well as a key mediator of the growth and differentiation of pluripotent stem cells," the researchers concluded.
According to the research team, these methods can be readily extended to identifying and sorting live embryonic stem cells, which could automate and improve the procedure for separating out stem cells that remain pluripotent from those that have begun to differentiate. However, Minerva acknowledged some technical limitations.
"At present, this is an imprecise and labor-intensive process that depends on the technician's ability to visually discriminate between cell types then manually dissect pluripotent cells without contaminating the pool with cells that have already entered the differentiation process," Minerva wrote. "To implement these therapies, one must have the ability to produce a replenishable supply of pluripotent stem cells, on a large scale, that can then be induced to differentiate into the desired cell types. Certain technical hurdles must be overcome before clinical therapies using pluripotent stem cells can become a reality. Improved methods for propagating pluripotent stem cells and ensuring their pluripotency must be developed."
The study, MUC1* Mediates the Growth of Human Pluripotent Stem Cells, was published Oct. 3 in the Public Library of Science journal PLoS ONE. DDN
