Stem cells need 'helper cells'
Engineered “helper cells” improve survival rate of transplanted stem cells, mouse study finds.
Just as volunteers hand out cups of energy drinks to marathon runners, specially engineered “helper cells”—transplanted along with stem cells—dole out growth factors and increase stem cells’ endurance, Johns Hopkins' researchers report.
The study, published in Experimental Neurology, is believed to be the first to test the helper-cell strategy, which is hoped will overcome a major barrier to successful stem cell transplantation.
“One of the bottlenecks with stem cell therapy is the survival of cells once they’re put in the body — about 80 to 90 percent often appear to die,” says Jeff Bulte, Ph.D., a professor in the Johns Hopkins University School of Medicine’s Institute for Cell Engineering. “We discovered it helps to put the stem cells in with some buddies that give off growth factors.”
Stem cells can morph to into any cell type the body needs, making them useful to treat conditions ranging from type 1 diabetes by replacing insulin-producing cells in the pancreas, to heart disease by replacing damaged heart cells.
The biggest problem for transplanted stem cells which are initially grown in a petri dish with ready access to oxygen, is that once inside the body, oxygen levels are low.
“They get a shock,” says Bulte.
Other research groups had had success with acclimating cells to lower oxygen levels before transplantation. And another promising strategy is to provide stem cells with scaffolds, giving them a structure better integrating them into the host.
Spearheaded by postdoctoral fellow Yajie Liang, Ph.D., the research team further enhanced stem cell survival through the addition of a steady dose of fibroblast growth factor (bFGF)—an “energy drink” that spurs cells to grow.
The team engineered greater-than-normal amounts of bFGF under the control of the drug doxycycline (dox). Making the bFGF gene responsive to dox gave researchers more control over bFGF, Liang explained.
The engineered helper cells combined with stem cells, were introduced to one set of mice; while untreated stem cells were transplanted into a separate group of mice. Both groups of stem cells had also been engineered to produce a luminescent protein, so that when using special optical instruments, researchers could measure stem cell rate of incorporation and survival.
For the first three days following injection, stem cells transplanted with helper cells gave off a noticeably stronger signals than stem cells transplanted without helper cells, Liang said. But within a few days, there was no difference between the two cell types.
Despite the short, 2 day duration of the 'helper cells’ effect, the experiment proved the potential for using helper cells—as those cells survived 6 times greater (see abstract results) than untreated stem cells.
The ultimate solution to keeping transplanted stem cells alive may be helper cells, boosted with fibroblast growth factor.
Cell-based therapy of neurological disorders is hampered by poor survival of grafted neural progenitor cells (NPCs). We hypothesized that it is possible to enhance the survival of human NPCs (ReNcells) by co-transplantation of helper cells expressing basic fibroblast growth factor (bFGF) under control of doxycycline (Dox). 293 cells or C17.2 cells were transduced with a lentiviral vector encoding the fluorescent reporter mCherry and bFGF under tetracycline-regulated transgene expression (Tet-ON). The bFGF secretion level in the engineered helper cells was positively correlated with the dose of Dox (Pearson correlation test; r = 0.95 and 0.99 for 293 and C17.2 cells, respectively). Using bioluminescence imaging (BLI) as readout for firefly luciferase-transduced NPC survival, the addition of both 293-bFGF and C17.2-bFGF helper cells was found to significantly improve cell survival up to 6-fold in vitro, while wild-type (WT, non-transduced) helper cells had no effect. Following co-transplantation of 293-bFGF or C17.2-bFGF cells in the striatum of Rag2−/− immunodeficient mice, in vivo human NPC survival could be significantly improved as compared to no helper cells or co-transplantation of WT cells for the first two days after co-transplantation. This enhancement of survival in C17.2-bFGF group was not achieved without Dox administration, indicating that the neuroprotective effect was specific for bFGF. The present results warrant further studies on the use of engineered helper cells, including those expressing other growth factors injected as mixed cell populations.
Other authors on the paper were Yajie Liang, Louise Ågren, Agatha Lyczek and Piotr Walczak, all of the Johns Hopkins University School of Medicine.
This study was funded by the National Institute of Neurological Disorders and Stroke (grant number 2RO1 NS045062) and the Anders Wall Foundation.
Original press release:http://www.hopkinsmedicine.org/news/media/releases/