· Long-term lentiviral transduction of human mesenchymal stem cells (hMSCs) greatly enhances the usefulness of these cells. However, such transduction currently requires the use of polybrene, which severely inhibits hMSC socialbookmarkingfacts.infoon: Rockville Pike, Bethesda, MD. ölproduktion Opec. Barrel mehr pro Tag Opec-Länder einigen sich auf höhere! Oil reached $80 per gold cradle diagram barrel this month causing Trump to ölproduktion opec tweet on Thursday:!
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Die Produktion nahm um 1,1 Millionen Barrel pro Tag.. When multiple comparisons were used, adjusted p values are reported. Optimizing transduction efficiency and transgene expression.
The total amount of virus was kept the same. Expression levels were compared with 1-day transduction. Expression levels were compared with static culture. Expression levels were compared with control. Each data point is a mean of three replicates of one experiment. FGF-2, fibroblast growth factor Consistency of MSC transduction. The transduction efficiency of hMSCs frozen and thawed at different passages compared with those that were maintained continuously in culture.
A graph of all the transductions from the different donors at different passages. No statistical significance was found between passages or within donors. To investigate whether protamine sulfate is a viable alternative for polybrene, hMSCs were transduced at various concentrations of protamine sulfate with a modified dual reporter gene LR that codes for a fusion protein containing both luciferase Luc and mRFP functional domains [ 31 ].
The transduction efficiency was determined by analyzing the fluorescence with flow cytometry Fig. An example of the flow cytometry analysis is shown in supplemental online Figure 1. Unlike polybrene, there was no statistical difference in cell proliferation between untreated cells and cells treated with protamine sulfate at any concentration tested for an extended period of time 7 days Fig. Effect of protamine sulfate, WPRE, and viral concentration. The transduction efficiency was measured by the red fluorescent intensity.
There was no statistical difference between the groups. No statistical difference t test. Difference in relative fluorescence values between the gene construct with or without WPRE. LR, lentivirus with luciferase and monomeric red fluorescent protein; MOI, multiplicity of infection; WPRE, woodchuck hepatitis post-transcriptional regulatory element. In addition to increasing transduction efficiency, labeling of hMSCs can be enhanced by increasing transgene expression.
In an attempt to increase expression of the transgene, a WPRE was added at the end of the transgene in the vector construct. This was confirmed by Western blot analysis, which showed a 2. This resulted in a sharp initial rise in transduction efficiency up to 20 MOI followed by smaller increments in increased efficiency with further increasing amounts of lentivirus Fig.
The high viral titers also had no significant effect on cell proliferation supplemental online Fig. In addition to changing the ratio of virus to cell i. Halving the transduction volume to 0.
In contrast, changing the seeding density and adjusting the viral particles to maintain a consistent MOI had no effect on efficiency supplemental online Fig. The increased transduction efficiency also correlated with higher expression levels Fig. There was no difference in cell proliferation as compared with untreated cells supplemental online Fig. Another method commonly used to increase transduction efficiency is centrifugation after the addition of virus to the medium [ 33 ].
Unlike the case with static cultures, centrifugation caused the cells to detach at much lower concentrations of protamine sulfate even without the addition of virus.
Importantly, centrifugation alone without the addition of protamine sulfate did not improve transduction efficiency. Centrifuging at lower than 1, rpm g had no effect data not shown. Although a key characteristic of the lentivirus is its ability to transduce nondividing cells, it transduces dividing cells more efficiently [ 34 , 35 ].
This led us to hypothesize that treatment of hMSCs with FGF-2, a known mitogen [ 36 ], could have a positive impact on transduction efficiency. In both cases, FGF-2 significantly increased transduction efficiency Fig.
Storage of hMSCs in liquid N 2 is commonly practiced to preserve the cells for later use. Freeze-thaw of the cells was shown to not negatively impact the transduction efficiency of the cells at any passage Fig.
We did notice a slight but significant increase in transduction efficiency with cells that were previously frozen in P1 and P3. We have also observed that thawed cells can exhibit increased proliferation unpublished data , which could explain this increase in transduction efficiency.
Such donor-to-donor variations are normal observations with hMSCs [ 37 ]. Donor age 27—61 years old and gender had no significant effect. In the chondrogenic pellet assay, both low and high expressing cells showed cartilage formation similar to that of untransduced cells. Furthermore, cells expanded in the presence of FGF-2 formed larger pellets and had more matrix Fig. The white arrows point to the cartilage matrix. In the adipogenic assay, lipid formation was observed in all conditions.
To confirm that the lipid formation was not isolated to untransduced cells, the MSCs were stained for adipophilin. Colocalization of red fluorescence with adipophilin staining indicated lipid formation in lentiviral transduced hMSCs Fig.
Human mesenchymal stem cells were cultured in adipogenic medium for 21 days. The cultures were imaged for red fluorescence and merged with the immunofluorescence stain for adipophilin green. Transduced cells show both red fluorescence and adipophilin staining. To test osteogenic potential, transduced MSCs were loaded into porous calcium phosphate ceramic scaffolds that were implanted subcutaneously on the dorsal surface of immunocompromised mice. After 6 weeks in vivo, bioluminescent imaging showed strong transgene expression Fig.
Concurrently, the same cells cultured in vitro confirmed that fluorescent expression remained consistent for at least seven passages about 7 weeks Fig. Histologic analysis of the implanted ceramic cubes showed that bone formation was similar in high and low sort and control cells. There was no statistical difference in the ceramic cube scores between the transduced and the control cells in both FGF-2 and non-FGFtreated cells.
Interestingly, cubes loaded with FGFtreated cells had more bone formation Fig. Sorted human mesenchymal stem cells hMSCs were seeded into ceramic cubes and implanted subcutaneously.
The transduced hMSCs continued to show strong bioluminescence after 6 weeks in vivo. An x-ray image shows the location of the ceramic cubes. The high sort cells were cultured for another seven passages, equivalent to 7 weeks, and their transduction efficiency was measured at each passage. The numbers in the bars indicate the passage numbers.
After 6 weeks, the ceramic cubes were harvested and stained for histologic analysis. The black arrows point to the bone matrix found in all ceramics. FGFtreated cells showed more bone matrix overall. Currently, the addition of polybrene during transduction is required to obtain efficient lentiviral transduction with hMSCs.
Unfortunately, we have found that polybrene dramatically impacts hMSC proliferation and possibly their differentiation capabilities as well [ 27 ]. Next we investigated variables affecting the virus, the cells, and the protocol.
All these methods had an impact on both transduction efficiency and transgene expression. Protamine sulfate is a Food and Drug Administration-approved, relatively inexpensive polycation most commonly used to neutralize heparin overdose.
It is believed to improve transduction by neutralizing the negative charge between the cell surface and the viral particles [ 38 ]. It was first suggested as an alternative to polybrene by Cornetta and Anderson in [ 39 ]. However, in addition to using a different viral vector, the cells used were rapidly dividing NIH 3T3 cells and another cell line, which typically experience greater transduction efficiencies than primary cells [ 39 ].
Investigators have since used protamine sulfate for labeling of MSCs with superparamagnetic iron oxide for cell tracking by magnetic resonance imaging [ 40 ] and attempted to use for transduction with lentivirus [ 41 , 42 ].
As a consequence, protamine sulfate is rarely used for hMSC transduction. Thus ultracentrifugation is not required to concentrate the viral supernatant in our studies.
Furthermore, unlike polybrene, protamine sulfate did not affect the cells' ability to divide, thus allowing lower amounts of virus to be used for clinical or experimental purposes, potentially decreasing the initial number of MSCs required for therapy, and thereby enhancing the utility for therapeutic applications in which MSCs serve as regenerative cells. Although not as drastic, we also found that polybrene affected the proliferation of human umbilical vein endothelial cells, whereas protamine sulfate does not data not shown.
Thus, these results are potentially applicable to other cell types. In addition to improving transduction efficiencies, we sought to improve expression levels with the addition of WPRE at the end of the gene construct, which had been shown to improve transgene expression of the viral vector [ 43 , 44 ]. Although constructs with WPRE have been used previously with hMSCs [ 45 — 47 ], the degree of enhancement on lentiviral transduction of hMSCs was unknown because such vectors have not previously been directly compared with constructs not containing this element.
The addition of the WPRE resulted in two benefits to our system. First, whereas the transduction efficiency did not increase with WPRE, the expression level of the transgene increased 2. This confirmed previous results with T cells, for which the addition of the WPRE did not increase the percentage of transduced cells, affect the copy number of the transgenes, or affect the frequency of transcription, but instead increased the expression of the vector, possibly through stabilization of the transcript in the nucleus [ 43 ].
Second, we observed that the addition of WPRE benefited viral production as viral titers approximately doubled. It is clear that viral concentration is key to obtaining high transduction efficiency. Increasing viral concentration can occur from either increasing the amount of virus in the transduction solution increasing MOI or by decreasing the transduction solution volume while keeping the MOI constant.
Both resulted in higher transduction efficiencies. Unfortunately, since hMSCs are not grown in suspension, the volume is limited to the lowest volume possible that does not desiccate the substrate-attached cells. An alternative method to increase transduction efficiency is the centrifugation of the cells in transduction medium, which is also termed spinoculation.
Despite the small size of the virus and the relatively low g force, centrifugation is believed to function by effectively increasing the concentration of viral particles near the cells [ 33 ]. However, unlike the case with T cells, centrifugation alone had no effect on improving hMSC transduction and protamine sulfate continues to be required. Alternatively, it is possible that the stress from centrifugation causes the cells to be more susceptible to deleterious effects of protamine sulfate.
Ultimately spinoculation of hMSCs presents a number of different challenges. A larger volume is needed to provide sufficient medium coverage, which decreases the viral concentration and counteracts any increase in concentration from the spinoculation itself.
There are also issues with scalability. It is difficult to expand beyond the six-well plates used in these experiments. Our attempts at spinning T75 flasks have led to regions of cell death on the flask due to desiccation.
Although important, viral concentration is not the only viral factor that affects transduction efficiency. When the total amount of virus was held constant but spread out over multiple days, efficiencies improved despite the lower viral concentration at each day. This suggests that at any given time, there are a limited number of cells that are susceptible to transduction.
In addition to manipulating the virus, it is possible to affect the cell as well. Human MSCs are slowly proliferating cells that can lose their differentiation potential with increasing passage [ 36 ], thus limiting the number of cells available from each donor.
The addition of FGF-2 to cultures has the advantage of increasing the proliferation rate while delaying the loss of chondrogenic potential senescence and maintaining immune suppressive capabilities with increasing passage [ 36 , 48 ].
In addition, FGFtreated hMSCs form larger pellets with more extracellular matrix in the chondrogenic pellet assay [ 4 , 36 ]. The increased proliferation of hMSCs provides another opportunity to increase transduction efficiency. Although it is true that lentiviruses can transduce nondividing cells [ 49 ], lentiviral transduction is superior with rapidly dividing cells [ 34 , 35 ].
When FGF-2 was added during the time of transduction, the improvement in efficiency and increase in transgene expression was donor-dependent. It is possible that this relates to the length of time it takes for the cells of a particular donor to respond to the mitogen.
In contrast, if the cells were cultured in FGF-2 for at least a week before transduction, we saw both increased efficiency and transgene expression. Human MSCs are known to have donor-to-donor variability [ 37 ], and there have been reports of donor-to-donor variability with hMSC transduction [ 45 ]. Interestingly we found this variability to be dependent on passage number. Furthermore, there can also be high intradonor variability. It is possible that this relates to the fact that proliferation rates vary between donors at passages 1 and 2, and that by passage 3 the proliferation rates stabilize.
Furthermore, inclusion of WPRE at the end of the transgene leads to higher viral titers and increased transgene expression. Transduction efficiency and transgene expression can be improved by transducing at passage 1 and by treatment with FGF-2 for 1 week prior to transduction.
With the capacity to easily, reliably, and inexpensively transduce hMSCs, it will be possible to efficiently use genetic engineering to add or delete a function, improve or replace an existing one, and gain insight into the biology of these cells through the use of reporter genes.
This will significantly impact not only scientific progress with these cells but also their clinical and therapeutic translational potential. Danielle MacKay for their help with the immunohistochemical stain, and Christine Lee for her assistance with the Western blot.
We also thank David Carrino for his help reviewing the manuscript and with the Western blot. This research was supported by the L. National Center for Biotechnology Information , U. Stem Cells Transl Med. Published online Nov Author information Article notes Copyright and License information Disclaimer.
Received Jul 5; Accepted Sep This article has been cited by other articles in PMC. Abstract Long-term lentiviral transduction of human mesenchymal stem cells hMSCs greatly enhances the usefulness of these cells. Mesenchymal stem cells, Lentiviral vector, Gene therapy, Transduction, Adult human bone marrow, Adult stem cells, Cellular therapy, Osteoblast. I ntroduction Mesenchymal stem cells MSCs are multipotent adult stem cells that can differentiate into adipocytes, chondrocytes, and osteoblasts [ 1 , 2 ].
Transduction Transductions were done in six-well plates. Differentiation Assays Human MSCs were transduced at P0 and cultured for an additional 4 days after the start of transduction. Open in a separate window.
Die Produktion nahm um 1,1 Millionen Barrel pro Tag.. Ursprungligen tillverkades öl av jäst, vatten och stärkelsebaserade..
We did notice a slight but significant increase in transduction efficiency with cells that were previously frozen in P1 and P3. Dilihat dari valuasinya, opsi adalah yang tersulit dan obligasi yang paling sederhana sementara saham, meskipun mempunyai banyak metode penilaian, berada di antara keduanya.