Cell-based tissue engineering for lung regeneration
Emphysema is a lung disease that results in permanently decreased lung volume and tissue loss. The authors of this paper evaluated a potential treatment of emphysema using tissue engineered scaffolds made from Gelfoam sponge. The purpose of the scaffold was to provide a temporary, biodegradable structure that would allow for migration of lung cells and the formation of new vasculature to help regenerate lung tissue. Gelfoam sponge is as a soft and pliable hemostatic material commonly used in surgeries. If the amounts of Gelfoam sponge used is small, it can be completely broken down and absorbed by the body over the course of 2-6 months, usually with minimal immune response and little or no scarring.
Small pieces of the sponge were implanted into the lungs of rats to determine how cells grew into and around the device. In 2-4 weeks, cell migration into the device was observed. After six months, the sponges completely dissolved and some cells remained in the area, but there was no new vasculature and no normal lung structure formed.
Small pieces of the sponge were implanted into the lungs of rats to determine how cells grew into and around the device. In 2-4 weeks, cell migration into the device was observed. After six months, the sponges completely dissolved and some cells remained in the area, but there was no new vasculature and no normal lung structure formed.
The experiment was repeated using sponges that had been seeded with progenitor cells that were isolated from fetal rats. After 100-128 days, the sponge began to degrade, but unlike the unseeded sponges, vascular-like structures were observed where the cell seeded sponge had been.
Fig. 1 Remodeling of sponge and formation of “alveolar-like structures.” A–C, day 100; D–F, day 128. In 100-128 days, the sponge degrades, leaving structured “lung tissue” in its place. F, surrounding alveolar units. Thin arrows indicate the vascular-like structures inside the sponge area, and open arrows indicate epithelial-like cells in sponge.
India blue ink was injected into the pulmonary artery and ink was seen in the sponge, indicating that the structures were connected to the circulatory system. The rats were injected with BrdU 24 hrs before being sacrificed and proliferation and division was observed in the cells within the sponge. An immunostain for proSP-C, a marker for type II epithelial cells, revealed the presence of epithelial cells within the sponge. The cells were also stained with an anti-CCSP antibody. CCSP-expressing cells are known to be important for epithelial cell renewal and these cells were also observed in the sponge. Interestingly, many of the cells that grew and proliferated in the sponge appear to be endogenous cells, not the seeded fetal progenitor cells. The researchers speculate that the fetal cells were releasing growth factors and these soluble factors encouraged other cells to migrate into the sponge.
Fig 2. Angiogenesis and immunohistochemistry staining in the
implanted sponges. A and B: India ink pigment found
inside the sponges (thin arrows). C: BrdU staining demonstrates
cell proliferation (thin arrows). D: anti- Clara cell secretory protein antibody (CCSP) (brown color, thin arrows) to demonstrate bronchiolar epithelial cells. E: alveolar
epithelial cell staining (proSP-C; thin arrows). F: endothelial cells were
stained with antibody for von Willebrand factor (VWF; thin
arrows). G: anti-CD45 antibody was used to illustrate the lack
of infiltrating leukocytes in the sponge. H: negative controls for each
antibody.
I found this paper interesting because it demonstrates that using a combination of biological factors and mechanical engineering can create a more effective treatment. A total artificial lung would be very difficult to create because it would require the formation of a complex, organized 3-D structure that is capable of connecting to both the vascular system and the air exchange structures. Also, since the lungs are repeatedly expanded and contracted, a permanently implanted material would have to be biocompatible, flexible and strong and ideally, remain flexible and strong for the patient’s lifetime. If the growth of new tissue can be encouraged and the breakdown products of the implanted material are biodegradable, this could allow some patients to avoid transplants and immunosuppressive drugs and not worry that their artificial lung might fail.
10 comments:
This is a breakout discovery if in the future that will be used in clinic trials to save the life of many. However, I wonder if the same technique can be applied to sufferers of lung cancer or the scars of tuberculosis? If we can just generate lung tissues, then perhaps the same techniques can be applied to heal patients in a broader range.
At what scale have these structures been shown to be "lung-like"? At the organ level? Organoid? Cell?
I'm curious about the scale of this device too. It seems like only a very small amount of Gelfoam can be used. Will too large a scaffold not degrade rapidly enough and undergo fibrotic encapsulation? If the main purpose of the Gelfoam is to provide a mechanical structure for cell migration, maybe other materials could be explored that will make scaling-up easier.
Interesting post. I have a few questions for you. Would cells be seeded onto the scaffold and grown ex vivo until the cells show lung-like functionality before it is implanted? Or would the scaffold degrade before the cells reach that point?
It's amazing how as our lungs contract and expand continuously, in the course of 2-6 months a sponge seeded with progenitor cells can be implanted, integrated, and vascularized. I wonder about the mechanical and fatigue testing of this cell-based tissue engineering approach.
As the Gelfoam sponge, seeded with progenitor cells, is implanted into the body, vascular-like tissues begin to form. I am wondering how do the scientists assure this new formed vascular-like tissue retains functionality of lung. Does this new tissue perform lung-like functions as real lungs?
To terry and ginger,
The implanted sponge was 5x5x2 mm, so its certainly larger than cell size, but smaller than organs. It's large enough that oxygen diffusion would present a problem. I think that's why the researchers were very happy to see development of new vasculature, as well as ingrowth of lung cells into the device seeded with fetal progenitor cells.
To kjlin,
I haven't seen any info about the mechanical strength of this device. There was no mention in the paper of mechanical wear from sponges implanted in mice after 2-6 months. The material is biodegradable, so I doubt it was designed for strength.
To Quyen,
I don't think vasculature would be formed ex-vivo, simply with the seeded progenitor cells. The paper mentioned that most of the cells seen in the device after 6 months had markers that matched the rat, not the seeded cells. Vasculature formation probably requires growth factors and other signals from the host.
To henry,
To determine if the vasculature in the device was connected to the circulatory system, a dye (India ink) was injected into the blood stream of the rats. The dye was found in the newly formed vasculature in the device. It would be interesting to see how the lung capacity of the rats changed after implantation of the device, but that authors did not perform this experiment.
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