Scientists found that mesenchymal stromal cells (MSCs) — cells that have similar properties to stem cells — individually coated with a soft microgel were able to reverse established lung tissue scarring in a mouse model of pulmonary fibrosis.
Their findings were reported in the study, “Inhibition of aberrant tissue remodeling by mesenchymal stromal cells singly coated with soft gels presenting defined chemo mechanical cues,” published in the journal Nature Biomedical Engineering.
Pulmonary fibrosis (PF) is a disease characterized by scarring — or fibrosis — of the lungs, making it difficult to breathe.
Fibrosis is the result of chronic inflammatory reactions triggered by a variety of stimuli, including autoimmune reactions, persistent infections, allergic responses, exposure to chemical insults, and radiation. Scar formation occurs when the production of the protein collagen exceeds the rate at which it is degraded, and increases over time.
MSCs are similar to stem cells and have been tested in clinical trials in people with fibrotic tissue injury. Their therapeutic effectiveness is derived from the release of anti-inflammatory, or immunomodulatory, factors that can suppress the inflammatory responses leading to fibrosis in the early stages of disease.
However, immune suppression alone is not enough to improve outcomes in people with well-established lung fibrosis.
“While previous studies tested the therapeutic effects of MSCs — which are known to suppress inflammation and to adapt to different tissue environments — their efficacy has so far been limited to early phases of the disease, when inflammation levels are high, and scar tissue is still forming,” Jae-Won Shin, PhD, the study’s lead author, said in a university press release.
To enhance the therapeutic potential of MSCs to degrade scar tissue and regenerate healthy tissue, Shin and his team from the University of Illinois Chicago engineered a soft microgel that encapsulates individual MSCs to facilitate the delivery — without major surgery — of both cells and materials deep into the lung tissue.
“Our approach was to optimize MSC-based therapeutics to work after inflammation has been reduced, which is when most people are diagnosed with fibrosis,” Shin said.
Investigators added a protein called tumor necrosis factor-alpha (TNF-alpha) to the microgel they used to encapsulate MSCs derived from mouse bone marrow. TNF-alpha is an inflammatory signal that stimulates MSCs to produce an enzyme called collagenase, which degrades excess collagen and promotes tissue repair.
The team also designed a special droplet microfluidic device to encapsulate single cells consistently and rapidly within the gel, and refined the process to minimize the volume of gel coating.
“We miniaturized down to the small scale, the individual cell, which is important for delivery of the therapeutic into the tiny airways of the lungs,” said Sing-Wan Wong, PhD, the study’s first author.
Experiments confirmed that mouse MSCs coated in a gel containing TNF-alpha were able to produce collagenase and degrade collagen. Similar effects were observed in MSCs derived from human bone marrow following gel coating.
To examine the therapeutic relevance of this approach, investigators triggered lung fibrosis in mice by exposing animals to bleomycin and then treated them with gel-coated and uncoated MSCs one week later. Gel-coated MSCs, but not uncoated MSCs, significantly limited total collagen deposition in the lungs.
Gel-coated MSCs also reduced lung tissue stiffness and the infiltration of inflammatory immune cells. Further, increasing the dose of uncoated MSCs administered failed to produce the same effects as gel-coated cells.
“Thus, gel coating of MSCs is an effective means of suppressing fibrotic lung injury while minimizing the number of required therapeutic donor cells,” the team wrote.
Additional experiments also confirmed the ability of gel-coated MSCs to suppress lung fibrosis was due to the production of collagenase, and not driven by long-term exposure to MSCs within lung tissue.
Using genetically engineered mice that were unable to produce TNF-alpha, researchers showed that gel-coated MSCs were no longer able to stop collagen deposition in the lungs and block the influx of immune cells. As pointed out by investigators, these observations indicate that TNF-alpha from the host is necessary for gel-coated MSCs to be effective.
Finally, the team tested the ability of gel-coated MSCs to reverse lung scarring at later time points when fibrosis had already set in and inflammation subsided.
Mice treated with gel-coated MSCs loaded with TNF-alpha three weeks after bleomycin treatment had less fibrotic tissue, lung stiffness, and collagen deposition. Immune cell influx also was reduced in these animals.
However, microgel loaded with TNF-alpha and collagenase alone (without MSCs) was not sufficient to resolve fibrosis.
“Our results show that engineered gel coating can be used to optimize … parameters to improve MSC-based therapeutics against fibrotic lung injury,” the authors wrote.
“This is really one of the first scientific demonstrations that collagen levels can be normalized well after fibrotic injury and that the cell environment, not just the cells themselves, can be designed at the single-cell level in a precise manner,” said Shin. “Our results suggest a feasible approach to predictively program cellular functions for desired therapeutic outcomes.”