Pig Cells Help Injured Soldiers Recover

Cells derived from pig bladders served as surgically implanted scaffolding to recruit native stem cells to help build muscle in the legs of five severely injured soldiers and civilians, researchers reported.

Three out of five patients with lower limb volumetric muscle loss experienced a measurable improvement in the ability to stand, walk, and climb stairs 6 months after surgical placement of porcine extracellular matrix (ECM) scaffolding, according to Stephen F. Badylak, MD, of the University of Pittsburgh, and colleagues.

The pig cells boosted ability of native stem cells to form dense muscle tissue, he said.

Procedural implantation of porcine ECM scaffolding showed promise in rodent testing prior to this small pre-clinical human trial, which researchers presented online in Science Translational Medicine.

"When you lose so much muscle that the gap is too large for the normal restorative processes to occur, the end result is typically filling that gap with scar tissue," Badylak said in a press conference. "[We found] an effective method for restoring ... new functional enervated and vascularized muscle tissue, using an approach that does not involve the delivery of any cells."

Badylak said that as the pig cells degraded they released peptides, which served as a homing device to recruit the body's endogenous stem cells to the injury site.

All five of the patients were male and had experienced anywhere from 58% to 90% of leg muscle loss from a serious injury at least 6 months prior to the experimental procedure.

For example, two men were injured by an IED while on active military duty, two had serious skiing accidents, and one had an exercise-related injury. Each patient also underwent unsuccessful multiple surgeries and physical therapy prior to receiving ECM scaffolding.

Prior to the scaffolding procedure, all of the patients participated in a custom-designed 12 to 16 week physical therapy program, and post procedure had additional physical therapy beginning 24 to 48 hours after surgery. Post-surgical physical therapy ranged from 5 to 23 weeks.

"The shortest time from injury to treatment for one individual was 13 months, and the longest was 7 years," Badylak said.

"As the stem and progenitor cells are recruited into the remodeling site, when those cells get there they depend upon local environmental cues to say, 'OK, now that I'm here, what do you want me to do?' and one of the most important cues is the mechanical force that is asked of the site.

"If that doesn't happen when they [the cells] get there, and they don't get those signals, they can turn into anything else: fat tissue, cartilage, bone," Badylak said.

The researchers stressed the need for a scar tissue-free area, with adjacent healthy tissue for the ECM scaffolding to take. "It's got to have a blood supply; [it's] got to be enervated," Badylak said. "If you put this material in the middle of a scar, all it's going to do is turn into more scar."

Success was measured by 25% improvement in day-to-day activities like getting out of a chair, taking steps, and being able to walk up stairs. All functional metrics were achieved by three of the patients. However, the two patients who were called failures obtained more than 25% improvement in all of their tasks except one, according to Badylak.

MRI, CT scans, and naked-eye observation confirmed the density of new tissue growth in the muscles.

While working on the rodent model, the Brian Sicari, MD, and Badylak identified perivascular stem cells, which were used in the remodeling process for the scaffold. "What's unique about these cells is that they're found in all vascularized tissues of the bodies," Sicari said in the press conference.

The researchers told reporters porcine ECM materials are being used in other surgeries including repair of abdominal wall hernias, breast reconstruction, and repair of chest wall defects caused by tumor resection.

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