Closing the Gap: Toward Functional, Bioengineered Esophageal Grafts

Abstract

In their recent Nature Biotechnology paper, Pablo De Coppi et al. integrate tissue engineering with organ transplantation in a pig model. They demonstrate that microinjection of autologous myogenic precursors and fibroblasts into a decellularized porcine scaffold, followed by bioreactor maturation, yields a graft that functionally integrates with the native esophagus.

The esophagus, a structurally and functionally complex hollow organ, has long posed a major challenge in regenerative medicine. After years of limited progress, a significant breakthrough has emerged: the generation of a bioengineered, muscularized segment capable of successfully integrating with the host esophagus¹.

In contrast to other relatively static tubular structures, the esophagus maintains luminal patency while performing coordinated, wave-like peristaltic contractions responsible for transporting ingested material from the pharynx to the stomach. This vital function relies on the integration of multiple tissue layers, including stratified squamous epithelium and vascularized connective tissue, ensheathed within regionally specialized muscular compartments that receive both enteric and extrinsic neural innervation. Consequently, the development of a fully functional esophagus requires not only tissue replacement but also the restoration of coordinated neuromuscular physiology. Nevertheless, the necessity for esophageal reconstruction in clinical settings remains significant. Congenital anomalies such as esophageal atresia (EA), with or without tracheoesophageal fistula (TEF), represent one of the most common foregut malformations (approximately 1 in 3500) and require early surgical intervention². Furthermore, acquired conditions include refractory strictures caused by caustic or radiation injury, as well as esophageal carcinoma, which often require partial or complete esophageal replacement (Figure 1). Present surgical methods, including gastric transposition, small bowel or colonic interposition, are linked with considerable morbidity and mortality and are unable to restore the native function of the esophagus.

Figure 1. Clinical application of functional esophageal graft.

The development of a functional esophageal implant involves isolation and expansion of pericyte-like myogenic progenitors (MABs) and tissue fibroblasts (TFs) from rectus abdominis biopsy samples of Göttingen minipigs. These cells are then microinjected into a decellularized porcine scaffold and matured within a bioreactor. This approach aims to help address the critical shortage of esophageal grafts for thoracic orthotopic transplantation in patients with esophageal diseases¹.

Early regenerative strategies centered on non-autologous acellular scaffolds to establish tubular structures, which can provide conduit function but lack peristalsis driven by neuromuscular activity. Consequently, these approaches resulted in graft stenosis, incomplete muscle development, inadequate functional peristalsis, and a requirement for immunosuppression following transplantation³. This underscores the limitations inherent in scaffold-centric, non-autologous graft methodologies. By contrast, De Coppi and colleagues harnessed autologous stem cells to engineer muscular tubes suitable for replacing tubular organs, including the first successful transplantation of a human tissue-engineered trachea into a pediatric patient, thereby demonstrating the feasibility for use in clinical settings⁴. Additionally, the group successfully generated multilayered tissue-engineered esophagus by seeding decellularized rat esophagus with human mesangioblasts (MABs), murine fibroblasts (FB), and murine neural crest cells, which were subsequently transplanted into immunocompromised mice⁵. They further translated these concepts to small animals through xenotransplantation of a multilayered decellularized porcine esophagus scaffold into a pre-clinical rabbit model⁶.

De Coppi and colleagues' pioneering research in tissue engineering has recently culminated in utilizing a dynamic-flow bioreactor incubation method to develop a multilayered esophageal segment that functions similarly to the native esophagus when transplanted into larger preclinical animal models such as Göttingen minipigs¹. The bioreactor, in conjunction with the co-injection of fibroblasts into a decellularized porcine esophageal scaffold, facilitates the maturation of pericyte-like myogenic precursors into both smooth and skeletal muscle cells. Upon implantation, the esophageal segment acts as a conduit for the transportation of food and liquids to the stomach and attracts host epithelial progenitor cells, fibroblasts, blood vessels, and neural cells over time. At six months, the implants were fully integrated with the native esophagus, exhibiting effective peristalsis to propel food through the esophageal lumen. The findings demonstrate successful tissue remodeling, epithelialization, and timely, clinically relevant structural integration in vivo, representing a significant milestone in translational esophageal engineering. Furthermore, this approach underscores the significance of regenerating a muscular conduit with integrated muscle and fibroblasts, thereby enabling the graft to heal naturally over time (Figure 1).

Moving forward, challenges may persist in constructing longer esophageal segments (>2.5cm), given the intricate regional specialization of the esophageal musculature⁷. While the proximal one-third of the esophagus consists of skeletal muscle, facilitating voluntary initiation of swallowing, the middle one-third serves as a transitional zone containing both skeletal and smooth muscle, enabling the shift from voluntary to involuntary control. The distal one-third is comprised of smooth muscle, which is responsible for the involuntary peristaltic propulsion of food towards the stomach. This regional specification is not solely structural but also functional, as it facilitates a coordinated progression for liquid and food bolus transport. Reproducing this gradient in tissue-engineered esophageal models is anticipated to be challenging, particularly given the reported difficulty in generating sufficient skeletal muscle¹. Future research may investigate whether skeletal muscles or their progenitor cells can be recruited through lineage tracing. Furthermore, strategies aimed at augmenting the recruitment and integration of native skeletal muscle cells could be developed, potentially by incorporating chemotactic cues or signals that emulate the niche environment to facilitate endogenous muscle cell migration and engraftment.

The elegance of the tissue-engineered implant is that it generates functional mucosal and submucosal glands by attracting neighboring epithelial stem/progenitor cells from the host esophagus¹. This crucial re-epithelialization is essential not only for safeguarding the underlying tissues but also for promoting lubrication and the transfer of ingested food. Previous research has established that human induced pluripotent stem cells (iPSCs) possess the capacity to differentiate into esophageal basal progenitor cells^8,9. Consequently, the incorporation of iPSC-derived esophageal progenitor cells into the graft, supplemented by bioreactor incubation, could constitute a promising approach for the development of elongated esophageal constructs intended for patients requiring reconstruction, such as those with esophageal carcinoma.

The field of esophageal tissue engineering has advanced substantially, progressing from inert scaffold replacements to biologically active, cell-based, and mechanically functional constructs. The work by Pablo De Coppi and colleagues, which produced a functional esophageal implant, represents a major milestone in the field. Looking ahead, continued progress will likely depend on integrating principles from developmental biology, leveraging multi-lineage stem cell technologies, and developing advanced bioengineered systems capable of recapitulating the complex structural and functional properties of this highly specialized organ.