Cardiac Surgery Resident University of Alberta Edmonton, Alberta, Canada
Background: Tissue engineering has been investigated over previous decades as a method of facilitating xenotranplantation by attenuating the immune response to foreign tissue. While there has been success in other fields, solid organ engineering has been limited to invitro and animal studies. While tissue engineering of whole lungs has been performed, there have been limited analyses into the immunogenicity of these engineered lung scaffolds.
METHODS AND RESULTS: Fresh lung tissue was harvested from juvenile Yorkshire pigs prior to sacrifice for other experimentation. The lungs underwent a multistep decellularization process including washes with SDS (Sodium Dodecyl Sulfate), Triton X-100, and DNAse. The decellularized tissue was recellularized using stem cells collected from sternal bone marrow from human patients undergoing cardiac surgery. Success of the engineering process was confirmed with DAPI (4′,6-diamidino-2-phenylindole) stain. Tissue samples (autologous human pericardium control, native porcine lung, decellularized porcine lung, and recellularized lung with human stem cells) were exposed to human whole blood with samples taken at days 1, 3, and 5 for analysis. Immunogenicity of the scaffold was confirmed by multiplex enzyme-linked immunosorbent assay for pro- and anti-inflammatory cytokines. DAPI staining confirmed the absence of cells following decellularization and the presence of mesenchymal stem cells after recellularization. Concentrations of pro-inflammatory cytokines GM-CSF, IL-1β, IL-6, and TNF-α were significantly elevated in the decellularized and recellularized groups at various time points (Figure 1). There were no significant differences for the pro-inflammatory cytokines IFNγ and IL-6. Anti-inflammatory cytokines, including IL-1ra and IL-10, were present in significantly higher concentrations in the decellularized and recellularized groups. Immunohistochemistry staining revealed the presence of T cells, B cells, macrophages, and plasma cells in all tissue types despite effective decellularization of nuclear material (Figure 2).
Conclusion: Tissue engineering of lung tissue has been previously demonstrated but with few analyses of the immunogenicity of the decellularized and recellularized pulmonary scaffold. Tissue engineering the lung is feasible but results in a highly immunogenic scaffold eliciting a greater immune response from human whole blood even compared to the unmodified porcine lung tissue with marginal attenuation achieved following recellularization. Future investigations into bioengineered lung should address the immune response to the engineered organ in order to assess the ability of bioengineering methods to produce an immune-compatible xenogenic pulmonary graft.
