Chorioallantoic membrane angiogenesis model for tissue engineering: a new twist on a classic model

Tissue-engineering (TE) applications include the isolation, culture, and seeding of cells into a suitable matrix or scaffold before in vivo transplantation. After transplantation, vascularization of the scaffold is a principal limiting factor for cell viability for the first 6-8 days posttransplantation. A model for systematic analysis of this process has been developed. Fertilized White Leghorn eggs were incubated (at 37.8 degrees C in 60% relative humidity) and opened on day 3 of incubation. Preadipocyte-seeded fibrin constructs were implanted in a specially designed plastic cylinder and placed through the opening on the surface of the chorioallantoic membrane (CAM) on day 8 of incubation. Vascularization of the constructs by chorioallantoic blood vessels was assessed for up to 8 days posttransplantation. The survival rate for embryos receiving transplanted constructs was about 90%. Histology confirmed transplant cell viability at day 4 posttransplantation and vascularization of the constructs by avian endothelial cells began at this time. A new in vivo model to study the effect of angiogenesis in TE constructs, including assessments of viability, proliferation, and differentiation of transplanted cells and biomaterial properties, is presented. Advantages include easy access to the vascular network of the CAM, lack of immunocompetence, low costs, and avoidance of animal experiments.     

Fas expression by tumor stroma is required for cancer eradication

The contribution of molecules such as perforin, IFN-γ (IFNγ), and particularly Fas ligand (FasL) by transferred CD8⁺ effector T (T_E) cells to rejection of large, established tumors is incompletely understood. Efficient attack against large tumors carrying a surrogate tumor antigen (mimicking a “passenger” mutation) by T_E cells requires action of IFNγ on tumor stroma cells to avoid selection of antigen-loss variants. Because “cancer-driving” antigens (CDAs) are rarely counterselected, IFNγ may be expected to be dispensable in elimination of cancers by targeting a CDA. Here, initial regression of large, established tumors required neither IFNγ, FasL, nor perforin by transferred CD8⁺ T_E cells targeting Simian Virus (SV) 40 large T as CDA. However, cytotoxic T_E cells lacking IFNγ or FasL could not prevent relapse despite retention of the rejection antigen by the cancer cells. Complete tumor rejection required IFNγ-regulated Fas by the tumor stroma. Therefore, T_E cells lacking IFNγ or FasL cannot prevent progression of antigenic cancer because the tumor stroma escapes destruction if its Fas expression is down-regulated.     

De novo mTOR inhibitor‐based immunosuppression in ABO‐incompatible kidney transplantation

ABO‐incompatible (ABOi) kidney transplantation (KTx) has become an accepted therapeutic option in renal replacement therapy for patients without a blood group‐compatible living donor. Using different desensitization strategies, most centers apply B‐cell depletion with rituximab and maintenance immunosuppression (IS) with tacrolimus and mycophenolic acid. This high load of total IS leads to an increased rate of surgical complications and virus infections in ABOi patients. Our aim was to establish ABOi KTx using an immunosuppressive regimen, which is effective in preventing acute rejection without increasing the risk for viral infections. Therefore, we selected a de novo immunosuppressive protocol with low‐dose calcineurin inhibitor and the mTOR inhibitor everolimus for our ABOi program. Here, we report the first 25 patients with a complete three‐yr follow‐up treated with this regimen. Three‐yr patient survival and graft survival were 96% and 83%. The rate of acute T‐cell‐mediated rejections was low (12%). Cytomegalovirus (CMV) infection was evident in one patient only (4%). Surgical complications were common (40%), but mild in 80% of cases. We demonstrate that ABOi KTx with a de novo mTOR inhibitor‐based regimen is feasible without severe surgical or immunological complications and a low rate of viral infections.