Modulation of human allogeneic and syngeneic pluripotent stem cells and immunological implications for transplantation

Tissues derived from induced pluripotent stem cells (iPSCs) are a promising source of cells for building various regenerative medicine therapies; from simply transplanting cells to reseeding decellularized organs to reconstructing multicellular tissues. Although reprogramming strategies for producing iPSCs have improved, the clinical use of iPSCs is limited by the presence of unique human leukocyte antigen (HLA) genes, the main immunologic barrier to transplantation. In order to overcome the immunological hurdles associated with allogeneic tissues and organs, the generation of patient-histocompatible iPSCs (autologous or HLA-matched cells) provides an attractive platform for personalized medicine. However, concerns have been raised as to the fitness, safety and immunogenicity of iPSC derivatives because of variable differentiation potential of different lines and the identification of genetic and epigenetic aberrations that can occur during the reprogramming process. In addition, significant cost and regulatory barriers may deter commercialization of patient specific therapies in the short-term. Nonetheless, recent studies provide some evidence of immunological benefit for using autologous iPSCs. Yet, more studies are needed to evaluate the immunogenicity of various autologous and allogeneic human iPSC-derived cell types as well as test various methods to abrogate rejection. Here, we present perspectives of using allogeneic vs. autologous iPSCs for transplantation therapies and the advantages and disadvantages of each related to differentiation potential, immunogenicity, genetic stability and tumorigenicity. We also review the current literature on the immunogenicity of syngeneic iPSCs and discuss evidence that questions the feasibility of HLA-matched iPSC banks. Finally, we will discuss emerging methods of abrogating or reducing host immune responses to PSC derivatives.

Deletion of gp130 in myeloid cells modulates IL-6-release and is associated with more severe liver injury of Con A hepatitis

IL-6/gp130 dependent signaling plays an important role in modulating inflammation in acute and chronic diseases. The course of Concanavalin A- (Con A) induced hepatitis can be modulated by different immune-mediated mechanisms. IL-6/gp130-dependent signaling has been shown to be protective in hepatocytes. However, the role of this pathway in myeloid cells has not yet been studied. In our present study we used macrophage/neutrophil-specific gp130 knockout (gp130(ΔLys), KO) animals and analyzed its relevance in modulating Con A-induced hepatitis. Additionally, we performed in vitro studies with gp130(ΔLys)-macrophages. We demonstrate that gp130(ΔLys) animals are more susceptible to Con A-induced hepatitis. This is reflected by higher transaminases, higher lethality and more severe liver injury as shown by histological staining. Using flow cytometry analysis we further could show that increased liver injury of gp130(ΔLys) animals is associated with a stronger infiltration of CD11b/F4/80 double-positive cells compared to wild-type (gp130(flox/flox), WT) controls. To further characterize our observations we studied thioglycolate-elicited peritoneal macrophages from gp130(ΔLys) animals. Interestingly, the LPS-dependent IL-6 release in gp130(ΔLys) macrophages is significantly reduced (p<0.05) compared to WT macrophages. Additionally, IL-6 blood levels in vivo after Con A injection were significantly lower in gp130(ΔLys) animals compared to WT animals (p<0.05). In summary, our results suggest that gp130-deletion in macrophages and granulocytes leads to diminished IL-6 release from these cells, which is associated with more severe Con A-induced hepatitis.

Foxl1 controls the Wnt/beta-catenin pathway by modulating the expression of proteoglycans in the gut

Foxl1 is a winged helix transcription factor expressed in the mesenchyme of the gastrointestinal tract. Foxl1 null mice display severe structural defects in the epithelia of the stomach, duodenum, and jejunum. Here we addressed the molecular mechanisms by which Foxl1 controls gastrointestinal differentiation. First we showed that the abnormalities found in the epithelia of the null mice are the result of an increase in the number of proliferating cells and not a change in the rate of cell migration. Next we investigated the regulatory circuits affected by Foxl1. We focused on the Wnt/beta-catenin signaling pathway as a possible target of Foxl1 as it has been shown to play a central role in gastrointestinal proliferation. We demonstrated that Foxl1 activates the Wnt/beta-catenin pathway by increasing extracellular proteoglycans, which act as co-receptors for Wnt. Thus we establish that Foxl1 is involved in the regulation of the Wnt/beta-catenin pathway, providing a novel link in mesenchymal/epithelial cross-talk in the gut. Moreover, we provide the first example implicating proteoglycans in the regulation of cellular proliferation in the gastrointestinal tract.

Hepatocyte nuclear factor 3beta (Foxa2) is dispensable for maintaining the differentiated state of the adult hepatocyte

Liver-specific gene expression is controlled by a heterogeneous group of hepatocyte-enriched transcription factors. One of these, the winged helix transcription factor hepatocyte nuclear factor 3beta (HNF3beta or Foxa2) is essential for multiple stages of embryonic development. Recently, HNF3beta has been shown to be an important regulator of other hepatocyte-enriched transcription factors as well as the expression of liver-specific structural genes. We have addressed the role of HNF3beta in maintenance of the hepatocyte phenotype by inactivation of HNF3beta in the liver. Remarkably, adult mice lacking HNF3beta expression specifically in hepatocytes are viable, with histologically normal livers and normal liver function. Moreover, analysis of >8,000 mRNAs by array hybridization revealed that lack of HNF3beta affects the expression of only very few genes. Based on earlier work it appears that HNF3beta plays a critical role in early liver development; however, our studies demonstrate that HNF3beta is not required for maintenance of the adult hepatocyte or for normal liver function. This is the first example of such functional dichotomy for a tissue specification transcription factor.