Approccio di terapia cellulare mediante l'utilizzo di cellule fetali isolate dal liquido amniotico per malattie del sistema ematopoieico

Cell therapy is an attractive perspective for the treatment of life threatening disorders. In this context, foetal tissues are gaining interest as sources of cells for auto- and allo-transplantation, because of their pluripotency, proliferative capability and their low, if any, immunogenicity. Recently a pluripotent stem cell population has been isolated from Amniotic Fluid (AF). It is able to proliferate for more than 18 months, maintaining their differentiative ability as well as a normal karyotype. In term of differentiation potential, we succeeded in obtaining in vitro mesenchymal-, ectodermal- and endodermal-derived tissues from human Amniotic Fluid Stem (AFS) cells. Furthermore, murine AFS cells injected in blastocytes took part to the formation not only of several different foetal organs, but also of the placenta and the umbilical cord. In the present study we investigated the possibility of differentiating AFS cells towards the hematopoietic pathway. AFS cells isolated from human amniotic fluid, collected during routine diagnostic procedures and obtained under informed consent, were firstly expanded in vitro and selected on the basis of their ckit expression. We achieved a reproducible erythroid differentiation by culturing hAFSCs as embryoid bodies (EBs) under serum free conditions with haematopoietic cytokines. Erythroid cells expressing CD235a constituted 70% of the total hAFSCs forming EBs showing also a co-expression of CD36 and CD71. Furthermore, human erythrocytes (human CD235a) were isolated from bone marrow and spleen of sublethally irradiated NOD/SCID mice at 3 months after the injection of hAFSCs. To determine if the expansion procedure had led to a restriction of the hematopoietic potential towards the erythroid pathway, we compared expanded AFSCs and freshly isolated cKit+ Lin- (AFKL) cells. We also harvested cKit+ Lin- KL cells from the membrane surrounding the AF, the Amnion, in search for a possible origin. We compared the hematopoietic potential of mAFKL and mAmKL to Fetal Liver KL, the main source of fetal HSC. When cultivated immediatly after their sorting, freshly isolated murine AFKL and AmKL cells gave rise to all the different hematopoietic lineages both in vitro and in vivo. Actually, when cocultivated with OP9(d)1 cells, AFKL and AmKL undergo complete T cell differentiation within 2 weeks. They also generate myeloid and erythroid colonies when cultivated in methylcellulose for clonogenic assay. The erythroid restricted potential of human AFS cells was thus probably linked to the in vitro expansion procedure. Moreover, cells belonging to all the three hematopoietic lineages (lymphoid, myeloid and erythroid) and arising from freshly isolated mAFKL and mAmKL are found in the peripheral blood of sublethally irradiated RAG1 deficient mice only 4 weeks after transplantation. Four month later, transplanted mice showed mAFKL-derived lymphoid, myeloid and erythroid cells, in all the hematopoietic organs. Successful econdary transplantation strongly suggest that mAFKL and mAmKL comprise HSC, with self-renewal ability. Those results were very similar to those obtained with mFLKL, confirming the strong hematopoietic potential of mAFKL and mAmKL. Experiments with freshly isolated hAFKL gave good results in the in vitro assays being able to give rise to erythroid, myeloid and lymphoid lineages, but failed to reconstitute the hematopoietic system in irradiated NOD/SCID mice, probably due to the poor amount of cells injected. This is the first report demonstrating that AFKL and AmKL do have an haematopoietic potential, supporting the idea that AF and Am may be an excellent source for therapeutic application.