In this project, utilizing stem cells, we are trying to generate not only cells for cell therapy but transplantable organs for those with end stage organ failure. The following is a summary of our progress made in the generation of cells and organs from stem cells.
Adoptive T-cell immunotherapy is a potential therapeutic strategy for combating various types of cancer. However, highly expanded T cells have not proven particularly effective. This is in part explained by exhaustion and losses of function that occur during the ex vivo expansion of T cells. For an effective adoptive immunotherapy, what we need is not the “exhausted” T cells, but large numbers of “young and active” T cells that can kill tumors. To address this issue, we have recently developed a novel system in which antigen-specific killer T cells (CTLs) can be rejuvenated by reprogramming them to induced pluripotent stem cells (iPSCs) and redifferentiating them while expanding their numbers, yielding abundant rejuvenated T cells (rejT cells). We confirmed the in vivo efficacy of these rejT cell against EBV-induced tumors inoculated in immunedeficient mice. To increase the safety of this novel rejT cell therapy, we inserted a drug inducible suicide system to T cell-derived iPSCs. Both the iPSCs and rejT cells derived from them induced cell death after administration of the inducing drug in vivo thereby demonstarting efficacy of this safety system. The results facilitate clinical application of the rejT cell therapy and other branches of iPSC-derived regenerative medicine.
To help patients with end-stage organ failure waiting for organ transplantation, we are trying to generate transplantable organs in livestock animals. Previously we have demonstrated the generation of rat pancreas in mouse using interspecific blastocyst complementation technique. This time, we succeeded in the generation of mouse pancreas in rats. The generated pancreata were composed of mouse PSC-derived cells but were of rat size. Islets were prepared from these pancreata and transplanted into diabetic mice. Transplanted islets successfully normalized and maintained host blood glucose levels for over 370 days. Because the transplanted islets contained small number of rat cells, immunosuppressive drug was given to the recipient mice for the first 5 days, but the rest of time, it was totally immunosuppression free. These data provide proof-of-principle evidence for the therapeutic potential of PSC-derived islets generated in a xenogeneic host using the blastocyst complementation technique, our ultimate goal.
In order to apply this principle to generation of human organs, human PSCs that can contribute to chimera formation are necessary. However, recent studies demonstrated that currently available human PSCs are epiblast-stage stem cells (EpiSCs) and not able to contribute to chimera formation. Using a rodent model, we discovered that if cell survival is transiently promoted by over expressing the anti-apoptotic gene (BCL2), EpiSCs and even lineage-committed progenitors can contribute to chimera formation upon injection into preimplantation embryos. We similarly showed that over expressing BCL2 in human PSCs could increase their survival following injection into sheep embryos in vitro. Having successfully engineered a platform to delete the pancreas in sheep using CRISPRs, we are now in a position to evaluate how well these modified human PSCs can contribute to pancreas formation in vivo. We believe application of our newly designed strategies may generate human PSC-derived organs whilst avoiding unwanted contributions to host gametes or neural tissues.