Natural immunity to pluripotency antigen OCT4 in humans. Proc Natl Acad Sci U S A. 2010;107:8718-8723. [PMID: 20404147 DOI: 10.1073/pnas.0915086107]

Pre-evaluated safe human iPSC-derived neural stem cells promote functional recovery after spinal cord injury in common marmoset without tumorigenicity

Murine and human iPSC-NS/PCs (induced pluripotent stem cell-derived neural stem/progenitor cells) promote functional recovery following transplantation into the injured spinal cord in rodents. However, for clinical applicability, it is critical to obtain proof of the concept regarding the efficacy of grafted human iPSC-NS/PCs (hiPSC-NS/PCs) for the repair of spinal cord injury (SCI) in a non-human primate model. This study used a pre-evaluated “safe” hiPSC-NS/PC clone and an adult common marmoset (Callithrix jacchus) model of contusive SCI. SCI was induced at the fifth cervical level (C5), followed by transplantation of hiPSC-NS/PCs at 9 days after injury. Behavioral analyses were performed from the time of the initial injury until 12 weeks after SCI. Grafted hiPSC-NS/PCs survived and differentiated into all three neural lineages. Furthermore, transplantation of hiPSC-NS/PCs enhanced axonal sparing/regrowth and angiogenesis, and prevented the demyelination after SCI compared with that in vehicle control animals. Notably, no tumor formation occurred for at least 12 weeks after transplantation. Quantitative RT-PCR showed that mRNA expression levels of human neurotrophic factors were significantly higher in cultured hiPSC-NS/PCs than in human dermal fibroblasts (hDFs). Finally, behavioral tests showed that hiPSC-NS/PCs promoted functional recovery after SCI in the common marmoset. Taken together, these results indicate that pre-evaluated safe hiPSC-NS/PCs are a potential source of cells for the treatment of SCI in the clinic.

Nuclear reprogramming and induced pluripotent stem cells: a review for surgeons

Induced pluripotent stem cells (iPSCs) are generated from somatic cells by the exogenous expression of defined transcription factors. iPSCs share the defining features of embryonic stem cells (ESCs) in that they are able to self-renew indefinitely and maintain the potential to develop into all cell types of the body. These cells have key advantages over ESCs in that they are autologous to the donor cells and can be generated from individuals at any age. iPSCs also circumvent ethical and political issues surrounding the destruction of embryos that is necessary in the isolation of ESCs. This review briefly describes the advent of iPSC technology and the concepts of nuclear reprogramming, and discusses the potential application of this powerful biological tool in both surgical research and regenerative medicine.

Concise review: Immune recognition of induced pluripotent stem cells

Autologous-induced pluripotent stem cells (iPSCs) may eventually be used in cell replacement therapies to treat a wide range of diseases and have been touted as a solution to the vexing problem of immune rejection in this context. Emerging evidence suggests, however, that ostensibly histocompatible iPSCs may be rejected following transplantation. Here, we review the mechanisms that contribute to immunogenicity in iPSCs and forward approaches to permit their acceptance in potential cell replacement therapies.

Anti-HLA antibodies in regenerative medicine stem cell therapy

Research on stem cell therapies for regenerative medicine is progressing rapidly. Although the use of autologous stem cells is a tempting choice, there are several instances in which they are either defective or not available in due time. Allogenic stem cells derived from healthy donors presents a promising alternative. Whether autologous or allogenic, recent advances have proven that stem cells are not as immune privileged as they were thought. Therefore understanding the interactions of these cells with the recipient immune system is paramount to their clinical application. Transplantation of stem cells induces humoral as well as cellular immune response. This review focuses on the humoral response elicited by stem cells upon their administration and consequences on the survival and maintenance of the graft. Current transplantation identifies pre- and post-transplantation anti-HLA antibodies as immune rejection and cell signaling effectors. These two mechanisms are likely to operate similarly in the context of SC therapeutics. Ultimately this knowledge will help to propose novel strategies to mitigate the allogenic barriers. Immunogenetics selection of the donor cell and immunomonitoring are key factors to allow the implementation of regenerative stem cell in the clinics.

Vaccines targeting cancer stem cells: are they within reach?

Increased appreciation of intraclonal heterogeneity of tumors in the past decade has led to the resurgence of the cancer stem cell hypothesis. This hypothesis also has potential implications for immunologic approaches targeting cancer, and it has been suggested that vaccines targeting cancer stem cells may be essential for durable antitumor immunity. Recent studies have provided novel insights into the nature of antigenic targets expressed on putative cancer stem cells and the capacity of both the innate and the adaptive immune system to target these cells, as well as the associated challenges. While the phenotypic properties of cancer stem cells may be plastic, their stemness and capacity for self-renewal may depend on a limited set of genes. Several of these genes overlap with those regulating stemness in embryonal stem cells and are also emerging as potential oncogenes in some cancers. Immunologic approaches targeting stemness-associated pathways in cancer may provide an important strategy for the prevention of diverse cancers, including those occurring in the context of regenerative therapies.

Therapeutic cancer vaccines: current status and moving forward

Concurrent with U.S. Food and Drug Administration (FDA) approval of the first therapeutic cancer vaccine, a wide spectrum of other cancer vaccine platforms that target a diverse range of tumor-associated antigens is currently being evaluated in randomized phase II and phase III trials. The profound influence of the tumor microenvironment and other immunosuppressive entities, however, can limit the effectiveness of these vaccines. Numerous strategies are currently being evaluated both preclinically and clinically to counteract these immunosuppressive entities, including the combined use of vaccines with immune checkpoint inhibitors, certain chemotherapeutics, small-molecule targeted therapies, and radiation. The potential influence of the appropriate patient population and clinical trial endpoint in vaccine therapy studies is discussed, as well as the potential importance of biomarkers in future directions of this field.

Challenges for the Therapeutic use of Pluripotent Stem Derived Cells

Human embryonic stem cells (hESC) and induced pluripotent stem cells (hiPSC) are an attractive cell source for regenerative medicine. These cells can be expanded to vast numbers and can be differentiated to many desired pluripotent stem cells (PSC) derived therapeutic cells. Cell replacement bears promises, but also challenges. The introduction of exogenous cells in a recipient must address several different topics; its safety, the exclusion of tumor formation, the immunological response and possible rejection, the cells cleanliness and their biological quality, and quantity representing the functionality of the PSC derived therapeutic cells. Tumor formation requires the removal of any PSC remaining after differentiation. Immunological rejection can be addressed with immunomodulation of the cells and the recipient. Cleanliness can be optimized using good manufacturing practice quality systems. At last, the functionality of the cells must be tested in in vitro and in animal models. After addressing these challenges, precise strategies are developed to monitor the status of the cells at different times and in case of undesired results, corresponding counteracting strategies must exist before any clinical attempt.

Reprogramming of somatic cells

Reprogramming of adult somatic cells into pluripotent stem cells may provide an attractive source of stem cells for regenerative medicine. It has emerged as an invaluable method for generating patient-specific stem cells of any cell lineage without the use of embryonic stem cells. A revolutionary study in 2006 showed that it is possible to convert adult somatic cells directly into pluripotent stem cells by using a limited number of pluripotent transcription factors and is called as iPS cells. Currently, both genomic integrating viral and nonintegrating nonviral methods are used to generate iPS cells. However, the viral-based technology poses increased risk of safety, and more studies are now focused on nonviral-based technology to obtain autologous stem cells for clinical therapy. In this review, the pros and cons of the present iPS cell technology and the future direction for the successful translation of this technology into the clinic are discussed.

Immune parameters affecting the efficacy of chemotherapeutic regimens

The outcome of chemotherapy can be influenced by the host immune system at multiple levels. Chemotherapy can kill cancer cells by causing them to elicit an immune response or alternatively, by increasing their susceptibility to immune attack. In addition, chemotherapy can stimulate anticancer immune effectors either in a direct fashion or by subverting immunosuppressive mechanisms. Beyond cancer-cell-intrinsic factors that determine the cytotoxic or cytostatic response, as well as the potential immunogenicity of tumor cells, the functional state of the host immune system has a major prognostic and predictive impact on the fate of cancer patients treated with conventional or targeted chemotherapies. In this Review, we surmise that immune-relevant biomarkers may guide personalized therapeutic interventions including compensatory measures to restore or improve anticancer immune responses.

Immunogenicity of induced pluripotent stem cells

Induced pluripotent stem cells (iPSCs), reprogrammed from somatic cells with defined factors, hold great promise for regenerative medicine as the renewable source of autologous cells. Whereas it has been generally assumed that these autologous cells should be immune-tolerated by the recipient from whom the iPSCs are derived, their immunogenicity has not been vigorously examined. We show here that, whereas embryonic stem cells (ESCs) derived from inbred C57BL/6 (B6) mice can efficiently form teratomas in B6 mice without any evident immune rejection, the allogeneic ESCs from 129/SvJ mice fail to form teratomas in B6 mice due to rapid rejection by recipients. B6 mouse embryonic fibroblasts (MEFs) were reprogrammed into iPSCs by either retroviral approach (ViPSCs) or a novel episomal approach (EiPSCs) that causes no genomic integration. In contrast to B6 ESCs, teratomas formed by B6 ViPSCs were mostly immune-rejected by B6 recipients. In addition, the majority of teratomas formed by B6 EiPSCs were immunogenic in B6 mice with T cell infiltration, and apparent tissue damage and regression were observed in a small fraction of teratomas. Global gene expression analysis of teratomas formed by B6 ESCs and EiPSCs revealed a number of genes frequently overexpressed in teratomas derived from EiPSCs, and several such gene products were shown to contribute directly to the immunogenicity of the B6 EiPSC-derived cells in B6 mice. These findings indicate that, in contrast to derivatives of ESCs, abnormal gene expression in some cells differentiated from iPSCs can induce T-cell-dependent immune response in syngeneic recipients. Therefore, the immunogenicity of therapeutically valuable cells derived from patient-specific iPSCs should be evaluated before any clinic application of these autologous cells into the patients.

Spontaneous and therapy-induced immunity to pluripotency genes in humans: clinical implications, opportunities and challenges

Recent studies have suggested that the core pathways regulating pluripotency in embryonal stem cells bear considerable overlap with oncogenesis. Here, we discuss recent insights into the capacity of the human immune system to target some of the key pluripotency-associated genes. Immunity to these genes is also induced in humans in the context of chemotherapy-induced cell death in patients with germ cell tumors. Immunologic targeting of pathways associated with stemness has implications for both immune regulation of tumor growth as well as emerging regenerative therapies with embryonal stem cells.

The dendritic cell-tumor cross-talk in cancer

The question as to whether the tumor grows because of or despite the host immune system is being progressively addressed with refined technology, gene targeting in mice and human translational research. The productive interplay between major actors of the antitumor immunity is actively compromised by the tumor microenvironment subverting the links between innate and cognate immunity and/or generating devastating new players. The complexity of the host-tumor equilibrium could be dissected at the reduced level of the dialogue between professional antigen presenting cells (APC), more precisely dendritic cells, and tumor cells that may profoundly dictate the outcome of the neoplasma. This review will summarize the novel mechanisms by which tumor cells regulate DC recruitment, differentiation, activation and cross-presenting functions in tumor beds and how innate players might counterbalance these interactions. Finally, we will highlight interesting strategies that harness the DC potential to fight against cancer.