Mini-TCRs: Truncated T cell receptors to generate T cells from induced pluripotent stem cells

Allogeneic T cell platforms utilizing induced pluripotent stem cell (iPSC) technology exhibit significant promise for the facilitation of adoptive immunotherapies. While mature T cell receptor (TCR) signaling plays a crucial role in generating T cells from iPSCs, the introduction of exogenous mature TCR genes carries a potential risk of causing graft-versus-host disease (GvHD). In this study, we present the development of truncated TCRα and TCRβ chains, termed mini-TCRs, which lack variable domains responsible for recognizing human leukocyte antigen (HLA)-peptide complexes. We successfully induced cytotoxic T lymphocytes (CTLs) from iPSCs by employing mini-TCRs. Combinations of TCRα and TCRβ fragments were screened from mini-TCR libraries based on the surface localization of CD3 proteins and their ability to transduce T cell signaling. Consequently, mini-TCR-expressing iPSCs underwent physiological T cell development, progressing from the CD4 and CD8 double-positive stage to the CD8 single-positive stage. The resulting iPSC-derived CTLs exhibited comparable cytokine production and cytotoxicity in comparison to that of full-length TCR-expressing T lymphocytes when chimeric antigen receptors (CARs) were expressed. These findings demonstrate the potential of mini-TCR-carrying iPSCs as a versatile platform for CAR T cell therapy, offering a promising avenue for advancing adoptive immunotherapies.

Engineering of human induced pluripotent stem cells via human artificial chromosome vectors for cell therapy and disease modeling

Genetic engineering of induced pluripotent stem cells (iPSCs) holds great promise for gene and cell therapy as well as drug discovery. However, there are potential concerns regarding the safety and control of gene expression using conventional vectors such as viruses and plasmids. Although human artificial chromosome (HAC) vectors have several advantages as a gene delivery vector, including stable episomal maintenance and the ability to carry large gene inserts, the full potential of HAC transfer into iPSCs still needs to be explored. Here, we provide evidence of a HAC transfer into human iPSCs by microcell-mediated chromosome transfer via measles virus envelope proteins for various applications, including gene and cell therapy, establishment of versatile human iPSCs capable of gene loading and differentiation into T cells, and disease modeling for aneuploidy syndrome. Thus, engineering of human iPSCs via desired HAC vectors is expected to be widely applied in biomedical research.

Detection of thalidomide embryotoxicity by in vitro embryotoxicity testing based on human iPS cells

The mouse embryonic stem cell test (mEST) is used to assess the embryotoxicity of drug candidates by evaluating the effects on the cardiac differentiation of stem cells. However, thalidomide embryotoxicity has not yet been reported using the mEST. To detect the effects of thalidomide, we used human induced pluripotent stem cells (hiPSCs) instead of mouse embryonic stem cells, and assessed three endpoints: the inhibition of cardiac differentiation, the cytotoxicity to hiPSCs, and the cytotoxicity to human dermal fibroblasts, according to the mEST. From these data (IC50 values), the embryotoxicity was classified into one of three different classes based on the mEST and our criteria. Valproate was used as a positive control and ascorbic acid was used as a negative control, and their effects were assessed. Similar to valproate, thalidomide was classified as a Class 2 agent, with weak embryotoxicity, by the mEST criteria, and was classified as Category 3 embryotoxic based on our criteria. Ascorbic acid was classified as a Class 1 / Category 1, non-embryotoxic agent, based on both criteria. Thalidomide embryotoxicity was detected in the embryonic stem cell test based on hiPSCs. This test system is thus considered to have a much greater predictive ability than the mEST.

Direct generation of induced pluripotent stem cells from human nonmobilized blood

The use of induced pluripotent stem cells (iPSCs) is an exciting frontier in the study and treatment of human diseases through the generation of specific cell types. Here we show the derivation of iPSCs from human nonmobilized peripheral blood (PB) and bone marrow (BM) mononuclear cells (MNCs) by retroviral transduction of OCT3/4, SOX2, KLF4, and c-MYC. The PB- and BM-derived iPSCs were quite similar to human embryonic stem cells with regard to morphology, expression of surface antigens and pluripotency-associated transcription factors, global gene expression profiles, and differentiation potential in vitro and in vivo. Infected PB and BM MNCs gave rise to iPSCs in the presence of several cytokines, although transduction efficiencies were not high. We found that 5 × 10(5) PB MNCs, which corresponds to less than 1 mL of PB, was enough for the generation of several iPSC colonies. Generation of iPSCs from MNCs of nonmobilized PB, with its relative efficiency and ease of harvesting, could enable the therapeutic use of patient-specific pluripotent stem cells.

Exogenous gene expression and growth regulation of hematopoietic cells via a novel human artificial chromosome

A number of gene delivery systems are currently being developed for potential use in gene therapy. Here, we demonstrate the feasibility of 21deltaqHAC, a newly developed human artificial chromosome (HAC), as a gene delivery system. We first introduced a 21deltaqHAC carrying an EGFP reporter gene and a geneticin-resistant gene (EGFP-21deltaqHAC) into hematopoietic cells by microcell-mediated chromosome transfer. These HAC-containing hematopoietic cells showed resistance to geneticin, expressed EGFP and retained the ability to differentiate into various lineages, and the EGFP-21deltaqHAC was successfully transduced into primary hematopoietic cells. Hematopoietic cells harboring the EGFP-21deltaqHAC could still be detected at two weeks post-transplantation in immunodeficient mice. We also showed effective expansion of hematopoietic cells by introducing the 21deltaqHAC containing ScFvg, a gp130-based chimeric receptor that transmits growth signals in response to specific-antigen of this receptor. All of these results demonstrate the usefulness of HAC in gene therapy.

Hematopoietic stem cells expanded by fibroblast growth factor-1 are excellent targets for retrovirus-mediated gene delivery

OBJECTIVE

For the study of the function of genes of interest in hematopoietic stem cells (HSCs) and for successful gene therapy, it is fundamental to develop a method of efficient gene transfer into HSCs. In mice experiments, efforts have been made to raise the transduction efficiency by modifying the vectors, administrating 5-fluorouracil (5-FU) to donor mice, selecting cytokine cocktails to better sustain the long-term repopulating potential of the stem cells, and so on. The objective of this study is to examine whether the use of fibroblast growth factor-1 (FGF-1)-expanded bone marrow cells provide an improved source for retroviral gene delivery to HSCs.

MATERIALS AND METHODS

Unfractionated bone marrow cells from one mouse were cultured in serum-free medium containing FGF-1. Both floating and attached cells were transferred to retronectin precoated dishes and infected with virus supernatant from MP34 cells stably transduced with pMY/GFP retrovirus. After 3-day infection, the green fluorescence protein-positive fraction was sorted and the cells were transplanted to lethally irradiated mice.

RESULTS

The experiments illustrated that the number of bone marrow-derived competitive repopulation units (CRUs) was increased from 600 to 9300 per mouse after a 3-week culture period with FGF-1. Following retroviral transduction of the expanded cells, the absolute number of sorted retrovirus-transduced CRUs was 4200. Using these retrovirus-transduced cells in noncompetitive reconstitution assay, we achieved radiation protection and long-term bone marrow reconstitution in 100% of the recipients with average myeloid and lymphoid chimerisms of 70% and 50%, respectively, even if we transplanted 150 recipients with cells derived from a single donor mouse.

CONCLUSION

In conclusion, FGF-1-expanded bone marrow cells constitute an excellent source of stem cells that could be used in a range of gene delivery protocols.

Stem cell leukemia protein directs hematopoietic stem cell fate

Stem cell leukemia (SCL) protein has been shown to be an essential transcription factor during hematopoietic development in the embryo. In adult hematopoiesis, however, the role for SCL has remained largely unknown, whereas it is expressed in bone marrow hematopoietic stem cells (HSCs). In this study, we performed HSC transplantation and an in vitro HSC differentiation assay using retrovirally transduced HSCs with wild-type (WT) and dominant-negative (DN) SCL. The transplantation experiments showed that SCL does not affect the long-term repopulating capacity of HSCs but that WT SCL and DN SCL increase the short-term contribution of the transduced HSCs in myeloid and lymphoid lineages, respectively. An in vitro single-cell assay using a fetal thymus organ culture system further demonstrated that WT SCL facilitates HSCs to differentiate into the myeloid lineage but that DN SCL facilitates HSCs to differentiate into the lymphoid lineage. We conclude that the up-regulation or down-regulation of SCL directs HSCs toward myeloid or lymphoid lineage, respectively, although SCL does not affect their long-term repopulating capacity. (Blood. 2004;103: 3336-3341)

Human CD4+ CD25+ regulatory T cells suppress NKT cell functions

CD4+CD25+ regulatory T cells play an important role in peripheral tolerance. These cells have been reported to be capable of suppressing the response of CD4+CD25- T cells in vitro. The depletion of these cells evokes effective immune responses to tumor cells in vivo. In this study, we demonstrate that CD4+CD25+ T cells also suppress all subsets of Valpha24+NKT cells (Valpha24+CD4-CD8- double negative, Valpha24+CD4+, and Valpha24+CD8+) in both proliferation and cytokine production [IFN-gamma, interleukin-4 (IL-4), IL-13, and IL-10]. This suppression is mediated by cell-to-cell contact but not by a humoral factor or the inhibition of antigen-presenting cells. Moreover, the cytotoxic activity of Valpha24+NKT cells against some tumor cell lines is suppressed by CD4+CD25+ T cells. This finding is important in developing an effective immunotherapy for cancer.

Identification of a novel fusion gene, TTL, fused to ETV6 in acute lymphoblastic leukemia with t(12;13)(p13;q14), and its implication in leukemogenesis

ETS variant gene 6 (ETV6)/translocation, ETS, leukemia (TEL)-involving chromosomal translocations are frequently observed in various hematologic neoplasms. We describe here a novel ETV6-involving translocation, t(12;13)(p13;q14), found in the case of acute lymphoblastic leukemia, in which ETV6 fused with a previously unknown gene, named Twelve-thirteen Translocation Leukemia gene (TTL), at 13q14. TTL was weakly but ubiquitously expressed in normal human tissues as detected by reverse transcribed-PCR. Three TTL splicing forms were identified, TTL-T from a human testis cDNA library, with an open-reading frame of 402 bp encoding 133 amino acids (aa), and TTL-B1 and -B2 from a human brain cDNA library. These proteins have no homology to known proteins. In leukemic cells from the patient, both reciprocal fusion transcripts, ETV6/TTL and TTL/ETV6, were expressed. The predominant fusion transcript, TTL/ETV6-1, encodes a predicted 530 aa fusion protein containing 89 aa of the N-terminal TTL fusing to the helix-loop-helix domain and ETS-binding domain of ETV6. Although the function of TTL is yet to be elucidated, our findings will provide another insight into the molecular pathogenesis of leukemia having ETV6-involving translocations.

Notch2 is preferentially expressed in mature B cells and indispensable for marginal zone B lineage development

The Notch genes play a key role in cellular differentiation. The significance of Notch1 during thymocyte development is well characterized, but the function of Notch2 is poorly understood. Here we demonstrate that Notch2 but no other Notch family member is preferentially expressed in mature B cells and that conditionally targeted deletion of Notch2 results in the defect of marginal zone B (MZB) cells and their presumed precursors, CD1d(hi) fraction of type 2 transitional B cells. Among Notch target genes, the expression level of Deltex1 is prominent in MZB cells and strictly dependent on that of Notch2, suggesting that Deltex1 may play a role in MZB cell differentiation.

Notch1 but not Notch2 is essential for generating hematopoietic stem cells from endothelial cells

Hematopoietic stem cells (HSCs) are thought to arise in the aorta-gonad-mesonephros (AGM) region of embryo proper, although HSC activity can be detected in yolk sac (YS) and paraaortic splanchnopleura (P-Sp) when transplanted in newborn mice. We examined the role of Notch signaling in embryonic hematopoiesis. The activity of colony-forming cells in the YS from Notch1(-/-) embryos was comparable to that of wild-type embryos. However, in vitro and in vivo definitive hematopoietic activities from YS and P-Sp were severely impaired in Notch1(-/-) embryos. The population representing hemogenic endothelial cells, however, did not decrease. In contrast, Notch2(-/-) embryos showed no hematopoietic deficiency. These data indicate that Notch1, but not Notch2, is essential for generating hematopoietic stem cells from endothelial cells.

HES-1 preserves purified hematopoietic stem cells ex vivo and accumulates side population cells in vivo

Mouse long-term hematopoietic reconstituting cells exist in the c-Kit+Sca-1+Lin- (KSL) cell population; among them, CD34(low/-) cells represent the most highly purified population of hematopoietic stem cells in the adult bone marrow. Here, we demonstrate that retrovirus-mediated transduction of CD34(low/-)c-Kit+Sca-1+Lin- (34-KSL) cells with the HES-1 gene, which encodes a basic helix-loop-helix transcription factor functioning downstream of the Notch receptor, and is a key molecule for the growth phase of neural stem cells in the embryo, preserves the long-term reconstituting activity of these cells in vitro. We also show that cells derived from the HES-1-transduced 34-KSL population produce progenies characterized by negative Hoechst dye staining, which defines the side population, and by CD34(low/-) profile in the bone marrow KSL population in each recipient mouse at ratios 3.5- and 7.8-fold those produced by nontransduced 34-KSL-derived competitor cells. We conclude that HES-1 preserves the long-term reconstituting hematopoietic activity of 34-KSL stem cells ex vivo. Up-regulation of HES-1 protein in the 34-KSL population before unnecessary cell division, that is, without retrovirus transduction, may represent a potent approach to absolute expansion of hematopoietic stem cells.

Hematopoietic stem cells differentiate into vascular cells that participate in the pathogenesis of atherosclerosis

Excessive accumulation of smooth-muscle cells (SMCs) has a key role in the pathogenesis of vascular diseases. It has been assumed that SMCs derived from the outer medial layer migrate, proliferate and synthesize extracellular matrix components on the luminal side of the vessel. Although much effort has been devoted to targeting migration and proliferation of medial SMCs, there is no effective therapy that prevents occlusive vascular remodeling. We show here that in models of post-angioplasty restenosis, graft vasculopathy and hyperlipidemia-induced atherosclerosis, bone-marrow cells give rise to most of the SMCs that contribute to arterial remodeling. Notably, purified hematopoietic stem cells differentiate into SMCs in vitro and in vivo. Our findings indicate that somatic stem cells contribute to pathological remodeling of remote organs, and may provide the basis for the development of new therapeutic strategies for vascular diseases through targeting mobilization, homing, differentiation and proliferation of bone marrow-derived vascular progenitor cells.

Expression of Notch ligands, Jagged1, 2 and Delta1 in antigen presenting cells in mice

Notch1 is indispensable for T cell development. It is anticipated that Notch1 and other Notch receptors expressed on the surface of thymic T cell precursors are activated by ligands present on environmental cells, including antigen presenting cells (APCs), and involved in positive and negative selections. Notch receptors on peripheral T cells may also be activated by ligands on APCs. Here, we examined the expression pattern of three Notch ligands, Jagged1, 2 and Delta1 in APCs by an immunofluorescence cell staining method and a reverse transcriptase-polymerase chain reaction (RT-PCR) method. Peritoneal macrophages were strongly positive for Jagged1 staining. In contrast, macrophages separated from spleen and dendritic cells (DCs) separated from spleen and thymus showed positive staining for all the three ligands at a similar intensity. An analysis by RT-PCR revealed that peritoneal and splenic macrophages and splenic and thymic DCs, show a distinct pattern in Notch ligand expression. These findings may represent that expression of various Notch ligands in APCs has a physiological relevance in each organ.

Identification of active regions for neurite outgrowth activity of neurocrescin

We previously identified and cloned a neurite outgrowth promoting protein, Neurocrescin (NC), from the extract of the chick denervated leg muscles. In this study, we explored the active region of NC for neurite outgrowth. Using the deletion mutants of NC, we tested their neurite outgrowth activity in the cultured telencephalic neurons of E5 chick embryos. We found three regions which independently had significant neurite outgrowth activity comparable with that of the extract of the chick denervated leg muscles. These regions were not homologous to any well-known active sites such as the laminin active region, IKVAV. In parallel, searching the endogenous deletion mutants of NC in the rat brain, we cloned a mutant in which the region including the larger part of one of the three active regions was deleted. The neurite outgrowth activity of the mutant was significantly lower than that of normal NC. These results suggest the physiological significance of these active regions.