Directed differentiation of induced pluripotent stem cells towards T lymphocytes

Adoptive cell transfer (ACT) of antigen-specific CD8(+) cytotoxic T lymphocytes (CTLs) is a promising treatment for a variety of malignancies (1). CTLs can recognize malignant cells by interacting tumor antigens with the T cell receptors (TCR), and release cytotoxins as well as cytokines to kill malignant cells. It is known that less-differentiated and central-memory-like (termed highly reactive) CTLs are the optimal population for ACT-based immunotherapy, because these CTLs have a high proliferative potential, are less prone to apoptosis than more differentiated cells and have a higher ability to respond to homeostatic cytokines (2-7). However, due to difficulties in obtaining a high number of such CTLs from patients, there is an urgent need to find a new approach to generate highly reactive Ag-specific CTLs for successful ACT-based therapies. TCR transduction of the self-renewable stem cells for immune reconstitution has a therapeutic potential for the treatment of diseases (8-10). However, the approach to obtain embryonic stem cells (ESCs) from patients is not feasible. Although the use of hematopoietic stem cells (HSCs) for therapeutic purposes has been widely applied in clinic (11-13), HSCs have reduced differentiation and proliferative capacities, and HSCs are difficult to expand in in vitro cell culture (14-16). Recent iPS cell technology and the development of an in vitro system for gene delivery are capable of generating iPS cells from patients without any surgical approach. In addition, like ESCs, iPS cells possess indefinite proliferative capacity in vitro, and have been shown to differentiate into hematopoietic cells. Thus, iPS cells have greater potential to be used in ACT-based immunotherapy compared to ESCs or HSCs. Here, we present methods for the generation of T lymphocytes from iPS cells in vitro, and in vivo programming of antigen-specific CTLs from iPS cells for promoting cancer immune surveillance. Stimulation in vitro with a Notch ligand drives T cell differentiation from iPS cells, and TCR gene transduction results in iPS cells differentiating into antigen-specific T cells in vivo, which prevents tumor growth. Thus, we demonstrate antigen-specific T cell differentiation from iPS cells. Our studies provide a potentially more efficient approach for generating antigen-specific CTLs for ACT-based therapies and facilitate the development of therapeutic strategies for diseases.     

Generation of activated and antigen-specific T cells with cytotoxic activity after co-culture with dendritic cells

Co-culturing of immunological effector cells with antigen-pulsed DC leads to an increase of cytotoxic activity against antigen-expressing tumour cells. Using this approach, we could detect up to 2.8% antigen-specific CTLs after co-culture with antigen-pulsed DC. However, the required high effector cell numbers remain a major obstacle in immunotherapy. In this study, we show an approach for generating activated and antigen-specific effector cells that enables us to decrease effector to target cell ratios. We used an interferon-gamma secretion assay to enrich activated effector cells after co-culture with antigen-pulsed dendritic cells (DC). Purified immunological effector cells lysed 58.3% of antigen-expressing tumour cells at an effector to target ratio of 1:1. Furthermore, using MHC-IgG complexes, we enriched effector cells expressing antigen-specific T-cell receptor after co-culture with DC. Performing ELISpot, flow cytometry and TCR analysis, we could show a significant increase of activated and specific TCR-expressing effector cells after co-culture with DC.     

Long-term engraftment of p18INK4C-deficient hematopoietic stem cells is enhanced in the sublethally-irradiated recipients

Hematopoietic stem cell transplantation (HSCT) has been widely used for the treatment of hematologi-cal malignancies and congenital deficiencies. In recent years, non-myeloablative and reduced-intensity condi-tioning regimens have significantly expanded t…     

Induction of tumor antigen-specific cytotoxic T cell responses in naïve mice by latex microspheres-based artificial antigen-presenting cell constructs

Latex microspheres-based artificial antigen-presenting cell constructs (aAPCs) are proved to be valuable tools to expand T cells ex vivo for adoptive cell therapy, but little is known about their potential for active immunization. In this report, HLA-A2/peptide tetramers were generated and co-coated with anti-mouse CD28 monoclonal antibody onto surface of cell-sized latex microspheres followed by immunization of na?ve HLA-A2/K(b) transgenic mice. Five- to six-fold expansion of tumor antigen-specific CTLs was observed in the spleen after three rounds of immunization. The consequent splenocytes can efficiently recognize endogenously expressed tumor antigen on the surface of human target cells and cytolyze the tumor cells in an antigen-specific manner. This report provides initially the experimental evidence that latex microspheres-based aAPCs can effectively prime antigen-specific CTL proliferation and cytolysis in na?ve mice. This may contribute to a better insight into the potential of microspheres-based aAPCs for active immunization.     

Safe and efficient methods of autologous hematopoietic stem cell transplantation for biomedical research in cynomolgus monkeys

We have established safe and efficient methods for autologous hematopoietic stem cell (HSC) transplantation in cynomolgus monkeys (Macaca fascicularis) that include regimens of supportive care to ensure survival during hematopoietic reconstitution following otherwise lethal total body irradiation. Eleven young adult cynomolgus monkeys were studied. Bone marrow was aspirated from the ilium and/or tuber ischiae after administration of recombinant human stem cell factor (SCF) and granulocyte colony-stimulating factor (G-CSF). Using the immunomagnetic selection method, CD34+ cells were then isolated (90 to 95% pure) as a fraction containing HSCs. Just prior to transplantation, the animals received myeloablative total body irradiation-500 to 550 cGy daily for two days. The monkeys re-infused with CD34+ cells developed moderate to severe myelosuppression, with some animals requiring intravenous hyperalimentation, antibiotic administration, and blood transfusion. Hematopoiesis was restored in all animals after transplantation. It took 12 days, on average, until the peripheral white blood cell count reached more than 1,000 cells/microl. Up to two years after transplantation, signs of radiation-induced pneumonitis or other radiation-related disorders were not evident at the aforementioned dose of irradiation. This transplantation model will be useful for testing new approaches using HSCs for therapy of many diseases and will offer unique insights into the biology of these cells.     

Rapid Lymphocyte Reconstitution of Unconditioned Immunodeficient Mice with Non-Self-Renewing Multipotent Hematopoietic Progenitors

The replacement of abnormal hematopoietic stem cells (HSCs) with normal transplanted HSCs can correct a wide range of hematologic disorders. Here, we provide evidence that transplantation of more differentiated progenitor cells can be used to more rapidly correct lymphoid deficiencies in unconditioned immunocompromised mice. Transplantation of flk2+ multipotent progenitors led to robust B and T cell reconstitution that was maintained for at least 16 weeks. Antigenic challenge at 16 weeks post-transplantation revealed that reconstituted lymphocytes maintained a functional repertoire. In contrast to the persistent lymphocytic engraftment, myeloid chimerism was lost by 12 weeks post-transplantation consistent with the fact that flk2+ progenitors are non-self-renewing. Thus, while more differentiated progenitors are capable of rescuing lymphoid deficiencies, transplantation of HSCs must be used for the correction of non-lymphoid disorders, and, we propose, very long-term immune reconstitution. Based on recent evidence, we discuss novel strategies to achieve the replacement of abnormal HSCs without the use of cytotoxic conditioning regimens.     

Immunotherapy of established tumors using bone marrow transplantation with antigen gene--modified hematopoietic stem cells

A major focus of cancer immunotherapy is to develop strategies to induce T-cell responses through presentation of tumor antigens by dendritic cells (DCs). Current vaccines are limited in their ability to efficiently transfer antigens to DCs in vivo. Ex vivo-generated DCs can be efficiently loaded with antigen but after reinjection, few DCs traffic to secondary lymphoid organs, the critical sites for antigen presentation. To enhance efficiency and durability of antigen presentation by DCs, we transduced hematopoietic stem-progenitor cells (HSCs) with a model tumor antigen and then transplanted the gene-modified cells into irradiated recipient mice, which resulted in efficient expression of the transgene in a large proportion of donor derived DCs in lymphoid organs. The combination of bone marrow transplantation (BMT) using transduced HSCs, systemic agents that generate and activate DCs, and mature T-cell infusion resulted in substantial expansion and activation of antigen-specific T cells. This tripartite strategy provided potent antigen-specific immunotherapy for an aggressive established tumor.     

Long-term engraftment of p18 INK4C-deficient hematopoietic stem cells is enhanced in the sublethally-irradiated recipients

Non-myeloablative regimens for host conditioning have been widely used in clinical hematopoietic stem cell transplantation due to their reduced toxicity on the recipients. But a milder conditioning regimen may require a higher engrafting ability of donor stem cells in competing with endogenous stem cells. Thus, new strategies for enhancing the competitiveness of donor stem cells in non-myeloablative recipients would have important implications for current clinical stem cell transplantation. It is known that the absence of p18 ^INK4C (p18) gene can enhance the self-renewal potential of hematopoietic stem cells (HSCs). We applied the approach of competitive bone marrow transplantation to evaluate the impact of p18 gene deletion on long-term engraftment of HSCs in sublethally irradiated hosts. We found that p18 ^−/− HSCs had a significant advantage over wild-type HSCs during long-term engraftment in the mouse recipients that received a sub-lethal irradiation (5-Gy). The engraftment efficiency of p18 ^−/− HSCs in the sub-lethally irradiated recipients was similar to that in the lethally irradiated (10-Gy) recipients. Our current study demonstrates that enhanced engraftment of donor HSCs in the absence of p18 does not strictly depend on the dose of irradiation used for host conditioning. Therefore, p18 might serve as a potential drug target for increasing the efficacy of stem cell transplant in the patients that are preconditioned with either a myeloablative or non-myeloablative regimen.     

Long-term engraftment of p18INK4C-deficient hematopoietic stem cells is enhanced in the sublethally-irradiated recipients

Non-myeloablative regimens for host conditioning have been widely used in clinical hematopoietic stem cell transplantation due to their reduced toxicity on the recipients. But a milder conditioning regimen may require a higher engrafting ability of donor stem cells in competing with endogenous stem cells. Thus, new strategies for enhancing the competitiveness of donor stem cells in non-myeloablative recipients would have important implications for current clinical stem cell transplantation. It is known that the absence of p18 ^INK4C (p18) gene can enhance the self-renewal potential of hematopoietic stem cells (HSCs). We applied the approach of competitive bone marrow transplantation to evaluate the impact of p18 gene deletion on long-term engraftment of HSCs in sublethally irradiated hosts. We found that p18 ^−/− HSCs had a significant advantage over wild-type HSCs during long-term engraftment in the mouse recipients that received a sub-lethal irradiation (5-Gy). The engraftment efficiency of p18 ^−/− HSCs in the sub-lethally irradiated recipients was similar to that in the lethally irradiated (10-Gy) recipients. Our current study demonstrates that enhanced engraftment of donor HSCs in the absence of p18 does not strictly depend on the dose of irradiation used for host conditioning. Therefore, p18 might serve as a potential drug target for increasing the efficacy of stem cell transplant in the patients that are preconditioned with either a myeloablative or non-myeloablative regimen.     

Ex vivo expanded hematopoietic stem cells overcome the MHC barrier in allogeneic transplantation

The lack of understanding of the interplay between hematopoietic stem cells (HSCs) and the immune system has severely hampered the stem cell research and practice of transplantation. Major problems for allogeneic transplantation include low levels of donor engraftment and high risks of graft-versus-host disease (GVHD). Transplantation of purified allogeneic HSCs diminishes the risk of GVHD but results in decreased engraftment. Here we show that ex?vivo expanded mouse HSCs efficiently overcame the major histocompatibility complex barrier and repopulated allogeneic-recipient mice. An 8-day expansion culture led to a 40-fold increase of the allograft ability of HSCs. Both increased numbers of HSCs and culture-induced elevation of expression of the immune inhibitor CD274 (B7-H1 or PD-L1) on the surface of HSCs contributed to the enhancement. Our study indicates the great potential of utilizing ex?vivo expanded HSCs for allogeneic transplantation and suggests that the immune privilege of HSCs can be modulated.     

Introduction of the green fluorescent protein gene into hematopoietic stem cells results in prolonged discrepancy of in vivo transduction levels between bone marrow progenitors and peripheral blood cells in nonhuman primates

Background

The green fluorescent protein (GFP) has proven a useful marker in retroviral gene transfer studies targeting hematopoietic stem cells (HSCs) in mice. However, several investigators have reported very low in vivo peripheral blood marking levels in nonhuman primates after transplantation of HSCs transduced with the GFP gene. We retrovirally marked cynomolgus monkey HSCs with the GFP gene, and tracked in vivo marking levels within both bone marrow progenitor cells and mature peripheral blood cells following autologous transplantation after myeloablative conditioning.

Methods

Bone marrow cells were harvested from three cynomolgus macaques and enriched for the primitive fraction by CD34 selection. CD34⁺ cells were transduced with one of three retroviral vectors all expressing the GFP gene and were infused after myeloablative total body irradiation (500 cGy × 2). Following transplantation, proviral levels and fluorescence were monitored among clonogenic bone marrow progenitors and mature peripheral blood cells.

Results

Although 13–37% of transduced cells contained the GFP provirus and 11–13% fluoresced ex vivo, both provirus and fluorescence became almost undetectable in the peripheral blood within several months after transplantation regardless of the vectors used. However, on sampling of bone marrow at multiple time points, significant fractions (5–10%) of clonogenic progenitors contained the provirus and fluoresced ex vivo reflecting a significant discrepancy between GFP gene marking levels within bone marrow cells and their mature peripheral blood progeny. The discrepancy (at least one log) persisted for more than 1 year after transplantation. Since no cytotoxic T lymphocytes against GFP were detected in the animals, an immune response against GFP is an unlikely explanation for the low levels of transduced peripheral blood cells. Administration of granulocyte colony stimulating factor and stem cell factor resulted in mobilization of transduced bone marrow cells detectable as mature granulocyte progeny which expressed the GFP gene, suggesting that transduced progenitor cells in bone marrow could be mobilized into the peripheral blood and differentiated into granulocytes.

Conclusions

Low levels of GFP‐transduced mature cells in the peripheral blood of nonhuman primates may reflect a block to differentiation associated with GFP; this block can be overcome in part by nonphysiological cytokine treatment ex vivo and in vivo. Copyright © 2002 John Wiley & Sons, Ltd.

     

Longitudinal analysis of feline leukemia virus-specific cytotoxic T lymphocytes: correlation with recovery from infection

Feline leukemia virus (FeLV) is a common naturally occurring gammaretrovirus of domestic cats that is associated with degenerative diseases of the hematopoietic system, immunodeficiency, and neoplasia. Although the majority of cats exposed to FeLV develop a transient infection and recover, a proportion of cats become persistently viremic and many subsequently develop fatal diseases. To define the dominant host immune effector mechanisms responsible for the outcome of infection, we studied the longitudinal changes in FeLV-specific cytotoxic T lymphocytes (CTLs) in a group of na?ve cats following oronasal exposure to FeLV. Using (51)Cr release assays to measure ex vivo virus-specific cytotoxicity, the emerging virus-specific CTL response was correlated with modulations in viral burden as assessed by detection of infectious virus, FeLV p27 capsid antigen, and proviral DNA in the blood. High levels of circulating FeLV-specific effector CTLs appeared before virus neutralizing antibodies in cats that recovered from exposure to FeLV. In contrast, persistent viremia was associated with a silencing of virus-specific humoral and cell-mediated host immune effector mechanisms. A single transfer of between 2 x 10(7) and 1 x 10(8) autologous, antigen-activated lymphoblasts was associated with a downmodulation in viral burden in vivo. The results suggest an important role for FeLV-specific CTLs in retroviral immunity and demonstrate the potential to modulate disease outcome by the adoptive transfer of antigen-specific T cells in vivo.     

Identification of two new HLA-A*1101-restricted tax epitopes recognized by cytotoxic T lymphocytes in an adult T-cell leukemia patient after hematopoietic stem cell transplantation

We previously reported that Tax-specific CD8(+) cytotoxic T lymphocytes (CTLs), directed to single epitopes restricted by HLA-A2 or A24, expanded in vitro and in vivo in peripheral blood mononuclear cells (PBMC) from some adult T-cell leukemia (ATL) patients after but not before allogeneic hematopoietic stem cell transplantation (HSCT). Here, we demonstrated similar Tax-specific CTL expansion in PBMC from another post-HSCT ATL patient without HLA-A2 or A24, whose CTLs equally recognized two newly identified epitopes, Tax88-96 and Tax272-280, restricted by HLA-A11, suggesting that these immunodominant Tax epitopes are present in the ATL patient in vivo.     

Self-renewal, differentiation or death: regulation and manipulation of hematopoietic stem cell fate.

Hematopoietic stem cells (HSCs) are the rare cells from which all hematopoietic cells are derived. The absence of HSCs is not compatible with life because many essential cells, such as myeloid and erythroid cells, are short lived. The hematopoietic system is the first essential organ system that fails following cytotoxic treatments. It is the vulnerability of HSCs that prevents regeneration following treatment and thus long-term survival. Because HSCs have the capacity to regenerate a functional hematopoietic system, the manipulation of these cells in vitro holds many promises for gene-therapeutic and other applications; however, these are severely curtailed by current difficulties in maintaining and expanding HSCs in culture. This review focuses on recent approaches towards understanding how the HSC compartment is regulated in vivo and discusses how this knowledge might be applied to manipulating HSC numbers.     

Rapid reconstitution of antibody responses following transplantation of purified allogeneic hematopoietic stem cells

Allogeneic hematopoietic cell transplantation has broad clinical applications extending from the treatment of malignancies to induction of immunologic tolerance. However, adaptive cellular and humoral immunity frequently remain impaired posttransplantation. Here, recovery of T-dependent and T-independent Ab responses was evaluated in mice transplanted with purified hematopoietic stem cells (HSCs) devoid of the mature immune cells believed to hasten immune recovery. Mixed and full donor chimeras were created by conditioning recipients with sublethal or lethal irradiation, respectively, across different donor/host genetic disparities. By 6 wk posttransplantation, all animals demonstrated robust T-independent Ab responses, and all mixed chimeras and recipients of MHC-matched or haploidentical HSCs with a shared MHC haplotype had T-dependent Ab responses equivalent to those of untransplanted controls. Full chimeras that received fully MHC-disparate HSCs showed delayed T-dependent Ab responses that recovered by 12 wk. This delay occurred despite early reconstitution and proper migration to germinal centers of donor-derived T(follicular helper) (T(FH)) cells. Congenic transplants into T(FH)-deficient CD4(-/-) mice revealed restoration of T-dependent Ab responses by 6 wk, leading us to conclude that MHC disparity caused delay in humoral recovery. These findings, together with our previous studies, show that, contrary to the view that depletion of graft lymphocytes results in poor posttransplant immunity, elimination of immune-suppressing graft-versus-host reactions permits superior immune reconstitution. This study also provides insight into the regeneration of T(FH) cells and humoral immunity after allogeneic HSC transplantation.     

A clinical microchip for evaluation of single immune cells reveals high functional heterogeneity in phenotypically similar T cells

Cellular immunity has an inherent high level of functional heterogeneity. Capturing the full spectrum of these functions requires analysis of large numbers of effector molecules from single cells. We report a microfluidic platform designed for highly multiplexed (more than ten proteins), reliable, sample-efficient (～1 × 10(4) cells) and quantitative measurements of secreted proteins from single cells. We validated the platform by assessment of multiple inflammatory cytokines from lipopolysaccharide (LPS)-stimulated human macrophages and comparison to standard immunotechnologies. We applied the platform toward the ex vivo quantification of T cell polyfunctional diversity via the simultaneous measurement of a dozen effector molecules secreted from tumor antigen-specific cytotoxic T lymphocytes (CTLs) that were actively responding to tumor and compared against a cohort of healthy donor controls. We observed profound, yet focused, functional heterogeneity in active tumor antigen-specific CTLs, with the major functional phenotypes quantitatively identified. The platform represents a new and informative tool for immune monitoring and clinical assessment.     

Adoptive immunotherapy of cancer using activated Autologous lymphocytes-current status and new strategies-

After the discovery of interleukin-2 (IL-2), lymphokine-activated killer (LAK) cells, tumor-infiltrating lymphocytes (TILs), and cytotoxic T lymphocytes (CTLs) sensitized with the mixed lymphocyte-tumor culture (MLTC) system have been conducted in adoptive immunotherapy (AIT) trials during past 15 years. Although the overall response rate of tumor shrinkage was marginal (9%), locoregional administration of TILs for malignant effusions was effective (77%) for a decrease or disappearance of the effusions even in terminally-ill patients, resulting in an improvement of QOL. Recent advances for molecular understanding of antigen presentation and recognition have promoted us to enhance the efficacy of AIT by using cultured dendritic cells (DCs) for generating antigen-specific CTLs in vitro. The peptide-pulsed DC-activated killer (PDAK) cells showed tumor recognition against antigen-expressing cells, and were efficiently propagated with the IL2 plus immobilized anti-CD3 antibody (IL-2/CD3) culture system. Clinical trials using PDAK cells against patients with lung metastases are now progressed, in which peptides suitable for generating CTLs were chosen in individual patients using the method designated as host-oriented peptide evaluation (HPOE) approach. Moreover, DCs were introduced with tumor-derived RNA, which was amplified with the T7 promoter system, and then were used for stimulating lymphocytes. The tumor RNA-introduced DC-activated killer (TRiDAK) cells showed tumor-specific interferon-gamma spots even in a patient in whom we failed to generate PDAK cells using DCs and peptides, suggesting that the clinical trial of AIT using TRiDAK cells is warranted for the treatment of patients with metastatic cancer. Thus, more understanding of antigen-presentation and -recognition mechanisms and immune regulation systems may promote clinical applications of AIT to establish a novel modality of cancer treatment.     

Novel plant virus-based vaccine induces protective cytotoxic T-lymphocyte-mediated antiviral immunity through dendritic cell maturation

Currently used vaccines protect mainly through the production of neutralizing antibodies. However, antibodies confer little or no protection for a majority of chronic viral infections that require active involvement of cytotoxic T lymphocytes (CTLs). Virus-like particles (VLPs) have been shown to be efficient inducers of cell-mediated immune responses, but administration of an adjuvant is generally required. We recently reported the generation of a novel VLP system exploiting the self-assembly property of the papaya mosaic virus (PapMV) coat protein. We show here that uptake of PapMV-like particles by murine splenic dendritic cells (DCs) in vivo leads to their maturation, suggesting that they possess intrinsic adjuvant-like properties. DCs pulsed with PapMV-like particles displaying the lymphocytic choriomeningitis virus (LCMV) p33 immunodominant CTL epitope (PapMV-p33) efficiently process and cross-present the viral epitope to p33-specific transgenic T cells. Importantly, the CTL epitope is also properly processed and presented in vivo, since immunization of p33-specific T-cell receptor transgenic mice with PapMV-p33 induces the activation of large numbers of specific CTLs. C57BL/6 mice immunized with PapMV-p33 VLPs in the absence of adjuvant develop p33-specific effector CTLs that rapidly expand following LCMV challenge and protect vaccinated mice against LCMV infection in a dose-dependent manner. These results demonstrate the efficiency of this novel plant virus-based vaccination platform in inducing DC maturation leading to protective CTL responses.     

Ex vivo expansion of polyclonal and antigen-specific cytotoxic T lymphocytes by artificial APCs expressing ligands for the T-cell receptor, CD28 and 4-1BB

The ex vivo priming and expansion of human cytotoxic T lymphocytes (CTLs) has potential for use in immunotherapy applications for cancer and infectious diseases. To overcome the difficulty in obtaining sufficient numbers of CTLs, we have developed artificial antigen-presenting cells (aAPCs) expressing ligands for the T-cell receptor (TCR) and the CD28 and 4-1BB co-stimulatory surface molecules. These aAPCs reproducibly activate and rapidly expand polyclonal or antigen-specific CD8(+) T cells. The starting repertoire of CD8+ T cells was preserved during culture. Furthermore, apoptosis of cultured CD8(+) T cells was diminished by this approach. This approach may have important therapeutic implications for adoptive immunotherapy.