Search

The targeted manipulation of the genetic program of single cells as well as of complete organisms has strongly enhanced our understanding of cellular and developmental processes and should also help to increase our knowledge of primary human stem cells, e.g., hematopoietic stem cells (HSCs), within the next few years. An essential requirement for such genetic approaches is the existence of a reliable and efficient method to introduce genetic elements into living cells. Retro- and lentiviral techniques are efficient in transducing primary human HSCs, but remain labor and time consuming and require special safety conditions, which do not exist in many laboratories. In our study, we have optimized the nucleofection technology, a modified electroporation strategy, to introduce plasmid DNA into freshly isolated human HSC-enriched CD34+ cells. Using enhanced green fluorescent protein (eGFP)-encoding plasmids, we obtained transfection efficiencies of approximately 80% and a mean survival rate of 50%. Performing functional assays using GFU-GEMM and long-term culture initiating cells (LTC-IC), we demonstrate that apart from a reduction in the survival rate the nucleofection method itself does not recognizably change the short- or long-term cell fate of primitive hematopoietic cells. Therefore, we conclude, the nucleofection method is a reliable and efficient method to manipulate primitive hematopoietic cells genetically.

The targeted manipulation of the genetic program of single cells as well as of complete organisms has strongly enhanced our understanding of cellular and developmental processes and should also help to increase our knowledge of primary human stem cells, e.g., hematopoietic stem cells (HSCs), within the next few years. An essential requirement for such genetic approaches is the existence of a reliable and efficient method to introduce genetic elements into living cells. Retro- and lentiviral techniques are efficient in transducing primary human HSCs, but remain labor and time consuming and require special safety conditions, which do not exist in many laboratories. In our study, we have optimized the nucleofection technology, a modified electroporation strategy, to introduce plasmid DNA into freshly isolated human HSC-enriched CD34+ cells. Using enhanced green fluorescent protein (eGFP)-encoding plasmids, we obtained transfection efficiencies of approximately 80% and a mean survival rate of 50%. Performing functional assays using GFU-GEMM and long-term culture initiating cells (LTC-IC), we demonstrate that apart from a reduction in the survival rate the nucleofection method itself does not recognizably change the short- or long-term cell fate of primitive hematopoietic cells. Therefore, we conclude, the nucleofection method is a reliable and efficient method to manipulate primitive hematopoietic cells genetically.

It is often predicted that stem cells divide asymmetrically, creating a daughter cell that maintains the stem-cell capacity, and 1 daughter cell committed to differentiation. While asymmetric stem-cell divisions have been proven to occur in model organisms (eg, in Drosophila), it remains illusive whether primitive hematopoietic cells in mammals actually can divide asymmetrically. In our experiments we have challenged this question and analyzed the developmental capacity of separated offspring of primitive human hematopoietic cells at a single-cell level. We show for the first time that the vast majority of the most primitive, in vitro–detectable human hematopoietic cells give rise to daughter cells adopting different cell fates; 1 inheriting the developmental capacity of the mother cell, and 1 becoming more specified. In contrast, approximately half of the committed progenitor cells studied gave rise to daughter cells, both of which adopted the cell fate of their mother. Although our data are compatible with the model of asymmetric cell division, other mechanisms of cell fate specification are discussed. In addition, we describe a novel human hematopoietic progenitor cell that has the capacity to form natural killer (NK) cells as well as macrophages, but not cells of other myeloid lineages.

It is often predicted that stem cells divide asymmetrically, creating a daughter cell that maintains the stem-cell capacity, and 1 daughter cell committed to differentiation. While asymmetric stem-cell divisions have been proven to occur in model organisms (eg, in Drosophila), it remains illusive whether primitive hematopoietic cells in mammals actually can divide asymmetrically. In our experiments we have challenged this question and analyzed the developmental capacity of separated offspring of primitive human hematopoietic cells at a single-cell level. We show for the first time that the vast majority of the most primitive, in vitro–detectable human hematopoietic cells give rise to daughter cells adopting different cell fates; 1 inheriting the developmental capacity of the mother cell, and 1 becoming more specified. In contrast, approximately half of the committed progenitor cells studied gave rise to daughter cells, both of which adopted the cell fate of their mother. Although our data are compatible with the model of asymmetric cell division, other mechanisms of cell fate specification are discussed. In addition, we describe a novel human hematopoietic progenitor cell that has the capacity to form natural killer (NK) cells as well as macrophages, but not cells of other myeloid lineages.

Spanholtz: Glycostem Therapeutics: Employment. Tordoir:Glycostem Therapeutics: Employment. Bohme:Glycostem Therapeutics: Employment. Kok:Glycostem Therapeutics: Employment.

Introduction

Adoptive transfer of allogeneic natural killer (NK) cells represents a promising treatment approach against cancer, including acute myeloid leukemia (AML). Previously, we reported a cytokine-based culture method for the generation of NK cell products with high cell number and purity. In this system, CD34+hematopoietic progenitor cells (HPC) were expanded and differentiated into NK cells under stroma-free conditions in the presence of IL-15 and IL-2. We show that combining IL-15 with IL-12 drives the generation of more mature and highly functional NK cells. In particular, replacement of IL-2 by IL-12 enhanced the cytolytic activity and IFNγ production of HPC-NK cells toward cultured and primary AML cells in vitro, and improved antileukemic responses in NOD/SCID-IL2Rγnull (NSG) mice bearing human AML cells. Phenotypically, IL-12 increased the frequency of HPC-NK cells expressing NKG2A and killer immunoglobulin-like receptor (KIR), which were more responsive to target cell stimulation. In addition, NK15/12 cell products demonstrated superior maturation potential, resulting in >70% positivity for CD16 and/or KIR within 2 weeks after infusion into NSG mice. We predict that higher functionality and faster in vivomaturation will favor HPC-NK cell alloreactivity toward malignant cells in patients, making this cytokine combination an attractive strategy to generate clinical HPC-NK cell products for cancer adoptive immunotherapy.

Natural killer (NK) cell-based immunotherapy is a promising adjuvant, relatively non-toxic therapy approach for AML. However, further improvement of NK cell-based therapy is needed to increase the clinical effect. In this regard, NK cells generated ex vivofrom hematopoietic progenitor cells (HPC) may have significant clinical benefits over enriched NK cells from adult donors, including the ability to choose an appropriate killer-cell immunoglobuline-like receptor (KIR)-ligand or KIR B haplotype alloreactive donor, as well as the capacity to reach high therapeutic dosages. Previously, we reported a GMP-compliant, cytokine/heparin-based culture protocol for the ex vivogeneration of highly active NK cells from CD34+HPC isolated from cryopreserved umbilical cord blood (UCB) units. Expansion in closed, large-scale bioreactors yields a clinically relevant dose of NK cells with high purity and cytolytic activity against AML cells in vitro.Currently, a clinical phase I trial with these HPC-NK cells is ongoing in our hospital. Trafficking studies in NOD/SCID/IL2Rgnull(NSG) mice demonstrated that these HPC-NK cells migrate to the bone marrow (BM) as well as to lymphoid organs where in vivoexpansion and maturation can take place. Analysis of the chemokine receptor expression profile of UCB-NK cells matched in vivofindings. Particularly, a firm proportion of UCB-NK cells functionally expressed CXCR4, what could trigger BM homing in response to its ligand CXCL12. In addition, high expression of CXCR3 and CCR6 supported the capacity of UCB-NK cells to migrate to inflamed tissues via the CXCR3/CXCL10-11 and CCR6/CCL20 axis. Importantly, a single HPC-NK cell infusion combined with supportive IL-15 administration was shown to efficiently inhibit growth of K562 leukemia cells implanted in the femur of NSG mice, resulting in significant prolongation of mice survival. Furthermore, we investigated whether modulation by the DNA methyltransferase (DNMT) inhibitors Azacytidine (Aza) and Decitabine (Deci) could further potentiate the antileukemic effect of HPC-NK cells against AML cells. In concordance with previous reports, we observed a dose-dependent effect of Aza and Deci on the growth of the AML cell lines THP1 and KG1a. In subsequent NK cell killing assays, we used clinical relevant low drug concentrations to pre-treat AML cells that did not affect HPC-NK cell viability and cytolytic function. Interestingly, increased killing of pre-treated THP1 and KG1a cells by HPC-NK cells could be observed, which was correlated with an increase in the NKG2D ligand ULBP2, the DNAM-1 ligands CD112 and CD155 as well as TRAIL-R2. Notably, maintenance of low-dose DNMT inhibitors during the KG1a/NK co-culture resulted in pronounced AML growth inhibition. To examine the effect of DNMT inhibitors in vivo, THP1.LucGFP-bearing NSG mice were treated with increasing dose of both agents, which were administered according to current standard protocols applied in humans. Data indicated that treatment with Aza or Deci at dosage equivalent in human to 12.5 and 5 mg/m2respectively was well tolerated with minimal and/or transient weight loss, and efficiently reduced the progression of THP-1.LucGFP cells in vivo. Currently, we explore whether HPC-NK cells and DNMT inhibitors can work together to combat AML in our xenograft models. These preclinical studies may provide a rationale to investigate the possible additive and/or synergistic anti-AML effects of adoptive HPC-NK cell transfer in combination with these DNMT inhibitors in AML patients.

Spanholtz: Glycostem Therapeutics: Employment.

Tordoir: Glycostem Therapeutics: Employment. Spanholtz:Glycostem Therapeutics: Employment.

The prominent role of dendritic cells (DCs) in T cell activation is the rational for DC-based immunotherapy of cancer and infectious diseases. In cancer, DC therapy aims to induce tumor-specific effector T cell responses that can reduce or eliminate the tumor, and to develop immunological memory to control tumor relapse. So far, the vast majority of DC vaccination studies have been performed with DCs differentiated from monocytes (Mo-DCs) that are loaded with tumor-associated antigens (TAAs) or minor histocompatibility antigens (MiHA). This strategy has been reported to induce the expansion of antigen-specific CD4+and/or CD8+T cells in the majority of patients, however only a fraction of the patients develop clinical responses. Strategies to improve the potency of DC-based vaccines are to increase the stimulatory and migratory capacity of Mo-DCs, or to use alternative DC subtypes, such as naturally circulating plasmacytoid DCs (pDCs), BDCA1+myeloid DCs (mDCs) or BDCA3+mDCs. These DC subsets are potent inducers of antigen-specific T cell responses, and are therefore attractive cells to exploit for DC-based therapy. However, since their frequency in blood is very low, it is a challenge to obtain high enough numbers for immunotherapy. It would be advantageous if DCs, which are phenotypically and functionally similar to blood pDCs and mDCs, could be generated from CD34+hematopoietic progenitor cells (HPCs). Interestingly, recent findings have indicated that the aryl hydrocarbon receptor (AhR) not only regulates toxic effects of environmental contaminants, but also plays a role in modulating hematopoiesis and the immune system. For instance, it has been reported that StemRegenin 1 (SR1), a small molecule inhibitor of AhR, promotes the ex vivoexpansion of human CD34+HPCs that are able to effectively engraft immunodeficient mice. Furthermore, differentiation of Langerhans cells and monocytes in vitrofrom HPCs can be inhibited by the addition of the AhR agonist VAF347. In light of these data, we investigated if we could generate DC subsets from CD34+HPCs by supplementing SR1. Therefore, we cultured CD34+HPCs in medium containing SCF, Flt3L, IL-6, TPO supplemented with 1 μM SR1 or DMSO as control. Interestingly, addition of SR1 explicitly promoted the emergence of pDCs (CD11c-HLA-DR+CD123hiBDCA2+BDCA4+cells), BDCA1+mDCs (Lin1-HLA-DR+BDCA1+BDCA3-cells) and BDCA3+mDCs (Lin1-HLA-DR+BDCA1-BDCA3+cells). After three weeks of culture, the frequency of these DC subsets was significantly higher in cultures with SR1 compared to control conditions; 2.9% vs. 0.04% for pDCs, 4.6% vs. 0.5% for BDCA1+mDCs and 1.1% vs. 0.1% for BDCA3+mDCs (n=3-5 donors). The average yield after three weeks of culture with SR1 starting from 105CD34+UCB cells was 3.8x106pDCs, 5.3x106BDCA1+mDCs and 1.2x106BDCA3+mDCs (n=3-5 donors). Furthermore, SR1 also promoted the differentiation of DC subsets from CD34+cells obtained from peripheral blood of G-CSF-mobilized donors. The average frequency of DCs in these SR1-cultures was 4.7%, 3.8% and 0.9% for pDCs, BDCA1+and BDCA3+mDCs, respectively (n=3 donors), which is comparable to the frequency obtained from UCB CD34+cells. But the expansion potential of G-CSF-mobilized blood CD34+HPCs was lower than that of UCB CD34+cells, resulting in average DC yields of 0.6x106, 0.5x106and 0.1x106from 105CD34+cells (n=3). Flow cytometry analysis demonstrated that the SR1-induced pDCs and mDCs are phenotypically comparable to their naturally occurring counterpart in blood. Furthermore, the ex vivo-generated pDCs potently responded to stimulation with TLR7 and TLR9 ligands by secreting high amounts of IFN-α and upregulating CD83, CD80, CD86 and CCR7. The HPC-mDC subsets also upregulate CD80 and CD83 upon TLR3, TLR4 or TLR7/8 ligation. Finally, both the ex vivo-generated pDCs and mDCs induced potent allogeneic T cell responses and activated CD8+effector T cells against hematopoietic-restricted MiHA. These findings demonstrate that our SR1 culture system not only allows detailed study of DC differentiation and molecular regulations in vitro, but it also offers the opportunity to evaluate the in vivoefficacy of cultured DC subsets upon vaccination into patients with cancer and viral infections.

Abstract 4130

Spanholtz: Glycostem Therapeutics: Employment. Groenewegen:Glycostem Therapeutics: Equity Ownership.

Spanholtz: Glycostem Therapeutics: Employment. Tordoir:Glycostem Therapeutics: Employment.

Abstract 2666

Alloreactive donor Natural Killer (NK) cells, displaying a KIR-ligand mismatch with the recipient play a pivotal role in graft-versus-leukemia (GVL) reactivity without significant graft-versus-host disease (GVHD) following haploidentical stem cell transplantation. Therefore, infusions of haploidentical NK cells are suggested to become an attractive approach for cancer immunotherapy. So far, difficulties in isolation and expansion of peripheral NK cells resulted in only limited data about safety and clinical efficacy of purified NK cell infusions. Therefore, we have developed a novel culture system without the use of feeder cells for the ex vivo generation of NK cells from CD34+ hematopoietic progenitor cells (HPCs) isolated from cord blood (CB) or bone marrow (BM). It is based on a two-step procedure using an expansion and a differentiation step. The NK cell generation system uses mainly cytokines such as SCF, TPO, Flt3-L, IL-2, IL-7 and IL-15 and specific modified glycosaminoglycans (GAGs) to direct and control the two phases. The developmental phase and the final NK cell product is controlled and characterized by immunophenotyping using multi-colour flow cytometry and CFSE-based cytotoxicity assays against various tumor cells. Our system generates a homogeneous final cell product of CD56+/CD3- cells with a purity of >99%. A total cell expansion of more than 5×10^4 fold allows to generate 5×10^10 NK cells from 1×10^6 CB CD34+ stem and progenitor cells within 4–5 weeks of culture. For BM cells an expansion rate of more than 1×10^4 fold was detected after a 5–6 week cell culture period. During the two week expansion phase step,we expand UCB CD34+ cells more than 100 fold. Phenotypic analysis showed a decrease of stem cell-specific antigens such as CD34 and CD117 during the first three weeks, whereas antigens specific for NK cell progenitors and mature NK cells such as CD56, CD94 and CD161 are up-regulated after initiating differentiation at day 14. Furthermore, distinct cell populations can be detected reflecting NK cell developmental stages in vitro. Effective differentiation of the expanded progenitor cells into mature NK cells is characterized by the expression of NK cell-specific antigens including CD56, CD94, NKG2A, NKG2D and NCRs as well as homing receptors such as CD62L, CXCR4 and CCR7. The final NK cell product shows high expression levels of inhibitory and activating receptors as well the intrinsic capability to express KIR, which is detected by flow cytometry after 6–7 weeks of culture. Cytotoxicity assays demonstrated robust lysis of more than 90% against AML as well as melanoma tumor cell lines. This system, with its huge expansion potential to generate highly activated NK cells with homing capability, is the basis for a first clinical trial in 2009, to infuse haploidentical NK cells generated from CD34+ cells in poor-risk AML patients. The use of our defined culture conditions enables new prospects in NK cell research, regarding NK cell development and NK cell maturation, as well as new aspects for the clinical use of NK cell products derived from HPCs.

Alloreactive donor Natural Killer (NK) cells, displaying a KIR-ligand mismatch with the recipient play a pivotal role in graft-versus-leukemia (GVL) reactivity without significant graft-versus-host disease (GVHD) following haploidentical stem cell transplantation. Therefore, infusions of haploidentical NK cells are suggested to become an attractive approach for cancer immunotherapy. So far, difficulties in isolation and expansion of peripheral NK cells resulted in only limited data about safety and clinical efficacy of purified NK cell infusions.