High Log-Scale Expansion of Functional Human Natural Killer Cells from Umbilical Cord Blood CD34-Positive Cells for Adoptive Cancer Immunotherapy

Immunotherapy based on natural killer (NK) cell infusions is a potential adjuvant treatment for many cancers. Such therapeutic application in humans requires large numbers of functional NK cells that have been selected and expanded using clinical grade protocols. We established an extremely efficient cytokine-based culture system for ex vivo expansion of NK cells from hematopoietic stem and progenitor cells from umbilical cord blood (UCB). Systematic refinement of this two-step system using a novel clinical grade medium resulted in a therapeutically applicable cell culture protocol. CD56+CD3− NK cell products could be routinely generated from freshly selected CD34+ UCB cells with a mean expansion of >15,000 fold and a nearly 100% purity. Moreover, our protocol has the capacity to produce more than 3-log NK cell expansion from frozen CD34+ UCB cells. These ex vivo-generated cell products contain NK cell subsets differentially expressing NKG2A and killer immunoglobulin-like receptors. Furthermore, UCB-derived CD56+ NK cells generated by our protocol uniformly express high levels of activating NKG2D and natural cytotoxicity receptors. Functional analysis showed that these ex vivo-generated NK cells efficiently target myeloid leukemia and melanoma tumor cell lines, and mediate cytolysis of primary leukemia cells at low NK-target ratios. Our culture system exemplifies a major breakthrough in producing pure NK cell products from limited numbers of CD34+ cells for cancer immunotherapy

Nucleofection, an efficient nonviral method to transfer genes into human hematopoietic stem and progenitor cells.

Contains fulltext : 49545.pdf (publisher's version ) (Open Access)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 type of stromal feeder used in limiting dilution assays influences frequency and maintenance assessment of human long-term culture initiating cells

The goal of this study was to evaluate if differences in culture conditions used in long-term culture assays affect enumeration of LTC-IC in freshly sorted or ex vivo expanded CD34+/HLA-DR(dim)/CD2-/CD7- (34+/Lin-) cells. The variables examined included different stromal feeders (murine bone marrow fibroblast cell line, M2-10B4 and murine fetal liver cell line, AFT024) and presence or absence of cytokines (MIP-1α + IL-3). The absolute LTC-IC frequency in 34+/Lin- cells measured in limiting dilution assays (LDA) on AFT024 (4.45 ± 0.69%) was significantly higher than in M2-10B4 (1.45 ± 0.20%) LDA. Addition of MIP-1α and IL-3 to AFT024 LDA increased the measured LTC-IC frequency to 6.8 ± 0.9%. We also determined the fraction of LTC-IC that persisted after 34+/Lin- cells were cultured for 5 weeks by replating progeny in the three LDA readout systems. The measured LTC-IC maintenance was significantly lower when M2-10B4 LDA (13.1 ± 3.5%, P <0.05) were used compared with AFT024 LDA (36.6 ± 5.5%) or AFT024 LDA supplemented with MIP-1α and IL-3 (29.1 ± 6.3%). Thus, the number of LTC-IC measured in freshly sorted 34+ cells depends on the stromal feeder used in LDA assays. Furthermore, and most important, assessment of LTC-IC expansion or maintenance may vary significantly depending on the type of stromal feeder used to enumerate LTC-IC

The myeloid-lymphoid initiating cell (ML-IC) assay assesses the fate of multipotent human progenitors in vitro

Hematopoietic stem cells (HSC) are cells with self-renewing multilineage differentiation potential. Although engraftment in xenogeneic recipients can be used to measure human HSC, these assays do not allow assessment of individual progenitors. We developed an in vitro assay that allows the identification of a single human bone marrow progenitor closely related to HSC, which we termed "Myeloid-Lymphoid Initiating Cell," or ML-IC, because it is capable of generating multiple secondary progenitors that can reinitiate long-term myeloid and lymphoid hematopoiesis in vitro. The assay is done in contact with murine AFT024 fetal liver stromal cells and with Flt3-Ligand, stem cell factor, and interleukin-7. In this assay, 0.2% to 1.7% of Lin -/34(+)/DRdim cells could generate 1 to 3 long-term culture initiating cells (LTC-IC) as well as 1 to 4 NK-IC after 4 to 6 weeks. In addition, this assay measures contribution of net-progenitor conservation and net-progenitor proliferation over time, providing insight in the fate of individual LTC-IC and NK-IC. This assay will prove useful to enumerate the number of very primitive human progenitors with multilineage differentiation potential, as well as to evaluate future ex vivo culture conditions.status: publishe

Primitive human hematopoietic cells give rise to differentially specified daughter cells upon their initial cell division.

Contains fulltext : 50393.pdf (publisher's version ) (Closed access)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