Selective in vitro expansion and efficient retroviral transduction of human CD34+ CD38- haematopoietic stem cells

Enhancing Lentiviral and Alpharetroviral Transduction of Human Hematopoietic Stem Cells for Clinical Application

Ex vivo retroviral gene transfer into CD34⁺ hematopoietic stem and progenitor cells (HSPCs) has demonstrated remarkable clinical success in gene therapy for monogenic hematopoietic disorders. However, little attention has been paid to enhancement of culture and transduction conditions to achieve reliable effects across patient and disease contexts and to maximize potential vector usage and reduce treatment cost. We systematically tested three HSPC culture media manufactured to cGMP and eight previously described transduction enhancers (TEs) to develop a state-of-the-art clinically applicable protocol. Six TEs enhanced lentiviral (LV) and five TEs facilitated alpharetroviral (ARV) CD34⁺ HSPC transduction when used alone. Combinatorial TE application tested with LV vectors yielded more potent effects, with up to a 5.6-fold increase in total expression of a reporter gene and up to a 3.8-fold increase in VCN. Application of one of the most promising combinations, the poloxamer LentiBOOST and protamine sulfate, for GMP-compliant manufacturing of a clinical-grade advanced therapy medicinal product (ATMP) increased total VCN by over 6-fold, with no major changes in global gene expression profiles or inadvertent loss of CD34⁺CD90⁺ HSPC populations. Application of these defined culture and transduction conditions is likely to significantly improve ex vivo gene therapy manufacturing protocols for HSPCs and downstream clinical efficacy.

New strategies in cord blood cells transplantation

For patients lacking a human leucocyte antigen-matched donor, umbilical cord blood (UCB) is an ideal, alternative source of haematopoietic stem cells (HSCs) for transplantation purposes. UCB has many advantages over bone marrow or peripheral blood taken from volunteer donors. UCB is also an important source of other stem cells, including endothelial progenitors, mesenchymal stem cells, very small embryonic/epiblast-like (VSEL) stem cells, and unrestricted somatic stem cells, which are potentially suitable for regenerative medicine. However, a significant clinical problem is that the number of HSCs in one cord-blood unit is not enough for an adult transplantation. The development of new approaches including use of multiple donors, ex vivo expansion, increasing efficiency of homing and engraftment, retrieving more cells from the placenta and cord blood is of crucial importance for the delayed engraftment after UCB transplantation. In the future, UCB will emerge as a source of cells for cellular therapies associated with tissue repair and regeneration.

Isolation of human and mouse hematopoietic stem cells

Hematopoietic stem cells (HSC) are rare with estimated frequencies of 1 in 10,000 bone marrow cells and 1 in every 100,000 blood cells. The most important characteristic of HSC is their capacity to provide complete restoration of all blood cell lineages after bone marrow ablation. Therefore they are considered as the ideal targets for various clinical applications including stem cell transplantation and gene therapy. In adult mice and men, the main stem cell source is the bone marrow. For clinical applications HSC derived from umbilical cord blood (UCB) and G-CSF mobilized peripheral blood (PB) have been demonstrated to have several advantages compared to bone marrow; therefore, they are slowly replacing BM as alternative source of stem cells. The mouse is the model organism of choice for immunological and hematological research; therefore, studies of murine HSC are an important research topic. Here we described the most often used protocols and methods to isolate human and mouse HSC to high purity.

Evaluation of different protocols for gene transfer into non-obese diabetes/severe combined immunodeficiency disease mouse repopulating cells

PURPOSE

Although gene transfer with retroviral vectors has shown distinct clinical success in defined settings, efficient genetic manipulation of hematopoietic progenitor cells remains a challenge. To address this issue we have evaluated different transduction protocols and retroviral constructs in the non-obese diabetes (NOD)/severe combined immunodeficiency disease (SCID) xenograft model.

METHODS

An extended transduction protocol requiring 144 h of in vitro manipulation was compared to a more conventional protocol requiring 96 h only.

RESULT

While pretransplantation analysis of cells transduced with a retroviral vector, expressing the enhanced green fluorescent protein (EGFP) marker gene, demonstrated significantly higher overall transduction rates for the extended protocol (33.6 +/- 2.3 vs. 22.1 +/- 3.8%), EGFP expression in CD34+ cells before transplantation (4.0 +/- 0.9 vs. 11.6 +/- 2.5%), engraftment of human cells in NOD/SCID bone marrow 4 weeks after transplantation (4.5 +/- 1.7 vs. 36.5 +/- 9.4%) and EGFP expression in these cells (0 +/- 0 vs. 11.3 +/- 2.8%) were significantly impaired. When the 96 h protocol was used in combination with the spleen focus forming virus (SFFV)/murine embryonic stem cell (MESV) hybrid vector SFbeta11-EGFP, high transduction rates for CD45+ (41.0 +/- 5.3%) and CD34+ (38.5 +/- 3.7%) cells prior to transplantation, as well as efficient human cell engraftment in NOD/SCID mice 4 weeks after transplantation (32.4 +/- 3.5%), was detected. Transgene expression was observed in B-lymphoid (15.9 +/- 2.0%), myeloid (36.5 +/- 3.5%) and CD34+ cells (10.1 +/- 1.5%).

CONCLUSION

Our data show that CD34+ cells maintained in cytokines for multiple days may differentiate and loose their capacity to contribute to the haematological reconstitution of NOD/SCID mice. In addition, the SFFV/MESV hybrid vector SFbeta11-EGFP allows efficient transduction of and gene expression in haematopoietic progenitor cells.

Decreased homing of retrovirally transduced human bone marrow CD34+ cells in the NOD/SCID mouse model

OBJECTIVE

Many clinical gene therapy trials have described poor engraftment of retrovirally transduced CD34(+) cells. Because engraftment is dependent upon successful homing of graft cells to the bone marrow (BM), we examined whether retroviral-mediated gene transfer (RMGT) induces a homing defect in CD34(+) cells.

METHODS

Homing of fluorescently labeled human BM CD34(+) cells transduced with three separate retroviral vectors (MFG-eGFP, LNC-eGFP, and LXSN) was assessed in nonobese diabetic/severe combined immunodeficient mice.

RESULTS

Homing of transduced CD34(+) cells was significantly decreased 20 hours after transplantation compared with freshly isolated control and cultured untransduced control cells. Specifically, homing of GFP(+) cells in the graft was preferentially decreased thus skewing the contribution of transduced cells to engraftment. Transduced cells were not selectively trapped in other organs and BM-homed transduced cells did not undergo apoptosis at a higher rate than untransduced cells. Adhesion molecule expression and binding activity was not altered by RMGT. This homing defect was reversed when transduced cells were cultured over CH-296 for 2 additional days with SCF only.

CONCLUSION

These data suggest that RMGT of hematopoietic cells may compromise their homing potential and implicate transduction-induced reduced homing in the observed low engraftment of retrovirally transduced CD34(+) cells. These results may have a direct clinical application in gene therapy protocols.

CD34 + Cells Home, Proliferate, and Participate in Capillary Formation, and in Combination With CD34 − Cells Enhance Tube Formation in a 3-Dimensional Matrix

Objective— Emerging evidence suggests that human blood contains bone marrow (BM)-derived endothelial progenitor cells that contribute to postnatal neovascularization. Clinical trials demonstrated that administration of BM-cells can enhance neovascularization. Most studies, however, used crude cell populations. Identifying the role of different cell populations is important for developing improved cellular therapies.

Methods and Results— Effects of the hematopoietic stem cell–containing CD34 + cell population on migration, proliferation, differentiation, stimulation of, and participation in capillary-like tubule formation were assessed in an in vitro 3-dimensional matrix model using human microvascular endothelial cells. During movement over the endothelial monolayer, CD34 + cells remained stuck at sites of capillary tube formation and time- and dose-dependently formed cell clusters. Immunohistochemistry confirmed homing and proliferation of CD34 + cells in and around capillary sprouts. CD34 + cells were transduced with the LNGFR marker gene to allow tracing. LNGFR gene–transduced CD34 + cells integrated in the tubular structures and stained positive for CD31 and UEA-1. CD34 + cells alone stimulated neovascularization by 17%. Coculture with CD34 − cells led to 68% enhancement of neovascularization, whereas CD34 − cells displayed a variable response by themselves. Cell–cell contact between CD34 + and CD34 − cells facilitated endothelial differentiation of CD34 + cells.

Conclusions— Our data suggest that administration of CD34 + -enriched cell populations may significantly improve neovascularization and point at an important supportive role for (endogenous or exogenous) CD34 − cells.

IL-3 or IL-7 increases ex vivo gene transfer efficiency in ADA-SCID BM CD34+ cells while maintaining in vivo lymphoid potential

To improve maintenance and gene transfer of human lymphoid progenitors for clinical use in gene therapy of adenosine deaminase (ADA)-deficient SCID we investigated several gene transfer protocols using various stem cell-enriched sources. The lymphoid differentiation potential was measured by an in vitro clonal assay for B/NK cells and in the in vivo SCID-hu mouse model. Ex vivo culture with the cytokines TPO, FLT3-ligand, and SCF (T/F/S) plus IL-3 or IL-7 substantially increased the yield of transduced bone marrow (BM) CD34(+) cells purified from ADA-SCID patients or healthy donors, compared to T/F/S alone. Moreover, the use of IL-3 or IL-7 significantly improved the maintenance of in vitro B cell progenitors from ADA-SCID BM cells and allowed the efficient transduction of B and NK cell progenitors. Under these optimized conditions transduced CD34(+) cells were efficiently engrafted into SCID-hu mice and gave rise to B and T cell progeny, demonstrating the maintenance of in vivo lymphoid reconstitution capacity. The protocol based on the T/F/S + IL-3 combination was included in a gene therapy clinical trial for ADA-SCID, resulting in long-term engraftment of stem/progenitor cells. Remarkably, gene-corrected BM CD34(+) cells obtained from one patient 4 and 11 months after gene therapy were capable of repopulating the lymphoid compartment of SCID-hu hosts.

Differential Gene Expression Profiling of CD34+CD133+Umbilical Cord Blood Hematopoietic Stem Progenitor Cells

Umbilical cord blood (CB)-derived primitive hematopoietic stem progenitor cells (HSPC) are a promising source for stem cell-based gene therapy due to the reduced incidence and severity of graftversus- host disease (GVHD) after human leukocyte antigen (HLA)-disparate CB transplantation. Cell-surface markers such as CD34 and CD133 have been used in combination to enrich primitive HSPC for research and clinical applications. To understand the molecular characteristics of the CB HSPC, we compared the global gene expression of freshly isolated CB CD34+ CD133+ cells with their progenies using a cDNA microarray containing 22,000 human cDNA clones printed on a single chip. A total of 139 genes were differentially expressed between CB HSPC and their progenies. These transcripts included a number of known genes that might play roles in key functions of CB HSPC as well as many genes of unknown function. Among the genes showing the greatest differential expression levels in HSPC were: psoriasin 1, CRHBP, HDAC3, MLLT3, HBEX2, SPINK2, c-kit, H2BFQ, CD133, HHEX, TCF4, ALDH1A1, and FHL1. These data provide more information on the molecular phenotype of CB HSPC and may lead to the identification of new genes critical to stem cell function.

Gene-expression profiling of CD34+cells from various hematopoietic stem-cell sources reveals functional differences in stem-cell activity

The replacement of bone marrow (BM) as a conventional source of stem cell (SC) by umbilical cord blood (UCB) and granulocyte-colony stimulating factor-mobilized peripheral blood SC (PBSC) has brought about clinical advantages. However, several studies have demonstrated that UCB CD34(+) cells and PBSC significantly differ from BM CD34(+) cells qualitatively and quantitatively. Here, we quantified the number of SC in purified BM, UCB CD34(+) cells, and CD34(+) PBSC using in vitro and in vivo assays for human hematopoietic SC (HSC) activity. A cobblestone area-forming cell (CAFC) assay showed that UCB CD34(+) cells contained the highest frequency of CAFC(wk6) (3.6- to tenfold higher than BM CD34(+) cells and PBSC, respectively), and the engraftment capacity in vivo by nonobese diabetic/severe combined immunodeficiency repopulation assay was also significantly greater than BM CD34(+), with a higher proportion of CD45(+) cells detected in the recipients at a lower cell dose. To understand the molecular characteristics underlying these functional differences, we performed several DNA microarray experiments using Affymetrix gene chips, containing 12,600 genes. Comparative analysis of gene-expression profiles showed differential expression of 51 genes between BM and UCB CD34(+) SC and 64 genes between BM CD34(+) cells and PBSC. These genes are involved in proliferation, differentiation, apoptosis, and engraftment capacity of SC. Thus, the molecular expression profiles reported here confirmed functional differences observed among the SC sources. Moreover, this report provides new insights to describe the molecular phenotype of CD34(+) HSC and leads to a better understanding of the discrepancy among the SC sources.