Efficient oncoretroviral transduction of extended long-term culture-initiating cells and NOD/SCID repopulating cells: enhanced reconstitution with gene-marked cells through an ex vivo expansion approach

Analysis of the clonal growth and differentiation dynamics of primitive barcoded human cord blood cells in NSG mice

Human cord blood (CB) offers an attractive source of cells for clinical transplants because of its rich content of cells with sustained repopulating ability in spite of an apparent deficiency of cells with rapid reconstituting ability. Nevertheless, the clonal dynamics of nonlimiting CB transplants remain poorly understood. To begin to address this question, we exposed CD34+ CB cells to a library of barcoded lentiviruses and used massively parallel sequencing to quantify the clonal distributions of lymphoid and myeloid cells subsequently detected in sequential marrow aspirates obtained from 2 primary NOD/SCID-IL2Rγ(-/-) mice, each transplanted with ∼10(5) of these cells, and for another 6 months in 2 secondary recipients. Of the 196 clones identified, 68 were detected at 4 weeks posttransplant and were often lympho-myeloid. The rest were detected later, after variable periods up to 13 months posttransplant, but with generally increasing stability throughout time, and they included clones in which different lineages were detected. However, definitive evidence of individual cells capable of generating T-, B-, and myeloid cells, for over a year, and self-renewal of this potential was also obtained. These findings highlight the caveats and utility of this model to analyze human hematopoietic stem cell control in vivo.

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.

Deficiency of oncoretrovirally transduced hematopoietic stem cells and correction through ex vivo expansion

BACKGROUND

Extensive efforts to develop hematopoietic stem cell (HSC) based gene therapy have been hampered by low gene marking. Major emphasis has so far been directed at improving gene transfer efficiency, but low gene marking in transplanted recipients might equally well reflect compromised repopulating activity of transduced cells, competing for reconstitution with endogenous and unmanipulated stem cells.

METHODS

The autologous settings of clinical gene therapy protocols preclude evaluation of changes in repopulating ability following transduction; however, using a congenic mouse model, allowing for direct evaluation of gene marking of lympho-myeloid progeny, we show here that these issues can be accurately addressed.

RESULTS

We demonstrate that conditions supporting in vitro stem cell self-renewal efficiently promote oncoretroviral-mediated gene transfer to multipotent adult bone marrow stem cells, without prior in vivo conditioning. Despite using optimized culture conditions, transduction resulted in striking losses of repopulating activity, translating into low numbers of gene marked cells in competitively repopulated mice. Subjecting transduced HSCs to an ex vivo expansion protocol following the transduction procedure could partially reverse this loss.

CONCLUSIONS

These studies suggest that loss of repopulating ability of transduced HSCs rather than low gene transfer efficiency might be the main problem in clinical gene therapy protocols, and that a clinically feasible ex vivo expansion approach post-transduction can markedly improve reconstitution with gene marked stem 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.

Lentiviral shRNA silencing of murine bone marrow cell CCR2 leads to persistent knockdown of CCR2 function in vivo

A major barrier in hematopoietic gene function studies is posed by the laborious and time-consuming generation of knockout mice with an appropriate genetic background. Here we present a novel lentivirus-based strategy for the in situ generation of hematopoietic knockdowns. A short hairpin RNA (shRNA) was designed targeting murine CC-chemokine receptor 2 (CCR2), which was able to specifically blunt CCR2 expression at the mRNA, protein, and functional levels in vitro. Reconstitution of irradiated recipient mice with autologous bone marrow that had been ex vivo transduced with shRNA lentivirus led to persistent down-regulation of CCR2 expression, which translated into a 70% reduction in CCR2-dependent recruitment of macrophages to an inflamed peritoneal cavity without noticeable side effects on related chemokine receptors or general inflammation status. These findings clearly demonstrate the potential of shRNA lentivirus-infected bone marrow transplantation as a rapid and effective method to generate hematopoietic knockdowns for leukocyte gene function studies.

Highly efficient lentiviral gene transfer in CD34+ and CD34+/38-/lin- cells from mobilized peripheral blood after cytokine prestimulation

Because mobilized peripheral blood (mPB) represents an attractive source of cells for gene therapy, we investigated lentiviral gene transfer in CD34(+) cells and the stem/progenitor-cell-enriched CD34(+)/38(-)/lin(-) cell subset isolated from mPB. In this study, we used an optimized third-generation self-inactivating lentiviral vector containing both the central polypurine tract and the woodchuck hepatitis posttranscriptional regulatory element sequences and encoding enhanced green fluorescent protein (EGFP) under the control of the elongation factor lalpha promoter. This lentivector was first used to compare multiplicity of infection (MOI)-dependent gene transfer efficiency in cord blood (CB) versus mPB CD34(+)-derived cells, colony-forming cells (CFCs), and long-term culture-initiating cells (LTC-ICs). Results showed a difference in the percentage of transduced cells particularly significant at low MOIs. A plateau was reached where 15% and 25% of CB and mPB cells, respectively, remained refractory to lentiviral trans-duction. Effects of a cytokine prestimulation period (18 hours) with interleukin-3, stem cell factor, Flt-3 ligand, and thrombopoietin were then analyzed in total cells, CFCs, and LTC-ICs derived from mPB CD34(+) cells. Transduction levels in those conditions demonstrated a two- and fourfold increase in CFCs and LTC-ICs, respectively, compared with unstimulated (<3 hours) control cells. Moreover, using the same transduction protocol, we were able to efficiently transduce CD34(+)/38(-)/lin(-) cells isolated from mPB, with up to >85% of colonies derived from LTC-ICs expressing EGFP and gene transfer levels remaining stable for 10 weeks in liquid culture. We therefore demonstrate a highly efficient gene transfer in this therapeutically relevant target cell population.