Combined ultrafiltration-transduction in a hollow-fiber bioreactor facilitates retrovirus-mediated gene transfer into peripheral blood lymphocytes from patients with mucopolysaccharidosis type II

Lymphocyte expansion in bioreactors: upgrading adoptive cell therapy

Bioreactors are essential tools for the development of efficient and high-quality cell therapy products. However, their application is far from full potential, holding several challenges when reconciling the complex biology of the cells to be expanded with the need for a manufacturing process that is able to control cell growth and functionality towards therapy affordability and opportunity. In this review, we discuss and compare current bioreactor technologies by performing a systematic analysis of the published data on automated lymphocyte expansion for adoptive cell therapy. We propose a set of requirements for bioreactor design and identify trends on the applicability of these technologies, highlighting the specific challenges and major advancements for each one of the current approaches of expansion along with the opportunities that lie in process intensification. We conclude on the necessity to develop targeted solutions specially tailored for the specific stimulation, supplementation and micro-environmental needs of lymphocytes’ cultures, and the benefit of applying knowledge-based tools for process control and predictability.

Improved gene transfer and normalized enzyme levels in primitive hematopoietic progenitors from patients with mucopolysaccharidosis type I using a bioreactor

BACKGROUND

One of the major barriers to the clinical application of hematopoietic stem cell (HSC) gene therapy has been relatively low gene transfer efficiency. Other inadequacies of current transduction protocols are related to their multi-step procedures, e.g., using tissue-culture flasks, roller bottles or gas-permeable bags for clinical application.

METHODS

In comparison with a conventional bag transduction protocol, a 'closed' hollow-fiber bioreactor system (HBS) was exploited to culture and transduce human peripheral blood CD34(+) progenitor cells (PBPC(MPS)) from patients with mucopolysaccharidosis type I (MPS I) using an amphotropic retroviral vector based on a murine Moloney leukemia virus LN prototype. Both short-term colony-forming cell (CFC) and long-term culture initiating cell (LTCIC) assays were employed to determine transduction frequency and transgene expression in committed progenitor cells and primitive progenitors with multi-lineage potentials.

RESULTS

A novel ultrafiltration-transduction method was established to culture and transduce enzyme-deficient PBPC(MPS) over a 5-day period without loss in viability and CD34 identity (n = 5). Significantly higher transduction efficiencies were achieved in primary CFC that derived from the HBS (5.8-14.2%) in comparison with those from gas-permeable bags (undetectable to 1.7%; p < 0.01). Up to 15-fold higher-than-normal enzyme activity was found in selected PBPC(MPS)-LP1CD transductants. Moreover, higher gene transfer (4.4-fold) and expression in very primitive progenitors were observed in products from the HBS compared with bag experiments as indicated by CFC derived from primitive LTCIC. Remarkably, with relatively modest gene transfer levels in LTCIC from HBS experiments, the expression of the IDUA transgene corrected the enzyme-deficiency in 5-week long-term cultures (LTC).

CONCLUSIONS

MPS I progenitor cells achieved normalized enzyme levels in LTC after transduction in a HBS system. These studies demonstrate the advantages of a bioreactor-transduction system for viral-mediated stem cell gene transfer.

Gene transfer strategies for correction of lysosomal storage disorders

Lysosomal storage diseases (LSDs) represent a large group of monogenic disorders of metabolism, which affect approximately 1 in 5000 live births. LSDs result from a single or multiple deficiency of specific lysosomal hydrolases, the enzymes responsible for the luminal catabolization of macromolecular substrates. The consequent accumulation of undigested metabolites in lysosomes leads to polysystemic dysfunction, including progressive neurologic deterioration, mental retardation, visceromegaly, blindness, and early death. In general, the residual amount of functional enzyme in lysosomes determines the severity and age at onset of the clinical symptoms, implying that even modest increases in enzyme activity might affect a cure. A key feature on which therapy for LSDs is based is the ability of soluble enzyme precursors to be secreted by one cell type and reinternalize by neighboring cells via receptor-mediated endocytosis and routed to lysosomes, where they function normally. In principle, somatic gene therapy could be the preferred treatment for LSDs if the patient's own cells could be genetically modified in vitro or in vivo to constitutively express high levels of the correcting enzyme and become the source of the enzyme in the patient. Both ex vivo and in vivo gene transfer methods have been experimented with for gene therapy of lysosomal disorders. Several of these methods have proved efficient for the transfer of genetic material into deficient cells in culture and reconstitution of enzyme activity. However, the same methods applied to humans or animal models have been giving inconsistent results, the bases of which are not fully understood. A broader knowledge of disease pathogenesis, facilitated by available, faithful animal models of LSDs, coupled to the development of better gene transfer systems as well as the understanding of vector host interactions will make somatic gene therapy for these devastating and complex diseases the most suitable therapeutic approach.

Optimisation of herpes simplex virus-based vectors for delivery to human peripheral blood mononuclear cells

Peripheral blood mononuclear cells (PBMCs) represent a significant target for gene delivery both for therapeutic and experimental purposes. Thus far however, it has proved difficult to develop vectors capable of high efficient gene delivery to unstimulated PBMCs. We have tested a range of different vectors derived from herpes simplex virus (HSV) which differ in their degree of disablement in terms of their gene delivery efficiency to unstimulated human PBMCs and ability to deliver a reporter gene. None of the viruses had any significant toxic effect in PBMCs. However, optimal gene delivery to unstimulated PBMCs was obtained with a semidisabled virus lacking functional genes encoding ICP34.5 and Vmw65 which was more efficient than either nondisabled or more extremely disabled viruses. Expression of green fluorescent protein (GFP) with this virus was observed in up to 50% of PBMCs 1 day after infection, and reporter gene expression was detectable by Western blotting and immunofluorescence at undiminished levels at the longest time points tested, up to 5 days after infection. This optimised HSV vector may thus represent an effective tool for gene delivery to unstimulated PBMCs in culture.

Optimization of retroviral vector generation for clinical application

BACKGROUND

For many inherited and acquired diseases of the blood system, gene transfer into hematopoietic cells is a promising strategy to alleviate disease-related symptoms or even correct genetic alterations. In clinical gene therapy applications, low transduction efficiencies have been a major limitation mainly because of insufficient effective titers of the retroviral supernatants used. Thus, optimization of clinical-grade vector production under current 'Good Manufacturing Practice' (GMP) conditions is a prerequisite for successful gene therapy trials.

METHODS

We established stable retroviral producer clones with single integrations of a retroviral vector encoding for the multidrug-resistance gene 1 (MDR1). Optimization of vector production in multi-tray cell factories (MTCFs) was studied with particular regard to harvest medium, cell density and harvest time point.

RESULTS

We demonstrated that high-titer vector stocks could be produced in serum-free medium. By reducing the volume of harvest medium, titers could be increased up to four-fold. Plating optimal cell densities of 1 x 10(4) cells/cm2, repetitive harvests of vector supernatant were feasible over four consecutive days. Combining the most advantageous culture and harvest parameters tested, we were able to produce large quantities of serum-free vector supernatant in 40-tray MTCFs. Highly efficient gene transfer into primary human CD34+ progenitor cells demonstrated the quality of these vector stocks.

CONCLUSION

The large-scale vector-production protocol in MTCFs described here is easy to handle, is applicable to a wide range of adherent producer cell lines and, most importantly, complies with current GMP guidelines.

Primary T lymphocytes as targets for gene therapy

Peripheral blood T lymphocytes have been considered an attractive target for gene therapy applications. They can be easily harvested and readily expanded ex vivo. The transduction efficiency of primary human lymphocytes with standard retroviral vectors approaches 50% or more using optimized methods of gene transfer. Other methods of gene transfer, including adenoviral, adeno-associated viral, and lentiviral vectors, or nonviral techniques, have also been used for gene transfer into primary lymphocytes. Despite encouraging results in vitro, human clinical trials using retroviral vectors to transduce primary lymphocytes have been hindered by low expression levels of transgenes and immune responses against transgene products. Strategies to overcome these problems need to be developed.

Closed hollow-fiber bioreactor: a new approach to retroviral vector production

BACKGROUND

The ability to obtain high-titer and large quantities of retroviral vector production in a 'closed' system would have profound implications in clinical and experimental gene therapy.

METHODS

We studied the cell growth and vector production of three retroviral packaging cell lines in a variety of conditions using hollow-fiber bioreactors designed as an 'artificial capillary system' (ACS) and enhanced with the application of a hermetically sealing device for sterile welding of connecting plastic tubings. Vector titer, fetal bovine serum (FBS) concentration, volume and the duration of productivity were assessed to optimize vector production.

RESULTS

In this pilot study, we observed that retroviral vector production (frozen-and-thawed) from cultures containing as low as 2.5% FBS yielded titers up to 2.2 x 10(7) cfu/ml, 14.4-fold higher than titers obtained from control dish cultures. Up to 3 liters of vector supernatant were generated during a 2-month large-scale production run. There was a potential to double this volume of higher-titer supernatant by increasing the frequency of harvest. It seemed that a lower metabolic rate (i.e. lactate production) in the packaging cell culture was associated with higher vector producing ability.

CONCLUSIONS

These data demonstrated the feasibility of producing retroviral vector with enhanced titers and clinically useful quantities in a 'closed' ACS. Thus a new approach for large-scale retroviral vector production is developed.