"Model t" cells: a time-tested vehicle for gene therapy

Cell-Based Therapy Manufacturing in Stirred Suspension Bioreactor: Thoughts for cGMP Compliance

Cell-based therapy (CBT) is attracting much attention to treat incurable diseases. In recent years, several clinical trials have been conducted using human pluripotent stem cells (hPSCs), and other potential therapeutic cells. Various private- and government-funded organizations are investing in finding permanent cures for diseases that are difficult or expensive to treat over a lifespan, such as age-related macular degeneration, Parkinson’s disease, or diabetes, etc. Clinical-grade cell manufacturing requiring current good manufacturing practices (cGMP) has therefore become an important issue to make safe and effective CBT products. Current cell production practices are adopted from conventional antibody or protein production in the pharmaceutical industry, wherein cells are used as a vector to produce the desired products. With CBT, however, the “cells are the final products” and sensitive to physico- chemical parameters and storage conditions anywhere between isolation and patient administration. In addition, the manufacturing of cellular products involves multi-stage processing, including cell isolation, genetic modification, PSC derivation, expansion, differentiation, purification, characterization, cryopreservation, etc. Posing a high risk of product contamination, these can be time- and cost- prohibitive due to maintenance of cGMP. The growing demand of CBT needs integrated manufacturing systems that can provide a more simple and cost-effective platform. Here, we discuss the current methods and limitations of CBT, based upon experience with biologics production. We review current cell manufacturing integration, automation and provide an overview of some important considerations and best cGMP practices. Finally, we propose how multi-stage cell processing can be integrated into a single bioreactor, in order to develop streamlined cGMP-compliant cell processing systems.

Highly efficient homology-driven genome editing in human T cells by combining zinc-finger nuclease mRNA and AAV6 donor delivery

The adoptive transfer of engineered T cells for the treatment of cancer, autoimmunity, and infectious disease is a rapidly growing field that has shown great promise in recent clinical trials. Nuclease-driven genome editing provides a method in which to precisely target genetic changes to further enhance T cell function in vivo. We describe the development of a highly efficient method to genome edit both primary human CD8 and CD4 T cells by homology-directed repair at a pre-defined site of the genome. Two different homology donor templates were evaluated, representing both minor gene editing events (restriction site insertion) to mimic gene correction, or the more significant insertion of a larger gene cassette. By combining zinc finger nuclease mRNA delivery with AAV6 delivery of a homologous donor we could gene correct 41% of CCR5 or 55% of PPP1R12C (AAVS1) alleles in CD8⁺ T cells and gene targeting of a GFP transgene cassette in >40% of CD8⁺ and CD4⁺ T cells at both the CCR5 and AAVS1 safe harbor locus, potentially providing a robust genome editing tool for T cell-based immunotherapy.

IL-12 conditioning improves retrovirally mediated transduction efficiency of CD8+ T cells

The ability to genetically modify T cells is a critical component to many immunotherapeutic strategies and research studies. However, the success of these approaches is often limited by transduction efficiency. As retroviral vectors require cell division for integration, transduction efficiency is dependent on the appropriate activation and culture conditions for T cells. Naive CD8(+) T cells, which are quiescent, must be first activated to induce cell division to allow genetic modification. To optimize this process, we activated mouse T cells with a panel of different cytokines, including interleukin-2 (IL-2), IL-4, IL-6, IL-7, IL-12, IL-15 and IL-23, known to act on T cells. After activation, cytokines were removed, and activated T cells were retrovirally transduced. We found that IL-12 preconditioning of mouse T cells greatly enhanced transduction efficiency, while preserving function and expansion potential. We also observed a similar transduction-enhancing effect of IL-12 preconditioning on human T cells. These findings provide a simple method to improve the transduction efficiencies of CD8(+) T cells.

State-of-the-art human gene therapy: part I. Gene delivery technologies

Safe and effective gene delivery is a prerequisite for successful gene therapy. In the early age of human gene therapy, setbacks due to problematic gene delivery vehicles plagued the exciting therapeutic outcome. However, gene delivery technologies rapidly evolved ever since. With the advancement of gene delivery techniques, gene therapy clinical trials surged during the past decade. As the first gene therapy product (Glybera) has obtained regulatory approval and reached clinic, human gene therapy finally realized the promise that genes can be medicines. The diverse gene delivery techniques available today have laid the foundation for gene therapy applications in treating a wide range of human diseases. Some of the most urgent unmet medical needs, such as cancer and pandemic infectious diseases, have been tackled by gene therapy strategies with promising results. Furthermore, combining gene transfer with other breakthroughs in biomedical research and novel biotechnologies opened new avenues for gene therapy. Such innovative therapeutic strategies are unthinkable until now, and are expected to be revolutionary. In part I of this review, we introduced recent development of non-viral and viral gene delivery technology platforms. As cell-based gene therapy blossomed, we also summarized the diverse types of cells and vectors employed in ex vivo gene transfer. Finally, challenges in current gene delivery technologies for human use were discussed.

Enhancement of the T-cell armamentarium as a cell-based therapy for prostate cancer

Prostate cancer is frequently characterized by a large inflammatory infiltrate that includes T cells. Although T cells traffic to cancer lesions in large numbers, they are unable to generate a therapeutic response because of the immunosuppressive microenvironment. Therefore, arming T cells with a cytotoxic agent that is capable of killing cancer cells independent of these immunosuppressive signals is a rational approach to enhance their potency. Essentially, the T cells would serve as a cell-based vector, or "Trojan Horse," to selectively deliver a protoxin to disseminated prostate cancer lesions. The selective delivery of a protoxin using T cells represents an ideal method to maximize their therapeutic potency through a "field effect." Because systemically infused T cells are expected to traffic to sites of inflammation other than cancer, an additional level of specificity may be needed to prevent toxicity to nontarget tissues. Toward this goal, genetic engineering can be used to make protoxin expression dependent upon T-cell recognition of the prostate-specific membrane antigen by a chimeric antigen receptor. Furthermore, selective activation of the protoxin using a tissue- or tumor-specific protease, such as PSA, can promote further specificity. Thus, T-cell potency can be enhanced by targeted protoxin secretion and greater specificity achieved using combinatorial antigen recognition and protoxin activation.