Insertion vectors for gene therapy

Macrophage Inhibitor Clodronate Enhances Liver Transduction of Lentiviral but Not Adeno-Associated Viral Vectors or mRNA Lipid Nanoparticles in Neonatal and Juvenile Mice

Recently approved adeno-associated viral (AAV) vectors for liver monogenic diseases haemophilia A and B are exemplifying the success of liver-directed viral gene therapy. In parallel, additional gene therapy strategies are rapidly emerging to overcome some inherent AAV limitations, such as the non-persistence of the episomal transgene in the rapidly growing liver and immune response. Viral integrating vectors such as in vivo lentiviral gene therapy and non-viral vectors such as lipid nanoparticles encapsulating mRNA (LNP-mRNA) are rapidly being developed, currently at the preclinical and clinical stages, respectively. Macrophages are the first effector cells of the innate immune response triggered by gene therapy vectors. Macrophage uptake and activation following administration of viral gene therapy and LNP have been reported. In this study, we assessed the biodistribution of AAV, lentiviral, and LNP-mRNA gene therapy following the depletion of tissue macrophages by clodronate pre-treatment in neonatal and juvenile mice. Both neonatal and adult clodronate-treated mice showed a significant increase in lentiviral-transduced hepatocytes. In contrast, clodronate pre-treatment did not modify hepatocyte transduction mediated by hepatotropic AAV8 but reduced LNP-mRNA transfection in neonatal and juvenile animals. These results highlight the importance of age-specific responses in the liver and will have translational applications for gene therapy programs.

Using CRISPR to enhance T cell effector function for therapeutic applications

T cells are critical to fight pathogenic microbes and combat malignantly transformed cells in the fight against cancer. To exert their effector function, T cells produce effector molecules, such as the pro-inflammatory cytokines IFN-γ, TNF-α and IL-2. Tumors possess many inhibitory mechanisms that dampen T cell effector function, limiting the secretion of cytotoxic molecules. As a result, the control and elimination of tumors is impaired. Through recent advances in genomic editing, T cells can now be successfully modified via CRISPR/Cas9 technology. For instance, engaging (post-)transcriptional mechanisms to enhance T cell cytokine production, the retargeting of T cell antigen specificity or rendering T cells refractive to inhibitory receptor signaling can augment T cell effector function. Therefore, CRISPR/Cas9-mediated genome editing might provide novel strategies for cancer immunotherapy. Recently, the first-in-patient clinical trial was successfully performed with CRISPR/Cas9-modified human T cell therapy. In this review, a brief overview of currently available techniques is provided, and recent advances in T cell genomic engineering for the enhancement of T cell effector function for therapeutic purposes are discussed.

Advances and Challenges in Cardiovascular Gene Therapy

Many promising cardiovascular gene therapy approaches have failed to fulfill expectations in clinical trials. However, 20 years of research and method development has laid a solid groundwork for future therapies, and the need for new treatment options still exists. The safety of gene therapy has been established with various viral vectors, transgenes and delivery methods. Improving success in clinical settings requires careful consideration of the translational process. This requires both improving animal models and preclinical end points, and new approach in patient recruitment and selection of clinical end points. This review focuses on bidirectional translationality from bench to bedside and back and proposes ways to improve the process. Developing a highly complex new therapy has taken an enormous amount of work and resources, but perhaps now after the hard lessons cardiovascular gene therapy is ready become a clinical reality.

miRNA control of tissue repair and regeneration

Tissue repair and regeneration rely on the function of miRNA, molecular silencers that enact post-transcriptional gene silencing of coding genes. Disruption of miRNA homeostasis is developmentally lethal, indicating that fetal tissue development is tightly controlled by miRNAs. Multiple critical facets of adult tissue repair are subject to control by miRNAs, as well. Sources of cell pool for tissue repair and regeneration are diverse and provided by processes including cellular dedifferentiation, transdifferentiation, and reprogramming. Each of these processes is regulated by miRNAs. Furthermore, induced pluripotency may be achieved by miRNA-based strategies independent of transcription factor manipulation. The observation that miRNA does not integrate into the genome makes miRNA-based therapeutic strategies translationally valuable. Tools to manipulate cellular and tissue miRNA levels include mimics and inhibitors that may be specifically targeted to cells of interest at the injury site. Here, we discuss the extraordinary importance of miRNAs in tissue repair and regeneration based on emergent reports and rapid advances in miRNA-based therapeutics.

CCR5 Gene Editing of Resting CD4(+) T Cells by Transient ZFN Expression From HIV Envelope Pseudotyped Nonintegrating Lentivirus Confers HIV-1 Resistance in Humanized Mice

CCR5 disruption by zinc finger nucleases (ZFNs) is a promising method for HIV-1 gene therapy. However, successful clinical translation of this strategy necessitates the development of a safe and effective method for delivery into relevant cells. We used non-integrating lentivirus (NILV) for transient expression of ZFNs and pseudotyped the virus with HIV-envelope for targeted delivery to CD4⁺ T cells. Both activated and resting primary CD4⁺ T cells transduced with CCR5-ZFNs NILV showed resistance to HIV-1 infection in vitro. Furthermore, NILV transduced resting CD4⁺ T cells from HIV-1 seronegative individuals were resistant to HIV-1 challenge when reconstituted into NOD-scid IL2rγc null (NSG) mice. Likewise, endogenous virus replication was suppressed in NSG mice reconstituted with CCR5-ZFN–transduced resting CD4⁺ T cells from treatment naïve as well as ART-treated HIV-1 seropositive patients. Taken together, NILV pseudotyped with HIV envelope provides a simple and clinically viable strategy for HIV-1 gene therapy.

Use of a lentivirus/VSV pseudotype virus for highly efficient genetic redirection of human peripheral blood lymphocytes

Genetic redirection of lymphocytes that have been engineered to recognize antigens other than those originally programmed by their rearranged germlines is a potentially powerful immunotherapeutic tool. The rationale for the protocol described here is that many cancers and persistent or latent viruses have developed strikingly similar mechanisms of evading attack by host immunity that can often be overcome by redirection of host lymphocytes using chimeric T-cell receptor (chTCR) genes. However, for human peripheral blood lymphocytes (PBLs), this is generally regarded as a technically demanding procedure with unacceptably low efficiency using either contemporary transfection methods or retroviral transduction. One of the main difficulties with retroviruses is their reliance on rapidly dividing cells for integration of their genomes carrying the desired chTCR. Here we describe a highly efficient protocol that uses a lentivirus/vesicular stomatitis virus pseudotyped virus to engineer CD3/CD28-stimulated human peripheral blood cells (i.e., primarily T cells), with near 100% efficiency.

Safety of adeno-associated virus gene therapy vectors: a current evaluation

An increasing number of strategies for molecular treatment of disease rely on the adeno-associated virus (AAV) as a therapeutic gene delivery vector. One of the most attractive features of this viral DNA vector is the perceived safety of AAV gene delivery. Recent applications in human clinical trials support the safety record established in preclinical trials, with evidence of gene transfer in the absence of cellular immune responses or tissue disturbance. Nevertheless, many aspects of the biology of the wild type AAV and its derivatives are still being explored. While the therapeutic potential of novel recombinant AAV therapeutics appears promising, recent insights suggest aspects of their pharmacokinetics, biodistribution and toxicity that require consideration to achieve the safest application of these molecular medicines.