ZAP-70 restoration in mice by in vivo thymic electroporation

Monopolar gene electrotransfer enhances plasmid DNA delivery to skin

A novel monopolar electroporation system and methodologies were developed for in vivo electroporation intended for potential clinical applications such as gene therapy. We hypothesized that an asymmetric anode/cathode electrode applicator geometry could produce favorable electric fields for electroporation, without the typical drawback associated with traditional needle and parallel plate geometries. Three monopolar electrode applicator prototypes were built and tested for gene delivery of reporter genes to the skin in a guinea pig model. Gene expression was evaluated in terms of kinetics over time and expression distribution within the treatment site. Different pulsing parameters, including pulse amplitude, pulse duration, and pulse number were evaluated. Monopolar gene electrotransfer significantly enhanced gene expression compared to controls over the course of 21 days. Gene expression distribution was observed throughout the full thickness of the epidermis, as well as notable expression in the deeper layers of the skin, including the dermis, and the underlying striated muscle without any damage at the treatment site, which is a substantial improvement over previously reported expression confined to the epidermis only. Expression distribution observed is consistent with the electric field distribution model, indicating that our novel electrode geometry results in targeted electroporation and gene transfer. This is important, as it may facilitate translation of many electroporation-based clinical therapies including gene therapies, IRE, and ECT.

Intrathymic adeno-associated virus gene transfer rapidly restores thymic function and long-term persistence of gene-corrected T cells

BACKGROUND

Patients with T-cell immunodeficiencies are generally treated with allogeneic hematopoietic stem cell transplantation, but alternatives are needed for patients without matched donors. An innovative intrathymic gene therapy approach that directly targets the thymus might improve outcomes.

OBJECTIVE

We sought to determine the efficacy of intrathymic adeno-associated virus (AAV) serotypes to transduce thymocyte subsets and correct the T-cell immunodeficiency in a zeta-associated protein of 70 kDa (ZAP-70)-deficient murine model.

METHODS

AAV serotypes were injected intrathymically into wild-type mice, and gene transfer efficiency was monitored. ZAP-70^-/- mice were intrathymically injected with an AAV8 vector harboring the ZAP70 gene. Thymus structure, immunophenotyping, T-cell receptor clonotypes, T-cell function, immune responses to transgenes and autoantibodies, vector copy number, and integration were evaluated.

RESULTS

AAV8, AAV9, and AAV10 serotypes all transduced thymocyte subsets after in situ gene transfer, with transduction of up to 5% of cells. Intrathymic injection of an AAV8-ZAP-70 vector into ZAP-70^-/- mice resulted in a rapid thymocyte differentiation associated with the development of a thymic medulla. Strikingly, medullary thymic epithelial cells expressing the autoimmune regulator were detected within 10 days of gene transfer, correlating with the presence of functional effector and regulatory T-cell subsets with diverse T-cell receptor clonotypes in the periphery. Although thymocyte reconstitution was transient, gene-corrected peripheral T cells harboring approximately 1 AAV genome per cell persisted for more than 40 weeks, and AAV vector integration was detected.

CONCLUSIONS

Intrathymic AAV-transduced progenitors promote a rapid restoration of the thymic architecture, with a single wave of thymopoiesis generating long-term peripheral T-cell function.

Correction of T cell deficiency in ZAP-70 knock-out mice by simple intraperitoneal adoptive transfer of thymocytes

The tyrosine kinase zeta chain-associated protein of 70 kDa (ZAP-70) plays a key role in T cell development and signalling. In the absence of ZAP-70, T cell development is arrested in the CD4⁺ CD8⁺ double-positive stage, thus ZAP-70 homozygous knockout (ZAP-70^-/- ) mice have no mature T cells in their peripheral lymphoid organs and blood, causing severe immunodeficiency. We investigated the early kinetics and long-term effects of wild-type thymocyte transfer on T cell repopulation in ZAP-70^-/- mice. We used a single intraperitoneal (i.p.) injection to deliver donor thymocytes to the recipients. Here, we show that after i.p. injection donor thymocytes leave the peritoneum through milky spots in the omentum and home to the thymus, where donor-originated CD4^- CD8^- double-negative thymocytes most probably restore T cell development and the disrupted thymic architecture. Subsequently, newly developed, donor-originated, single-positive αβ T cells appear in peripheral lymphoid organs, where they form organized T cell zones. The established chimerism was found to be stable, as donor-originated cells were present in transferred ZAP-70^-/- mice as late as 8 months after i.p. injection. We demonstrate that a simple i.p. injection of ZAP-70^+/+ thymocytes is a feasible method for the long-term reconstitution of T cell development in ZAP-70-deficient mice.

Avoiding neuromuscular stimulation in liver irreversible electroporation using radiofrequency electric fields

Electroporation-based treatments typically consist of the application of high-voltage dc pulses. As an undesired side effect, these dc pulses cause electrical stimulation of excitable tissues such as motor nerves. The present in vivo study explores the use of bursts of sinusoidal voltage in a frequency range from 50 kHz to 2 MHz, to induce irreversible electroporation (IRE) whilst avoiding neuromuscular stimulation. A series of 100 dc pulses or sinusoidal bursts, both with an individual duration of 100 µs, were delivered to rabbit liver through thin needles in a monopolar electrode configuration, and thoracic movements were recorded with an accelerometer. Tissue samples were harvested three hours after treatment and later post-processed to determine the dimensions of the IRE lesions. Thermal damage due to Joule heating was ruled out via computer simulations. Sinusoidal bursts with a frequency equal to or above 100 kHz did not cause thoracic movements and induced lesions equivalent to those obtained with conventional dc pulses when the applied voltage amplitude was sufficiently high. IRE efficacy dropped with increasing frequency. For 100 kHz bursts, it was estimated that the electric field threshold for IRE is about 1.4 kV cm^-1 whereas that of dc pulses is about 0.5 kV cm^-1.

Immune Defense Protein Expression in Highly Purified Mouse Lung Epithelial Cells

Lung epithelial cells play critical roles in initiating and modulating immune responses during pulmonary infection or injury. To better understand the spectrum of immune response-related proteins present in lung epithelial cells, we developed an improved method of isolating highly pure primary murine alveolar type (AT) II cells and murine tracheal epithelial cells (mTECs) using negative selection for a variety of lineage markers and positive selection for epithelial cell adhesion molecule (EpCAM), a pan-epithelial cell marker. This method yielded 2-3 × 10(6) ATII cells/mouse lung and 1-2 × 10(4) mTECs/trachea that were highly pure (>98%) and viable (>98%). Using these preparations, we found that both ATII cells and mTECs expressed the Lyn tyrosine kinase, which is best studied as an inhibitory kinase in hematopoietic cells. However, we found little or no expression of Syk in either ATII cells or mTECs, which is in contrast to earlier published reports. Both cell types expressed C-type lectin receptors, anaphylatoxin receptors, and various Toll-like receptors (TLRs). In addition, stimulation of ATII cells with TLR ligands led to secretion of various cytokines and chemokines. Interestingly, lyn(-/-) ATII cells were hyperresponsive to TLR3 stimulation, suggesting that, as in hematopoietic cells, Lyn might be playing an inhibitory role in ATII cells. In conclusion, the improved isolation method reported here, along with expression profiles of various immune defense proteins, will help refocus investigations of immune-related signaling events in pulmonary epithelium.

Gene therapy for primary immune deficiencies: a Canadian perspective

The use of gene therapy (GT) for the treatment of primary immune deficiencies (PID) including severe combined immune deficiency (SCID) has progressed significantly in the recent years. In particular, long-term studies have shown that adenosine deaminase (ADA) gene delivery into ADA-deficient hematopoietic stem cells that are then transplanted into the patients corrects the abnormal function of the ADA enzyme, which leads to immune reconstitution. In contrast, the outcome was disappointing for patients with X-linked SCID, Wiskott-Aldrich syndrome and chronic granulomatous disease who received GT followed by autologous gene corrected transplantations, as many developed hematological malignancies. The malignancies were attributed to the predilection of the viruses used for gene delivery to integrated at oncogenic areas. The availability of safer and more efficient self-inactivating lentiviruses for gene delivery has reignited the interest in GT for many PID that are now in various stages of pre-clinical studies and clinical trials. Moreover, advances in early diagnosis of PID and gene editing technology coupled with enhanced abilities to generate and manipulate stem cells ex vivo are expected to further contribute to the benefit of GT for PID. Here we review the past, the present and the future of GT for PID, with particular emphasis on the Canadian perspective.

Aire Downregulation Is Associated with Changes in the Posttranscriptional Control of Peripheral Tissue Antigens in Medullary Thymic Epithelial Cells

Autoimmune regulator (Aire) is a transcriptional regulator of peripheral tissue antigens (PTAs) and microRNAs (miRNAs) in medullary thymic epithelial cells (mTECs). In this study, we tested the hypothesis that Aire also played a role as an upstream posttranscriptional controller in these cells and that variation in its expression might be associated with changes in the interactions between miRNAs and the mRNAs encoding PTAs. We demonstrated that downregulation of Aire in vivo in the thymuses of BALB/c mice imbalanced the large-scale expression of these two RNA species and consequently their interactions. The expression profiles of a large set of mTEC miRNAs and mRNAs isolated from the thymuses of mice subjected (or not) to small-interfering-induced Aire gene knockdown revealed that 87 miRNAs and 4,558 mRNAs were differentially expressed. The reconstruction of the miRNA–mRNA interaction networks demonstrated that interactions between these RNAs were under Aire influence and therefore changed when this gene was downregulated. Prior to Aire-knockdown, only members of the miR-let-7 family interacted with a set of PTA mRNAs. Under Aire-knockdown conditions, a larger set of miRNA families and their members established this type of interaction. Notably, no previously described Aire-dependent PTA interacted with the miRNAs, indicating that these PTAs were somehow refractory. The miRNA–mRNA interactions were validated by calculating the minimal free energy of the pairings between the miRNA seed regions and the mRNA 3′ UTRs and within the cellular milieu using the luciferase reporter gene assay. These results suggest the existence of a link between transcriptional and posttranscriptional control because Aire downregulation alters the miRNA–mRNA network controlling PTAs in mTEC cells.

Advances of gene therapy for primary immunodeficiencies

In the recent past, the gene therapy field has witnessed a remarkable series of successes, many of which have involved primary immunodeficiency diseases, such as X-linked severe combined immunodeficiency, adenosine deaminase deficiency, chronic granulomatous disease, and Wiskott-Aldrich syndrome. While such progress has widened the choice of therapeutic options in some specific cases of primary immunodeficiency, much remains to be done to extend the geographical availability of such an advanced approach and to increase the number of diseases that can be targeted. At the same time, emerging technologies are stimulating intensive investigations that may lead to the application of precise genetic editing as the next form of gene therapy for these and other human genetic diseases.

Expression profile of peripheral tissue antigen genes in medullary thymic epithelial cells (mTECs) is dependent on mRNA levels of autoimmune regulator (Aire)

In the thymus of non-obese diabetic (NOD) mice, the expression of the autoimmune regulator (Aire) gene varies with age, and its down-regulation in young mice precedes the later emergence of type 1 diabetes mellitus (T1D). In addition, the insulin (Ins2) peripheral tissue antigen (PTA) gene, which is Aire-dependent, is also deregulated in these mice. Based in these findings, we hypothesized that the imbalance in PTA gene expression in the thymus can be associated with slight variations in Aire transcript levels. To test this, we used siRNA to knockdown Aire by in vivo electro-transfection of the thymus of BALB/c mice. The efficiency of the electro-transfection was monitored by assessing the presence of irrelevant Cy3-labeled siRNA in the thymic stroma. Importantly, Aire-siRNA reached medullary thymic epithelial cells (mTECs) down-regulating Aire. As expected, the in vivo Aire knockdown was partial and transient; the maximum 59% inhibition occurred in 48 h. The Aire knockdown was sufficient to down-regulate PTA genes; however, surprisingly, several others, including Ins2, were up-regulated. The modulation of these genes after in vivo Aire knockdown was comparable to that observed in NOD mice before the emergence of T1D. The in vitro transfections of 3.10 mTEC cells with Aire siRNA resulted in samples featuring partial (69%) and complete (100%) Aire knockdown. In these Aire siRNA-transfected 3.10 mTECs, the expression of PTA genes, including Ins2, was down-regulated. This suggests that the expression profile of PTA genes in mTECs is affected by fine changes in the transcription level of Aire.

Electrodes for in vivo localised subcutaneous electropulsation and associated drug and nucleic acid delivery

BACKGROUND

Drug and nucleic acids can be delivered in vivo by an injection of the product followed by the application of a train of electric pulses.

OBJECTIVE

The success of the method is linked to the proper distribution of the electric field in the target tissue. This is under the control of the design of the electrodes.

METHODS

The field distribution can be obtained by computer simulation mainly by using numerical methods and simplifying hypothesis. The conclusions are validated by comparing the computed current and its experimental values on phantoms. A good agreement is obtained.

RESULTS/CONCLUSION

Targeting the delivery to the skin can be obtained by using an array of very short needle electrodes, by pinching the skin between two parallel plate electrodes, or by using contact wire electrodes.

Electroporation and ultrasound enhanced non-viral gene delivery in vitro and in vivo

Non-viral vectors are less efficient than the use of viral vectors for delivery of genetic material to cells in vitro and especially in vivo. However, viral vectors involve the use of foreign proteins that can stimulate both the innate and acquired immune response. In contrast, plasmid DNA can be delivered without carrier proteins and is non-immunogenic. Plasmid gene delivery can be enhanced by the use of physical methods that aid the passage of the plasmid through the cell membrane. Electroporation and microbubble-enhanced ultrasound are two of the most effective physical delivery methods and these can be applied to a range of different cell types in vitro and a broad range of tissues in vivo. Both techniques also have the advantage that, unlike viral vectors, they can be used to target specific tissues with systemic delivery. Although electroporation is often the more efficient of the two, microbubble-enhanced ultrasound causes less damage and is less invasive. This review provides an introduction to the methodology and summarises the range of cells and tissues that have been genetically modified using these techniques.