Analysis of Surface Expression of NMDAR Subunits in Primary Hippocampal Neurons.

The expression and activity of ionotropic glutamate receptors control signal transduction at the excitatory synapses in the CNS. The NMDAR comprises two obligatory GluN1 subunits and two GluN2 or GluN3 subunits in different combinations. Each GluN subunit consists of four domains: the extracellular amino-terminal and agonist-binding domains, the transmembrane domain, and the intracellular C-terminal domain (CTD). The CTD interaction with various classes of intracellular proteins is critical for trafficking and synaptic localization of NMDARs. Amino acid mutations or the inclusion of premature stop codons in the CTD could contribute to the emergence of neurodevelopmental and neuropsychiatric disorders. Here, we describe the method of preparing primary hippocampal neurons and lentiviral particles expressing GluN subunits that can be used as a model to study cell surface expression and synaptic localization of NMDARs. We also show a simple method of fluorescence immunostaining of eGFP-tagged GluN2 subunits and subsequent microscopy technique and image analysis to study the effects of disease-associated mutations in the CTDs of GluN2A and GluN2B subunits.

Comparing chemical transfection, electroporation, and lentiviral vector transduction to achieve optimal transfection conditions in the Vero cell line.

BACKGROUND: Transfection is an important analytical method for studying gene expression in the cellular environment. There are some barriers to efficient DNA transfection in host cells, including circumventing the plasma membrane, escaping endosomal compartmentalization, autophagy, immune sensing pathways, and translocating the nuclear envelope. Therefore, it would be very useful to introduce an optimum transfection approach to achieve a high transfection efficiency in the Vero cell line. The aim of this study was to compare various transfection techniques and introduce a highly efficient method for gene delivery in Vero cells. METHODS: In the current study, three transfection methods were used, including chemical transfection, electroporation, and lentiviral vector transduction, to obtain the optimum transfection conditions in the Vero cell line. Vero cells were cultured and transfected with chemical transfection reagents, electroporation, or HIV-1-based lentivectors under different experimental conditions. Transfection efficiency was assessed using flow cytometry and fluorescence microscopy to detect GFP-positive cells. RESULTS: Among the tested methods, TurboFect™ chemical transfection exhibited the highest efficiency. Optimal transfection conditions were achieved using 1 µg DNA and 4 µL TurboFect™ in 6 × 104 Vero cells. CONCLUSION: TurboFect™, a cationic polymer transfection reagent, demonstrated superior transfection efficiency in Vero cells compared with electroporation and lentivirus particles, and is the optimal choice for chemical transfection in the Vero cell line.

Detection of small ruminant Lentivirus proviral DNA in red deer from Poland.

Small ruminant lentiviruses (SRLVs) are widespread and infect goats and sheep. Several reports also suggest that SRLVs can infect wild ruminants. The presence of specific antibodies against SRLVs has been identified in wild ruminants from Poland, but no studies have been conducted to detect proviral DNA of SRLVs in these animals. Therefore, the purpose of this study was to examine samples from Polish wild ruminants to determine whether these animals can serve as reservoirs of SRLVs under natural conditions. A total of 314 samples were tested from red deer (n = 255), roe deer (n = 52) and fallow deer (n = 7) using nested real-time PCR. DNA from positive real-time PCR samples was subsequently used to amplify a CA fragment (625 bp) of the gag gene, a 1.2 kb fragment of the pol gene and an LTR-gag fragment. Three samples (0.95%) were positive according to nested real-time PCR using primers and probe specific for CAEV (SRLV group B). All the samples were negative for the primers and probe specific for MVV (SRLV A group). Only SRLV LTR-gag sequences were obtained from two red deer. Phylogenetic analysis revealed that these sequences were more closely related to CAEV than to MVV. Our results revealed that deer can carry SRLV proviral sequences and therefore may play a role in the epidemiology of SRLVs. To our knowledge, this is the first study describing SRLV sequences from red deer.

Lentivirus-mediated gene therapy corrects ribosomal biogenesis and shows promise for Diamond Blackfan anemia.

This study lays the groundwork for future lentivirus-mediated gene therapy in patients with Diamond Blackfan anemia (DBA) caused by mutations in ribosomal protein S19 (RPS19), showing evidence of a new safe and effective therapy. The data show that, unlike patients with Fanconi anemia (FA), the hematopoietic stem cell (HSC) reservoir of patients with DBA was not significantly reduced, suggesting that collection of these cells should not constitute a remarkable restriction for DBA gene therapy. Subsequently, 2 clinically applicable lentiviral vectors were developed. In the former lentiviral vector, PGK.CoRPS19 LV, a codon-optimized version of RPS19 was driven by the phosphoglycerate kinase promoter (PGK) already used in different gene therapy trials, including FA gene therapy. In the latter one, EF1α.CoRPS19 LV, RPS19 expression was driven by the elongation factor alpha short promoter, EF1α(s). Preclinical experiments showed that transduction of DBA patient CD34+ cells with the PGK.CoRPS19 LV restored erythroid differentiation, and demonstrated the long-term repopulating properties of corrected DBA CD34+ cells, providing evidence of improved erythroid maturation. Concomitantly, long-term restoration of ribosomal biogenesis was verified using a potentially novel method applicable to patients' blood cells, based on ribosomal RNA methylation analyses. Finally, in vivo safety studies and proviral insertion site analyses showed that lentivirus-mediated gene therapy was nontoxic.

Generation of stable suspension producer cell lines for serum-free lentivirus production.

The production of lentiviral vectors (LVs) pseudotyped with the vesicular stomatitis virus envelope glycoprotein (VSV-G) is limited by the associated cytotoxicity of the envelope and by the production methods used, such as transient transfection of adherent cell lines. In this study, we established stable suspension producer cell lines for scalable and serum-free LV production derived from two stable, inducible packaging cell lines, named GPRG and GPRTG. The established polyclonal producer cell lines produce self-inactivating (SIN) LVs carrying a WAS-T2A-GFP construct at an average infectious titer of up to 4.64 × 107 TU mL-1 in a semi-perfusion process in a shake flask and can be generated in less than two months. The derived monoclonal cell lines are functionally stable in continuous culture and produce an average infectious titer of up to 9.38 × 107 TU mL-1 in a semi-perfusion shake flask process. The producer clones are able to maintain a productivity of >1 × 107 TU mL-1 day-1 for up to 29 consecutive days in a non-optimized 5 L stirred-tank bioreactor perfusion process, representing a major milestone in the field of LV manufacturing. As the producer cell lines are based on an inducible Tet-off expression system, the established process allows LV production in the absence of inducers such as antibiotics. The purified LVs efficiently transduce human CD34+ cells, reducing the LV quantities required for gene and cell therapy applications.

[In vitro and in vivo validation of cytotoxicity of targeting human epidermal growth factor receptor-2 chimeric antigen receptor T (HER2-CAR-T) cells].

Objective To evaluate the toxicology of targeting human epidermal growth factor receptor-2 chimeric antigen receptor T (HER2-CAR-T) cells and to provide a safety basis for the clinical evaluation of HER2-CAR-T cell therapy. Methods The recombinant lentiviral vector was used to generate HER2-CAR-T cells. Soft agar colony formation assay was used to observe the colony formation of HER2-CAR-T cells, and the colony formation rate was statistically analyzed. The HER2-CAR-T cell suspension was co-incubated with rabbit red blood cell suspension, and the hemolysis of red blood cells was evaluated by direct observation and microplate reader detection. The HER2-CAR-T cell preparation was injected into the ear vein of male New Zealand rabbits, and the stimulating effect of HER2-CAR-T cells on the blood vessels of the animals was observed by staining of tissue sections. The vesicular stomatitis virus envelope glycoprotein (VSV-G) gene of pMD 2.G vector was used as the target sequence, and the safety of the lentiviral vector was verified by real-time fluorescence quantitative PCR. The heart, liver, lung, and kidney of mice receiving HER2-CAR-T cell infusion were collected, and the lesions were observed by HE staining. Results The HER2-CAR-T cells were successfully prepared. These cells did not exhibit soft agar colony formation ability in vitro, and the HER2-CAR-T cell preparation did not cause hemolysis in New Zealand rabbit red blood cells. After the infusion of HER2-CAR-T cells into the ear vein of New Zealand rabbits, no obvious vascular stimulation response was found, and no specific amplification of VSV-G was detected. No obvious lesions were found in the heart, liver, lung and kidney tissues of the treatment group. Conclusion The prepared HER2-CAR-T cells have reliable safety.

Non-clinical safety assessment of novel drug modalities: Genome safety perspectives on viral-, nuclease- and nucleotide-based gene therapies.

Gene therapies have emerged as promising treatments for various conditions including inherited diseases as well as cancer. Ensuring their safe clinical application requires the development of appropriate safety testing strategies. Several guidelines have been provided by health authorities to address these concerns. These guidelines state that non-clinical testing should be carried out on a case-by-case basis depending on the modality. This review focuses on the genome safety assessment of frequently used gene therapy modalities, namely Adeno Associated Viruses (AAVs), Lentiviruses, designer nucleases and mRNAs. Important safety considerations for these modalities, amongst others, are vector integrations into the patient genome (insertional mutagenesis) and off-target editing. Taking into account the constraints of in vivo studies, health authorities endorse the development of novel approach methodologies (NAMs), which are innovative in vitro strategies for genotoxicity testing. This review provides an overview of NAMs applied to viral and CRISPR/Cas9 safety, including next generation sequencing-based methods for integration site analysis and off-target editing. Additionally, NAMs to evaluate the oncogenicity risk arising from unwanted genomic modifications are discussed. Thus, a range of promising techniques are available to support the safe development of gene therapies. Thorough validation, comparisons and correlations with clinical outcomes are essential to identify the most reliable safety testing strategies. By providing a comprehensive overview of these NAMs, this review aims to contribute to a better understanding of the genome safety perspectives of gene therapies.

Checkpoint inhibitor-expressing lentiviral vaccine suppresses tumor growth in preclinical cancer models.

BACKGROUND: While immunotherapy has been highly successful for the treatment of some cancers, for others, the immune response to tumor antigens is weak leading to treatment failure. The resistance of tumors to checkpoint inhibitor therapy may be caused by T cell exhaustion resulting from checkpoint activation. METHODS: In this study, lentiviral vectors that expressed T cell epitopes of an experimentally introduced tumor antigen, ovalbumin, or the endogenous tumor antigen, Trp1 were developed. The vectors coexpressed CD40 ligand (CD40L), which served to mature the dendritic cells (DCs), and a soluble programmed cell death protein 1 (PD-1) microbody to prevent checkpoint activation. Vaccination of mice bearing B16.OVA melanomas with vector-transduced DCs induced the proliferation and activation of functional, antigen-specific, cytolytic CD8 T cells. RESULTS: Vaccination induced the expansion of CD8 T cells that infiltrated the tumors to suppress tumor growth. Vector-encoded CD40L and PD-1 microbody increased the extent of tumor growth suppression. Adoptive transfer demonstrated that the effect was mediated by CD8 T cells. Direct injection of the vector, without the need for ex vivo transduction of DCs, was also effective. CONCLUSIONS: This study suggests that therapeutic vaccination that induces tumor antigen-specific CD8 T cells coupled with a vector-expressed checkpoint inhibitor can be an effective means to suppress the growth of tumors that are resistant to conventional immunotherapy.

Genetic Characterization of Small Ruminant Lentiviruses Isolated from Dairy Sheep in Greece.

The high genetic heterogeneity of small ruminant lentiviruses (SRLV) renders the genetic characterization of the circulating strains crucial for the epidemiological investigation and the designation of effective diagnostic tools. In Greece, research data regarding the genetic diversity of the circulating SRLV strains is scarce, hindering the implementation of efficient surveillance and control programs. The objective of the study was to genetically characterize SRLV strains isolated from intensive dairy sheep farms in Greece and evaluate the variability of the immunodominant regions of the capsid protein. For this reason, a total of 12 SRLV-infected animals from four intensive dairy sheep farms with purebred Chios and Lacaune ewes were used for the amplification and sequencing of an 800 bp gag-pol fragment. The phylogenetic analyses revealed a breed-related circulation of strains; Chios ewes were infected with strains belonging exclusively to a separate group of genotype A, whereas strains belonging to subtype B2 were isolated from Lacaune ewes. Immunodominant epitopes of capsid protein were quite conserved among the strains of the same genotype, except for the Major Homology Region which showed some unique mutations with potential effects on viral evolution. The present study contributes to the extension of the current knowledge regarding the genetic diversity of SRLV strains circulating in sheep in Greece. However, broader genetic characterization studies are warranted for the exploration of possible recombinant events and the more comprehensive classification of the circulating strains.

Lentivirus-Mediated BCL-XL Overexpression Inhibits Stem Cell Apoptosis during Ex Vivo Expansion and Provides Competitive Advantage Following Xenotransplantation.

Hematopoietic reconstitution after hematopoietic stem cell transplantation (HSCT) is influenced by the number of transplanted cells. However, under certain conditions donor cell counts are limited and impair clinical outcome. Hematopoietic stem and progenitor cell (HSPC) expansion prior to HSCT is a widely used method to achieve higher donor cell counts and minimize transplantation-related risks such as graft failure or delayed engraftment. Still, expansion in a non-physiological environment can trigger cell death mechanisms and hence counteract the desired effect. We have shown earlier that during HSCT a relevant amount of HSPCs were lost due to apoptosis and that cell death inhibition in donor HSPCs improved engraftment in xenotransplantation experiments. Here, we assessed the effect of combined ex vivo expansion and cell death inhibition on HSPC yield and their reconstitution potential in vivo. During expansion with cytokines and the small molecule inhibitor StemRegenin 1, concomitant lentiviral overexpression of antiapoptotic BCL-XL resulted in an increased yield of transduced HSPCs. Importantly, BCL-XL overexpression enhanced the reconstitution potential of HSPCs in xenotransplantation experiments in vivo. In contrast, treatment with caspase and necroptosis inhibitors had no favorable effects on HSPC yields nor on cell viability. We postulate that overexpression of antiapoptotic BCL-XL, both during ex vivo expansion and transplantation, is a promising approach to improve the outcome of HSCT in situations with limited donor cell numbers. However, such apoptosis inhibition needs to be transient to avoid long-term sequelae like leukemia.

A lentivirus-vectored feline erythropoietin gene therapy strategy in tissue culture and rodent models for the potential treatment of chronic renal disease-associated anemia.

OBJECTIVE: The aim of this study was to assess the efficacy and safety of a third-generation lentivirus-based vector encoding the feline erythropoietin (EPO) (feEPO) gene in vitro and in rodent models in vivo. This vector incorporates a genetic mechanism to facilitate the termination of the therapeutic effect in the event of supraphysiologic polycythemia, the herpes simplex virus thymidine kinase (HSV-TK) "suicide gene." ANIMALS: CFRK cells and replication-defective lentiviral vectors encoding feEPO were used for in vitro experiments. Eight Fischer rats were enrolled in the pilot in vivo study, 24 EPO-deficient mice were used in the initial mouse study, and 15 EPO-deficient mice were enrolled in the final mouse study. METHODS: Efficacy of a third-generation lentivirus encoding feEPO was determined in vitro using western blot assays. Subsequently, in a series of rodent experiments, animals were administered the viral vector in progressively increasing inoculation doses with serial measurements of blood packed cell volume (PCV) over time. RESULTS: We documented production of feEPO protein in transduced CRFK cells with subsequent cessation of production when treated with the HSV-TK substrate ganciclovir. In vivo, we demonstrated variably persistent elevated PCV values in treated rats and mice with eventual return to baseline values over time. CLINICAL RELEVANCE: These results provide justification for a lentiviral gene therapy approach to the treatment of nonregenerative anemia associated with chronic renal disease in cats.

Bioinformatics Insights on Viral Gene Expression Transactivation: From HIV-1 to SARS-CoV-2.

Viruses provide vital insights into gene expression control. Viral transactivators, with other viral and cellular proteins, regulate expression of self, other viruses, and host genes with profound effects on infected cells, underlying inflammation, control of immune responses, and pathogenesis. The multifunctional Tat proteins of lentiviruses (HIV-1, HIV-2, and SIV) transactivate gene expression by recruiting host proteins and binding to transacting responsive regions (TARs) in viral and host RNAs. SARS-CoV-2 nucleocapsid participates in early viral transcription, recruits similar cellular proteins, and shares intracellular, surface, and extracellular distribution with Tat. SARS-CoV-2 nucleocapsid interacting with the replication-transcription complex might, therefore, transactivate viral and cellular RNAs in the transcription and reactivation of self and other viruses, acute and chronic pathogenesis, immune evasion, and viral evolution. Here, we show, by using primary and secondary structural comparisons, that the leaders of SARS-CoV-2 and other coronaviruses contain TAR-like sequences in stem-loops 2 and 3. The coronaviral nucleocapsid C-terminal domains harbor a region of similarity to TAR-binding regions of lentiviral Tat proteins, and coronaviral nonstructural protein 12 has a cysteine-rich metal binding, dimerization domain, as do lentiviral Tat proteins. Although SARS-CoV-1 nucleocapsid transactivated gene expression in a replicon-based study, further experimental evidence for coronaviral transactivation and its possible implications is warranted.

Impact of CRISPR/HDR editing versus lentiviral transduction on long-term engraftment and clonal dynamics of HSPCs in rhesus macaques.

For precise genome editing via CRISPR/homology-directed repair (HDR), effective and safe editing of long-term engrafting hematopoietic stem cells (LT-HSCs) is required. The impact of HDR on true LT-HSC clonal dynamics in a relevant large animal model has not been studied. To track the output and clonality of HDR-edited cells and to provide a comparison to lentivirally transduced HSCs in vivo, we developed a competitive rhesus macaque (RM) autologous transplantation model, co-infusing HSCs transduced with a barcoded GFP-expressing lentiviral vector (LV) and HDR edited at the CD33 locus. CRISPR/HDR-edited cells showed a two-log decrease by 2 months following transplantation, with little improvement via p53 inhibition, in comparison to minimal loss of LV-transduced cells long term. HDR long-term clonality was oligoclonal in contrast to highly polyclonal LV-transduced HSCs. These results suggest marked clinically relevant differences in the impact of current genetic modification approaches on HSCs.

Cultivation, Differentiation, and Lentiviral Transduction of Human-Induced Pluripotent Stem Cell (hiPSC)-Derived Glutamatergic Neurons for Studying Human Tau.

Tau pathology is a major hallmark of many neurodegenerative diseases summarized under the term tauopathies. In most of these disorders,  such as Alzheimer's disease, the neuronal axonal microtubule-binding Tau protein becomes mislocalized to the somatodendritic compartment. In human disease, this missorting of Tau is accompanied by an abnormally high phosphorylation state of the Tau protein, and several downstream pathological consequences (e.g., loss of microtubules, degradation of postsynaptic spines, impaired synaptic transmission, neuronal death). While some mechanisms of Tau sorting, missorting, and associated pathologies have been addressed in rodent models, few studies have addressed human Tau in physiological disease-relevant human neurons. Thus, suitable human-derived in vitro models are necessary. This protocol provides a simple step-by-step protocol for generating homogeneous cultures of cortical glutamatergic neurons using an engineered Ngn2 transgene-carrying WTC11 iPSC line. We further demonstrate strategies to improve neuronal maturity, that is, synapse formation, Tau isoform expression, and neuronal activity by co-culturing hiPSC-derived glutamatergic neurons with mouse-derived astrocytes. Finally, we describe a simple protocol for high-efficiency lentiviral transduction of hiPSC-derived neurons at almost all stages of differentiation.

Autologous gene therapy for hemoglobinopathies: From bench to patient's bedside.

In recent years, a growing number of clinical trials have been initiated to evaluate gene therapy approaches for the treatment of patients with transfusion-dependent ß-thalassemia and sickle cell disease (SCD). Therapeutic modalities being assessed in these trials utilize different molecular techniques, including lentiviral vectors to add functional copies of the gene encoding the hemoglobin ß subunit in defective cells and CRISPR-Cas9, transcription activator-like effector protein nuclease, and zinc finger nuclease gene editing strategies to either directly address the underlying genetic cause of disease or induce fetal hemoglobin production by gene disruption. Here, we review the mechanisms of action of these various gene addition and gene editing approaches and describe the status of clinical trials designed to evaluate the potentially for these approaches to provide one-time functional cures to patients with transfusion-dependent ß-thalassemia and SCD.

Redifferentiation of genetically modified dedifferentiated chondrocytes in a microcavitary hydrogel.

OBJECTIVES: We genetically modified dedifferentiated chondrocytes (DCs) using lentiviral vectors and adenoviral vectors encoding TGF-ß3 (referred to as transgenic groups below) and encapsulated these DCs in the microcavitary hydrogel and investigated the combinational effect on redifferentiation of the genetically manipulated DCs. RESULTS: The Cell Counting Kit-8 data indicated that both transgenic groups exhibited significantly higher cell viability in the first week but inferior cell viability in the subsequent timepoints compared with those of the control group. Real-time polymerase chain reaction and western blot analysis results demonstrated that both transgenic groups had a better effect on redifferentiation to some extent, as evidenced by higher expression levels of chondrogenic genes, suggesting the validity of combination with transgenic DCs and the microcavitary hydrogel on redifferentiation. Although transgenic DCs with adenoviral vectors presented a superior extent of redifferentiation, they also expressed greater levels of the hypertrophic gene type X collagen. It is still worth further exploring how to deliver TGF-ß3 more efficiently and optimizing the appropriate parameters, including concentration and duration. CONCLUSIONS: The results demonstrated the better redifferentiation effect of DCs with the combinational use of transgenic TGF-ß3 and a microcavitary alginate hydrogel and implied that DCs would be alternative seed cells for cartilage tissue engineering due to their easily achieved sufficient cell amounts through multiple passages and great potential to redifferentiate to produce cartilaginous extracellular matrix.

Lentiviral mediated delivery of CRISPR/Cas9 reduces intraocular pressure in a mouse model of myocilin glaucoma.

Mutations in myocilin (MYOC) are the leading known genetic cause of primary open-angle glaucoma, responsible for about 4% of all cases. Mutations in MYOC cause a gain-of-function phenotype in which mutant myocilin accumulates in the endoplasmic reticulum (ER) leading to ER stress and trabecular meshwork (TM) cell death. Therefore, knocking out myocilin at the genome level is an ideal strategy to permanently cure the disease. We have previously utilized CRISPR/Cas9 genome editing successfully to target MYOC using adenovirus 5 (Ad5). However, Ad5 is not a suitable vector for clinical use. Here, we sought to determine the efficacy of adeno-associated viruses (AAVs) and lentiviruses (LVs) to target the TM. First, we examined the TM tropism of single-stranded (ss) and self-complimentary (sc) AAV serotypes as well as LV expressing GFP via intravitreal (IVT) and intracameral (IC) injections. We observed that LV_GFP expression was more specific to the TM injected via the IVT route. IC injections of Trp-mutant scAAV2 showed a prominent expression of GFP in the TM. However, robust GFP expression was also observed in the ciliary body and retina. We next constructed lentiviral particles expressing Cas9 and guide RNA (gRNA) targeting MYOC (crMYOC) and transduction of TM cells stably expressing mutant myocilin with LV_crMYOC significantly reduced myocilin accumulation and its associated chronic ER stress. A single IVT injection of LV_crMYOC in Tg-MYOCY437H mice decreased myocilin accumulation in TM and reduced elevated IOP significantly. Together, our data indicates, LV_crMYOC targets MYOC gene editing in TM and rescues a mouse model of myocilin-associated glaucoma.

Droplet digital polymerase chain reaction-based quantitation of therapeutic lentiviral vector copies in transduced hematopoietic stem cells.

BACKGROUND AIMS: Gene therapy using lentiviral vectors (LVs) that harbor a functional ß-globin gene provides a curative treatment for hemoglobinopathies including beta-thalassemia and sickle cell disease. Accurate quantification of the vector copy number (VCN) and/or the proportion of transduced cells is critical to evaluate the efficacy of transduction and stability of the transgene during treatment. Moreover, commonly used techniques for LV quantification, including real-time quantitative polymerase chain reaction (PCR) or fluorescence-activated cell sorting, require either a standard curve or expression of a reporter protein for the detection of transduced cells. In the present study, we describe a digital droplet PCR (ddPCR) technique to measure the lentiviral VCN in transduced hematopoietic stem and progenitor cells (HSPCs). METHODS: After HSPCs were transduced with an LV encoding the therapeutic ß-globin (ßA-T87Q) gene, the integrated lentiviral sequence in the host genome was amplified with primers that targeted a sequence within the vector and the human RPP30 gene. The dynamic range of ddPCR was between 5 × 10-3 ng and 5 × 10-6 ng of target copy per reaction. RESULTS: We found that the ddPCR-based approach was able to estimate VCN with high sensitivity and a low standard deviation. Furthermore, ddPCR-mediated quantitation of lentiviral copy numbers in differentiated erythroblasts correlated with the level of ßA-T87Q protein detected by reverse-phase high-performance liquid chromatography. CONCLUSIONS: Taken together, the ddPCR technique has the potential to precisely detect LV copy numbers in the host genome, which can be used for VCN estimation, calculation of infectious titer and multiplicity of infection for HSPC transduction in a clinical setting.

Lentiviral expression of wild-type LAMA3A restores cell adhesion in airway basal cells from children with epidermolysis bullosa.

The hallmark of epidermolysis bullosa (EB) is fragile attachment of epithelia due to genetic variants in cell adhesion genes. We describe 16 EB patients treated in the ear, nose, and throat department of a tertiary pediatric hospital linked to the United Kingdom's national EB unit between 1992 and 2023. Patients suffered a high degree of morbidity and mortality from laryngotracheal stenosis. Variants in laminin subunit alpha-3 (LAMA3) were found in 10/15 patients where genotype was available. LAMA3 encodes a subunit of the laminin-332 heterotrimeric extracellular matrix protein complex and is expressed by airway epithelial basal stem cells. We investigated the benefit of restoring wild-type LAMA3 expression in primary EB patient-derived basal cell cultures. EB basal cells demonstrated weak adhesion to cell culture substrates, but could otherwise be expanded similarly to non-EB basal cells. In vitro lentiviral overexpression of LAMA3A in EB basal cells enabled them to differentiate in air-liquid interface cultures, producing cilia with normal ciliary beat frequency. Moreover, transduction restored cell adhesion to levels comparable to a non-EB donor culture. These data provide proof of concept for a combined cell and gene therapy approach to treat airway disease in LAMA3-affected EB.

Envelope protein-specific B cell receptors direct lentiviral vector tropism in vivo.

While studying transgene expression after systemic administration of lentiviral vectors, we found that splenic B cells are robustly transduced, regardless of the types of pseudotyped envelope proteins. However, the administration of two different pseudotypes resulted in transduction of two distinct B cell populations, suggesting that each pseudotype uses unique and specific receptors for its attachment and entry into splenic B cells. Single-cell RNA sequencing analysis of the transduced cells demonstrated that different pseudotypes transduce distinct B cell subpopulations characterized by specific B cell receptor (BCR) genotypes. Functional analysis of the BCRs of the transduced cells demonstrated that BCRs specific to the pseudotyping envelope proteins mediate viral entry, enabling the vectors to selectively transduce the B cell populations that are capable of producing antibodies specific to their envelope proteins. Lentiviral vector entry via the BCR activated the transduced B cells and induced proliferation and differentiation into mature effectors, such as memory B and plasma cells. BCR-mediated viral entry into clonally specific B cell subpopulations raises new concepts for understanding the biodistribution of transgene expression after systemic administration of lentiviral vectors and offers new opportunities for BCR-targeted gene delivery by pseudotyped lentiviral vectors.