mRNA transfection of a novel TAL effector nuclease (TALEN) facilitates efficient knockout of HIV co-receptor CCR5.

Homozygosity for a natural deletion variant of the HIV-coreceptor molecule CCR5, CCR5Δ32, confers resistance toward HIV infection. Allogeneic stem cell transplantation from a CCR5Δ32-homozygous donor has resulted in the first cure from HIV ('Berlin patient'). Based thereon, genetic disruption of CCR5 using designer nucleases was proposed as a promising HIV gene-therapy approach. Here we introduce a novel TAL-effector nuclease, CCR5-Uco-TALEN that can be efficiently delivered into T cells by mRNA electroporation, a gentle and truly transient gene-transfer technique. CCR5-Uco-TALEN mediated high-rate CCR5 knockout (>90% in PM1 and >50% in primary T cells) combined with low off-target activity, as assessed by flow cytometry, next-generation sequencing and a newly devised, very convenient gene-editing frequency digital-PCR (GEF-dPCR). GEF-dPCR facilitates simultaneous detection of wild-type and gene-edited alleles with remarkable sensitivity and accuracy as shown for the CCR5 on-target and CCR2 off-target loci. CCR5-edited cells were protected from infection with HIV-derived lentiviral vectors, but also with the wild-type CCR5-tropic HIV-1BaL strain. Long-term exposure to HIV-1BaL resulted in almost complete suppression of viral replication and selection of CCR5-gene edited T cells. In conclusion, we have developed a novel TALEN for the targeted, high-efficiency knockout of CCR5 and a useful dPCR-based gene-editing detection method.

The Impact of a New Interleukin-2-Based Immunotherapy Candidate on Urothelial Cells to Support Use for Intravesical Drug Delivery.

(1) Background: The intravesical instillation of interleukin-2 (IL-2) has been shown to be very well tolerated and promising in patients with bladder malignancies. This study aims to confirm the use of a new IL-2 containing immunotherapy candidate as safe for intravesical application. IL-2, produced in mammalian cells, is glycosylated, because of its unique solubility and stability optimized for intravesical use. (2) Materials and Methods: Urothelial cells and fibroblasts were generated out of porcine bladder and cultured until they reached second passage. Afterwards, they were cultivated in renal epithelial medium (REM) and Dulbecco's modified Eagles medium (DMEM) with the IL-2 candidate (IMS-Research) and three more types of human interleukin-2 immunotherapy products (IMS-Pure, Natural IL-2, Aldesleukin) in four different concentrations (100, 250, 500, 1000 IU/mL). Cell proliferation was analyzed by water soluble tetrazolium (WST) proliferation assay after 0, 3, and 6 days for single cell culture and co-culture. (3) Results: Proliferation assays showed that all IL-2 products induced very similar cultivation results and none of the IL-2 variants had a negative impact on the proliferation of urothelial cells and fibroblast in either concentration. (4) Conclusion: Human recombinant glycosylated IL-2 as well as human non-glycosylated IL-2 have no negative influence on the tissue cell proliferation of porcine urothelial cells and fibroblasts in vitro and represent a promising and innovative potential intravesical therapy candidate for patients in high need.

Novel lentiviral vectors with mutated reverse transcriptase for mRNA delivery of TALE nucleases.

TAL-effector nucleases (TALENs) are attractive tools for sequence-specific genome modifications, but their delivery still remains problematic. It is well known that the presence of multiple sequence repeats in TALEN genes hampers the use of lentiviral vectors. We report that lentiviral vectors readily package full-length vector mRNAs encoding TALENs, but recombination during reverse transcription prevents successful delivery. We reasoned that preventing reverse transcription of lentiviral-vector RNA would allow transfer of TALENs as mRNA. We demonstrate that lentiviral particles containing genetically inactivated reverse transcriptase (RT) mediated efficient transduction of cultured cells and supported transient transgene expression. For proof-of-principle, we transferred CCR5- and TCR-specific TALEN pairs for efficient targeted genome editing and abrogated expression for each of the receptor proteins in different cell lines. Combining the high specificity of TALENs with efficient lentiviral gene delivery should advance genome editing in vitro and potentially in vivo, and RT-deficient lentiviral vectors may be useful for transient expression of various other genes-of-interest.

Influenza virus-specific TCR-transduced T cells as a model for adoptive immunotherapy.

Adoptive transfer of T lymphocytes equipped with tumor-antigen specific T-cell receptors (TCRs) represents a promising strategy in cancer immunotherapy, but the approach remains technically demanding. Using influenza virus (Flu)-specific T-cell responses as a model system we compared different methods for the generation of T-cell clones and isolation of antigen-specific TCRs. Altogether, we generated 12 CD8(+) T-cell clones reacting to the Flu matrix protein (Flu-M) and 6 CD4(+) T-cell clones reacting to the Flu nucleoprotein (Flu-NP) from 4 healthy donors. IFN-γ-secretion-based enrichment of antigen-specific cells, optionally combined with tetramer staining, was the most efficient way for generating T-cell clones. In contrast, the commonly used limiting dilution approach was least efficient. TCR genes were isolated from T-cell clones and cloned into both a previously used gammaretroviral LTR-vector, MP91 and the novel lentiviral self-inactivating vector LeGO-MP that contains MP91-derived promotor and regulatory elements. To directly compare their functional efficiencies, we in parallel transduced T-cell lines and primary T cells with the two vectors encoding identical TCRs. Transduction efficiencies were approximately twice higher with the gammaretroviral vector. Secretion of high amounts of IFN-γ, IL-2 and TNF-α by transduced cells after exposure to the respective influenza target epitope proved efficient specificity transfer of the isolated TCRs to primary T-cells for both vectors, at the same time indicating superior functionality of MP91-transduced cells. In conclusion, we have developed optimized strategies to obtain and transfer antigen-specific TCRs as well as designed a novel lentiviral vector for TCR-gene transfer. Our data may help to improve adoptive T-cell therapies.