Maximizing lentiviral vector gene transfer in the CNS.

Gene transfer is a widely developed technique for studying and treating genetic diseases. However, the development of therapeutic strategies is challenging, due to the cellular and functional complexity of the central nervous system (CNS), its large size and restricted access. We explored two parameters for improving gene transfer efficacy and capacity for the selective targeting of subpopulations of cells with lentiviral vectors (LVs). We first developed a second-generation LV specifically targeting astrocytes for the efficient expression or silencing of genes of interest, and to better study the importance of cell subpopulations in neurological disorders. We then made use of the retrograde transport properties of a chimeric envelope to target brain circuits affected in CNS diseases and achieve a broad distribution. The combination of retrograde transport and specific tropism displayed by this LV provides opportunities for delivering therapeutic genes to specific cell populations and ensuring high levels of transduction in interconnected brain areas following local administration. This new LV and delivery strategy should be of greater therapeutic benefit and opens up new possibilities for the preclinical development of gene therapy for neurodegenerative diseases.

Guillain-Barré syndrome after adoptive cell therapy with tumor-infiltrating lymphocytes.

BACKGROUND: Adoptive cell therapy (ACT) using tumor-infiltrating lymphocytes (TILs) is a promising experimental immunotherapy that has shown high objective responses in patients with melanoma. Current protocols use a lymphodepletive chemotherapy before infusion of ex vivo expanded TILs, followed by high-dose interleukin-2 (IL-2). Treatment-related toxicities are mainly attributable to the chemotherapy regimen and to the high-dose IL-2 and are generally reversible. Neurological side effects have rarely been described. Nevertheless, due to improvements in cell production techniques and due to combinations with other immunomodulating molecules, side effects not previously described may be encountered. CASE PRESENTATION: We report the case of a 53-year-old heavily pretreated patient with melanoma who developed Guillain-Barré syndrome (GBS) 19 days after ACT using autologous TILs, given in the context of a phase I trial. He presented with dorsal back pain, unsteady gait and numbness in hands and feet. Lumbar puncture showed albuminocytological dissociation, and nerve conduction studies revealed prolonged distal motor latencies in median, ulnar, tibial and peroneal nerves, compatible with a GBS. The patient was treated with intravenous immunoglobulins and intensive neurological rehabilitation, with progressive and full recovery at 21 months post-TIL-ACT. Concomitant to the onset of GBS, a cytomegalovirus reactivation on immunosuppression was detected and considered as the most plausible cause of this neurological side effect. CONCLUSION: We describe for the first time a case of GBS occurring shortly after TIL-ACT for melanoma, even though we could not identify with certainty the triggering agent. The report of such rare cases is of extreme importance to build on the knowledge of immune cellular therapies and their specific spectrum of toxicities.

Therapeutic efficacy of regulable GDNF expression for Huntington's and Parkinson's disease by a high-induction, background-free "GeneSwitch" vector.

Gene therapy is currently an irreversible approach, without possibilities to fine-tune or halt the expression of a therapeutic gene product. Especially when expressing neurotrophic factors to treat neurodegenerative disorders, options to regulate transgene expression levels might be beneficial. We thus developed an advanced single-genome inducible AAV vector for expression of GDNF, under control of the approved small molecule drug mifepristone. In the rat brain, GDNF expression can be induced over a wide range up to three hundred-fold over endogenous background, and completely returns to baseline within 3-4 weeks. When applied with appropriate serotype and titre, the vector is absolutely free of any non-induced background expression. In the BACHD model of Huntington's disease we demonstrate that the vector can be kept in a continuous ON-state for extended periods of time. In a model of Parkinson's disease we demonstrate that repeated short-term expression of GDNF restores motor capabilities in 6-OHDA-lesioned rats. We also report on sex-dependent pharmacodynamics of mifepristone in the rodent brain. Taken together, we show that wide-range and high-level induction, background-free, fully reversible and therapeutically active GDNF expression can be achieved under tight pharmacological control by this novel AAV - "Gene Switch" vector.

Preclinical Evaluation of a Lentiviral Vector for Huntingtin Silencing.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder resulting from a polyglutamine expansion in the huntingtin (HTT) protein. There is currently no cure for this disease, but recent studies suggest that RNAi to downregulate the expression of both normal and mutant HTT is a promising therapeutic approach. We previously developed a small hairpin RNA (shRNA), vectorized in an HIV-1-derived lentiviral vector (LV), that reduced pathology in an HD rodent model. Here, we modified this vector for preclinical development by using a tat-independent third-generation LV (pCCL) backbone and removing the original reporter genes. We demonstrate that this novel vector efficiently downregulated HTT expression in vitro in striatal neurons derived from induced pluripotent stem cells (iPSCs) of HD patients. It reduced two major pathological HD hallmarks while triggering a minimal inflammatory response, up to 6 weeks after injection, when administered by stereotaxic surgery in the striatum of an in vivo rodent HD model. Further assessment of this shRNA vector in vitro showed proper processing by the endogenous silencing machinery, and we analyzed gene expression changes to identify potential off-targets. These preclinical data suggest that this new shRNA vector fulfills primary biosafety and efficiency requirements for further development in the clinic as a cure for HD.

The Self-Inactivating KamiCas9 System for the Editing of CNS Disease Genes.

Neurodegenerative disorders are a major public health problem because of the high frequency of these diseases. Genome editing with the CRISPR/Cas9 system is making it possible to modify the sequence of genes linked to these disorders. We designed the KamiCas9 self-inactivating editing system to achieve transient expression of the Cas9 protein and high editing efficiency. In the first application, the gene responsible for Huntington's disease (HD) was targeted in adult mouse neuronal and glial cells. Mutant huntingtin (HTT) was efficiently inactivated in mouse models of HD, leading to an improvement in key markers of the disease. Sequencing of potential off-targets with the constitutive Cas9 system in differentiated human iPSC revealed a very low incidence with only one site above background level. This off-target frequency was significantly reduced with the KamiCas9 system. These results demonstrate the potential of the self-inactivating CRISPR/Cas9 editing for applications in the context of neurodegenerative diseases.