Lentiviral Vectors – the Gamechangers in Gene Therapy

Fabio Michelet, Senior Scientist (Viral Vectors) 


The hypothesis of using exogenous genetic material as a tool to inactivate or replace disease-causing genes or restore correct cellular function, dates back to the 70s. Since then, scientists have been working to develop a system to efficiently and safely insert genetic material into human cells. 


In the early 90s, the development of replication-defective retroviruses and adeno-associated viruses (AAV), paved the way for the first gene therapy clinical trials. Unfortunately, the results of these pioneering studies highlighted a number of complications: from critical inflammatory responses, to malignancies caused by insertional mutations in the proximity of oncogene regulatory sequences. The questions arising from these issues boosted more than 20 years of research in virology and immunology and resulted in the tremendous technological advancements that led to the development of self-inactivating (SIN), third generation, lentiviral vectors (LV). 


Finally, after decades of efforts, in 2017, clinical success led to the first market approval of cell therapy treatments including chimeric antigen receptor (CAR)-T cells for the treatment of acute lymphoblastic leukemia (ALL) and AAV vectors for in vivo treatment of congenital blindness. 


These first approved treatments demonstrated the efficacy of viral vector-based gene therapies and are now leading the way for the approval of advanced therapies targeting many other conditions: from spinal muscular atrophy, to Duchenne muscular dystrophy, hemophilia and beta-thalassemia. 


As more programs move from clinical to commercial stages, progress in high titre, clinical grade viral vector manufacturing is critical to meet market demand. 


At CellVec we believe that lentiviral vectors are invaluable therapeutic tools and we have developed optimized Good Manufacturing Practice (GMP) compliant LV manufacturing processes that combine high titer upstream production with an efficient downstream process generating a high titer, high purity, high yield product that meets regulatory expectations and allow our client’s programs to rapidly transition from the pre-clinical to the clinical stage. 


Here are some reasons lentiviral vectors have a distinctive advantage for human gene therapy applications: 


1.    Lentiviral vectors can integrate genes of interest in the host cell genome 


Unique to viral vectors derived from the Retroviradae family of viruses, lentiviral vectors have the ability to integrate their genetic material into the host cell genome, thereby allowing stable genetic reprogramming of human cells. This provides the possibility whereby a single step of cellular manipulation could result in a lasting therapeutic outcome. 


2.    Lentiviral vectors can transduce a broad range of human cell types 


The most common lentiviral vectors utilize the vesicular stomatitis virus surface glycoprotein (VSV-G), which can transduce a broad range of primary human cell types. Unlike retroviral vectors, lentiviral vector has the ability to transduce both dividing and non-dividing cell types. 


3.    Lentiviral vectors can deliver around 8 kb of DNA. 


Compared to other viral vectors such as adeno-associated viral vectors, lentiviral vectors have a larger transgene capacity. Coupled with their ability to transduce dividing and non-dividing cells, lentiviral vectors are particularly useful for applications requiring long-term sustained transgene expression and are the vector of choice for large or polycistronic transgenes. 


4.    Lentiviral vectors have low immunogenic profile 


Typically, the human body activates primary immune responses against viral proteins. Lentiviral vectors pseudotyped with VSV-G have been shown to be resistant to human serum inactivation, since humans are not natural hosts of VSV infections. VSV-G envelope is not only responsible for low immunogenicity, but it also confers broad tropism and high stability to lentiviral vectors, making them a flexible tool for therapies involving different target cells and requiring lengthy purification processes in commercial manufacture. 


Advancing treatment with lentiviral production technology 


CellVec prides itself on extensive know-hows on lentiviral vector molecular development and GMP compliant manufacture process development that enable the production of vectors with high titers, superior yields and in-keeping with current quality and regulatory expectations for safe and efficacious human applications. The heart of CellVec’s advanced lentiviral vector platform technology comprises of: 


●      An optimized helper plasmid system, which have been developed and validated in-house for lentiviral vector manufacture. 


●      A third generation, self-inactivating lentiviral vector designed in-house for efficient transgene expression 


●      A fully characterized HEK 293T Master Cell Bank, adapted and conditioned for enhanced recovery and cell growth 


●      A scalable GMP compliant LV manufacturing process that produces high titer, high yield and high purity vector products 


CellVec is constantly innovating to match the ever-evolving needs of our clients and the cell and gene therapy industry, where cost-effective large-scale manufacturing and compliance to regulatory standards are major challenges. From optimizing our lentiviral helper sequences and developing novel stable producer cell lines, to defining our chemical formulations and purification processes, our developmental efforts are focused on improving every part of our manufacturing process in order to produce high quality lentiviral vectors with novel properties that boost titer, yield, purity, stability and cell-type specific transduction. We offer highly efficient processes and bespoke services that enable the costs of lentiviral production to be kept low, allowing gene therapies to be more accessible to wider patient populations and ensuring that our innovation is for patient benefit. 


The unique properties of lentiviral vectors as a genetic delivery vehicle enable the creation of gene therapies for the treatment of a range of otherwise untreatable conditions. I’m excited to be part of this journey and look forward to both witnessing and contributing to the advancement of this technology for human applications.