Viruses have evolved to become capable of infecting cells and physically inserting their genes into the host cell genome as a part of the process of infection. The genetic material that is inserted into the host genome contains crucial information about viral replication using the host cell machinery. Research has enabled the use of viruses as vectors to transfer specific genes into human cells, after removing the disease-causing genes from the viruses. However, the viral genes responsible for their entry and gene transfer to the host must be left intact. The method is well established and is widely used procedure in gene therapy.
Although the process appears to be relatively simple, viral vectors can affect different type of cells upon their entry into the host. Furthermore, the insertion of the genetic material could be effected at undesired locations leading to genetic mutations with serious implications including cancer. Also, any undesired genetic mutation in the germ lines can produce effects that would be inherited from one generation to the next.
Chimeric antigen receptor (CAR) T cell therapy is one of the promising cancer therapies that involve the modification of T cells harvested from a patient and re-insertion of the modified cells into the patient body to escalate the immune response against cancer. The process of T cell modification involves the incubation of T cells (from the patient) with viral vectors that encode the chimeric antigen receptor. The viral vectors infect the T cells to enter into them and introduce the genetic material (RNA) into the T cells. The host T cells reverse transcribe the RNA into DNA and permanently incorporates the CAR gene into its genome. Lentiviral vectors have been commonly used in CAR T therapies.
Currently, CAR T therapies using non-viral gene transfer techniques are being used in several clinical trials to avoid the risk associated with viral vectors. Non-viral gene transfer techniques include the use of Sleeping Beauty (SB) transposon system. The SB transposon system allows a high-level stable gene transfer with sustained transgene expression. Transposons have been optimised and SB variants have been developed to improve CAR T therapy. Gene delivery using nanoparticles, nanostructures and microfluidics are some of the other alternatives of non-viral gene transfer methods.
In contrast to viral gene transfer techniques, the use of CRISPR/Cas9 gene editing technology allows the precise insertion of CAR genes at the desired location to generate modified T cells which are then re-introduced into the patient’s body as a part of CAR T therapy. This method allows for physiologically normal introduction of the new gene into T cells, thus offering improved genetic regulation of the CAR gene and enhanced CAR T therapy efficacy.