In vitro research on recombination between HIV and lentiviral vectors

With ex vivo gene therapy, a patient’s cells are modified outside the body. The body’s own blood or stem cells are collected from the patient and genetically modified in the laboratory. Replication-deficient lenti- or retroviral vectors are used to integrate the therapeutic gene into the genome of the treated cells. After the genetic modification, these GM cells are returned to the patient via infusion. This application is mainly used as a treatment for hematological cancers.

The lentiviral vectors used are self-inactivating (SIN) vectors produced with a third generation production system. For these systems, the presence of replication-competent lentivirus is excluded, the vectors are no longer capable of mobilization after insertion into the host genome.

In the (environmental) risk assessment of experiments with viral vectors, one of the considerations is whether there is a chance of complementation or recombination with a potentially infecting wild-type virus, and whether this could create a new recombinant virus. In clinical trials with lentiviral vectors, HIV-infected patients or subjects are sometimes excluded due to the theoretical risk of recombination of the vector used with the virus. Treatment of the patient with antiviral drugs (cART) prevents recombination, but also prevents successful treatment because the viral vector is also inhibited.

A European-wide generic environmental risk assessment has been drawn up for gene therapy studies with ex-vivo transduced cells, in order to streamline GMO licensing. Partly based on this risk assessment, and on various COGEM recommendations, a Permit under fixed conditions (VoV) has been established for these clinical trials in the Netherlands. The exclusion of HIV-positive individuals was canceled on January 1, 2023, because the chance that a better replicating HIV variant could arise through recombination was considered very small by COGEM.

This assessment is based on previous experiences with clinical studies and expert judgment. However, experimental data and scientific literature on the likelihood of recombination and the risk of the emergence of a recombinant virus are largely lacking. There is literature on the mobilization of integrated lentiviral transfer vectors in transduced cells after infection with wild-type HIV, but no literature that addresses the question of whether recombination between wild-type HIV and a lentiviral vector is possible and whether this can result in an HIV variant with different properties. In addition, certain sequences or genetic elements, such as PRE, are incorporated into lentiviral vectors that may influence the chance and outcome of recombination. For this project, experiments will be conducted to investigate whether recombination between HIV and SIN lentiviral vectors is possible.