Clinical Prospects for Integrase-Deficient Lentivirus (IDLV)

HIV-1 derived lentiviral vector is an efficient transporter for delivering desired genetic materials into the targeted cells among many viral vectors. Genetic material transduced by lentiviral vector is integrated into the cell genome to introduce new functions, repair defective cell metabolism, and stimulate certain cell functions. Various measures have been administered in different generations of lentiviral vector systems to reduce the vector's replicating capabilities. Despite numerous demonstrations of an excellent safety profile of integrative lentiviral vectors, the precautionary approach has prompted the development of integrase-deficient versions of these vectors. The generation of integrase-deficient lentiviral vectors by abrogating integrase activity in lentiviral vector systems reduces the rate of transgenes integration into host genomes. With this feature, the integrase-deficient lentiviral vector is advantageous for therapeutic implementation and widens its clinical applications.

Introduction and Characteristics of IDLV

The HIV-derived LV is first reported for its functions in in vivo gene delivery and stable transduction of non-dividing cells. The vector is packaged by transfection of packaging elements that code for viral particles like HIV. While IPLV processes genomic integration of the vector DNA via the integrase enzyme, integrase-deficient lentiviral vector (IDLV) is dedicated to the reduction of genomic integration. IDLV is formed from a disabled, reduced efficiency integrase enzyme and vector RNA. As a consequence of reduced genomic integration, the resulting vector DNA remains in the nucleus of the transduced cell and does not get replicated during cell proliferation. Together with the removal of non-essential viral elements in the packaging vector and introduction of self-inactivating LTR (SIN-LTR), these "inert" characters of the vector not only provide safety and stability but also support transient expression of protein in the transduced cell. These properties allow IDLV to be exploited and improvised for application in clinical studies and therapeutics, such as gene delivery and gene therapy.

Production of IDLV

Despite numerous demonstrations of good safety profile of integrating lentiviral vectors, precautionary solution has been developed to generate integrase-deficient versions of these vectors. Integration-deficient lentiviral vectors (IDLVs) typically have mutations in the IN gene. Without the functioning IN enzyme, the vector DNA will exist as non-replicating episomes in transduced cells and unable to enter host cell genome. Dividing cells therefore will lose the vector DNA gradually and reduce the risk of any possible insertional mutagenesis.

Fig. 1 A schematic representation of HIV-1 integrase (IN) and mutated amino acids to produce IDLV. (Yew, et al., 2022)

IDLV can be designed by introducing mutations in the LTR integrase attachment site (Δatt). There are many types of point mutations that can be induced to residues in the three domains: the N-terminal domain, the core domain, and the C-terminal domain to produce IDLVs. These mutations can be divided into Class I and Class II mutations. There are three types of class I mutations (also known as the IN-core domain): D64, D116 and E152. Among the three, D64 mutations is most used in gene therapy. Class I mutations introduced to the integrase enzyme negatively impacts the machinery required for recognition, binding and recombination between the provirus, host DNA and integrase. Class II mutations can be performed by exchanging the standard gag or pol packaging plasmid with an IN-mutant strain. Class II mutations can also affect the reverse transcription and impair the vital viral life cycle stages and cause pleiotropic effects that can make them unsuitable for vector developments.

Since there are a few numbers of possible mutations, it is important to compare the transducing efficacy and integration rates of IDLVs from different amino acid substitutions. However, there are limited studies that compared these IN mutations because there are also other cofactors that affects the transducing efficacy and integration rates of the IDLVs.

Applications of IDLV for clinical implementations

While there is wide use of common viral vectors, such as those derived from adenovirus, IPLV, SIV and some other retrovirus in clinical applications, recent studies also utilize IDLV as a vehicle to deliver transgenes into the transcriptional location of the cells. Due to defective IN, these transgenes normally remain in the nucleus and are targeted for transcription and translation without directed access to the genome of the cell. The transcription and translation of these transgenes promoted desired functions in the cells. These functions may serve for the studies of gene editing, gene integration, gene therapy, immunization, or vaccination, promoting cell death, cell reprogramming, etc.

Fig. 2 Possible applications of IDLV for clinical settings. (Yew, et al., 2022)

Limitations and Prospects

While it is safer, pseudotyping and prudent transgene vector design of IDLV would provide flexibility and control over transduction of specific cells at desired conditions, making them an ideal choice of vector for delivery. Combined with other advanced technology such as nanotechnology and molecular editing mechanisms, the intrinsic characteristics of IDLV may be advantageous in inducing de novo expression, eliminating or repairing functions, or even encouraging new avenues apposite to health concerns.

Reference

Yew, C. H. T.; et al. Integrase deficient lentiviral vector: prospects for safe clinical applications. PeerJ. 2022, 10: e13704.

* For research use only. Not intended for any clinical use.

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Clinical Prospects for Integrase-Deficient Lentivirus (IDLV)

Introduction and Characteristics of IDLV

Production of IDLV

Applications of IDLV for clinical implementations

Limitations and Prospects

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