Vectored Immunotherapeutics for Infectious Diseases: Can rAAVs Be The Game Changers for Fighting Transmissible Pathogens?

Abstract

Conventional vaccinations and immunotherapies have encountered major roadblocks in preventing infectious diseases like HIV, influenza, and malaria. These challenges are due to the high genomic variation and immunomodulatory mechanisms inherent to these diseases. Passive transfer of broadly neutralizing antibodies may offer partial protection, but these treatments require repeated dosing. Some recombinant viral vectors, such as those based on lentiviruses and adeno-associated viruses (AAVs), can confer long-term transgene expression in the host after a single dose. Particularly, recombinant (r)AAVs have emerged as favorable vectors, given their high in vivo transduction efficiency, proven clinical efficacy, and low immunogenicity profiles. Hence, rAAVs are being explored to deliver recombinant antibodies to confer immunity against infections or to diminish the severity of disease. When used as a vaccination vector for the delivery of antigens, rAAVs enable de novo synthesis of foreign proteins with the conformation and topology that resemble those of natural pathogens. However, technical hurdles like pre-existing immunity to the rAAV capsid and production of anti-drug antibodies can reduce the efficacy of rAAV-vectored immunotherapies. This review summarizes rAAV-based prophylactic and therapeutic strategies developed against infectious diseases that are currently being tested in pre-clinical and clinical studies. Technical challenges and potential solutions will also be discussed.

Keywords: adeno-associated virus; gene therapy; immunotherapy; vaccines; vectors.

Figure 1

Overview of AAV vectors harnessed for vectored immunoprophylaxis and therapeutics. (A) AAVs are small (~25 nm), non-enveloped viruses and have a 4.7-kb, single-stranded, linear DNA (ssDNA) genome encoding four open reading frames. (B) rep encodes the four genes required for genome replication (Rep78, Rep68, Rep52, and Rep40) and cap encodes the structural proteins of the viral capsid (VP1, VP2 and VP3). A third gene, which encodes assembly activating protein (AAP), is embedded within the cap coding sequence in a different reading frame and has been shown to promote virion assembly. The fourth ORF encodes for the recently discovered membrane associated accessory protein (MAAP). The role of MAAP is yet to be clearly defined. (C) Providing rep and cap in trans enables a transgene of interest to be packaged inside the capsid to generate a replication-incompetent vector (recombinant AAV; rAAV). (D) rAAVs may be delivered via intramuscnular (IM), intranasal (IN), intracerebral (IC), and intravenous (IV) routes. (E) rAAVs expressing mAbs, eCD4-Ig and pathogenic antigens can be administered via different routes for therapeutics and immunization against infectious diseases. Created with BioRender.com.

Figure 2

Comparisons between non-vectored and vectored immunotherapeutic strategies. (A) Most vaccines today function by delivering antigen in the form of live-attenuated or inactivated pathogens or antigen subunits. This induces polyclonal humoral and cellular responses and immunological memory that protect the host from infections. (B) In rapidly mutating pathogens that evade normal vaccine-induced immunity, protective mAbs may be directly delivered to the blood stream via passive infusion to mediate protective function. (C) Alternatively, genetic material may be delivered in LNPs or viral vectors, such as AdV or LV. This mediates de novo synthesis of the antigen in the natural conformation, or allows the modification of immune cells into stronger effector cells. (D) rAAV vectors deliver the genetic material of the encoded antigen or therapeutic molecule putatively to the nucleus, as persistent episomes for gene expression. This enables long-term expression of the antigen or therapeutic molecule in a native conformation and topology, and reduces the need for drug redosing. Created with BioRender.com.