Immunomodulation in Administration of rAAV: Preclinical and Clinical Adjuvant Pharmacotherapies

Abstract

Recombinant adeno-associated virus (rAAV) has attracted a significant research focus for delivering genetic therapies to target cells. This non-enveloped virus has been trialed in many clinical-stage therapeutic strategies but important obstacle in clinical translation is the activation of both innate and adaptive immune response to the protein capsid, vector genome and transgene product. In addition, the normal population has pre-existing neutralizing antibodies against wild-type AAV, and cross-reactivity is observed between different rAAV serotypes. While extent of response can be influenced by dosing, administration route and target organ(s), these pose concerns over reduction or complete loss of efficacy, options for re-administration, and other unwanted immunological sequalae such as local tissue damage. To reduce said immunological risks, patients are excluded if they harbor anti-AAV antibodies or have received gene therapy previously. Studies have incorporated immunomodulating or suppressive regimens to block cellular and humoral immune responses such as systemic corticosteroids pre- and post-administration of Luxturna^® and Zolgensma^®, the two rAAV products with licensed regulatory approval in Europe and the United States. In this review, we will introduce the current pharmacological strategies to immunosuppress or immunomodulate the host immune response to rAAV gene therapy.

Keywords: adeno associated virus; gene therapy; immune response; immunomodulation; immunosuppression; pharmacotherapies.

Figure 1

Mechanisms of action of approved pharmacotherapies for immunomodulation with rAAV gene therapy. Pre-existing NAb can inhibit receptor-mediated endocytosis thus transduction of rAAV (A). TLR9 recognizes CpG motifs, and TLR2 on cell surface or endosomal membrane recognizes vector capsid, both of which lead to release of pro-inflammatory cytokines (B). Recent evidence shows that ITRs facilitate bidirectional transcription to form dsRNA, which triggers cytosolic MDA5 and downstream type I interferon response (C). Upon endosomal escape, rAAV can be degraded by proteasome and loaded on MHC class I by the endoplasmic reticulum (D). Recognition by memory CTL (E) leads to expansion and differentiation into CTL, and both can commence effector functions leading to loss of transgene expression (F). On the other hand, rAAV can also transduce APC, for instance dendritic cells, and transgene protein product can be phagocytosed (G). They are processed by proteasomes and endosomes respectively and the antigens can be presented on MHC class II molecules (H), leading to downstream activation of T_H and B-cells; among other actions, B cells would differentiate into plasma cells and produce antigen-specific antibodies (I). Created with BioRender.com. APC, antigen presenting cells; ATO, arsenic trioxide; CCS, corticosteroids; Chemo, chemotherapeutics; CIs, calcineurin inhibitors; CTL, cytotoxic T lymphocytes; dsRNA, double-stranded ribonucleic acid; HCQ, hydroxychloroquine; IFN, interferon; IL, interleukin; ITR, inverted terminal repeats; MHC, major histocompatibility complex; MMF, mycophenolate mofetil; NAbs, neutralizing antibodies; NF-κB, nuclear factor kappa B; PIs, proteasome inhibitors; RAPA, rapamycin; rATG, rabbit anti-thymocyte globulin; RTX, rituximab; TH, T helper cells; TNF, tumor necrosis factor; TLR, toll-like receptor.