IgM-and IgG-cleaving enzyme facilitates AAV gene transfer in AAV-seropositive macaques

AAV gene therapy is a promising approach for long-term delivery of antiviral proteins that can control HIV replication, but pre-existing circulating AAV-specific antibodies can preclude successful AAV transduction and pose a challenge for AAV vector re-administration in cases where transgene protein expression falls below effective levels. IceMG is a novel, engineered, dual-function immunoglobulin (Ig)-cleaving enzyme that cleaves human and non-human primate IgM and IgG. Here, we sought to evaluate the ability of IceMG to transiently reduce AAV-specific humoral immunity and facilitate successful AAV transduction and gene transfer in AAV-seropositive, SHIV-infected rhesus and cynomolgus macaques. Intravenous administration of IceMG to macaques resulted in cleavage and transient depletion of circulating IgG and IgM, in contrast to dosing with IdeS, an IgG-specific immunoglobulin-cleaving enzyme, which resulted in cleavage and transient depletion of IgG but not IgM. Dosing of either IceMG or IdeS temporarily decreased SHIV Env-binding IgG plasma concentrations, which were associated with concomitant increases in SHIV plasma viral loads, underscoring the role of Env-specific humoral immunity in SHIV control. Critically, IceMG or IdeS dosing also transiently decreased AAV9-specific neutralizing antibody titers in AAV-seropositive macaques that had previously received AAV9 vectors. Re-dosing macaques with IceMG or IdeS months later reduced circulating intact IgG, SHIV Env-binding IgG titers, and AAV-specific neutralizing antibody titers with similar efficacy as the initial dose. Finally, IceMG administration to macaques prior to AAV9 vector boosting enabled a second round of successful AAV transduction and transgene expression, in contrast to macaques that did not receive IceMG where AAV vector boosting failed to produce detectable transgene. However, AAV vector boosting also led to rebound of AAV-specific neutralizing antibody titers in all macaques, and in some cases, increases in anti-drug antibodies (ADA) targeting the AAV vector transgene protein and subsequent loss of transgene protein from circulation. Overall, these results substantiate the use of Ig-cleaving enzymes as tools to overcome pre-existing AAV humoral immunity, but highlight other challenges that follow AAV vector re-administration, such as resurgence of AAV humoral immunity and AAV transgene-directed ADA.