AAV-Delivered Antibody Mediates Significant Protective Effects against SIVmac239 Challenge in the Absence of Neutralizing Activity

Abstract

Long-term delivery of potent broadly-neutralizing antibodies is a promising approach for the prevention of HIV-1 infection. We used AAV vector intramuscularly to deliver anti-SIV monoclonal antibodies (mAbs) in IgG1 form to rhesus monkeys. Persisting levels of delivered mAb as high as 270 μg/ml were achieved. However, host antibody responses to the delivered antibody were observed in 9 of the 12 monkeys and these appeared to limit the concentration of delivered antibody that could be achieved. This is reflected in the wide range of delivered mAb concentrations that were achieved: 1–270 μg/ml. Following repeated, marginal dose, intravenous challenge with the difficult-to-neutralize SIVmac239, the six monkeys in the AAV-5L7 IgG1 mAb group showed clear protective effects despite the absence of detectable neutralizing activity against the challenge virus. The protective effects included: lowering of viral load at peak height; lowering of viral load at set point; delay in the time to peak viral load from the time of the infectious virus exposure. All of these effects were statistically significant. In addition, the monkey with the highest level of delivered 5L7 mAb completely resisted six successive SIVmac239 i.v. challenges, including a final challenge with a dose of 10 i.v. infectious units. Our results demonstrate the continued promise of this approach for the prevention of HIV-1 infection in people. However, the problem of anti-antibody responses will need to be understood and overcome for the promise of this approach to be effectively realized.

Use of a gamma-2 herpesvirus as a vector to deliver antibodies to rhesus monkeys

“…However, the levels were drastically lower in comparison to what was observed in the study conducted by Fuchs and colleagues 17 where recombinant AAV-mediated delivery of 4L6 and 5L7 lead to antibody concentrations between 1 μg/ml to 270 μg/ml. Although slightly delayed, the overall kinetics of antibodies delivered by recombinant RRV were comparable to recombinant AAV-delivered 4L6 where initial peaks post-recombinant-AAV inoculation were followed by a strong decline in 4L6 IgG1 levels in the vast majority of the research animals.…”

“…17, 18, 33 Comparable to our previous studies using AAV 17, 33 the anti-4L6 responses in our present study with recombinant RRV were higher than the measured responses against 5L7. Furthermore, both recombinant RRV-4L6 recipients showed clear anti-antibody responses, whereas only one of the two recombinant RRV-5L7 recipients exhibited measurable anti-antibodies; this also reflects the AAV results where anti-anti responses were consistently observed in six of six monkeys with 4L6 delivery but only in three of six monkeys with 5L7 delivery.…”

“…15–19 The only protein product derived from the AAV vector comes from the transgene that is placed into it; as long as that protein product is not viewed as foreign, protein expression may continue for years following intramuscular administration. 17, 20, 21 Muscle cells turn over very little if at all, helping to ensure the long term delivery. At least three of the monkey studies have suffered from strong antibody responses of the host to the delivered antibody that severely limited the concentrations of the mAbs that could be achieved.…”

“…At least three of the monkey studies have suffered from strong antibody responses of the host to the delivered antibody that severely limited the concentrations of the mAbs that could be achieved. 15, 17, 18 To what extent unnatural expression of the mAbs in muscle cells plays a role in these anti-anti responses is not clear.…”

Simian Immunodeficiency Virus SIVmac239, but Not SIVmac316, Binds and Utilizes Human CD4 More Efficiently than Rhesus CD4

“…Expi293 cells were grown in Expi293 expression medium (Thermo Fisher Scientific). Plasmids V132 and V82 for the expression of antibodies 4L6 and 5L7, respectively, were provided by Ronald Desrosiers, as were plasmids encoding SIV mac 239 SpX, SIV mac 316 open SpX, and SIVsmE543-3 full-length viral genomes, and SIVmac251 stock virus (5,16,17,38). SIVmac1A11 infectious molecular clone, also from the NIH AIDS reagent program, was supplied by Paul Luciw (39).…”