Date Published: July 5, 2017
Publisher: Public Library of Science
Author(s): Lautaro G. Perez, David R. Martinez, Allan C. deCamp, Abraham Pinter, Phillip W. Berman, Donald Francis, Faruk Sinangil, Carter Lee, Kelli Greene, Hongmei Gao, Sorachai Nitayaphan, Supachai Rerks-Ngarm, Jaranit Kaewkungwal, Punnee Pitisuttithum, James Tartaglia, Robert J. O’Connell, Merlin L. Robb, Nelson L. Michael, Jerome H. Kim, Peter Gilbert, David C. Montefiori, Aftab A. Ansari.
Non-neutralizing IgG to the V1V2 loop of HIV-1 gp120 correlates with a decreased risk of HIV-1 infection but the mechanism of protection remains unknown. This V1V2 IgG correlate was identified in RV144 Thai trial vaccine recipients, who were primed with a canarypox vector expressing membrane-bound gp120 (vCP1521) and boosted with vCP1521 plus a mixture gp120 proteins from clade B and clade CRF01_AE (B/E gp120). We sought to determine whether the mechanism of vaccine protection might involve antibody-dependent complement activation. Complement activation was measured as a function of complement component C3d deposition on V1V2-coated beads in the presence of RV144 sera. Variable levels of complement activation were detected two weeks post final boosting in RV144, which is when the V1V2 IgG correlate was identified. The magnitude of complement activation correlated with V1V2-specific serum IgG and was stronger and more common in RV144 than in HIV-1 infected individuals and two related HIV-1 vaccine trials, VAX003 and VAX004, where no protection was seen. After adjusting for gp120 IgA, V1V2 IgG, gender, and risk score, complement activation by case-control plasmas from RV144 correlated inversely with a reduced risk of HIV-1 infection, with odds ratio for positive versus negative response to TH023-V1V2 0.42 (95% CI 0.18 to 0.99, p = 0.048) and to A244-V1V2 0.49 (95% CI 0.21 to 1.10, p = 0.085). These results suggest that complement activity may have contributed in part to modest protection against the acquisition of HIV-1 infection seen in the RV144 trial.
The ALVAC-HIV (vCP1521) prime and recombinant gp120 AIDSVAX B/E + vCP1521 boost vaccine reduced the risk of HIV-1 infection by an estimated 31.2% compared to placebo in the RV144 efficacy trial in a community-based population in Thailand . Reduced infection risk was significantly associated with total plasma IgG binding to a murine leukemia virus gp70 scaffold containing HIV-1 gp120 variable regions 1 and 2 (gp70-V1V2) [2, 3]. A similar correlation was seen with total plasma IgG binding to linear V2 peptides , and with plasma IgG3 binding to gp70-V1V2 scaffolds . These V1V2 antibodies appear to bind the mid-loop region of V2 with a strong dependency on lysine (K) at position 169 and valine (V) at position 172 [6, 7]. Consistent with these findings, two genetic sieve analyses of RV144 breakthrough viruses found increased efficacy against viruses containing lysine (K) at position 169 [8, 9]. Because virus-specific CD8+ T cells  and tier 2 virus neutralizing antibodies  were nearly absent in this trial, the hypothesis has been raised that protection was mediated by non-neutralizing antibodies [11, 12]. In this regard, results of several RV144 follow-up studies implicate a role for non-neutralizing, Fc receptor (FcR)-mediated antibody effector functions [13, 14], including antibody-dependent cellular cytotoxicity (ADCC) [15–18] and phagocytosis .
We sought to determine whether the V1V2-specific IgG responses that correlated with a decreased risk of HIV-1 infection in RV144 were associated with a possible complement-mediated mechanism of protection. HIV-1 resists terminal complement pathway activation and MAC formation; however, early pathway activation and opsonization by activated C3 fragments could promote interactions with complement receptors on follicular dendritic cells and red blood cells to facilitate antibody responses in germinal centers [51, 52] and HIV-1 clearance through the mononuclear phagocytic system [40, 41]. As indicated by C3d deposition on V1V2 antigen-coated beads, plasma samples obtained two-week post final vaccination in RV144 exhibited variable levels of complement activation. The magnitude of antibody-mediated complement activation correlated with V1V2 IgG and was most pronounced against V1V2 of the vaccine strain in vCP1521 (92TH023) and to a lesser degree V1V2 of A244gp120 used in the protein boost. The V1V2 of these two CRF01_AE strains are closely related, though not identical, and share a common sequence in the RV144 V2-reactive hotspot region (Fig 1). Notably, they differ by four glycans and a number of non-sequon amino acids over the entire length of the scaffold, including a six amino acid insertion in A244. Minor differences in reactivity against these two V1V2 scaffolds may be due to differences in the balance of polyclonal specificities, or in the structure and glycan shielding of the V2 hotspot . The near absence of activity against V1V2 of the clade B MNgp120 that was also used in the protein boost is likely explained by low IgG levels against this more divergent V1V2. Moderate activity was seen against the non-vaccine-matched Ce1086-V1V2, which shares partial sequence homology to 92TH023 and A244, especially in the RV144 V2-reactive hotspot region (Fig 1).