An autoreactive antibody from an SLE/HIV-1 individual broadly neutralizes HIV-1

Abstract

Broadly HIV-1-neutralizing antibodies (BnAbs) display one or more unusual traits, including a long heavy chain complementarity-determining region 3 (HCDR3), polyreactivity, and high levels of somatic mutations. These shared characteristics suggest that BnAb development might be limited by immune tolerance controls. It has been postulated that HIV-1-infected individuals with autoimmune disease and defective immune tolerance mechanisms may produce BnAbs more readily than those without autoimmune diseases. In this study, we identified an HIV-1-infected individual with SLE who exhibited controlled viral load (<5,000 copies/ml) in the absence of controlling HLA phenotypes and developed plasma HIV-1 neutralization breadth. We collected memory B cells from this individual and isolated a BnAb, CH98, that targets the CD4 binding site (CD4bs) of HIV-1 envelope glycoprotein 120 (gp120). CH98 bound to human antigens including dsDNA, which is specifically associated with SLE. Anti-dsDNA reactivity was also present in the patient's plasma. CH98 had a mutation frequency of 25% and 15% nt somatic mutations in the heavy and light chain variable domains, respectively, a long HCDR3, and a deletion in the light chain CDR1. The occurrence of anti-dsDNA reactivity by a HIV-1 CD4bs BnAb in an individual with SLE raises the possibility that some BnAbs and SLE-associated autoantibodies arise from similar pools of B cells.

Figure 1. Identification of neutralizing CD4bs antibodies in CH5329 serum.

(A) CH5329 plasma and mAb CH98 neutralization profiles, measured as ID₅₀ and IC₅₀,respectively, in TZM-bl assay. Transmitted/founder HIV-1 isolates are italicized. For plasma neutralization: red, ID₅₀ >1,000; orange, ID₅₀ 100 to 1,000; yellow, ID₅₀ >20 and <100; white, ID₅₀ <20 (absence of neutralization). For CH98 BnAb: red, IC₅₀ <1 μg/ml; orange, IC₅₀ 1 to 50 μg/ml; white, IC₅₀ >50 μg/ml (absence of neutralization). (B) Differential binding by CH5329 serum to the RSC3 protein and the CD4bs knockout RSC3Δ371I/P363N, graphed as ELISA endpoint titer (final reciprocal serum dilution with background-corrected OD ≥0.1). (C) CD4bs-directed neutralizing activity in CH5329 serum, shown as percent reduction in ID₈₀ in the presence of RSC3 compared with the knockout RSC3Δ371I/P363N against HIV-1 JRFL and HxB2 strains. Values for the BnAbs VRC01 and 2F5 are included as positive and negative control, respectively. In B and C, error bars represent SEM from 2 independent experiments.

Figure 2. Effect of point mutation of the YU2 core protein on CD4-Fc and on CH98, CH31–CH34, VRC01 and b12 CD4bs BnAbs, and the non-neutralizing CD4bs b6 mAb.

The effect of point mutations on the binding to the YU2 core protein of CH98 and other CD4bs mAbs and CD4-Fc is expressed as percentage normalized to binding to the WT YU2 gp120 core protein and color coded as indicated. Positioning within the CD4bs (green), or adjacent or nearby (black), is indicated at far right.

Figure 3. Threading of CH98 onto the gp120 complexed structures of CD4bs VRC01 and CH103 BnAbs.

(A) CH98 model based on threading onto the gp120 complexed VRC01 crystal structure. The CH98 heavy chain (HC; dark blue) and light chain (LC; light blue) threaded onto the VRC01 structure complexed with gp120 (gray) resulted in an incompatible model, with a clash between the gp120 D loop (red) and the LCDR3 (green). (B) CH98 model based on threading onto the gp120 complexed CH103 crystal structure. The CH98 heavy chain (dark blue) and light chain (light blue) threaded onto the CH103 structure complexed with gp120 (gray) resulted in a model in which HCDR3 (magenta) dominates the binding to the CD4bs region and engages in direct contact with gp120 residues in positions 365, 368, 473, and 282, all of which affect CH98 binding. The residue in position 461 makes direct contact with LCDR1. Each residue that affects CH98 binding in the epitope mapping is illustrated using the corresponding color in Figure 2.

Figure 4. Autoreactivity of CH98.

(A) CH98 reactivity against common antigens associated with autoimmune diseases, tested with a commercial ANA-II Plus test system. The threshold for positivity was 120 RU (dashed line). (B) CH5329 plasma reactivity against common antigens associated with autoimmune diseases, tested with the commercial ANA-II Plus test system. Results from 3 independent experiments are shown. The threshold for negativity was 100 RU (solid line), and that for positivity was 120 RU (dashed line); values of 100–120 RU were considered equivocal specimens. (C–E) Hep-C IFA staining of BnAb CH98. Antibody concentration was 25 μg/ml, and exposure time was 8 seconds. Original magnification, ×40; inset in D is enlarged ×1.5. (F and G) Reactivity of CH98 on a panel of 9,400 human proteins tested using a ProtoArray 5 microchip, compared with nonautoreactive mAb 151K (F) or palivizumab (G). Values for STUB1 are encircled.