HIV-1 envelope gp41 antibodies can originate from terminal ileum B cells that share cross-reactivity with commensal bacteria

Abstract

Monoclonal antibodies derived from blood plasma cells of acute HIV-1-infected individuals are predominantly targeted to the HIV Env gp41 and cross-reactive with commensal bacteria. To understand this phenomenon, we examined anti-HIV responses in ileum B cells using recombinant antibody technology and probed their relationship to commensal bacteria. The dominant ileum B cell response was to Env gp41. Remarkably, a majority (82%) of the ileum anti-gp41 antibodies cross-reacted with commensal bacteria, and of those, 43% showed non-HIV-1 antigen polyreactivity. Pyrosequencing revealed shared HIV-1 antibody clonal lineages between ileum and blood. Mutated immunoglobulin G antibodies cross-reactive with both Env gp41 and microbiota could also be isolated from the ileum of HIV-1 uninfected individuals. Thus, the gp41 commensal bacterial antigen cross-reactive antibodies originate in the intestine, and the gp41 Env response in HIV-1 infection can be derived from a preinfection memory B cell pool triggered by commensal bacteria that cross-react with Env.

Figure 1. Characteristics of Antibodies Isolated from Terminal Ileum Plasma Cells and Memory B Cells of EHI Individuals

(A) The total number of mAbs generated from wells with one V_HD_HJ_H and one V_LJ_L gene isolated is indicated in the center of the pie chart. The percentages of mAbs binding to gp41, gp120, p24, and non-HIV-1 antigens are indicated by colors. (B) Frequency of somatic mutations in V_H gene segments of HIV-1-reactive antibodies compared to non-HIV-1-reactive or nondefined mAbs from terminal ileum plasma cells and memory B cells of six EHI individuals. Mean and SEM are indicated by lines. (C) The HCDR3 lengths of HIV-1-reactive mAbs compared to non-HIV-1-reactive or nondefined antibodies isolated from terminal ileum B cells, with plasma cells and memory B cells pooled. Mean and SEM are indicated by lines. (D) Six recombinant mAbs (DH300, DH301, DH302, DH303, DH304, and DH305) produced in a rIgG1 backbone were evaluated for reactivity with HIV-1 rgp41, SP62 = 2F5 MPER gp41 epitope peptide (QQEKNEQELLELDKWASLWN), and sp400 = gp41 immunodominant peptide (RVLAVERYLRDQQLLG IWGCSGKLICTTAVPWNASWSNKSLNK) by ELISA. They were tested in 3-fold dilutions ranging from 100 to 0.05 μg/ml (x axis). See also Tables S1, S2, and S3.

Figure 2. Characteristics of Antibodies Isolated from Terminal Ileum Plasma Cells of CHI Individuals

(A) The total number of mAbs generated is indicated in the center of the pie chart. The percentages of mAbs binding to gp41, gp120, p24, and non-HIV-1/nondefined antigens are indicated by colors. (B) Frequency of somatic mutations in V_H gene segments of HIV-1-reactive antibodies compared to non-HIV-1- or nondefined reactive antibodies from terminal ileum plasma cells and memory B cells of three CHI subjects. Mean and SEM are indicated by lines. (C) The HCDR3 lengths of HIV-1-reactive antibodies compared to non-HIV-1- or nondefined reactive antibodies isolated from terminal plasma cells of three CHI individuals. Mean and SEM are indicated by lines. (D) A total of 16 recombinant mAbs (DH306, DH307, DH308, DH309, DH310, DH311, DH312, DH313, DH314, DH315, DH316, DH317, DH318, DH319, DH320, and DH321) produced in a rIgG1 backbone were evaluated for reactivity with HIV-1 rgp41, p24, sp62 = 2F5 MPER gp41 epitope peptide (QQEKNEQELLELDKWASLWN) and sp400 = gp41 immunodominant peptide (RVLAVERYLRD QQLLGIWGCSGKLICTTAVPWNASWSNKSLNK), and MN gp120 gD- by ELISA. They were tested in 3-fold dilutions ranging from 100 to at least 0.05 μg/ml (x axis). See also Tables S1, S2, S4, and S5.

Figure 3. Commensal Bacteria Cross-Reactivity of HIV-1-Reactive Antibodies Isolated from Terminal Ileum Plasma Cells and Memory B Cells of EHI and CHI Individuals

(A) HIV-1-reactive mAbs isolated from terminal ileum plasma cells and memory B cells of EHI and CHI individuals were tested for reactivity to anaerobic commensal bacteria by SPR. The response unit and off rate for each antibody that reacted with anaerobic commensal bacteria in this assay is plotted. Antibodies isolated from EHI individuals are indicated in red, and antibodies isolated from CHI individuals are indicated in black. The HIV-1 reactivity of the antibodies is indicated by shapes. (B) The avidity score (response unit [RU] / off rate [kd]) of the terminal ileum HIV-1-reactive antibodies binding to anaerobic WCL by SPR. (C) HIV-1-reactive mAbs isolated from EHI terminal ileum B cells were also tested for reactivity to anaerobic and aerobic commensal bacteria WCL by SDS-PAGE western blot. A total of 100 μg of each anaerobic and aerobic WCL was loaded in individual lanes, and mAbs were tested at 20 μg/ml in both nonreducing and reducing conditions. Three representative westerns under nonreducing conditions are shown. (D) HIV-1-reactive mAbs isolated from terminal ileum plasma cells and memory B cells of EHI individuals were tested for reactivity to anaerobic and aerobic commensal bacteria by BAMA at 100 μg/ml. Mean and SEM are indicated by lines. (E) HIV-1-reactive mAbs isolated from CHI terminal ileum B cells were also tested for reactivity to anaerobic and aerobic commensal bacteria WCLs by SDS-PAGE western blot. A total of 100 μg of anaerobic and aerobic WCLs was loaded in individual lanes, and mAbs were tested at 20 μg/ml in both nonreducing and reducing conditions. Four representative westerns under nonreducing conditions are shown. (F) HIV-1-reactive mAbs isolated from terminal ileum plasma cells and memory B cells of CHI individuals were also tested for reactivity to anaerobic and aerobic commensal by BAMA at 100 μg/ml. Mean and SEM are indicated by lines. See also Figures S1–S3 and Tables S2 and S6.

Figure 4. HIV-1 gp41 and Commensal Bacteria Cross-Reactive Antibodies from the Terminal Ileum Show Affinity Maturation to Autologous and Heterologous HIV-1 Envelope

(A–C) SPR binding curves of UCA and mature mAbs immobilized with an anti-Fc receptor antibody binding to titrations of autologous HIV-1 gp140 from individual 004-0 and to MN gp41. Relative binding to commensal bacteria was also determined by SPR. (A) DH306 UCA and DH306; (B) DH309 UCA and DH309; and (C) DH308 UCA and DH308. (D) Table of the on rates, off rates, and apparent dissociation constant (K_D) for each mature mAb and UCA pair binding to the HIV-1 Envs tested and the response unit and off rate of mAb binding to anaerobic bacteria WCL. N/A: this antibody was not tested for binding to 004-0 gp140. (E and F) SPR binding curves of UCA and mature mAbs immobilized with an anti-Fc receptor antibody binding to titrations of MN gp41. Autologous Env was not available for these two mAbs. Relative binding to commensal bacteria was also determined by SPR. (E) DH305 UCA and DH305. (F) DH319 UCA and DH319.

Figure 5. HIV-1-Reactive Antibodies Isolated from Terminal Ileum Plasma Cells and Memory B Cells of Uninfected Individuals React to Both HIV-1 gp41 and Commensal Bacteria

(A) SPR strategy used to confirm HIV-1 reactivity of mAbs isolated from the terminal ileum of uninfected individuals. Signal generated by antibody binding to catalase was subtracted from signal generated by antibody binding to recombinant MN gp41. (B) Antibodies DH366 and DH367 isolated from terminal ileum plasma cells that were natural IgG1 and IgG3 antibodies, respectively, were produced in a rIgG1 backbone and were evaluated for reactivity with HIV-1 MN gp41 by SPR. The V_Hs of DH366 and DH367 were mutated 6.6% and 11.8%, respectively. (C) DH366 and DH367 were tested for reactivity to anaerobic and aerobic commensal bacteria by BAMA. Dilutions were 2-fold, ranging from 100–3.1 μg/ml (x axis). (D) Reactivity to anaerobic and aerobic commensal bacteria under nonreducing and reducing conditions by SDS-PAGE western blot.

Figure 6. Identification of E. coli RNA Polymerase as One Cross-Reactive Commensal Bacterial Antigen Recognized by HIV-1 gp41 Antibodies

(A) Western blot analysis following NativePAGE gel run showing that mAb 558_2 (Liao et al., 2011) binds to an ~520 kDa protein band in anaerobic and aerobic intestinal bacterial WCL. (B). Protein fractions from bacterial WCL with molecular weight of ~500 kDa were collected following size exclusion chromatography (SEC). (C) The ~500 kDa fraction shows enrichment of the 520 kDa protein by 1D native Coomassie blue (lanes 1 and 2) and blue native western blotting with mAb558_2 (lane 3). The ~520 kDa bands from two gels, identified in two red boxes, were excised from the gel and determined to be E. coli RNA polymerase by LC-MS/MS. (D) Recombinant E. coli RNA polymerase core protein was run on a denaturing SDS-PAGE gel under both reducing and nonreducing conditions and blotted with mAb558_2 and a hemagglutinin (HA) flu-reactive antibody Ab1248 as a negative control. (E–H) Reactivity of terminal ileum Env gp41 commensal bacteria cross-reactive antibodies with rE. coli RNA polymerase was determined by BAMA. Dilutions were 2-fold, ranging from 100–3.1 μg/ml (x axis). (E) HIV-1 gp41 commensal bacteria cross-reactive mAbs isolated from the terminal ileum of EHI individuals. (F) HIV-1 gp41 commensal bacteria cross-reactive mAbs isolated from the terminal ileum of CHI individuals. DH309 and DH316 are representative of the other lowest binders, DH317 and DH318. (G) H308, a gp41 mAb isolated from a terminal ileum plasma cell from CHI individual 004-0, is the strongest rE. coli RNA polymerase binder. DH308 used the V_H gene segment 1–69, which was 8.6% mutated and was naturally IgG1. (H) HIV-1 gp41 commensal bacteria cross-reactive mAbs isolated from the terminal ileum of uninfected individuals. See also Figure S4.

Figure 7. Phylogenetic Trees of Ig Heavy-Chain Clonal Lineages with Members Derived from Blood B Cells and Terminal Ileum B Cells, with Known Antibody Reactivity

(A–C) Trees are rooted on the inferred UCA. Nodes are labeled with the antibody or sequence ID and sample they were isolated from. Red nodes indicate B cells isolated by single-cell PCR from terminal ileum B cells that were produced in large scale and screened for reactivity to HIV-1 antigens and commensal bacteria WCLs. The reactivity of the terminal ileum mAb is noted below each tree. Black nodes indicate V_HD_HJ_H sequences identified by pyrosequencing of time-matched peripheral PBMCs. Tree IDs are located to the left of each tree: TR3666 (A), TR3669 (B), and TR3684 (C). See also Figures S5–S7 and Table S7.