HIV-1 envelope induces memory B cell responses that correlate with plasma antibody levels after envelope gp120 protein vaccination or HIV-1 infection

Abstract

Successful vaccines (i.e., tetanus and diphtheria) can induce long-lived Ab levels that are maintained by bone marrow plasma cells and plasma Ab levels do not correlate with numbers of blood memory B cells. Destruction of CD4(+) T cells early in HIV-1 acute infection may result in insufficient induction of neutralizing Ab responses; thus, an HIV-1 vaccine should elicit high levels of durable Abs by long-lived plasma cells to be protective. We asked if HIV-1 envelope-specific memory responses were sustained by memory B cells in the settings of HIV-1 gp120 envelope vaccination and chronic HIV-1 infection. Levels of anti-HIV-1 envelope plasma Abs and memory B cells were found to correlate in both settings. Moreover, whereas the expected half-life of plasma Ab levels to protein vaccines was >10 years when maintained by long-lived plasma cells, anti-envelope Ab level half-lives were approximately 33-81 wk in plasma from antiretroviral drug-treated HIV-1(+) subjects. In contrast, anti-p55 Gag Ab level half-life was 648 wk, and Ab titers against influenza did not decay in-between yearly or biennial influenza vaccine boosts in the same patients. These data demonstrated that HIV-1 envelope induces predominantly short-lived memory B cell-dependent plasma Abs in the settings of envelope vaccination and HIV-1 infection. The inability to generate high titers of long-lived anti-envelope Abs is a major hurdle to overcome for the development of a successful HIV-1 vaccine.

FIGURE 1

Frequency of total, gp140 envelope-specific, and MN V3 epitope-specific circulating IgG memory B cells in VaxGen VAX004 rgp120 vaccine and placebo recipients, and correlation between plasma Ab levels and epitope-specific IgG memory B cells. A, ELISPOT assay on stimulated PBMCs from 25 Vaxgen VAX004 rgp120 vaccine recipients. Circulating IgG memory B cells were detected in all tested samples. HIV-1 consensus B gp140 Env-specific and MN V3-specific ASCs were detected in 20 of 25 samples and 15 of 25 samples, respectively. Anti-gp140 Env-and anti MN V3-specific ASC frequencies were 2 and 3 orders of magnitude lower than total IgG ASCs, respectively (line at mean). The difference was statistically significant in-between all the groups (two-tailed paired Student’s t tests). B, The mean total IgG ASCs (line) in placebo recipients was comparable to that in vaccinees. No HIV-specific responses were detected (n = 5). One spot against MN V3 was detected in one placebo recipient and could be due to cross-reactivity. C, Statistical linear correlation (r = 0.66, p = 0.003) between the plasma Ab levels (1/40 plasma dilution is shown; x-axis) and the percentage of consensus B gp140-spe-cific ASCs over total IgG ASCs assay (y-axis). D, Seemingly, the correlation between the plasma Ab levels (OD₄₀₅ at 1/12.5 plasma dilution is shown) and the percentage of MN V3-specific ASCs over total IgG ASCs was statistically significant (r = 0.75, p = 0.003). All plasmas were assayed at the same time and the same dilution was used for each OD reading across patients; in every case, the OD at the dilution used was within the linear range of the ELISA.

FIGURE 2

Production of IgG ASCs is induced by in vitro stimulation with pokeweed mitogen, CpG-oligodeoxynucleotides and IL-15 in both HIV-positive and HIV-negative samples. IgG ASCs were enumerated by ELISPOT assay after a 6-day culture with or without pokeweed mitogen, CpG-oligodeoxynucleotides and IL-15 to measure the effect of the stimulation in driving resting memory B cells into ASCs. The results are expressed as ASCs per million viable PBMCs at the end of culture. Both HIV-positive (n = 26; A) and HIV-negative (n = 19; B) samples showed a statistically significant (two-tailed paired Student’s t test) increased number of IgG-secreting cells upon stimulation (line at mean). ASCs from unstimulated cultured cells (spontaneously secreting cells) were subtracted as background from the total IgG memory B cell ASC counts in subsequent analyses.

FIGURE 3

Frequency of total, gp140 Env-specific, and MN V3 epitope-specific circulating IgG memory B cells in chronically HIV-1-infected or HIV-1-negative subjects, and correlation between plasma Ab levels and epitope-specific circulating IgG memory B cells. A, Circulating IgG memory B cells were detected in 24 of 26 samples from HIV-1-infected subjects (line at mean). HIV-1 consensus B gp140 Env-specific responses were detected in 21 of 26 samples, and MN V3-specific memory responses were detected in 9 of 11 samples. Comparison among consensus B gp140-and MN V3-specific frequencies of IgG ASCs shows a pattern that is similar to vaccinated individuals. Statistical differences were calculated with paired Student’s t tests. B, The frequency of total IgG in 19 HIV-negative individuals was comparable to that in HIV-positive samples. No HIV-specific responses were detected. C, The plasma Ab levels detected by ELISA (OD₄₀₅ at 1/800 dilution; x-axis) of 19 HIV-positive samples were correlated to the percentage of consensus B gp140-specific ASCs over total IgG ASCs detected by ELISPOT assay (y-axis) for which paired observations were available. A significant linear correlation was detected (r = 0.5, p = 0.031). All plasmas were assayed at the same time and the same dilution was used for each OD reading across patients; in every case, the OD at the dilution used was within the linear range of the ELISA. D, On the contrary, no correlation was found in the same subjects between MN V3-specific ASCs and plasma Ab levels.

FIGURE 4

IgG memory B cells and plasma Ab levels against the MPER gp41 cluster II 2F5 epitope. A and B, As a sensitive measurement of the plasma Abs binding to the MPER cluster II gp41 2F5 epitope, we tested the ability of plasma (at 1/50 dilution) to block the binding of either the broadly neutralizing 2F5 (A) or the non-neutralizing 13H11 (B) mAbs, both of which bind to the MPER gp41 cluster II 2F5 epitope, to the clade B JRFL gp140 oligomer by comparing the extent of biotin-mAb binding detected with or without preincubating the JRFL envelope with plasma. The data shown are expressed as follows: 100 − (sera triplicate mean/no inhibition control mean)100. Triplicate wells were background subtracted and averaged. The threshold (vertical line) was conservatively calculated as 3 times the mean readout of multiple HIV-negative samples + 3 SEM. C, Only 4 (16.7%) of the 24 HIV-positive samples tested had detectable IgG ASCs against the MPER cluster II gp41 2F5 epitope. The magnitude of the response was significantly lower than that against the MN V3 epitope (p < 0.0001, Mann-Whitney U test). No ASCs against the MPER cluster II gp41 2F5 epitope were detected in 18 HIV-negative samples.

FIGURE 5

Ab responses in chronically HIV-1-infected subjects upon initiation of anti-retroviral therapy. Eight HIV-positive subjects were followed-up for up to 378 wk upon initiation of ART and suppression of viremia. For each of them the (A) anti-gp120, (B) anti-gp41, (C) anti-p55, (D) anti-tetanus toxoid, and (E) anti-influenza plasma IgG Ab levels are shown over the entire 7-year period (colored lines), and (F) the plasma anti-influenza Ab half-lives of the individual intervals of time after each documented boost of influenza vaccine are shown. The calculated plasma Ab level half-lives have been modeled as described in Materials and Methods and are shown with the black line.