Characteristics of the Earliest Cross-Neutralizing Antibody Response to HIV-1

Recent cross-sectional analyses of HIV-1+ plasmas have indicated that broadly cross-reactive neutralizing antibody responses are developed by 10%–30% of HIV-1+ subjects. The timing of the initial development of such anti-viral responses is unknown. It is also unknown whether the emergence of these responses coincides with the appearance of antibody specificities to a single or multiple regions of the viral envelope glycoprotein (Env). Here we analyzed the cross-neutralizing antibody responses in longitudinal plasmas collected soon after and up to seven years after HIV-1 infection. We find that anti-HIV-1 cross-neutralizing antibody responses first become evident on average at 2.5 years and, in rare cases, as early as 1 year following infection. If cross-neutralizing antibody responses do not develop during the first 2–3 years of infection, they most likely will not do so subsequently. Our results indicate a potential link between the development of cross-neutralizing antibody responses and specific activation markers on T cells, and with plasma viremia levels. The earliest cross-neutralizing antibody response targets a limited number of Env regions, primarily the CD4-binding site and epitopes that are not present on monomeric Env, but on the virion-associated trimeric Env form. In contrast, the neutralizing activities of plasmas from subjects that did not develop cross-neutralizing antibody responses target epitopes on monomeric gp120 other than the CD4-BS. Our study provides information that is not only relevant to better understanding the interaction of the human immune system with HIV but may guide the development of effective immunization protocols. Since antibodies to complex epitopes that are present on the virion-associated envelope spike appear to be key components of earliest cross-neutralizing activities of HIV-1+ plasmas, then emphasis should be made to elicit similar antibodies by vaccination

Development and Characteristics of the Earliest Cross-Neutralizing Antibody Response to HIV-1

Thesis (Ph.D.)--University of Washington, 2012

Evolution of Cross-Neutralizing Antibody Specificities to the CD4-BS and the Carbohydrate Cloak of the HIV Env in an HIV-1-Infected Subject

<div><p>Broadly neutralizing antibodies are considered an important part of a successful HIV vaccine. A better understanding of the factors underlying their development during infection and of the epitopes they target is needed to elicit similar antibody responses by vaccination. We and others reported that, on average, it takes 2 to 3 years for cross-reactive neutralizing antibodies to become detectable in the sera of HIV-1-infected subjects and that they target a limited number of epitopes on the HIV Envelope. Here we investigated the emergence and evolution of the earliest cross-reactive neutralizing antibody specificities in one HIV-1-infected individual, AC053. We defined two distinct epitopes on Env that are targeted by the broadly neutralizing antibody responses developed by AC053. The first specificity became evident at 3 years post infection and targeted the CD4-binding site of Env. Antibodies responsible for that specificity neutralized most, but not all, viruses susceptible to neutralization by the plasma antibodies of AC053. The second specificity became apparent approximately a year later. It was due to PG9-like antibodies, which were able to neutralize those viruses not susceptible to the anti-CD4-BS antibodies in AC053. These findings improve <b><u>our</u></b> understanding of the co-development of broadly neutralizing antibodies that target more than one epitope during natural HIV-1-infection in selected HIV+ subjects. They support the hypothesis that developing broadly neutralizing antibody responses targeting distinct epitopes by immunization could be feasible.</p> </div

Neutralization of kifunensine- and swainsonine-treated virions by monoclonal antibodies.

<p>Neutralization curves were plotted for MAbs PG9, PG16, VRC01 and 2G12 with untreated (black circles), kifunensine-treated (red squares), and swainsonine-treated (blue triangles) <b><u>SC422661 pseudovirus</u></b>.</p

Timeline of the epitope evolution of cross-reactive NAb responses in AC053.

<p>The breadth of neutralizing antibody responses (i.e., the percent of heterologous isolates neutralized by plasma samples out of the total isolates tested <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0049610#pone.0049610-Mikell1" target="_blank">[14]</a>), was plotted for all available time-points for subject AC053. The arrows on the timeline correspond to approximate years post infection when particular neutralizing antibody specificities became evident. Breadth is color-coded as follows: blue 0–19%, green 20–39%, orange 40–74%, red 75–100%.</p

Contribution of different anti-gp120 specificities for the cross-reactive neutralizing activity of AC053 plasma. (

<p>A) Log10 decrease in IC50 titers by elimination of anti-WT SF162 gp120 or competition of anti-D368R SF162 gp120 antibodies, as reported in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0049610#pone.0049610-Mikell1" target="_blank">[14]</a>, which demonstrates the CAAN is not susceptible to the anti-CD4BS cross-reactive NAb responses of AC053. (B) Log10 decrease in IC50 titers by elimination of anti-WT SF162 gp120 or anti-K160N SF162 antibodies, indicative of a glycan-specific cross-neutralizing response. Light blue: no effect or less than 0.5 Log10 decrease; Orange: decrease between 0.5 and 0.9 Log10; Red: over 0.9 Log10 decrease.</p

Glycan-dependent neutralizing specificity of plasma samples.

<p>Percent change in the plasma IC50 titers of kifunensine-treated (red) and swainsonine-treated (green) SF162 K160N was calculated relative to the untreated virus. Years post infection and percent isolates neutralized are indicated for each sample. (A) Yearly longitudinal AC053 plasma samples from 1.75 years to 6.85 years demonstrated sensitivity to kifunensine treatment only, while the 0.82 samples could not neutralize either treated virus. PG9 is included as a positive control. (B) Plasma samples from the MGH cohort, characterized in detail in a previous report <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0049610#pone.0049610-Mikell1" target="_blank">[14]</a>, were tested for neutralization of treated and untreated viruses. Four plasmas with narrow breadth (≤35% breadth) and four plasmas with cross-reactive NAb responses (≥75% breadth) were selected. AC053 was the only plasma that demonstrated the PG9-like resistance of kifunensine-, but not swainsonine-treated pseudoviruses.</p

Cumulative IC50 titers of AC053 longitudinal plasma samples as previously reported [14].

<p>The IC50 neutralizing plasma antibody titers against 19 heterologous Clade A (blue), B (green), and C (orange) isolates were determined at distinct time points during infection. The sum of these titers (cumulative IC50 titer) is shown. The neutralizing antibody response gradually increased in breadth and potency, and at the highest recorded breadth (5.31 ypi), AC053 neutralized 16 of these isolates (80% breadth). The most potent neutralizing activities were against Clade B isolates.</p

Neutralization of kifunensine- or swainsonine-treated viruses by AC053 plasma collected at 5.31 yrs post infection.

<p>The percent neutralization of viruses produced in 293 T cells either in the presence or absence of 20 µM kifunensine or swainsonine glycosidase inhibitors (as described in the <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0049610#s2" target="_blank">Materials and Methods</a>) was determine at a given plasma dilution. Black circles – no treatment, red squares – kifunensine treatment, blue triangles – swainsonine treatment.</p