The induction of broadly neutralizing antibodies (bNAbs) is a major goal of HIV vaccine efforts. In chronic infection however, only a small percentage of HIV–infected individuals (?2%) is able to mount this type of humoral response and the lymph node (LN)–specific parameters associated with such outcomes in the context of persistent viremia remain to be elucidated. To address this question, we performed a detailed analysis of the topology and immunophenotype of LN-resident CD4 T–cell and B–cell populations in viremic HIV+ volunteers with and without broadly neutralizing activity profiles.
LN cell suspensions and matched formalin–fixed, paraffin embedded (FFPE) tissue sections derived from chronically infected HIV+ individuals were analyzed using 30–colour multiparametric flow cytometry and quantitative multiplexed confocal imaging. Neutralization activity of matched serum samples was determined using a single–round infectivity assay. Breadth of neutralization was defined by calculating the percent of HIV-1 Env-pseudoviruses that achieved an ID[sub]50[/sub] > 20
The analysis of LN-architecture and germinal center (GC) topology revealed greater follicular GC disruption in HIV+ non–neutralizers compared to neutralizers as measured by total CD20hi/dim Ki67+ follicular area (p<0.001), light-zone (LZ)/dark zone (DZ) polarization and level of IgD+ involution. Neutralization activity was associated with an increased CD4+ T-cell memory (CD27 hi/lo CD45RO hi) frequency (p=0.026). Higher frequencies of activated (CD95+) ICOS+ and CD57+ expressing Tfh were also observed in neutralizers, consistent with potentially an increased capacity for optimal T-cell help. In addition, a lower frequency of unswitched CD27hi IgD+ memory B cells was found in neutralizers compared to non-neutralizers when B-cell populations were examined (p=0.030).
Neutralizing activity is associated with a greater degree of follicular GC preservation in the LN of chronically infected HIV individuals, higher levels of Tfh differentiation and lower frequencies of unswitched memory B cells. Thus, the implementation of strategies directed at preserving GC architecture during viremia may hold particular promise for the generation of broadly neutralizing antibodies in individuals affected by HIV.