Preexisting memory CD4+ T cells contribute to the primary response in an HIV-1 vaccine trial

Abstract

Naive and memory CD4+ T cells reactive with human immunodeficiency virus type 1 (HIV-1) are detectable in unexposed, unimmunized individuals. The contribution of preexisting CD4+ T cells to a primary immune response was investigated in 20 HIV-1-seronegative volunteers vaccinated with an HIV-1 envelope (Env) plasmid DNA prime and recombinant modified vaccinia virus Ankara (MVA) boost in the HVTN 106 vaccine trial (clinicaltrials.gov NCT02296541). Prevaccination naive or memory CD4+ T cell responses directed against peptide epitopes in Env were identified in 14 individuals. After priming with DNA, 40% (8/20) of the elicited responses matched epitopes detected in the corresponding preimmunization memory repertoires, and clonotypes were shared before and after vaccination in 2 representative volunteers. In contrast, there were no shared epitope specificities between the preimmunization memory compartment and responses detected after boosting with recombinant MVA expressing a heterologous Env. Preexisting memory CD4+ T cells therefore shape the early immune response to vaccination with a previously unencountered HIV-1 antigen.

Keywords: Cellular immune response; Clinical Trials; Immunology; T cells.

Figures

Figure 1. The preimmunization repertoire of Env-specific memory CD4+ T cells.

Preimmunization repertoires of 20 donors were screened for Env reactivity using the T cell library method with 2 pools of overlapping peptides collectively spanning the entire consensus sequence protein (ConS). Positive control wells included phytohemagglutinin (PHA) and IL-2. Proliferative responses are shown for memory CD4+ T cells isolated from all 20 volunteers before vaccination (V2). Data are shown after background subtraction (mean ± SD). Positive responses were defined as greater than 3,000 cpm, with a stimulation index greater than 5 (dotted line).

Figure 2. Precursor frequency and epitope specificity of preimmunization Env-reactive naive and memory CD4+ T cells.

Env-reactive CD4+ T cell lines derived from the preimmunization naive and memory repertoires of 20 donors were mapped for epitope specificity. Precursor frequencies were calculated from the initial limiting dilution. (A) Naive and memory precursor frequencies for each specificity. Each symbol represents one CD4+ T cell line. Bars show mean values. (B) Epitope specificities and precursor frequencies determined for memory CD4+ T cells.

Figure 3. Epitope specificity of preimmunization and postvaccination Env-reactive CD4+ T cells.

Postvaccination CD4+ T cell responses were mapped and quantified at V7 using ex vivo and cultured IFN-γ ELISpot assays. (A) Heatmaps showing the combined epitope mapping data from all volunteers at V7 (left) alongside a comparison with the epitope mapping data from all 20 volunteers at V2 (right). Ex vivo results are shown if both ex vivo and cultured data were available. Mean values are shown. SFU, spot-forming unit. (B) Identification of matching epitope-specific responses in the preimmunization and postvaccination repertoires of 4 donors immunized with ConS DNA. The scale for ex vivo and cultured data is shown on the left y axis, and the scale for naive (yellow) or memory (orange) precursor frequencies is shown on the right y axis. Mean ± SEM.

Figure 4. Clonotype representation in the preimmunization and postvaccination repertoires of Env-reactive CD4+ T cells.

(A) CD4+ T cell clones were derived from preimmunization repertoires (V2) of 2 volunteers, 106-009 and 106-039, who showed matching postvaccination responses to ConS peptides (V7). Expressed TRA and TRB gene rearrangements were sequenced from mRNA. (B) Protein-level expression of the corresponding TCR Vβ segments at each time point determined by flow cytometry. Plots are gated on live CD3+ cells. (C) The postvaccination TCR Vβ–defined populations shown in B were isolated by FACS to purity. Expressed TRB gene rearrangements were sequenced from mRNA. Each pie chart segment represents a distinct clonotype and the matching clonotype sequences from A.