Immunization with an SIV-based IDLV Expressing HIV-1 Env 1086 Clade C Elicits Durable Humoral and Cellular Responses in Rhesus Macaques

Abstract

The design of an effective HIV-1 vaccine remains a major challenge. Several vaccine strategies based on viral vectors have been evaluated in preclinical and clinical trials, with largely disappointing results. Integrase defective lentiviral vectors (IDLV) represent a promising vaccine candidate given their ability to induce durable and protective immune responses in mice after a single immunization. Here, we evaluated the immunogenicity of a SIV-based IDLV in nonhuman primates. Six rhesus monkeys were primed intramuscularly with IDLV-Env and boosted with the same vector after 1 year. A single immunization with IDLV-Env induced broad humoral and cellular immune responses that waned over time but were still detectable at 1 year postprime. The boost with IDLV-Env performed at 1 year from the prime induced a remarkable increase in both antibodies and T-cell responses. Antibody binding specificity showed a predominant cross-clade gp120-directed response. Monkeys' sera efficiently blocked anti-V2 and anti-CD4 binding site antibodies, neutralized the tier 1 MW965.26 pseudovirus and mediated antibody-dependent cellular cytotoxicity (ADCC). Durable polyfunctional Env-specific T-cell responses were also elicited. Our study demonstrates that an IDLV-Env-based vaccine induces functional, comprehensive, and durable immune responses in Rhesus macaques. These results support further evaluation of IDLV as a new HIV-1 vaccine delivery platform.

Figure 1

IDLV-Env immunization induced durable Env-specific antibody responses. (a) Schematic representation of the self-inactivating vector (SIN) used in this study. CMV, cytomegalovirus immediate-early promoter; R, repeat element; U5, 5' untranslated region; U3, 3' untranslated region; PBS, primer binding site; SD, splice donor site; Ψ, packaging signal; cPPT, central polypurine tract; RRE, Rev response element; SA, splice acceptor site; ▵U3, SIN deletion in U3 region of 3' LTR; WPRE, woodchuck hepatitis virus post-transcriptional regulatory element; bGHpA, bovine growth hormone polyadenylation signal. (b–e) Anti C.1086 gp140 binding Abs induced by IDLV-Env immunization. The magnitude and durability of anti-Env IgG were measured in six animals in both plasma (b and c, Ab titer and concentration are shown, respectively) and mucosal secretions (d and e). Results for saliva and rectal Abs expressed as µg of HIV-specific IgG versus mg of total IgG, in order to account for differences in volume of fluid absorbed by the weck-cel sponges between animals. Lines indicate the predicted mean values at each time point as estimated by a system of piecewise linear regressions including all anti-Env IgG measurements within a structural equation modelling (SEM) frame work.

Figure 2

Conformational Binding Specificities and ADCC activity of IDLV-Env induced Abs. Blocking of two V2-specific mAbs, CH58 (a) and CH59 (b), was assessed on plasma samples collected at the peak response of binding Abs, post-prime and post boost. (c) Blocking activity against the V1/V2 specific broadly neutralizing mAb (bNab) CH01, the V1/V2-specific bNab PG9 and the CD4-binding site-specific bNab CH106 was assessed on plasma samples postboost. Blocking of soluble CD4 binding to gp120 is also shown. (d) Plasma ADCC peak activity. ADCC activity against target cells infected with a molecular clone designed to encode the HIV-1 subtype C 1086.C was measured using the GTL assay. ADCC activity was detected in three out of six animals after the first immunization and in all animals postboost (serum dilution 1:100; cut off: 15%).

Figure 3

Env-specific T-cell responses. (a) IFN-γ ELISPOT responses. Persistent cellular immunity was developed in all animals. Results are expressed as mean IFN-γ secreting cells, measured as spot forming cells (SFC) per million PBMC, at different time points. Error bars denote mean with SEM. (b) Total Env-specific CD4+ T cells producing IFN-γ, IL-2, and TNFα. IDLV-Env immunization induced Env-specific CD4+ T-cell response in all animals. Data are shown as percent of total CD4+ CD69+ cytokine+ T cells. Dots represent individual responses measured at the indicated time points. Horizontal lines show the median values at a given time point. (c) Polyfunctional Env-specific CD4+ T cells at indicated time point postprime (left panels) and postboost (right panels). Percentage of single, double, and triple cytokine producing CD4+ T cells are shown. Phenotypes of CD4+ TFNα+ T cells are illustrated in the pie chart, as a proportion of CM (central memory), TM (transitional memory), and EM (effector memory) T cells.

Figure 4

Env-specific CD8+ T-cell response. (a) IDLV-Env immunization induced Env-specific CD8+ T-cell responses. Data are shown as percent of total CD8+ CD69+ cytokine+ T cells. (b) Polyfunctional Env-specific CD8+ T cells from monkey 4461 postprime (left panels) and postboost (right panels). Phenotype of CD8+ TNF-α+ + T cells are shown in the pie chart. CM, central memory; EM, effector memory; TM, transitional memory.