Therapeutic Vaccination Refocuses T-cell Responses Towards Conserved Regions of HIV-1 in Early Treated Individuals (BCN 01 study)

Abstract

Background: Strong and broad antiviral T-cell responses targeting vulnerable sites of HIV-1 will likely be a critical component for any effective cure strategy.

Methods: BCN01 trial was a phase I, open-label, non-randomized, multicenter study in HIV-1-positive individuals diagnosed and treated during early HIV-1 infection to evaluate two vaccination regimen arms, which differed in the time (8 versus 24 week) between the ChAdV63.HIVconsv prime and MVA.HIVconsv boost vaccinations. The primary outcome was safety. Secondary endpoints included frequencies of vaccine-induced IFN-γ⁺ CD8⁺ T cells, in vitro virus-inhibitory capacity, plasma HIV-1 RNA and total CD4⁺ T-cells associated HIV-1 DNA. (NCT01712425).

Findings: No differences in safety, peak magnitude or durability of vaccine-induced responses were observed between long and short interval vaccination arms. Grade 1/2 local and systemic post-vaccination events occurred in 22/24 individuals and resolved within 3 days. Weak responses to conserved HIV-1 regions were detected in 50% of the individuals before cART initiation, representing median of less than 10% of their total HIV-1-specific T cells. All participants significantly elevated these subdominant T-cell responses, which after MVA.HIVconsv peaked at median (range) of 938 (73-6,805) IFN-γ SFU/10⁶ PBMC, representing on average 58% of their total anti-HIV-1 T cells. The decay in the size of the HIV-1 reservoir was consistent with the first year of early cART initiation in both arms.

Interpretation: Heterologous prime-boost vaccination with ChAdV63-MVA/HIVconsv was well-tolerated and refocused pre-cART T-cell responses towards more protective epitopes, in which immune escape is frequently associated with reduced HIV-1 replicative fitness and which are common to most global HIV-1 variants.

Funding: HIVACAT Catalan research program for an HIV vaccine and Fundació Gloria Soler. Vaccine manufacture was jointly funded by the Medical Research Council (MRC) UK and the UK Department for International Development (DFID) under the MRC/DFID Concordat agreements (G0701669.

Research in context: Evidence Before this Study: T cells play an important role in the control of HIV infection and may be particularly useful for HIV-1 cure by killing cells with reactivated HIV-1. Evidence is emerging that not all T-cell responses are protective and mainly only those targeting conserved regions of HIV-1 proteins are effective, but typically immunologically subdominant, while those recognizing hypervariable, easy-to-escape immunodominant 'decoys' do not control viremia and do not protect from a loss of CD4 T cells. We pioneered a vaccine strategy focusing T-cell responses on the most conserved regions of the HIV-1 proteome using an immunogen designated HIVconsv. T cells elicited by the HIVconsv vaccines in HIV-uninfected UK and Kenyan adults inhibited in vitro replication of HIV-1 isolates from 4 major global clades A, B, C and D.Added Value of this Study: The present study demonstrated the concept that epitopes subdominant in natural infection, when taken out of the context of the whole HIV-1 proteome and presented to the immune system by a potent simian adenovirus prime-poxvirus MVA boost regimen, can induce strong responses in patients on antiretroviral treatment and efficiently refocus HIV-1-specific T-cells to the protective epitopes delivered by the vaccine.Implications of all the Available Evidence: Nearly all HIV-1 vaccine strategies currently emphasize induction of broadly neutralizing Abs. The HIVconsv vaccine is one of a very few approaches focussing exclusively on elicitation of T cells and, therefore, can complement antibody induction for better prevention and cure. Given the cross-clade reach on the HIVconsv immunogen design, if efficient, the HIVconsv vaccines could be deployed globally. Effective vaccines will likely be a necessary component in combination with other available preventive measures for halting the HIV-1/AIDS epidemic.

Fig. 1

Disposition of participants and flow chart of the study. Consolidated Standards of Reporting Trials (CONSORT) flow diagram for the trial. Trial BCN 01 was a non-randomized, open label, sequence allocation study. CONSORT diagram delineates the study enrollment of 54 subjects who underwent sequential allocation to the long, short vaccination arms and the control group. Three subjects withdrew from the study before vaccination and/or week 24 and were replaced during enrollment period. All the participants in the Long and Short arms (b) received the ChAdV63.HIVconsv and MVA.HIVconsv vaccines, while 24 individuals in the control arm did not receive any vaccine. All 48 subjects completed the study as per protocol. The 24 vaccinated individuals were included in the safety and immunological analyses. Latent viral reservoir was measured in all 48 participants.

Fig. 2

Immune recovery after early treatment initiation. Evolution of pVL (a) and CD4 T-cell counts (b) and CD4/CD8 ratio (c) over the first 60 weeks after early-cART start with TDF/FTC/RAL in study participants.

Fig. 3

Vaccination immunogenicity. Cryopreserved, unexpanded PBMC were stimulated with pools P1–P6 of overlapping 15-mer peptides across the HIVconsv immunogen in an IFN-γ ELISPOT assay. (a) Schematic representation of the employed conserved regions in the HIV proteome from different HIV-1 clades included in the HIVconsv immunogen and distribution of the set of 6 peptide pools used for immunogenicity studies. Magnitude of total HIVconsv-specific responses (sum of SFU/10⁶ PBMC to pools P1-P6) over trial duration in the Long (b) and Short (c) vaccination arms are shown. (d) Total magnitude of HIVconsv-specific responses before and at peak immunogenicity in all vaccinated individuals. Median total frequency for the entire cohort is shown in red. Wilcoxon signed-rank p value is shown (e) Comparison of total magnitude of HIVconsv-specific responses between Long and Short vaccination arms at different time points of the clinical study. Mann–Whitney U-test is used for comparisons between Long and Short arms, and Wilcoxon signed-rank for comparisons within timepoints in the same individual.

Fig. 4

Breadth of vaccine-elicited HIVconsv-specific T-cells. (a) Comparison (ANOVA p-value) of the frequency of each participant's response to individual peptide pools at the peak immunogenicity time point after MVA.HIVconsv booster vaccination and (b) percentages of participants showing a detectable response (‘responders’) to HIVconsv peptide pools either before any vaccination (white bars) or at the peak immunogenicity time point (gray bars). (c) Comparison of the frequency of responses detected at the peak immunogenicity time point reflecting either de-novo induced or vaccine-boosted (‘pre-existing’) responses. Mann–Whitney U-test p value is shown.

Fig. 5

Changes in T-cell dominance patterns. (a) Schematic representation of the average distribution of total HIV-1 T-cells among different HIV-1 proteins at baseline (BL), its decrease during viral suppression and its expansion at peak responses. HIVconsv-specific responses are shown in purple. Sizes of pie charts are to scale with total frequencies of responses. Acc - Accessory proteins. (b) Median frequency of total HIVconsv-specific T cells (green bars) and changes in median HIVconsv immunodominance (red line) are shown over time. (c) Mean ± SD frequencies of T cells specific for OUT and CEF peptide pools are shown over time. (d) Comparison of the frequency of individual HIVconsv peptide pool responses detected in 15 study subjects using two sets of 15-mer peptides covering (P1-P6, + junctions) or avoiding (P1-P6, − junctions) the junctional regions is shown. Wilcoxon signed-rank t-test is used.

Fig. 6

High CD8⁺ T-cell viral inhibitory capacity and low levels of PD-1-expressing CD8⁺ T cells in early-treated individuals. (a) Comparison (Mann–Whitney U-test) of levels of CD8⁺ T-cell viral inhibition is shown for HIV-1_Bal (E:T 1:1) in individuals, who started cART during chronic infection (Chronic), participants in BCN 01 (Early_cART) 24 weeks after cART initiation and before any vaccination (C₀), and elite and viremic controllers (EC/VC). (b) Levels of CD8⁺ T-cell viral inhibition are shown for HIV-1_Bal (E:T ratio 1:1, 1:2 and 1:10) for individuals in the Long and Short Arms before vaccination (C₀), at peak of vaccine-induced immunogenicity (M_peak) and at the end of trial (M₂₄). (c) Expression of PD-1 by CD8⁺ T cells for the same time points.

Fig. 7

Changes in ultrasensitive pVL after MVA.HIVconsv booster vaccination and proviral DNA decay dynamics. (a) Copies of HIV-1 RNA per mL of plasma are shown for each vaccine group just before MVA.HIVconsv (M₀) and 1 week later (M₁) with censored values below the limit of detection shown in gray. Prentice-Wilcoxon p values are shown. (b) Correlation (Spearman r) between total frequency of HIVconsv-specific T cells at the peak immunogenicity timepoint and the absolute increase in pVL. (c) Total HIV-1 DNA copies/10⁶ CD4⁺ T cells for each vaccination group are shown at week 24 (before vaccination) and at week 56/60 after treatment initiation (Wilcoxon signed-rank p values are shown for comparisons within timepoints in same individual) (d) Comparison (ANOVA) of fold change of proviral DNA over 1 year after viral suppression from week 24 of cART in all groups (mean ± SE).

Appendix Fig. 1

Correlation between baseline CD4 T-cell counts (left), CD4 T-cell counts increase at week 60 (right) and age of individuals at study entry is shown.

Appendix Fig. 2

Net frequencies of cells specific for each pool (color-coded) are shown for each participant. Participant's numbers are shown above the graphs, A and B corresponding to the Long and Short vaccination arms, respectively.

Appendix Fig. 3

Correlation between the baseline plasma viremia (log10 HIV-1 RNA copies/mL of plasma) and proviral HIV-1 DNA levels (log10 copies/106 CD4 + T cells) 24 (left) and 60 weeks (right) after treatment initiation in all vaccinated and non-vaccinated individuals (Spearman r).