A tonsillar PolyICLC/AT-2 SIV therapeutic vaccine maintains low viremia following antiretroviral therapy cessation

Abstract

Background: HIV-infected individuals rely on antiretroviral therapy (ART) to control viral replication. Despite abundant demonstrable benefits, the multiple limitations of ART point to the potential advantages of therapeutic vaccination approaches that could provide sustained host control of viral replication after discontinuation of ART. We provide evidence from a non-human primate model that a therapeutic vaccine applied to the tonsils can maintain low viral loads after cessation of ART.

Methodology/principal findings: Animals received 40 weeks of ART initiated 9 weeks after rectal SIVmac239 infection. During ART, animals were vaccinated (or not) with AT-2 inactivated SIVmac239 using CpG-C ISS-ODN (C274) or polyICLC as adjuvants. PolyICLC/AT-2 SIV vaccinated animals maintained viral loads <3×10(3) copies/ml for up to 16 weeks post-ART, whereas the C274/AT-2 SIV vaccinated and non-vaccinated animals' viremia ranged between 1×10(4)-4×10(5) copies/ml (p<0.03). Neutralizing Ab activity in plasma was increased by polyICLC/AT-2 tonsillar vaccination under ART, compared to controls (p<0.03). Subsequent vaccination of all animals with polyICLC/AT-2 SIV in the absence of ART did not alter viral loads. Other immune parameters measured in blood and tissues were comparable between groups.

Conclusions/significance: These results provide support for the potential benefit of mucosally delivered vaccines in therapeutic immunization strategies for control of AIDS virus infection.

Figure 1. Viral loads of polyICLC-treated animals are significantly lower, after cessation of ART.

(A) Plasma SIV RNA copies/ml were determined by PCR. Each symbol indicates an individual animal. The ART treatment period is indicated by the shaded grey box. Arrows indicate immunization time-point. (B) Average (geometric means) viral loads (±SEM) are shown for the ART-responding animals (5 in the C274/AT-2 SIV group, 5 in the polyICLC/AT-2 SIV group and 4 in the control group). Asterisks indicate significant differences between: polyICLC vs both C274 and controls at weeks 2, 4, 8 and 16, p<0.03; polyICLC vs C274 at weeks 3 and 10, p<0.02; polyICLC vs control at week 13, p<0.03. (C) Average Area Under the Curve (AUC) is shown for the ART-responding animals in each group (±SEM). p<0.03 for polyICLC vs C274 and p<0.02 for polyICLC vs control.

Figure 2. Similar SIV-specific responses in immunized and control animals.

(A) Average SIV-specific (to AT-2 SIV) IFNγ ELISPOT responses are illustrated (±SEM). SIV specific responses were determined by subtracting the appropriate MV-induced background. (B) Percentage of cytokine producing (IFNγ, TNFα, IL-2 and combinations) CD3⁺CD4⁺ (upper panel) and CD3⁺CD4⁻ (lower panel) cells were measured in PBMC, by flow cytometry at weeks 17–18 post-ART. Results shown in panels A and B (±SEM) are for 5 animals in the C274/AT-2 SIV group, 5 in the polyICLC/AT-2 SIV group and 4 in the control group.

Figure 3. PolyICLC/AT-2 SIV vaccination increases neutralizing Ab activity.

Neutralizing Ab titers in the plasma were determined before and after vaccination (vaccination on weeks 26, 32, 38, and 44 post infection). Levels were measured in samples taken 22 weeks after infection and 46 weeks post infection for all animals except CK25 (week 42) and EL02 and GJ65 (week 49) (asterisk). The titer (the last dilution tested at which infection was blocked) is shown for each animal and the mean for each group is marked by the horizontal bar. The circled symbols denote the animals that were ART partial or non-responders. Animal ID numbers are indicated for animals with outlier values relative to the rest of their respective groups.

Figure 4. Viral loads are not impacted by late immunization with polyICLC/AT-2 SIV without ART.

(A) Plasma viral loads were determined before, during and after treatment. Each symbol indicates an individual animal. Arrows indicate immunization time-point. (B) The average viremia (geometric means) for each group (±SEM) is shown. Asterisks denote the statistically significantly lower virus levels in the polyICLC group compared to the original C274 and/or control groups; p<0.04 for polyICLC vs C274 at weeks 23–46, p<0.03 for polyICLC vs control at weeks 20–34, for good ART responders. (C) Average AUC is shown for each group (±SEM) for the time period shown in panel A. Asterisks mark the statistically significant differences: polyICLC vs C274 at weeks 16–34, p<0.03; polyICLC vs control at weeks 16–34, p<0.03; polyICLC vs C274 at weeks 34–46, p<0.05. Each group's original treatment under ART is indicated in each panel.

Figure 5. SIV-specific T cell responses were similar across groups.

The average SIV-specific (to AT-2 SIV) IFNγ ELIPSOT responses during the vaccination are illustrated (±SEM). SIV specific responses were determined by subtracting the appropriate MV response.