PD-1 blockade during chronic SIV infection reduces hyperimmune activation and microbial translocation in rhesus macaques

Abstract

Hyperimmune activation is a strong predictor of disease progression during pathogenic immunodeficiency virus infections and is mediated in part by sustained type I IFN signaling in response to adventitious microbial infection. The immune inhibitory receptor programmed death-1 (PD-1) regulates functional exhaustion of virus-specific CD8(+) T cells during chronic infections, and in vivo PD-1 blockade has been shown to improve viral control of SIV. Here, we show that PD-1 blockade during chronic SIV infection markedly reduced the expression of transcripts associated with type I IFN signaling in the blood and colorectal tissue of rhesus macaques (RMs). The effect of PD-1 blockade on type I IFN signaling was durable and persisted even under conditions of high viremia. Reduced type I IFN signaling was associated with enhanced expression of some of the junction-associated genes in colorectal tissue and with a profound decrease in plasma LPS levels, suggesting a possible repair of gut-associated junctions and decreased microbial translocation into the blood. PD-1 blockade enhanced immunity to gut-resident pathogenic bacteria, control of gut-associated opportunistic infections, and survival of SIV-infected RMs. Our results suggest PD-1 blockade as a potential novel therapeutic approach to enhance combination antiretroviral therapy by suppressing hyperimmune activation in HIV-infected individuals.

Figure 1. PD-1 blockade downregulates type I IFN responses in SIV-infected RMs.

(A) IPA of differentially regulated genes (P < 0.05 and >1.5-fold change) in blood and colorectum (Gut) of SIV-infected RMs at 14 days following PD-1 blockade. Percentage of genes that were up- or downregulated in a pathway in the PD-1 antibody–treated (n = 5) compared with control antibody–treated group (n = 3) are shown. (B) Heat maps of ISGs in SIV-negative (Uninfected; n = 4), control antibody–treated (Control, n = 3), and PD-1 antibody–treated (PD-1, n = 5) animals that were significantly downregulated at 14 days following PD-1 blockade. Mean mRNA expression for each group is shown. The fold changes (FC) in the PD-1 group compared with control group are shown. (C) qPCR analysis of MX1 mRNA in gut tissue of early chronic animals. Fold changes represent fold increase relative to preinfection value of the same RM. Arrows indicate the time of antibody treatments. (D) SIV RNA copies in the gut of PD-1– and control antibody–treated early chronic RMs. *P < 0.05.

Figure 2. PD-1 blockade enhances gut junction–associated gene expression and reduces microbial translocation in SIV-infected RMs.

(A) Heat map of junction-associated genes in the control antibody–treated (n = 3) and PD-1 antibody–treated (n = 5) animals that were significantly upregulated at 14 days following PD-1 blockade. Mean mRNA expression for each group is shown. The fold changes in the PD-1 group compared with the control antibody–treated group are shown. (B) qPCR analysis of CLDN5, JAM2, and Cx45 junctional genes in gut tissue. Fold changes represent fold increase relative to the average expression in 6 SIV-infected control RMs. (C) LPS levels in plasma in PD-1 antibody– and control antibody–treated SIV-infected RMs. Arrows indicate the time of antibody treatments. The LPS levels in the PD-1 group were significantly lower (P = 0.009; Wilcoxon rank-sum test) than in the control group at 90 days following blockade.

Figure 3. In vivo PD-1 blockade enhances immunity to pathogenic gut bacteria, decreases occurrence of opportunistic infections, and prolongs survival of SIV-infected RMs.

(A) Anti-Campylobacter antibody titers in serum. (B) IFN-γ⁺ CD8⁺ T cell responses in blood. Pre, 0–25 days prior to initiation of antibody therapy. IFN-γ⁺CD8⁺ T cell responses in the PD-1 group at 14 days and 90 days following blockade were significantly greater than in the control group (P < 0.01; Wilcoxon rank-sum test). (C) Incidence of non-SIV-related opportunistic infections in controls (8 no antibody–treated and 3 control antibody–treated) or PD-1 antibody–treated (PD-1) SIV-infected early chronic RMs. See Supplemental Tables 1 and 2 for details about the nature of opportunistic infections. Shaded region indicates the period of antibody treatments. *P = 0.01, t test. (D) Kaplan-Meier survival plot of SIV-infected RMs shown in C. The 8 SIV-infected RMs in the “no antibody” control group were selected based on set point plasma viral load (between 10⁶ and 10⁷) to match with the set point viral load in the early chronic PD-1 group at the initiation of PD-1 blockade.