PD-1 blockade following ART interruption enhances control of pathogenic SIV in rhesus macaques

Abstract

Programmed death-1 (PD-1) blockade during chronic Simian immunodeficiency virus (SIV) infection results in restoration of CD8 T-cell function and enhances viral control. Here, we tested the therapeutic benefits of PD-1 blockade administered soon after anti-retrovial therapy (ART) interruption (ATI) by treating SIV-infected and ART-suppressed macaques with either an anti-PD-1 antibody (n = 7) or saline (n = 4) at 4 wk after ATI. Following ATI, the plasma viremia increased rapidly in all animals, and the frequency of SIV-specific CD8 T cells also increased in some animals. PD-1 blockade post ATI resulted in higher proliferation of total memory CD8 and CD4 T cells and natural killer cells. PD-1 blockade also resulted in higher proliferation of SIV-specific CD8 T cells and promoted their differentiation toward better functional quality. Importantly, four out of the seven anti-PD-1 antibody-treated animals showed a rapid decline in plasma viremia by 100- to 2300-fold and this was observed only in animals that showed measurable SIV-specific CD8 T cells post PD-1 blockade. These results demonstrate that PD-1 blockade following ATI can significantly improve the function of anti-viral CD8 T cells and enhance viral control and strongly suggests its potential synergy with other immunotherapies that induce functional CD8 T-cell response under ART. These results have important implications for HIV cure research.

Keywords: HIV; HIV cure; PD-1; SIV.

Fig. 1.

PD-1 blockade post ATI enhances proliferation of CD8 T, CD4 T, and NK cells in the blood. (A) Schematic of monkey study design. (B and D) Temporal frequency of proliferating (K_i-67⁺) total CD8 (B) or CD4 (D) T cells post PD-1 blockade. (C and E) Frequency of K_i-67⁺ total, central memory (CD28⁺CD95⁺), effector memory (CD28⁻CD95⁺) CD8 (C), or CD4 (E) T cells at day 7 post PD-1 blockade. (F) Temporal frequency of proliferating NK cells. (G) Frequency of perforin⁺ and granzyme-B⁺ NK cells at day 7 post PD-1 blockade. The Mamu-A*01⁺ animals are identified with square symbol in (C), (G), and (E).

Fig. 2.

PD-1 blockade post ATI enhances the functional phenotype of SIV-Gag-CM9⁺ CD8 T cells in blood. (A) Representative fluorescence-activated cell sorter (FACS) plots showing the Gag-CM9 tetramer⁺ CD8 T cells. Numbers on the FACS plots represent the frequency of tetramer⁺ cells as a percent of total CD8 T cells. (B) Temporal frequency of Gag-CM9 tetramer⁺ CD8 T cells post ATI in anti-PD-1 Ab treated (n = 4 Mamu-A*01⁺) and control (n = 2 Mamu-A*01⁺) animals. (C–F) Frequency of tetramer⁺ cells coexpressing K_i-67 (C), CD28 (D), CCR7 (E), and CD127 (F) following PD-1 blockade.

Fig. 3.

PD-1 blockade after ATI improved cytokine producing function of SIV-specific CD8 T cells. (A) Representative flow plots showing the frequency of Gag-CM9 tetramer⁺ cells and IFN-γ⁺ CD8 T cells following stimulation with Gag-CM9 peptide. Numbers with bold red font on the FACS plots represent the percent of IFN-γ⁺ producing cells as a percent of tetramer⁺ cells. (B) Percent of IFN-γ⁺ producing cells as a percent of tetramer⁺ cells at multiple time points post PD-1 blockade. (C) Comparison of percent of IFN-γ⁺ producing cells as a percent of tetramer⁺ cells at day 7 post PD-1 blockade. (D) Temporal frequency of SIV-Gag-specific IFN-γ⁺ CD8 T cells in the blood. (E) Temporal frequency of SIV-Gag-specific IFN-γ⁺TNF-α⁺ CD8 T cells in the blood. (F) Temporal frequency of SIV-Gag-specific IFN-γ⁺ CD4 T cells in the blood. (G) Temporal frequency of SIV-Gag-specific IFN-γ⁺TNF-α⁺ CD4 T cells in the blood.

Fig. 4.

PD-1 blockade post ATI enhances SIV control. (A) Plasma SIV RNA viral levels post ATI for individual animals and after initiation of anti–PD-1 Ab or saline infusion. Limit of detection is 80 copies/mL indicated with a dotted horizontal line. (B) Comparison of plasma SIV RNA for individual RMs preblockade time point (week 4 post ATI) and dip (lowest measure between weeks 4 and 8 post ATI) post PD-1 blockade. (C) Comparison of set-point plasma SIV RNA levels (copies/mL) pre-ART and post ATI (week 30). (D) Association between SIV-specific IFN-γ⁺ CD8 T cells at peak post PD-1 blockade with SIV viral RNA levels at the dip in PD-1-treated animals and control animals.