Enhancing SIV-specific immunity in vivo by PD-1 blockade

Abstract

Chronic immunodeficiency virus infections are characterized by dysfunctional cellular and humoral antiviral immune responses. As such, immune modulatory therapies that enhance and/or restore the function of virus-specific immunity may protect from disease progression. Here we investigate the safety and immune restoration potential of blockade of the co-inhibitory receptor programmed death 1 (PD-1) during chronic simian immunodeficiency virus (SIV) infection in macaques. We demonstrate that PD-1 blockade using an antibody to PD-1 is well tolerated and results in rapid expansion of virus-specific CD8 T cells with improved functional quality. This enhanced T-cell immunity was seen in the blood and also in the gut, a major reservoir of SIV infection. PD-1 blockade also resulted in proliferation of memory B cells and increases in SIV envelope-specific antibody. These improved immune responses were associated with significant reductions in plasma viral load and also prolonged the survival of SIV-infected macaques. Blockade was effective during the early (week 10) as well as late ( approximately week 90) phases of chronic infection even under conditions of severe lymphopenia. These results demonstrate enhancement of both cellular and humoral immune responses during a pathogenic immunodeficiency virus infection by blocking a single inhibitory pathway and identify a novel therapeutic approach for control of human immunodeficiency virus infections.

Figure 1. In vivo PD-1 blockade during chronic SIV infection increases the Gag CM9-specific CD8 T cells with improved functional quality in both blood and gut

a) Representative FACS plots for the macaque RRk10. The magnitude and phenotype of Gag CM9-tetramer positive CD8 T cells in blood (b) and gut (colorectal mucosal tissue) (c). Representative FACS plots are shown on the left and summary for all Mamu A*01 positive animals is shown on the right. Numbers on the FACS plots represent the frequency of tetramer positive cells as a percent of total CD8 T cells. Arrows and vertical dotted lines indicate anti-PD-1 Ab or control Ab treatment.

Figure 2. In vivo PD-1 blockade during chronic SIV infection increases the polyfunctional virus-specific CD8 T cells

a) Frequency of Gag-specific cytokine secreting CD8 T cells as a percent of total CD8 T cells. Representative FACS plots are shown on the left and summary for the group is shown on the right. Arrows and vertical dotted lines indicate anti-PD-1 Ab or control Ab treatment. Green lines represent anti-PD-1 Ab treated macaques and red lines represent control Ab treated macaques. b) Cytokine co-expression subsets expressed as a percent of total cytokine positive cells. Mean for the group is shown.

Figure 3. In vivo PD-1 blockade during chronic SIV infection enhances SIV-specific humoral immunity

a) Expression of PD-1 on memory (CD20+CD27+CD21-) and naïve (CD20+CD27-CD21+) B cells in blood following SIV infection and prior to in vivo PD-1 blockade. b) Titers of anti-SIV Env binding Ab in serum following blockade. c) Ki-67 expression (marker for proliferation) on memory and naïve B cells following blockade. Numbers on the FACS plots represent Ki-67 positive cells as a percent of respective total cells. Macaques RAf11 and RJd11 were treated simultaneously with anti-PD-1 Ab and anti-retroviral therapy at 22 weeks post SIV infection.

Figure 4. In vivo PD-1 blockade reduces plasma viremia and prolongs survival of SIV-infected macaques

Plasma viral load in a) macaques treated with anti-PD-1 Ab during the early chronic phase b) macaques treated with anti-PD-1 Ab during the late chronic phase and c) macaques treated with control Ab during the early/late chronic phase of SIV infection. d) Fold reduction in plasma viral load between day 0 and day 28 (early chronic study) or day 0 and day 21 (late chronic study). e) Survival of SIV-infected macaques following PD-1 blockade. =, death of animal.