Treatment with Anti‐PD‐L1 Antibody improves antimicrobial immunity during burn wound Sepsis

Abstract

BackgroundPatients with large burns are highly susceptible to infection and sepsis, partly due to immune system dysfunction. Lymphocyte dysfunction is increasingly being recognized as playing a key role in sepsis pathophysiology. Previous studies show that, the interaction between programmed death‐1 (PD‐1) on T cells and its ligand, programmed death ligand‐1 (PD‐L1) on antigen presenting cells, will inhibit T cell functions and significantly contribute to sepsis‐induced T cell dysfunction. This not only causes impaired ability to clear existing pathogens, but also renders the host susceptible to opportunistic infections. The factors that contribute to burn‐associated immune system dysfunction are not completely understood. Clinical studies from our laboratory show that PD‐1 and PD‐L1 expression are increased on circulating T cells and monocytes, respectively, from patients who ultimately die following severe burns, as compared to survivors. Therefore, studies were undertaken to evaluate the therapeutic potential of anti‐PD‐L1 antibody in a clinically relevant mouse model of burn wound infection and sepsis.Methods10–12 weeks old male BALB/c mice were subjected to 35% total body surface area full thickness burn and the wound was infected with Pseudomonas aeruginosa on day 4 post‐burn. Flow cytometry was used to characterize the numbers and phenotype of CD4+ and CD8+ T cells and antigen presenting cells in spleen and wound draining lymph nodes. Anti‐PD‐L1 antibody (50 μg, i.p.) was administered on day 3 following burn injury (one day prior to infection) to determine its effect on the pathogenesis of burn wound infection.ResultsSepsis was evident in our model of burn wound infection, as Pseudomonas aeruginosa was detected at significant levels in the blood and lungs of wound infected mice, leading to multi‐organ injury (increased markers of liver and kidney injury) and high mortality rate (>90%) by seven days post infection. The absolute lymphocyte count was significantly decreased (>80%) in the blood at day 2 post infection. Sepsis caused an increase in the expression of PD‐L1 on antigen presenting cells, including dendritic cells, F4/80+ macrophages and Ly6C+ inflammatory monocytes in the spleen. There was no change in PD‐1 expression on CD4+ and CD8+ T cells. Treatment with anti‐PD‐L1 antibody inhibited the systemic spread of infection, as evidenced by significantly decreased levels of Pseudomonas aeruginosa in the blood and lungs of anti‐PD‐L1 treated mice as compared to mice treated with isotype control antibody. Importantly, treatment with anti‐PD‐L1 antibody significantly improved survival rate (>80%) post sepsis, as compared to mice treated with isotype control antibody (<10% survival).ConclusionAnti‐PD‐L1 antibody represents a novel therapeutic agent, with a strong potential to reverse immunosuppression and improve survival during burn wound sepsis, which merits further investigation.Support or Funding InformationN.K.P is supported by a Postdoctoral Grant from the American Heart Association (16POST29920007) and this work is also supported by the National Institute of Health grant NIH R01 GM66885 to E.R.S