Gamma-irradiated bacille calmette-guÉrin vaccination does not modulate the innate immune response during experimental human endotoxemia

Introduction

Recent insights in sepsis pathology have led to the view that not the initial hyperinflammatory state, but rather a profoundly suppressed state of the immune system, also called immunoparalysis, accounts for the majority of sepsis-related deaths. Therefore, reconstitution of immunocompetence in sepsis is emerging as a promising therapeutic target to improve outcome. Bacille Calmette-Guérin (BCG) vaccine not only protects against tuberculosis, but exerts beneficial effects on other infectious diseases as well. These non-specific effects of BCG seem to be mediated by potentiation of adaptive immunity through heterologous effects, as well as epigenetic functional reprogramming of innate immune cells to an enhanced phenotype, a process described as 'trained immunity', which has been shown in vitro, ex vivo, and in animal models. Therefore, BCG-vaccination could represent a novel therapeutic option to treat sepsis-induced immunoparalysis, although its immunomodulatory effects in humans in vivo have not yet been investigated. Furthermore, the live BCG vaccine presents a potential risk of disseminated disease in immunoparalyzed patients, which can be circumvented by inactivating the vaccine through gamma-irradiation.

Objectives

To determine the effects of gamma-irradiated BCG-vaccination on the in vivo innate immune responses induced by human endotoxemia. Also, to determine the effects of gamma-irradiated BCG-vaccination on ex vivo responsiveness of leukocytes to various inflammatory stimuli.

Methods

In a randomized double blind placebo-controlled study, healthy male volunteers were vaccinated with gamma-irradiated BCG (n = 10) or placebo (n = 10) and received 1 ng/kg lipopolysaccharide (LPS) intravenously on day 5 after vaccination to assess the in vivo immune response. Peripheral blood mononuclear cells were stimulated with various related and unrelated pathogens 5, 8 to 10, and 25 to 35 days after vaccination to assess ex vivo immune responses.

Results

LPS administration elicited a profound systemic immune response, characterized by increased levels of pro-and anti-inflammatory cytokines, hemodynamic changes, and flu-like symptoms. However, BCG neither modulated this in vivo immune response (Figure 1), nor ex vivo leukocyte responses at any time-point (Figure 2).

Figure 1

In the panels A and B, median values of pro-inflammatory cytokines TNF-α and Il-6 are depicted while in panel C median values of the anti-inflammatory cytokine IL-10 is shown (n = 10 per group). Panels D-F depict median ± interquartile range of area under curve (AUC) of the respective cytokines (n = 10 per group). P values calculated using Mann-Whitney U-tests.

Figure 2

Data expressed as median and interquartile range of the fold change compared with day 1 (before vaccination) (n = 10 per group). p-values calculated using repeated measures two-way analysis of variance (ANOVA, time and interaction terms) on log transformed data. Day 6 was the endotoxemia experiment day.

Conclusions

Gamma-irradiated BCG does not modulate the innate immune response in vivo in humans and is therefore unlikely to represent an effective treatment option to restore immunocompetence in patients with sepsis-induced immunoparalysis.

Grant Acknowledgment

M.G.N. was supported by a Vici grant of the Netherlands Organization for Scientific Research and an ERC Consolidator Grant (#310372).