Protective anti‐mycobacterial T cell responses through exquisite in vivo activation of vaccine‐targeted dendritic cells

Abstract

Vaccine efficacy largely depends upon DC targeting and activation. The most potent TLR soluble ligands induce diffuse DC activation, which may be associated with marked pro‐inflammatory responses and possibly adverse effects. This raises the concern that effective vaccine adjuvants may similarly rely on widespread DC activation. Using a promising candidate vaccine against tuberculosis (fusion protein of Ag85B and 6‐kDa early secretory antigenic target (ESAT‐6)) formulated in the potent IC31® adjuvant, DC targeting and activation was studied in vivo, following the fate of antigen and adjuvant in the draining lymph nodes, to define the magnitude of DC targeting/activation required in vivo to induce protective vaccine responses. Unexpectedly, protective IFN‐γ‐mediated Ag85B‐ESAT‐6/IC31® responses were associated to the activation of a minute population (less than 0.3%) of CD11c+ lymph node DC, without detectable systemic pro‐inflammatory responses. This activated peripheral tissue‐derived DC population, characterized by enhanced CD80, CD86, CD40 and IL‐12p40 expression, was only identified when focusing on adjuvant‐ or antigen‐labeled CD11c+ DC, which were found to support T cell proliferation. Immunization with aluminum hydroxide adjuvant (Alum) resulted in a similar proportion of antigen‐associated DC but without detectable enhancement of CD80, CD86, CD40 or IL‐12p40 expression. Thus, potent protective IFN‐γ‐producing responses may be elicited by the exquisite activation of a minute number of in vivo targeted DC.

IC31®, a Two‐Component Novel Adjuvant Mixed with a Conjugate Vaccine Enhances Protective Immunity against Pneumococcal Disease in Neonatal Mice

“…We have shown that alum-enhanced neonatal Ab response to meningococcal protein antigens, but serum bactericidal activity which is a surrogate for protective efficacy [36] was less enhanced than if Th-promoting adjuvants such as CpG-ODN or LT-K63 were given with the vaccine [37]. Recently, Siegrist et al [23] showed enhanced IFN-c production in mice receiving IC31 Ò , whereas alum only enhanced IL-5 production, which was in accordance with enhanced expression of co-stimulatory molecules and IL12-p40 of vaccineassociated DC by IC31 but not alum.…”

“…Although KLK by itself induces a Th2-biased cytokine profile [19], IC31 Ò enhances a strong Th1 response detected by high interferon (IFN)-c levels [20][21][22] even in aged mice [22]. IC31 Ò elicits a potent but focused dendritic cell (DC) activation without triggering bystander proinflammatory responses [23]. Based on these results we expected that IC31 Ò could be a suitable adjuvant to enhance the weak neonatal immune responses and correct the Th2 bias.…”

Synchronization of Dendritic Cell Activation and Antigen Exposure Is Required for the Induction of Th1/Th17 Responses

“…Cell preparation, cell staining, and flow cytometry For T cell analysis, cells from the spleen or, as indicated, the draining LN (dLN) were obtained by homogenization, whereas for APC analysis, dLN were digested as previously described (22,24). The brachial and axillary LN were harvested after s.c. immunization at the scruff of the neck and the mediastinal LN after i.p.…”

“…Cytokines were determined by ELISA (72-h stimulation, IFN-g, IL-5, IL-10, TNF-a, IL-17, TGF-b), ELISPOT assay (48-h simulation, IFN-g, IL-5), and intracellular cytokine staining by FACS (6-h stimulation, IFN-g, TNF-a, IL-2) as previously described (22,24).…”

A high ratio of IC31®adjuvant to antigen is necessary for H4 TB vaccine immunomodulation

“…The DCs subsequently drain to lymph nodes where they stimulate specific immunity. 10,11 Recent work in mice suggests protective immunity induced by H4-IC31 is highly sensitive to antigen dose, 12 while a clinical response to a similar vaccine was directly influenced by the adjuvant dose. 13 Understanding the functional relationship between the adjuvant and antigen is critical to define vaccine formulations.…”