The adjuvant effects of the toll-like receptor 3 ligand polyinosinic-cytidylic acid poly (I:C) on antigen-specific CD8+ T cell responses are partially dependent on NK cells with the induction of a beneficial cytokine milieu
Introduction
Conserved microbial structures, termed pathogen-associated molecular patterns (PAMPs), are recognized by receptors of the innate immune system such as Toll-like receptors (TLRs) [1], [2]. Ligation of TLRs by their specific PAMPs results in the induction of pro-inflammatory mediators, including NF-κB, cytokines, and costimulatory molecules by cells of the innate immune system such as NK cells, macrophages (Mϕ), and dendritic cells (DCs). So far, 13 TLRs (1–13) have been found to be expressed on the cell surface of sentinel cells of the innate immune system [3]. Double-stranded RNA (dsRNA), a natural product of viral replication, has recently been identified as a specific ligand for TLR3 [4]. TLR3 is expressed on NK cells, Mϕ, DCs [5], and CD4 T cells [6]. Polyriboinosinic polyribocytidylic acid (poly (I:C)), a synthetic dsRNA mimic copolymer, is also a specific TLR3 ligand [7], [8].
Recent in vitro studies have shown that poly (I:C) can efficiently mature both murine and human DCs, and induce cross-presentation of different antigens by these cells [9], [10], [11], [12]. Furthermore, stimulation of TLR3 alone or in combination with CD40 triggering during active vaccination appears to enhance CD8+ T cell responses [13], [14], [15]. We have found that treatment of poly (I:C) can enhance antigen-specific CD8+ T cell responses to both self and non-self peptides, and is associated with effective antitumor immunity [16]. However, the mechanisms underlying the adjuvant effects of poly (I:C) on CD8+ T cells have not been fully explored in vivo. Several components of the innate immune system including NK cells, Mϕ, and DCs are considered to be the initial targets of PAMPs [3]. After ligation of TLRs, these cells produce an array of inflammatory cytokines and chemokines, leading to autocrine and paracrine stimulation of both the innate and adaptive immune systems [17]. Previous studies have shown that ligation of TLR3 by poly (I:C) results in the activation of DCs, as well as the production of inflammatory cytokines by NK cells, and DCs [4], [18], [19], [20], [21]. However, it remains to be determined which of the pleiomorphic effects of poly (I:C) is primarily responsible for mediating the adjuvant effects of this agent on adaptive CD8+ T cell responses in vivo.
Specific goals of the present study include defining the following parameters associated with poly (I:C) treatment: (1) the optimal timing of treatment, (2) the early activation kinetics of the innate immune system following treatment, (3) the nature, kinetics, source, reciprocal interaction, and adjuvant effects of cytokines induced by poly (I:C), and (4) the role of NK cells in mediating the adjuvant effects of poly (I:C). Ultimately, defining the mechanisms underlying the adjuvant effects of poly (I:C) on antigen-specific CD8+ T cells will improve our ability to rationally and predictably apply this promising TLR3 agonist as a cancer vaccine adjuvant.
Section snippets
Mice
B6.SJL (Ly5.1), C57BL/6 (Ly5.2), BALB/c, TNF-α, IL-6, IL-12Rβ2, and IFN-γ deficient mice on the C57BL/6 background, and CD1 deficient mice on the BALB/c background were purchased from Jackson Laboratory (Bar Harbor, ME). IFN-α/βR KO mice are a gift from Dr. Jonathan Sprent (The Scripps Research Institute, La Jolla, CA). IL-15 deficient mice were obtained from Taconic (Germantown, NY). OT-1 TCR transgenic (Vα2/Vβ5) mice (Jackson Lab.) were bred with B6.SJL mice to generate Ly5.1/Ly5.1 mice
The adjuvant effects of poly (I:C) are exquisitely dependent on the timing of its treatment relative to peptide vaccination
We have previously shown that treatment of poly (I:C) at the time of peptide vaccination results in a dramatic enhancement of the antigen-specific CD8+ T cell response, with decreased CD8+ T cell apoptosis, and enhanced CD8+ T cell proliferation and function [16]. To initially explore the mechanisms underlying the adjuvant effects of poly (I:C) treatment, the response to peptide vaccination and poly (I:C) treatment was determined where poly (I:C) was administered immediately before, at the time
Discussion
Primary CD8+ T cell responses are characterized by a dramatic expansion phase followed by an equally dramatic contraction phase [29]. It is becoming increasingly apparent that cytokines may be involved in modulating this process [30], [31], and that the timing of cytokine production and/or treatment may significantly impact on the survival of CD8+ T cells [22], [32], [33], [34], [35], [36], [37], [38]. We have recently demonstrated that poly (I:C) treatment at the time of peptide vaccination
Acknowledgement
This work was supported by the National Institutes of Health Grant 1 R01 CA94856-01.
References (68)
- et al.
Innate immunity: impact on the adaptive immune response
Curr Opin Immunol
(1997) - et al.
Establishment of a monoclonal antibody against human Toll-like receptor 3 that blocks double-stranded RNA-mediated signaling
Biochem Biophys Res Commun
(2002) - et al.
Cytokines as a link between innate and adaptive antitumor immunity
Trends Immunol
(2002) - et al.
CTLA-4 blockade reverses CD8+ T cell tolerance to tumor by a CD4+ T cell- and IL-2-dependent mechanism
Immunity
(1999) - et al.
Poly I:C prevents T cell-mediated hepatitis via an NK-dependent mechanism
J Hepatol
(2006) - et al.
Involvement of natural killer cells in PolyI:C-induced liver injury
J Hepatol
(2004) - et al.
Apoptosis: an overview of the process and its relevance in disease
Adv Pharmacol
(1997) - et al.
IFN-gamma production by antigen-presenting cells: mechanisms emerge
Trends Immunol
(2001) - et al.
The interferon system and interferon regulatory factor transcription factors—studies from gene knockout mice
Cytokine Growth Factor Rev
(2001) - et al.
The human cytotoxic T cell granule serine protease granzyme H has chymotrypsin-like (chymase) activity and is taken up into cytoplasmic vesicles reminiscent of granzyme B-containing endosomes
J Biol Chem
(1999)