The vaccine adjuvant alum inhibits IL‐12 by promoting PI3 kinase signaling while chitosan does not inhibit IL‐12 and enhances Th1 and Th17 responses

Abstract

Alum is the principal vaccine adjuvant for clinical applications but it is a poor inducer of cellular immunity and is not an optimal adjuvant for vaccines where Th1 responses are required for protection. The mechanism underlying the inefficiency of alum in promoting Th1 responses is not fully understood. We show that aluminium hydroxide, aluminium phosphate, and calcium phosphate adjuvants inhibit the secretion of the Th1 polarizing cytokine, IL-12 by dendritic cells (DCs). Alum selectively inhibited DC expression of the IL-12p35 subunit and the inhibitory effect results from adjuvantinduced PI3 kinase signaling. To develop a more effective adjuvant for promoting cellmediated immunity, we investigated alternative particulates and found that in contrast to alum, the cationic polysaccharide chitosan did not inhibit IL-12 secretion. A combination of chitosan and the TLR9 agonist CpG activated the NLRP3 inflammasome and enhanced secretion of IL-12 and the other key Th1 and Th17-cell polarizing cytokines. When used as an adjuvant, CpG-chitosan induced NLRP3-dependent antigen-specific Th1 and Th17 responses. A combination of alum and CpG also enhanced Th1 and Th17 responses but was less effective than CpG-chitosan. Therefore, chitosan is an attractive alternative to alum in adjuvants for vaccines where potent cell-mediated immunity is required. Keywords IntroductionThere is a pressing need for novel vaccine adjuvants that are effective in safely promoting cellular immunity for diseases including Correspondence: Dr. Ed C. Lavelle e-mail: lavellee@tcd.ie tuberculosis (TB), malaria, and HIV [1]. Alum is the most widely used adjuvant for clinical applications and has been used in multiple vaccines for the past 80 years. However, while alum is a very effective adjuvant for promoting humoral immunity and Th2 type * These authors contributed equally to this work. The inefficiency of alum and related adjuvants as activators of Th1 responses suggests that additional signals are required for particulates to effectively promote cell-mediated immunity. Indeed, it has been shown that combining alum with IL-12 enhanced IgG2a antibody and Th1 responses to an HIV antigen compared with alum alone [19]. Combinations of emulsions, alum, or microparticles with PAMPs, particularly TLR4 agonists, are being used to amplify adaptive immunity [20][21][22] and are under active investigation for inclusion in a new generation of vaccines. To advance the development of this new generation of vaccine adjuvants with greater potency, it is essential to optimize both the particulate and immunostimulatory adjuvants to produce systems that act in synergy to drive appropriate T-cell responses. A recent report suggests that co-administration of CpG with alum results in a suppression of Th1-dependent antigen-specific IgG2a responses compared with administration of CpG alone [23]. We demonstrate that alum strongly inhibits the secretion of TLR agonistinduced IL-12 by DCs and these inhibitory effects are dependent on PI3 kinase signaling. In contrast to a...

Involvement of CD300a Phosphatidylserine Immunoreceptor in Aluminum Salt Adjuvant–Induced Th2 Responses

“…Because DCs do not produce IL-4, an important cytokine for Th2 differentiation, we assumed that Th2 suppression in CD300a-deficient mice might result from increased production of cytokines, such as IL-12 and IFN-g, which promote Th1 differentiation and/or proliferation (29)(30)(31). Indeed, recent reports have shown the possibility that alum inhibits production of IL-12p35 or IL-12p40 by DCs, resulting in promoted Th2 responses (5,32). However, we found that Il12p35, Il12p40, and Ifng mRNA expressions were not upregulated in CD300a-deficient iDCs.…”

Distinct Pathways of Humoral and Cellular Immunity Induced with the Mucosal Administration of a Nanoemulsion Adjuvant

“…Similar to the TLR-MyD88 deficiency, lack of either IL-12 or IL-12Rb1 had no detrimental effect on Ab responses with NE adjuvant. Taken together, these results demonstrate that W 80 5EC NE adjuvant mediates a balanced cellular response involving both IL-12-dependent Th-1 and Th-17 cellular immunity and IL-12-independent humoral immunity, a process that is fundamentally different from the activity of alum adjuvant (79)(80)(81).…”

On vaccine's adjuvants and autoimmunity: Current evidence and future perspectives

“…Another hypothesis that has been proposed to explain alum adjuvant action is related to the activation of the Syk-PI3 kinase pathway [53][54][55]. Alum has been suggested to be sensed by plasma membrane lipids and to induce a receptor-independent activation of the Syk-PI3 kinase…”

“…Such activation has been described to inhibit IL-12p70 secretion and to promote PGE 2 production, thus shaping immunity by suppressing the TH1 phenotype [43,54,55].…”