Targeting Antigen to Clec9A Primes Follicular Th Cell Memory Responses Capable of Robust Recall

Abstract

Targeting Ags to dendritic cell (DC) surface receptors can induce a variety of responses depending on the DC type targeted, the receptor targeted, and the adjuvant used. Clec9A (DNGR-1), which is expressed by CD8+ DCs, has been shown to bind F-actin exposed on damaged cells. Targeting Ag to this receptor in mice and nonhuman primates induces strong humoral immunity even in the absence of adjuvant, a process seen for a few select DC receptors. In contrast with other receptors, however, targeting Clec9A induces long-lived, affinity-matured Ab responses that are associated with efficient CD4+ T cell responses shown to possess properties of follicular Th cells (TFH). In this article, we provide definitive evidence that Clec9A targeting promotes the development of TFH by showing that responding CD4 T cells express CXCR5, PD1, the TFH transcription factor Bcl6, and the cytokine IL-21, and that these cells localize to germinal centers. Furthermore, we extend studies from the model Ag OVA to the viral Ag glycoprotein D of HSV-1 and examine the capacity of primed TFH to form functional memory. We show that targeting glycoprotein D to Clec9A even in the absence of adjuvant induced long-lived memory CXCR5+ PD1hi CD4+ T cells that proliferated extensively upon secondary challenge and rapidly developed into effector TFH. This was associated with enhanced germinal center B cell responses and accelerated Ab production. Our study indicates that targeting Ags to Clec9A in the absence of adjuvant routinely generates TFH responses that form long-lived memory capable of robust secondary TFH responses.

Development of a Novel CD4+ TCR Transgenic Line That Reveals a Dominant Role for CD8+ Dendritic Cells and CD40 Signaling in the Generation of Helper and CTL Responses to Blood-Stage Malaria

“…This agrees with existing literature showing that the CD8 + DC subset preferentially generates Th1 responses over Th2 responses (35,36) and is efficient at promoting Tfh cell immunity (73,74). The consequences of this functional capacity for CD8 + DC, however, are likely to differ depending on the model studied, resulting in the induction of pathology or immunity.…”

“…DC subsets can influence the expression of transcription factors by T cells and drive their differentiation into particular Th phenotypes (35,36,(73)(74)(75). To address the role of CD8 + DC on the differentiation of PbT-II cells after PbA infection, XCR1-DTRvenus mice were adoptively transferred with PbT-II cells and then infected with 10 4 PbA iRBC.…”

Monocyte differentiation and antigen-presenting functions

“…The location of monocytes within the interfollicular region suggests that they may directly or indirectly contribute to B cell maturation and/or antibody production. Indeed, an elegant study by Chakarov and Fazilleau 128,129 demonstrated that, similarly to cDCs [130][131][132][133][134][135][136] , Toll-like receptor 9 (TLR9)-stimulated monocytes directly present antigen and induce the differentiation of T FH cells via IL-6 production. Another study using a high-dose antigen regimen suggested that in the absence of cDCs, LY6C + monocytes (along with B cells) induce T FH cell development 137 .…”

C-type lectin receptors in the control of T helper cell differentiation

“…Their use has been extensively investigated for enhancing antigen presentation, but their ability to trigger CLR signalling has been only marginally investigated. A few soluble antibodies are known to induce CLR signalling: the CLEC9A-trageting antibody 24/04-10B4 has been shown to induce T FH cell responses 97 , and the polyclonal DC-SIGN-targeting antibody H-200 triggers signalling similar to that of mannose ligands 111 . The high specificity of antibodies underscores their possible application in triggering CLRs.…”

“…Therefore, vaccines that induce efficient T FH cell responses might elicit these broadly neutralizing anti bodies. Interestingly, in contrast to other PRRs, some CLRs, such as DC-SIGN and CLEC9A, have been shown to specifically elicit T FH cell responses 11,97 . Thus, CLR targeting might also present an important opportunity to induce strong antibody responses against HIV-1.…”