Voie d'immunisation et séquence d'administration de l ... - TEL
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tel-00827710, version 1 - 29 May 2013 2) Is poly I:C action on cells similar regardless of the timing of delivery? The effects of poly I:C described here were similar for both treatment time points: recruitment of immune cells into the lymph node, DC maturation and death. The only observable difference between the two delivery time points was whether antigen phagocytosis had already occured. This question alone may be the explanation for such dramatically different effects. There are two hypotheses that could both explain the differential effects based on adjuvant timing. First, whathever the time point, adjuvant treatment induces DC maturation, terminal differentiation and death (Figure 53A, B hypothesis 1). If antigen was not phagocytosed yet, the stimulated DCs will no longer be able to capture it; if antigen has already been engulfed, then the adjuvant stimulates DC maturation at an optimal time point, allowing for T cell activation, prior to DC death. Figure 53. Two hypothesis to explain effects of poly I:C on DCs. (A) When poly I:C is delivered prior to antigen uptake, it induces DC maturation and death. (B) When poly I:C is detected after antigen uptake, either poly I:C acts in a similar way (hypothesis 1); or the fact that antigen was already taken up modulates poly I:C action on DCs (hypothesis 2). However, another potential explanation can be envisioned. Perhaps poly I:C acts differently on DCs depending on the timing of delivery, and this switch in poly I:C effector function is 158
tel-00827710, version 1 - 29 May 2013 regulated at the level of antigen engulfment When adjuvant is delivered prior to antigen uptake, it induces DC maturation and death (Figure 53A). Yet, if antigen has already been engulfed, poly I:C may activate the DC differently, inducing, for instance, a different survival program, enhanced persistence of antigen inside the DC, or longer interactions with antigen- specific T cells (Figure 53B, hypothesis 2). Differentiating between these two hypotheses is difficult to address in vivo because, while many DCs will sense poly I:C, only few of them will phagocytose antigen (Figure 44). In order to address this on a per cell basis, the aim would be to develop an in vitro model that could compare DCs sensing only poly I:C and DCs that detect both antigen and poly I:C. In order to do this, bone-marrow-derived DCs could be cultivated with Flt3-ligand to obtain CD8α + -like DCs. Liposomes containing phosphatidylserine may be used to mimic dying cells. In this way, we could be able to identify and compare the adjuvant treated versus adjuvant + antigen treated populations of DCs by looking at their maturation state, or doing RNA expression analysis to study regulation of cell survival genes. The transcription factors STAT would be viable targets for analysis, as the STAT molecules responsible for transmitting type I IFN signaling have already been shown to differ depending on the DC maturation state (Longman et al., 2007). 3) Poly I:C versus type I IFN effects In our model, we used poly I:C as a type I IFN-inducer. We investigated the specific effects of type I IFN by using IFNAR -/- and IRF3/7 DKO mice as recipients, as well as IFNAR -/- OT- I responding T cells. However, we cannot exclude a concurrent effect of poly I:C on the cellular targets. (a) Cross-talk between TLR3 and type I IFN pathways CD8α + DCs are the only DC subset that expresses TLR3. We observed a disappearance of these cells upon poly I:C injection. Interestingly, Hasan and colleagues studied the survival of human DCs after treatment with several different TLR ligands: TLR3 ligands that signal through TRIF, TLR5 ligands signaling through Myd88 and TLR4 ligands that can signal through both pathways. They showed that TLR5 ligands induced DC survival, while treatment with TRL3 or TLR4 ligands, poly I:C and LPS respectively, trigerred DC death. Importantly, DC survival was restored if the type I IFN pathway was blocked by anti-IFNAR neutralizing antibodies (Hasan et al., 2007). These results demonstrated that TLR signaling can impact the DC life cycle depending on which intracellular pathway is engaged and that this phenomenon can be modulated by type I IFN. Page 159 of 256
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tel-00827710, version 1 - 29 May 2013<br />
2) Is poly I:C action on cells similar regardless of the timing of <strong>de</strong>livery?<br />
The effects of poly I:C <strong>de</strong>scribed here were similar for both treatment time points: recruitment<br />
of immune cells into the lymph no<strong>de</strong>, DC maturation and <strong>de</strong>ath. The only observable<br />
difference b<strong>et</strong>ween the two <strong>de</strong>livery time points was wh<strong>et</strong>her antigen phagocytosis had<br />
already occured. This question alone may be the explanation for such dramatically different<br />
effects. There are two hypotheses that could both explain the differential effects based on<br />
adjuvant timing. First, whathever the time point, adjuvant treatment induces DC maturation,<br />
terminal differentiation and <strong>de</strong>ath (Figure 53A, B hypothesis 1). If antigen was not<br />
phagocytosed y<strong>et</strong>, the stimulated DCs will no longer be able to capture it; if antigen has<br />
already been engulfed, then the adjuvant stimulates DC maturation at an optimal time point,<br />
allowing for T cell activation, prior to DC <strong>de</strong>ath.<br />
Figure 53. Two hypothesis to explain effects of poly I:C on DCs. (A) When poly I:C is <strong>de</strong>livered<br />
prior to antigen uptake, it induces DC maturation and <strong>de</strong>ath. (B) When poly I:C is d<strong>et</strong>ected after<br />
antigen uptake, either poly I:C acts in a similar way (hypothesis 1); or the fact that antigen was<br />
already taken up modulates poly I:C action on DCs (hypothesis 2).<br />
However, another potential explanation can be envisioned. Perhaps poly I:C acts differently<br />
on DCs <strong>de</strong>pending on the timing of <strong>de</strong>livery, and this switch in poly I:C effector function is<br />
158