Target Discovery and Validation Reviews and Protocols

312 Sioud
Because of their important role in immunity, ex vivo-generated antigen-loaded
DCs have now been used as vaccines to improve immunity. Although DCs can
be obtained from several sources, for clinical trials monocyte-derived DCs are
the most widely used DCs. Monocytes can be differentiated into either macrophages,
which function as scavengers, or DCs, which induce specific immune
responses. Different cytokines skew the in vivo differentiation of monocytes
into DCs with different phenotypes and functions. Alteration of DC function
can be achieved by transfection with immunomodulatory molecules. Endogenous
signal also can be inhibited by several techniques, such as the use of
antisense oligonucleotides and siRNAs.
It is worth noting that the inherent immunogenicity of DCs can be unregulated
by stimulation of these cells through various receptors, such as the
TLRs. More recently, we have found that certain siRNA sequences activated
monocytes and DCs via endosomal TLRs, leading to the production of TNFα
and IFNα (98). Internalization of siRNAs was a prerequisite to activate TLR7
and -8 signaling pathways, suggesting that encapsulation of immunostimulatory
siRNA in liposomes may increase their recognition by the innate effector
cells such DCs and macrophages. Besides the activation of DC maturation
by immunostimulatory siRNAs, the inhibition of immunosuppressive
cytokines and host factors by siRNAs should lead to successful cancer vaccines.
Notably, IL-10–producing Treg cells and IL-10–producing regulatory
DCs suppress cellular immune responses. By targeting IL-10 with an
immunostimulatory siRNA, we hope to both downregulate the expression IL-
10 and activate innate type 1 response against tumors, as illustrated in Fig. 14.
Several recent studies have documented the utility of siRNA-mediated gene
silencing in vitro and in vivo (90). Therapeutic vaccination combined with
strategies that seek to inactivate the function of Treg cells via the use the RNA
interference should lead to the design of better vaccines.
References
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isolated tumour-infiltrating T-lymphocytes have a high cytotoxic potential, as