mRNA as a mediator of immunological information transfer in vivo

描述（由申请人提供）：在体内注射mRNA触发对编码蛋白的免疫反应，并赋予对疾病的保护。由于这个和其他原因，RNA疫苗具有巨大的临床潜力，因此了解它们如何诱导免疫是很重要的。我假设RNA疫苗可能利用了一种生物途径，这种途径已经进化到专门捕获、内化和翻译mRNA。我认为这一途径促进了免疫信息向未感染的树突状细胞（dc）的转移，从而在调节CD8+ T细胞对许多病毒和细菌感染的反应中发挥了关键作用。几乎所有的急性病毒感染都会诱导强烈的CD8+ T细胞反应，当原始的CD8+ T细胞与表达适当共刺激分子的dc表面的MHC类I /表位肽复合物接触时，CD8+ T细胞就会被激活。然而，许多病毒并不感染dc；一些感染dc的病毒也会编码一些蛋白质，这些蛋白质可以有效地抑制MHC I类的呈现。这些事实提出了一个难题：由这些病毒编码的表位是如何被dc有效呈现的？答案来自于交叉呈现的识别，如果它导致触发

DESCRIPTION (provided by applicant): In vivo injection of mRNA triggers immune responses to the encoded proteins, and confers protection against disease. For this and other reasons, outlined below, RNA vaccines have great clinical potential, so it is important that we understand how they induce immunity. I hypothesize that RNA vaccines may be exploiting a biological pathway that has evolved specifically to capture, internalize, and translate mRNA. I propose that this pathway facilitates the transfer of immunological information into uninfected dendritic cells (DCs), thereby playing a key part in regulating CD8+ T cell responses to many viral and bacterial infections. Almost all acute virus infections induce strong CD8+ T cell responses, which are initiated when na�ve CD8+ T cells are activated by contact with an MHC class I / epitope peptide complex on the surface of DCs that express appropriate costimulatory molecules. However, many viruses do not infect DCs; and some viruses that infect DCs also encode proteins that quite effectively inhibit MHC class I presentation. These facts posed a puzzle: how could epitopes encoded by these viruses be effectively presented by DCs? The answer came with the identification of cross-presentation which, if it results in the triggering of naive CD8+ T cells, causes cross-priming. However, two in vivo observations show that cross-presentation/cross-priming (hereinafter, CP) is not always highly-efficient. First, enteroviruses replicate to very high titers and induce CD4+ T cells and antibodies, yet (unique among acute virus infections) they completely avoid triggering na�ve CD8+ T cells. Second, extracellular bacterial infections, in which microbial protein is hugely abundant, do not induce strong CD8+ T cell responses. For reasons described below, I hypothesize that both observations can be explained by proposing that some transfer of immunological information into uninfected DCs may rely on mRNA (rather than protein). So, this proposal has two goals: First, to evaluate how naked RNA induces immunity. Second, to test the hypothesis that, during most microbial infections, mRNA is transferred to uninfected DCs; if it is translated therein, the encoded protein will reach the class I MHC pathway, inducing strong CD8+ T cell responses; I have named this mechanism TATOR (transfer and translation of RNA). Conversely, if the mRNA cannot be translated, the organism is undetectable by CD8+ T cells. Thus, the specific characteristics of their mRNAs renders enteroviruses and extracellular bacteria invisible to CD8+ T cells. Aim 1. To identify and characterize the DC subset that is involved in RNA-triggered immunity. Aim 2. To ask if mRNA coding strategy explains how enteroviruses can almost completely evade naive CD8+ T cells, while most viruses induce strong CD8+ T cell responses. Aim 3. To determine if mRNA regulatory sequences explain why extracellular bacteria fail to induce strong CD8+ T cell responses.