Non-Invasive Quantification of Vaccine-Mediated Antigen Delivery to

限制疫苗免疫反应的一个主要参数是激活的抗原提呈细胞(APC)的数量，这些细胞从疫苗部位捕获抗原并迁移到引流淋巴结(LNS)，也就是T和B细胞启动的地方。目前，一种用于监测体内抗原捕获和清除的定量非侵入性技术尚不成熟。使用细胞磁共振成像(MRI)是一种很有前途的方法；然而，细胞成像目前需要在体外用造影剂预先标记细胞，然后将细胞重新引入被监测对象。利用小鼠模型，我们建立了一种体内标记方法，该方法依赖于内源性抗原提呈细胞原位捕获疫苗抗原相关的超顺磁性氧化铁(SPIO)，以定量AFC向LNS的输送。在这个系统中，MRI能够监测体内磁性标记的APC的运输，这些APC负责诱导肿瘤特异性免疫反应。使用专用软件对淋巴结MR图像进行分析，可以通过生成像素强度直方图来量化信号。体内和体外定量疫苗抗原负载的APC之间有很好的相关性，分辨率足以检测到佐剂引起的APC转运增加。此外，捕获SPIO(和抗原)并传输到LN的APC随后可以在体外被磁性恢复，从而允许对影响疫苗诱导免疫的传入臂的上游参数进行详细的细胞和分子研究。 使用针对肺癌的小鼠疫苗模型，我们现在建议检查MRI测量的APC运输程度与下游免疫反应的数量和质量之间的相关性。 这些信息将被用来评估候选疫苗佐剂增强这一产生系统免疫的关键步骤的能力。我们还将把这项技术扩展到更多的疫苗平台，为临床应用奠定基础。

A major parameter limiting immune responses to vaccination is the number of activated antigen presenting cells (APCs) that capture antigen from the vaccine site and migrate to draining lymph nodes (LNs), the site where T and B cell priming occurs. Currently, a quantitative non-invasive technique for monitoring in vivo antigen capture and dehvery is laclting. The use of cellular magnetic resonance imaging (MRI) is a promising approach for this purpose; however, cellular imaging currently requires ex vivo pre-labeling of cells with contrast agents followed by reintroduction of cells into the subject being monitored. Using mouse models, we have developed an in vivo labehng method which relies upon the capture of vaccine antigen-associated superparamagnetic iron oxide (SPIO) by endogenous antigen presenting cells, in situ, in order to quantify AFC delivery to LNs. In this system, MRI is capable of monitoring the trafficking of magnetically labeled APCs in vivo that are responsible for inducing tumor-specific immune responses. Analysis of lymph node MR images using dedicated software enables signal quantification through the generation of pixel intensity histograms. Excellent correlation is observed between in vivo and ex vivo quantification of vaccine antigen-loaded APCs, with resolution sufficient to detect increased APC trafficking elicited by an adjuvant. Furthermore, APCs that capture SPIO (and antigen) and traffic to LN can subsequently be magnetically recovered ex vivo, allowing for detailed cellular and molecular studies of the upstream parameters that influence the afferent arm of vaccine-induced immunity. Using murine vaccine models targeting lung cancer, we now propose to examine the correlation between the extent of APC trafficking as measured by MRI and the quantity and quality of the downstream immune response. This information will be used to evaluate candidate vaccine adjuvants for their ability to augment this critical step In generating systemic immunity. We will also extend this technology to additional vaccine platforms setting the stage for clinical application.