Table_1_CCR2- and Flt3-Dependent Inflammatory Conventional Type 2 Dendritic Cells Are Necessary for the Induction of Adaptive Immunity by the Human Vaccine Adjuvant System AS01.docx

The Adjuvant System AS01 contains monophosphoryl lipid A (MPL) and the saponin QS-21 in a liposomal formulation. AS01 is included in recently developed vaccines against malaria and varicella zoster virus. Like for many other adjuvants, induction of adaptive immunity by AS01 is highly dependent on the ability to recruit and activate dendritic cells (DCs) that migrate to the draining lymph node for T and B cell stimulation. The objective of this study was to more precisely address the contribution of the different conventional (cDC) and monocyte-derived DC (MC) subsets in the orchestration of the adaptive immune response after immunization with AS01 adjuvanted vaccine. The combination of MPL and QS-21 in AS01 induced strong recruitment of CD26+XCR1+ cDC1s, CD26+CD172+ cDC2s and a recently defined CCR2-dependent CD64-expressing inflammatory cDC2 (inf-cDC2) subset to the draining lymph node compared to antigen alone, while CD26-CD64+CD88+ MCs were barely detectable. At 24 h post-vaccination, cDC2s and inf-cDC2s were superior amongst the different subsets in priming antigen-specific CD4+ T cells, while simultaneously presenting antigen to CD8+ T cells. Diphtheria toxin (DT) mediated depletion of all DCs prior to vaccination completely abolished adaptive immune responses, while depletion 24 h after vaccination mainly affected CD8+ T cell responses. Vaccinated mice lacking Flt3 or the chemokine receptor CCR2 showed a marked deficit in inf-cDC2 recruitment and failed to raise proper antibody and T cell responses. Thus, the adjuvant activity of AS01 is associated with the potent activation of subsets of cDC2s, including the newly described inf-cDC2s.

佐剂系统AS01以脂质体制剂形式存在，包含单磷酰脂质A（monophosphoryl lipid A，MPL）与皂苷QS-21（saponin QS-21）。AS01已被纳入近年来开发的抗疟疾及水痘带状疱疹病毒疫苗中。与多数其他佐剂类似，AS01介导的适应性免疫诱导高度依赖其招募并激活树突状细胞（dendritic cells，DCs）的能力——这类DCs会迁移至引流淋巴结，以刺激T细胞与B细胞。本研究旨在更精准地解析，在使用AS01佐剂疫苗免疫后，不同的常规树突状细胞（conventional dendritic cell，cDC）亚群与单核细胞源性树突状细胞（monocyte-derived DC，MC）亚群在适应性免疫应答的协同调控中所发挥的作用。相较于单独抗原组，AS01中MPL与QS-21的组合可强力招募CD26+XCR1+ cDC1亚群、CD26+CD172+ cDC2亚群，以及新近定义的CCR2依赖性表达CD64的炎性cDC2亚群（inflammatory cDC2，inf-cDC2）至引流淋巴结；而CD26-CD64+CD88+ MC亚群则几乎无法被检测到。免疫后24小时，在所有亚群中，cDC2亚群与inf-cDC2亚群在启动抗原特异性CD4+ T细胞方面表现更优，同时还可向CD8+ T细胞呈递抗原。在免疫前使用白喉毒素（diphtheria toxin，DT）耗竭所有DCs，可完全消除适应性免疫应答；而在免疫后24小时进行DC耗竭，则主要影响CD8+ T细胞应答。缺失Fms样酪氨酸激酶3（Flt3）或趋化因子受体CCR2（chemokine receptor CCR2）的免疫小鼠，其inf-cDC2亚群的招募存在显著缺陷，且无法产生正常的抗体与T细胞应答。综上，AS01的佐剂活性与cDC2亚群（包括新近发现的inf-cDC2亚群）的强力激活密切相关。