Sedegah Martha, Hollingdale Michael R, Farooq Fouzia, Ganeshan Harini, Belmonte Maria, Kim Yohan, Peters Bjoern, Sette Alessandro, Huang Jun, McGrath Shannon, Abot Esteban, Limbach Keith, Shi Meng, Soisson Lorraine, Diggs Carter, Chuang Ilin, Tamminga Cindy, Epstein Judith E, Villasante Eileen, Richie Thomas L
US Military Malaria Vaccine Program, Naval Medical Research Center, Silver Spring, Maryland, United States of America.
La Jolla Institute for Allergy and Immunology, La Jolla, California, United States of America.
PLoS One. 2014 Sep 11;9(9):e106241. doi: 10.1371/journal.pone.0106241. eCollection 2014.
Fifteen volunteers were immunized with three doses of plasmid DNA encoding P. falciparum circumsporozoite protein (CSP) and apical membrane antigen-1 (AMA1) and boosted with human adenovirus-5 (Ad) expressing the same antigens (DNA/Ad). Four volunteers (27%) demonstrated sterile immunity to controlled human malaria infection and, overall, protection was statistically significantly associated with ELISpot and CD8+ T cell IFN-γ activities to AMA1 but not CSP. DNA priming was required for protection, as 18 additional subjects immunized with Ad alone (AdCA) did not develop sterile protection.
METHODOLOGY/PRINCIPAL FINDINGS: We sought to identify correlates of protection, recognizing that DNA-priming may induce different responses than AdCA alone. Among protected volunteers, two and three had higher ELISpot and CD8+ T cell IFN-γ responses to CSP and AMA1, respectively, than non-protected volunteers. Unexpectedly, non-protected volunteers in the AdCA trial showed ELISpot and CD8+ T cell IFN-γ responses to AMA1 equal to or higher than the protected volunteers. T cell functionality assessed by intracellular cytokine staining for IFN-γ, TNF-α and IL-2 likewise did not distinguish protected from non-protected volunteers across both trials. However, three of the four protected volunteers showed higher effector to central memory CD8+ T cell ratios to AMA1, and one of these to CSP, than non-protected volunteers for both antigens. These responses were focused on discrete regions of CSP and AMA1. Class I epitopes restricted by A03 or B58 supertypes within these regions of AMA1 strongly recalled responses in three of four protected volunteers. We hypothesize that vaccine-induced effector memory CD8+ T cells recognizing a single class I epitope can confer sterile immunity to P. falciparum in humans.
CONCLUSIONS/SIGNIFICANCE: We suggest that better understanding of which epitopes within malaria antigens can confer sterile immunity and design of vaccine approaches that elicit responses to these epitopes will increase the potency of next generation gene-based vaccines.
15名志愿者用三剂编码恶性疟原虫环子孢子蛋白（CSP）和顶端膜抗原1（AMA1）的质粒DNA进行免疫，并用人腺病毒5（Ad）表达相同抗原进行加强免疫（DNA/Ad）。4名志愿者（27%）对受控人类疟疾感染表现出无菌免疫，总体而言，保护作用在统计学上与针对AMA1而非CSP的ELISpot和CD8 + T细胞IFN-γ活性显著相关。保护作用需要DNA启动，因为另外18名仅用Ad免疫（AdCA）的受试者未产生无菌保护。
方法/主要发现：我们试图确定保护的相关因素，认识到DNA启动可能诱导与单独AdCA不同的反应。在受保护的志愿者中，分别有2名和3名对CSP和AMA1的ELISpot和CD8 + T细胞IFN-γ反应高于未受保护的志愿者。出乎意料的是，AdCA试验中未受保护的志愿者对AMA1的ELISpot和CD8 + T细胞IFN-γ反应等于或高于受保护的志愿者。通过细胞内细胞因子染色评估IFN-γ、TNF-α和IL-2的T细胞功能同样在两项试验中均未区分受保护和未受保护的志愿者。然而，4名受保护志愿者中的3名对AMA1的效应记忆CD8 + T细胞与中央记忆CD8 + T细胞的比例高于未受保护的志愿者，其中1名对CSP的该比例也高于未受保护的志愿者。这些反应集中在CSP和AMA1的离散区域。在AMA1这些区域内受A03或B58超型限制的I类表位在4名受保护志愿者中的3名中强烈唤起反应。我们假设，识别单个I类表位的疫苗诱导效应记忆CD8 + T细胞可赋予人类对恶性疟原虫的无菌免疫。
结论/意义：我们建议，更好地了解疟疾抗原中的哪些表位可赋予无菌免疫，并设计引发对这些表位反应的疫苗方法，将提高下一代基于基因的疫苗的效力。
