Clinical Trials of Vaccines for Respiratory Syncytial Virus and Related Viruses

我们正在遵循两种策略来开发一种儿童RSV减毒活疫苗。(I)我们的主要策略是开发活减毒RSV毒株，其减毒主要通过缺失几个非必需基因中的一个以及错义和密码子缺失突变来提供，这些突变主要存在于L聚合酶中，并已通过反向遗传学稳定下来对抗减毒。眼下的目标是确定一到两个适合进一步开发为鼻腔内儿童RSV疫苗的主要候选疫苗。(Ii)二次疫苗策略是使用PIV3的减毒版本作为载体来表达RSV抗原(主要是融合F蛋白)，从而提供活的双价HPIV3/RSV疫苗。这些PIV载体疫苗的临床前发展在附带的报告“副流感病毒的实验室和临床前研究”中有描述。这两种疫苗战略都是根据与赛诺菲的合作研究和开发协议(CRADA)开发的。到目前为止，我们的临床试验主要集中在减毒活病毒株上。我们将于2023年在临床上对两种PIV载体疫苗进行评估。 活体减毒RSV候选疫苗的一个谱系涉及编码小(90个氨基酸)病毒M2-2蛋白的ORF的缺失。M2-2蛋白在调节RSV RNA合成中起作用，它的缺失导致病毒RNA复制下调(导致病毒衰弱)，并在全球范围内上调病毒基因转录和抗原合成。每个基因组的抗原表达增加了每个感染颗粒的免疫原性增加的可能性。 在过去的几年中，对名为RSV Med1/delM2-2和RSV LID/delM2-2的delM2-2候选原型进行了评估和报告；最近发表了关于delM2-2候选的两份报告，RSV LID/delM2-2/1030s(NCT02794870和NCT0252339)和D46/NS2/N/delM2-2-HindIII(NCT03099291和NCT03102034)。在这些候选病毒中，LID/delM2-2/1030s是最有希望的病毒。它通过M2-2的缺失和L聚合酶中由Y1321K和S1313(TCA)突变组成的称为1030S的稳定错义突变来减弱。在对6-24个月大的RSV血清阴性儿童进行的第一阶段研究中，LID/delM2-2/1030s耐受性良好，具有良好的传染性，没有遗传不稳定性的证据，诱导了持久的免疫，并为野生型RSV感染的强烈记忆抗体反应做好了准备，使其成为进一步评估的有吸引力的候选药物。在2022年和2023年财政年度，一项更大规模的研究正在进行，以进一步评估LID/delM2-2/1030在RSV血清阴性儿童中的安全性和免疫原性。这项研究现已完全纳入，后续工作将持续到2024年初春。 RSV候选疫苗的第二个谱系包含NS2基因的缺失，其编码的蛋白对抗宿主干扰素和对病毒感染的细胞凋亡反应。候选RSVdelNS2/del1313/I1314L包含delNS2突变和称为del1313/I1314L的突变，该突变包括L聚合酶中1313密码子的缺失，以及邻近的对衰减稳定的错义突变I1314L。该疫苗正在进行1/2期研究，与另一种基于delNS2的候选疫苗RSV delNS2/1030s进行并列比较。这种病毒将DelNS2突变与称为1030S的稳定错义突变相结合，该突变由L聚合酶中的Y1321K和S1313(TCA)突变组成。1030S突变比del1313/I1314L突变更弱，因此RSV delNS2/1030S应该比RSV/delNS2/del1313/I1314L更弱。目前正在对RSV delNS2/1030S和RSV/delNS2/del1313/I1314L候选病毒进行面对面的评估，对血清阴性的婴幼儿进行1/2期临床试验(NCT03916185)。 RSV候选疫苗的第三个谱系包含NS1基因的缺失，该基因与NS2一样，编码一种对抗宿主干扰素和细胞凋亡反应的蛋白质，但比NS2更有效，因此可能提供更弱和更具免疫原性的表型。制备了两种病毒，每种病毒都含有delNS1缺失作为唯一的减毒元件，但在一种病毒中，F和G基因被移动到第一和第二基因组位置，以增加它们的表达(RSV 6120/delNS1和6120/F1G2/delNS1)。这些病毒目前正在一期临床试验(NCT03596801)中进行面对面的比较。 野生型RSV A2株的cDNA衍生版本目前正在健康成年志愿者身上进行剂量递增研究(NCT02484417)进行评估。我们还在评估最近的一种临床分离株RSV A/MARLAND/001/11，我们已经为其开发了反向遗传系统，并在健康成年志愿者(NCT03624790)的第一阶段试验中恢复了一种重组病毒。这些研究将提供一种感染模型，可用于评估RSV治疗候选和成人RSV候选疫苗，并研究病毒的致病机理和宿主反应。

We are following two strategies to develop a live-attenuated pediatric RSV vaccine. (i) Our primary strategy is to develop live-attenuated RSV strains, with attenuation provided mainly by deletion of one of several nonessential genes and by missense and codon-deletion mutations that are mainly in the L polymerase and have been stabilized against de-attenuation using reverse genetics. The immediate goal is to identify one or two lead candidates suitable for further development as an intranasal pediatric RSV vaccine. (ii) A secondary vaccine strategy is to use attenuated versions of PIV3 as vectors to express RSV antigen (primarily the fusion F protein) which provide live bivalent HPIV3/RSV vaccines. The pre-clinical development of these PIV-vectored vaccines is described in the accompanying report "Laboratory and Pre-Clinical Studies of Parainfluenza Viruses". Both vaccine strategies are being developed under a Cooperative Research and Development Agreement (CRADA) with Sanofi. To date, our clinical trials have focused on live-attenuated RSV strains. We will evaluate two PIV-vectored vaccines in the clinic in 2023. One lineage of live-attenuated RSV vaccine candidates involves deletion of the ORF encoding the small (90 amino acids) viral M2-2 protein. The M2-2 protein plays a role in regulating RSV RNA synthesis, and its deletion results in down-regulated viral RNA replication (causing viral attenuation) and a global up-regulation of viral gene transcription and antigen synthesis. Increased antigen expression per genome raises the possibility of increased immunogenicity per infectious particle. Prototype delM2-2 candidates called RSV MEDI/delM2-2 and RSV LID/delM2-2 were evaluated and reported upon in past years; two reports on delM2-2 candidates were recently published, RSV LID/delM2-2/1030s (NCT02794870 and NCT0252339) and D46/NS2/N/delM2-2-HindIII (NCT03099291 and NCT03102034). Among these candidates, LID/delM2-2/1030s emerged as the most promising virus. It is attenuated through deletion of M2-2, combined with a stabilized missense mutation called 1030s that consists of Y1321K and S1313(TCA) mutations in the L polymerase. In a Phase 1 study in 6-24 months-old RSV seronegative children, LID/delM2-2/1030s was well tolerated, had excellent infectivity without evidence of genetic instability, induced durable immunity, and primed for strong anamnestic antibody responses to wildtype RSV infection, making it an attractive candidate for further evaluation. Over the 2022 and 2023 fiscal years, a larger study to further evaluate the safety and immunogenicity of LID/delM2-2/1030s in RSV seronegative children has been ongoing. This study is now fully enrolled, and follow-up will continue through the early spring of 2024. A second lineage of RSV vaccine candidates contains a deletion of the NS2 gene, whose encoded protein antagonizes host interferon and apoptosis responses to viral infection. The candidate RSV delNS2/del1313/I1314L contains the delNS2 mutation combined with a mutation called del1313/I1314L comprising deletion of codon 1313 in the L polymerase plus an adjacent missense mutation I1314L that stabilizes against de-attenuation. This vaccine is being evaluated in a Phase 1/2 study in a side-by-side comparison with a second delNS2-based vaccine candidate, RSV delNS2/1030s. This virus combines the delNS2 mutation with a stabilized missense mutation called 1030s that consists of Y1321K and S1313(TCA) mutations in the L polymerase. The 1030s mutation is somewhat less attenuating than the del1313/I1314L mutation, and therefore RSV delNS2/1030s should be less attenuated than RSV/delNS2/del1313/I1314L. The RSV delNS2/1030s and RSV/delNS2/del1313/I1314L candidates are presently being evaluated head-to-head in a Phase 1/2 clinical trial in seronegative infants and young children (NCT03916185). A third lineage of RSV vaccine candidates contains a deletion of the NS1 gene that, like NS2, encodes a protein that antagonizes host interferon and apoptosis responses, but does so more efficiently than NS2 and thus might confer a phenotype that is more attenuated and immunogenic. Two viruses were made that each contain the delNS1 deletion as the sole attenuating element, but in one virus the F and G genes have been moved to the first and second genome positions in order to increase their expression (RSV 6120/delNS1 and 6120/F1G2/delNS1, respectively). These viruses presently are being compared head-to-head in a Phase 1 clinical trial (NCT03596801). The cDNA-derived version of the wildtype RSV strain A2 is presently being evaluated in healthy adult volunteers in a dose-escalation study (NCT02484417). We also are evaluating a recent clinical isolate RSV A/Maryland/001/11 for which we have developed a reverse genetic system and recovered a recombinant virus in a Phase 1 trial in healthy adult volunteers (NCT03624790). These studies will provide an infection model that can be used to evaluate RSV therapeutic candidates and adult RSV vaccine candidates, and to study viral pathogenesis and the host response.