大多数美尔克细胞癌（Merkel cell carcinoma，MCC）是一种罕见且高度侵袭性的神经内分泌性皮肤癌，与美尔克细胞多瘤病毒（Merkel cell polyomavirus，MCPyV）感染有关。 MCPyV整合到宿主基因组中，在感染细胞中产生包括病毒大T抗原（LT）截短形式在内的致癌蛋白。这些致癌蛋白是治疗性癌症疫苗的一个有吸引力的靶点。我们设计了一种促进对MCPyV-LT产生强有力的抗原特异性CD4T细胞反应的癌症疫苗。为了在体内激活抗原特异性CD4 T细胞，我们利用我们的核酸平台UNITE™（UNiversal Intracellular Targeted Expression），将肿瘤相关抗原与溶酶体相关膜蛋白1（LAMP1）融合。这种溶酶体定向技术能够增强抗原呈递和强大的抗原特异性T细胞反应。编码MCPyV-LT的突变形式，降低其促癌性能力的LTS220A，被引入到UNITE™平台中。LTS220A-UNITE™DNA疫苗（ITI-3000）的疫苗接种诱导了抗原特异性CD4 T细胞反应和强大的体液免疫反应，足以延缓表达LTS220A的B16F10黑色素瘤细胞系的肿瘤生长。该效应依赖于CD4 T细胞产生IFNγ的能力。此外，ITI-3000诱导了有利于肿瘤微环境（TME）的形成，包括Th1型细胞因子和显著增强的CD4和CD8 T细胞，以及NK和NKT细胞的数量。此外，ITI-3000与α-PD-1免疫检查点抑制剂协同作用，进一步减缓肿瘤生长并增强生存。这些发现强烈暗示，在临床前研究中，使用UNITE™平台的ITI-3000 DNA免疫接种增强对MCPyV-LT的CD4 T细胞反应，从而导致显著的抗肿瘤免疫反应。这些数据支持进行第一例人体试验（FIH）的开放标签随机研究，以评估ITI-3000在多瘤病毒阳性MCC患者中的安全性、耐受性和免疫原性（NCT05422781）。版权所有© 2023 Buchta Rosean，Leyder，Hamilton，Carter，Galloway，Koelle，Nghiem和Heiland。

Most cases of Merkel cell carcinoma (MCC), a rare and highly aggressive type of neuroendocrine skin cancer, are associated with Merkel cell polyomavirus (MCPyV) infection. MCPyV integrates into the host genome, resulting in expression of oncoproteins including a truncated form of the viral large T antigen (LT) in infected cells. These oncoproteins are an attractive target for a therapeutic cancer vaccine.We designed a cancer vaccine that promotes potent, antigen-specific CD4 T cell responses to MCPyV-LT. To activate antigen-specific CD4 T cells in vivo, we utilized our nucleic acid platform, UNITE™ (UNiversal Intracellular Targeted Expression), which fuses a tumor-associated antigen with lysosomal-associated membrane protein 1 (LAMP1). This lysosomal targeting technology results in enhanced antigen presentation and potent antigen-specific T cell responses. LTS220A, encoding a mutated form of MCPyV-LT that diminishes its pro-oncogenic properties, was introduced into the UNITE™ platform.Vaccination with LTS220A-UNITE™ DNA vaccine (ITI-3000) induced antigen-specific CD4 T cell responses and a strong humoral response that were sufficient to delay tumor growth of a B16F10 melanoma line expressing LTS220A. This effect was dependent on the CD4 T cells' ability to produce IFNγ. Moreover, ITI-3000 induced a favorable tumor microenvironment (TME), including Th1-type cytokines and significantly enhanced numbers of CD4 and CD8 T cells as well as NK and NKT cells. Additionally, ITI-3000 synergized with an α-PD-1 immune checkpoint inhibitor to further slow tumor growth and enhance survival.These findings strongly suggest that in pre-clinical studies, DNA vaccination with ITI-3000, using the UNITE™ platform, enhances CD4 T cell responses to MCPyV-LT that result in significant anti-tumor immune responses. These data support the initiation of a first-in-human (FIH) Phase 1 open-label study to evaluate the safety, tolerability, and immunogenicity of ITI-3000 in patients with polyomavirus-positive MCC (NCT05422781).Copyright © 2023 Buchta Rosean, Leyder, Hamilton, Carter, Galloway, Koelle, Nghiem and Heiland.