National Center for Radiation Research in Oncology, Dresden, Germany.
PLoS One. 2011;6(11):e26517. doi: 10.1371/journal.pone.0026517. Epub 2011 Nov 14.
Microsatellite instability (MSI) resulting from inactivation of the DNA mismatch repair system (MMR) characterizes a highly immunological subtype of colorectal carcinomas. Those tumors express multiple frameshift-mutated proteins which present a unique pool of tumor-specific antigens. The DNA MMR protein MSH3 is frequently mutated in MSI(+) colorectal tumors, thus making it an attractive candidate for T cell-based immunotherapies.
METHODOLOGY/PRINCIPAL FINDINGS: FSP-specific CD8(+) T cells were generated from a healthy donor using reverse immunology. Those T cells specifically recognized T2 cells sensitized with the respective peptides. Specific recognition and killing of MSI(+) colorectal carcinoma cells harbouring the mutated reading frame was observed. The results obtained with T cell bulk cultures could be reproduced with T cell clones obtained from the same cultures. Blocking experiments (using antibodies and cold target inhibition) confirmed peptide as well as HLA-A0201-specificity.
We identified two novel HLA-A0201-restricted cytotoxic T cell epitopes derived from a (-1) frameshift mutation of a coding A(8) tract within the MSH3 gene. These were (386)-FLLALWECSL (FSP18) and (387)-LLALWECSL (FSP19) as well as (403)-IVSRTLLLV (FSP23) and (402)-LIVSRTLLLV (FSP31), respectively. These results suggest that MSH3(-1) represents another promising MSI(+)-induced target antigen. By identifying two distinct epitopes within MSH3(-1), the sustained immunogenicity of the frameshift mutated sequence was confirmed. Our data therefore encourage further exploitation of MSH3 as a piece for peptide-based vaccines either for therapeutic or--even more important--preventive purposes.
由于错配修复系统（MMR）的失活导致的微卫星不稳定性（MSI）是结直肠癌的一种高度免疫亚型。这些肿瘤表达多种框移突变蛋白，提供了独特的肿瘤特异性抗原池。DNA MMR 蛋白 MSH3 在 MSI(+)结直肠肿瘤中经常发生突变，因此成为 T 细胞为基础的免疫治疗的有吸引力的候选物。
方法/主要发现：使用反向免疫学从健康供体中产生 FSP 特异性 CD8(+)T 细胞。这些 T 细胞特异性识别用相应肽段致敏的 T2 细胞。观察到对携带突变阅读框的 MSI(+)结直肠癌细胞的特异性识别和杀伤。用 T 细胞批量培养获得的结果可以用从同一培养物中获得的 T 细胞克隆重现。阻断实验（使用抗体和冷靶抑制）证实了肽段和 HLA-A0201 特异性。
我们鉴定了两个新的 HLA-A0201 限制性细胞毒性 T 细胞表位，来源于 MSH3 基因中 A(8) 框移突变的(-1)移码。它们分别是（386）-FLLALWECSL（FSP18）和（387）-LLALWECSL（FSP19）以及（403）-IVSRTLLLV（FSP23）和（402）-LIVSRTLLLV（FSP31）。这些结果表明 MSH3(-1)是另一种有前途的 MSI(+)诱导靶抗原。通过鉴定 MSH3(-1)内的两个不同表位，证实了移码突变序列的持续免疫原性。因此，我们的数据鼓励进一步利用 MSH3 作为基于肽的疫苗的一部分，用于治疗甚至更重要的预防目的。
