IL-12 induces myeloid cells in situ to cross-present antigen

Myeloid-derived cells comprising the tumor stroma represent a heterogeneous population of cells critical to the structure, function and growth of established cancers. We have recently found that engineering tumor-specific CD8+ T cells to secrete IL-12 (IL-12TD) can lead to striking improvements in T-cell activity against established melanomas in murine models. Surprisingly, IL-12-dependent enhancement of CD8+ T-cell anti-tumor function did not occur through direct ligation of receptors on lymphocytes or NK cells. Instead, IL-12 sensitized host bone marrow-derived tumor-stromal cells, partly through interferon-gamma, to indirectly enhance the effects of adoptively-transferred T cells. Direct presentation of antigen by tumor was not necessary, but MHC class I expression on endogenous cells was essential for IL-12 mediated anti-tumor enhancements. Upon successful treatment with IL-12TD cells, we observed the selective elimination of tumor-infiltrating CD11b+ F4/80+ macrophages, CD11b+/ClassII+/CD11c+ dendritic cells and CD11b+/Ly6C+/Ly6G- but not CD11b+/Ly6C+/Ly6G+ myeloid-derived suppressor cells within regressing lesions. These results are consistent with a model whereby IL-12 triggers the maturation of myeloid-derived cells into competent antigen cross-presenting cells. Licensed recognition of these antigens by effector T cells may in turn trigger the collapse of the tumor stroma and aid in the regression of large vascularized lesions. Samples were collected at 3 days and 7 days from tumors treated in-vivo with no treatment, Mock pmel-1 CD8+ cell treatment, or IL-12 pmel-1 CD8+ cell treatment. There were 4 biological replicates of each sample type. There were a total of 24 samples.

构成肿瘤间质的髓系来源细胞（Myeloid-derived cells）是一类异质性细胞群，对已形成实体瘤的结构维持、功能发挥及生长进程均具有关键作用。我们近期的研究证实，对肿瘤特异性CD8+ T细胞进行工程化修饰以使其分泌IL-12（简称IL-12TD），可在小鼠模型中显著增强其对抗已形成黑色素瘤的免疫活性。令人意外的是，IL-12对CD8+ T细胞抗肿瘤功能的增强作用并非通过直接结合淋巴细胞或自然杀伤（NK）细胞表面受体实现。相反，IL-12可通过干扰素-γ（interferon-gamma）介导的途径致敏宿主骨髓来源的肿瘤间质细胞，从而间接强化过继转移T细胞的抗肿瘤效应。肿瘤细胞直接呈递抗原并非该过程的必需条件，但内源性细胞表面的MHC I类分子（MHC class I）表达对于IL-12介导的抗肿瘤功能增强至关重要。在使用IL-12TD细胞完成成功治疗后，我们观察到消退中的肿瘤病灶内选择性清除了肿瘤浸润性CD11b+ F4/80+巨噬细胞、CD11b+/ClassII+/CD11c+树突状细胞以及CD11b+/Ly6C+/Ly6G-细胞群，但未对CD11b+/Ly6C+/Ly6G+髓系来源抑制细胞（myeloid-derived suppressor cells）产生清除效应。上述研究结果契合如下模型：IL-12可诱导髓系来源细胞分化为具备功能的抗原交叉呈递细胞。效应T细胞对这些抗原的特异性识别可进一步促使肿瘤间质崩解，助力大型血管化肿瘤病灶的消退。本研究分别对未处理、Mock pmel-1 CD8+细胞处理、IL-12 pmel-1 CD8+细胞处理的荷瘤小鼠，于造模后第3天和第7天采集肿瘤样本；每种样本类型设置4次生物学重复，总计24份样本。