Germ cell neoplasia in situ (GCNIS) is the noninvasive precursor of testicular germ cell tumors type II, the most common cancer in young men, which originates from embryonic germ cells blocked in their maturation. GCNIS is associated with impaired Sertoli cells (SCs) that express fetal keratin 18 (KRT18) and the pluripotency factor SRY-Box transcription factor 2 (SOX2). According to the current theory concerning the origin of GCNIS, these SCs are prepubertal cells arrested in their maturation due to (epi)genetic anomalies and/or environmental antiandrogens. Thus, they are unable to support the development of germ cells, which leads to their maturational block and further progresses into GCNIS. Alternatively, these SCs are hypothesized to be adult cells dedifferentiating secondarily under the influence of GCNIS. To examine whether tumor cells can dedifferentiate SCs, we established a coculture model of adult human SCs (FS1) and a seminoma cell line similar to GCNIS (TCam-2). After 2 wk of coculture, FS1 cells showed progressive expression of KRT18 and SOX2, mimicking the in vivo changes. TCam-2 cells showed SOX2 expression and upregulation of further pluripotency- and reprogramming-associated genes, suggesting a seminoma to embryonal carcinoma transition. Thus, our FS1/TCam-2 coculture model is a valuable tool for investigating interactions between SCs and seminoma cells. Our immunohistochemical and ultrastructural studies of human testicular biopsies with varying degrees of GCNIS compared to biopsies from fetuses, patients with androgen insensitivity syndrome, and patients showing normal spermatogenesis further suggest that GCNIS-associated SCs represent adult cells undergoing progressive dedifferentiation.

原位生殖细胞瘤形成 (GCNIS) 是睾丸生殖细胞肿瘤 II 型的非侵入性前体，这是年轻男性中最常见的癌症，其起源于成熟受阻的胚胎生殖细胞。GCNIS 与表达胎儿角蛋白 18 (KRT18) 和多能性因子 SRY-Box 转录因子 2 (SOX2) 的受损支持细胞 (SC) 相关。根据目前关于 GCNIS 起源的理论，这些 SCs 是由于（表观）遗传异常和/或环境抗雄激素而在成熟过程中停滞的青春期前细胞。因此，它们无法支持生殖细胞的发育，从而导致它们的成熟受阻并进一步发展为 GCNIS。或者，这些 SCs 被假设为在 GCNIS 的影响下二次去分化的成体细胞。为了检查肿瘤细胞是否可以去分化 SCs，我们建立了成人 SCs (FS1) 和类似于 GCNIS (TCam-2) 的精原细胞系的共培养模型。共培养 2 周后，FS1 细胞表现出 KRT18 和 SOX2 的进行性表达，模仿体内变化。TCam-2 细胞显示 SOX2 表达和进一步的多能性和重编程相关基因的上调，表明精原细胞瘤向胚胎癌转变。因此，我们的 FS1/TCam-2 共培养模型是研究 SCs 和精原细胞之间相互作用的宝贵工具。我们对具有不同程度 GCNIS 的人类睾丸活检与胎儿、雄激素不敏感综合征患者的活检进行了免疫组织化学和超微结构研究，