Cloudman S91 Syngeneic Model Overview
The Cloudman S91 syngeneic model is one of the oldest and most widely characterized murine melanoma systems, originally derived from a spontaneous skin melanoma in DBA/2 mice. This model has long served as a foundational platform for melanoma biology and immuno-oncology research due to its stable growth, high melanin production, and immunogenic properties. Unlike the C57BL/6-derived B16 series, the S91 line arises in the DBA/2 background, providing an alternative immunogenetic context for melanoma studies, particularly those exploring antigen presentation, macrophage activity, and pigment-related pathways in tumor progression.
When implanted subcutaneously into DBA/2 mice, Cloudman S91 cells generate heavily pigmented, well-defined melanomas that exhibit moderate aggressiveness and predictable kinetics. The model is suitable for evaluating the efficacy of immunotherapies, radiotherapy, and cytokine-based interventions, and for mechanistic investigations of melanogenesis, angiogenesis, and immune escape. Its reproducibility and distinctive pigmentation make it a valuable system for both visual tumor tracking and molecular analysis in preclinical melanoma research.
Request a Custom Quote for Cloudman S91 Syngeneic ModelBiological and Molecular Characteristics
The Cloudman S91 cell line was established from a spontaneous melanoma in a DBA/2 mouse in the early 1940s and remains one of the most extensively studied melanoma models. The tumor exhibits an epithelial-to-spindle cell morphology and produces high levels of melanin, reflecting active tyrosinase and melanosome synthesis pathways. The model is moderately immunogenic, expressing tumor-associated antigens such as gp100, TRP-1, and tyrosinase-related proteins, which can elicit antigen-specific T-cell responses in immunocompetent hosts.
Cytokine profiling of Cloudman S91 tumors reveals the presence of IL-6, TGF-β, and VEGF, indicating an inflammatory and angiogenic microenvironment. The tumor stroma contains macrophages, lymphocytes, and fibroblasts, forming a complex immunological niche that supports tumor growth and resistance to cytotoxic stress. The S91 model’s high pigmentation and strong immune responsiveness make it a distinctive and informative system for examining the interplay between melanin metabolism, oxidative stress, and immune modulation in melanoma.
| Parameter | Description |
|---|---|
| Host strain | DBA/2 (female, 6–8 weeks) |
| Tumor origin | Spontaneous cutaneous melanoma (mouse) |
| Histological type | Pigmented malignant melanoma |
| Inoculation route | Subcutaneous or intradermal |
| Tumor take rate | >90% |
| Doubling time | Approximately 4–5 days in vivo |
| Metastatic potential | Low; localized, with rare distant spread |
| Immunophenotype | Moderately immunogenic; macrophage and lymphocyte infiltration |
| Common applications | Immunotherapy, pigment biology, macrophage modulation, radiotherapy studies |
In Vivo Model Development and Tumorigenicity
In vivo establishment of the Cloudman S91 model is achieved through subcutaneous implantation of viable melanoma cells into DBA/2 mice, resulting in visible tumors within 7–10 days post-inoculation. The tumors are heavily pigmented and grow as well-circumscribed nodules, facilitating visual monitoring and volumetric assessment. Growth kinetics are consistent, and tumor take rates exceed 90%, making the model suitable for both short-term efficacy and long-term immune monitoring studies.
Although S91 tumors typically remain localized, their growth dynamics and immune accessibility make them valuable for mechanistic studies of tumor–immune interactions and treatment-induced immune activation. The model’s pigmentation also enables optical imaging of tumor progression and regression without reliance on exogenous labeling, an advantage for longitudinal monitoring in preclinical settings.
Request a Custom Quote for Cloudman S91 Syngeneic ModelHistopathology and Immunohistochemical Profile
Histopathological examination of Cloudman S91 tumors reveals densely packed, melanin-rich melanoma cells with spindle and polygonal morphologies. Tumors display well-organized cellular architecture with focal necrosis and moderate angiogenesis. The stroma is composed of fibroblasts, immune cells, and vascular channels, forming a supportive microenvironment for tumor progression.
Immunohistochemical staining demonstrates strong expression of melanocytic differentiation markers such as tyrosinase and TRP-1. Ki-67 staining indicates moderate proliferative activity, while CD3 and CD8 immunostaining confirm T-cell infiltration at the tumor periphery. Macrophage markers F4/80 and CD11b are abundantly expressed, consistent with the macrophage-enriched microenvironment. PD-L1 expression is variable but increases in response to interferon signaling or immunotherapy. Collectively, these histological features mirror human melanoma morphology and provide translational relevance for testing immunomodulatory and pigment-targeted therapies.
Preclinical Applications and Drug Response
The Cloudman S91 syngeneic model has been extensively used in immuno-oncology, pigment metabolism, and radiotherapy research for over half a century. It demonstrates measurable responsiveness to immunotherapies, including IL-2, interferon-α, and checkpoint blockade, as well as to radiotherapeutic regimens that induce immune activation. The model’s high melanin content makes it particularly suitable for exploring oxidative stress and the immunological effects of pigment-associated antigens.
Checkpoint inhibitors targeting PD-1 and CTLA-4 yield variable tumor regression in S91-bearing mice, often enhanced by concurrent cytokine therapy or macrophage reprogramming. The model has also been applied in studies of pigment-based radiosensitization and melanin-targeted drug delivery. Because of its reproducible growth, visible pigmentation, and immunocompetent background, the Cloudman S91 system remains an essential tool for preclinical evaluation of melanoma immunotherapies and for dissecting the immunobiological mechanisms underlying melanoma progression.
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To request the Cloudman S91 syngeneic model for your preclinical studies, please use the form below. A customized quote and additional model specifications will be provided upon inquiry.
Request a Custom Quote for Cloudman S91 Syngeneic Model