Cloudman S91 / S91-luc Orthotopic Mouse Model Service for Melanoma

The Cloudman S91 / S91-luc orthotopic mouse model establishes a melanin-producing murine melanoma intradermally in immunocompetent DBA/2 hosts — the syngeneic counterpart whose checkpoint, radiation, and chemotherapy response benchmarks were quantified in industry pharmacology programs that the B16-F10 model, refractory to most immunomodulators, cannot provide. Alfa Cytology delivers this responsive melanoma platform with subcutaneous benchmarking and intradermal orthotopic configurations, pigmentation-aware quality control, quantitative luciferase imaging in vivo, and immune-profiling endpoints matched to its myeloid-dominated microenvironment, so your checkpoint combinations, radiation pairings, and targeted agents are tested in a melanoma that actually responds.

Overview of Cloudman S91 / S91-luc Orthotopic Mouse Model for Melanoma

Cloudman S91, published by Cloudman in 1941 and carried into modern culture as the adherent, epithelial-like Clone M-3 (Cellosaurus CVCL_J817; clone CVCL_4512), is a melanocyte-derived mouse melanoma from a male DBA/2 mouse and one of the oldest transplantable tumor lines in continuous use. Its signature property is pigment: the cells constitutively synthesize melanin — roughly 1–3 pg per cell across characterized subclones — and express the melanoma differentiation antigen suite (gp100/Pmel, tyrosinase, TRP-2) together with MHC class I and ICAM-1, making pigmentation itself a trackable, visible biomarker in vivo. The line retains melanocortin-1 receptor expression and the classic melanocyte-stimulating-hormone responsiveness of melanogenesis research, and its cytogenetic near-tetraploidy has been documented by array-CGH. Engineered derivatives extend its reach: M3-EGFR preserves human EGFR expression in immunocompetent hosts (where B16-derived EGFR tumors lose it), HER3 is expressed strongly enough to benchmark HER3-directed antibody–drug conjugates, and an anoikis-selected S91Nadh subline models metastatic behavior.

Fig 1. Cloudman S91 tumor growth in male and female DBA/2 brown mice. (Jiao, R., et al., 2020)

In vivo, S91 in DBA/2J mice is the best-quantified responsive syngeneic melanoma available. Subcutaneous implantation of 10⁶ cells into the high axilla produces tumors with a mean doubling time of approximately four days and typical study horizons of 20–25 days, while intradermal implant — the orthotopic route for skin melanoma — grows measurably slower, a kinetics difference that must be designed into timelines. The tumor microenvironment is myeloid-dominated and suppressive yet responsive: baseline profiling of 300–500 mm³ tumors shows undefined CD11b⁺ myeloid cells and about 34% monocytic MDSCs alongside 9% M2 and 6% M1 macrophages, with NK cells at 4.3% and minimal T-cell infiltration. Against that background, benchmark efficacy is exceptional for a murine melanoma: anti-mPD-1 delivered 116% increased time to progression, anti-mPD-L1 41%, and anti-mCTLA-4 over 283% with 20% tumor-free survivors; focal radiation was dose-responsive from 2.5 to 20 Gy with regressions at higher doses and 10% tumor-free survivors at 20 Gy; and cisplatin (5 mg/kg) and paclitaxel (20 mg/kg) yielded 143% and 121% increased time to progression respectively. Notably, the syngeneic S91 model appears in Genentech's FDA pharmacology review for atezolizumab, where anti-PD-L1 at 10 mg/kg intraperitoneally three times weekly slowed established 200 mm³ tumors — an anchor of regulatory pedigree few syngeneic lines can claim. The S91-luc configuration adds quantitative whole-body bioluminescence in vivo for disseminated and combination designs.

Cell Line Information: Cloudman S91 / S91-luc

Cloudman S91 grows in vitro as an adherent epithelial-like monolayer in DMEM or DMEM/F-12 with 10% fetal bovine serum, with medium refresh every two days and gentle handling given its comparatively loose adhesion. Pigmentation is maintained through culture and is verified per batch — a practical quality attribute, since depigmented drift would compromise both the visual biomarker and differentiation-antigen biology. The S91-luc derivative adds firefly luciferase for quantitative imaging in vivo, with monoclonal selection of high-signal clones in vitro recommended for uniform bioluminescence.

Our Services

Melanoma models punish two operational shortcuts: drifting pigmentation quietly changes the biology under study, and transplanting B16-style kinetics onto an S91 timeline wrecks power calculations. Alfa Cytology runs Cloudman S91 programs with per-batch pigmentation verification, both subcutaneous and intradermal configurations with their distinct growth curves planned into the design, quantified reference arms from the published benchmark matrix — anti-PD-1, anti-CTLA-4, focal radiation, cisplatin, and paclitaxel — and immune-profiling endpoints matched to the model's myeloid-dominated microenvironment, so combination and radiation–immunotherapy claims land on defensible data.

Workflow of Cloudman S91 / S91-luc Orthotopic Mouse Model Construction

S91 model construction is operationally simple but pigment- and site-sensitive: the same cells behave differently intradermally than subcutaneously, and study power depends on respecting that difference. The workflow below covers both configurations from pigment-verified cell preparation through microenvironment-matched endpoints.

1. Cell Expansion and Pigmentation Quality Control: Cloudman S91 or S91-luc cells are expanded in vitro in DMEM or DMEM/F-12 + 10% FBS with medium refresh every two days; batches are confirmed mycoplasma-negative, STR-authenticated, and verified for pigmentation and gp100/tyrosinase expression, with monoclonal luciferase populations confirmed for tagged lines.
2. Host Selection and Acclimatization: DBA/2J mice, typically 6–8 weeks of age, are acclimatized for approximately one week under SPF conditions and health-screened before assignment to study cohorts.
3. Inoculum Preparation: Cells are detached with gentle trypsinization or EDTA (loose adhesion requires care), washed in PBS, and resuspended at the working concentration; the standard challenge is 10⁶ cells in a small volume (~25–50 µL) for either route.
4. Orthotopic Intradermal or Subcutaneous Implantation: For the orthotopic configuration, cells are injected intradermally into the shaved flank skin using a fine needle, forming a visible pigment-positive bleb; for the benchmark configuration, the same inoculum is implanted subcutaneously into the high axilla, where growth is measurably faster — both sites recorded for downstream kinetics.
5. Monitoring with Pigmentation Awareness: Tumors are monitored by caliper two to three times weekly, with visible pigmentation photographed as a qualitative biomarker; S91-luc cohorts are imaged weekly by bioluminescence in vivo after D-luciferin administration, and body weight is recorded throughout.
6. Randomization and Treatment: Animals are randomized once tumors reach predefined volumes (commonly ~100–200 mm³ for checkpoint arms, later for orthotopic cohorts given the slower kinetics); test agents are dosed on study-defined schedules, with published benchmark regimens — anti-mPD-1, anti-mCTLA-4, focal radiation fractions, cisplatin, paclitaxel — available as reference arms.
7. Survival Follow-Up: Animals are followed to standard tumor-burden euthanasia criteria — historically reached at 20–25 days in untreated subcutaneous cohorts — with Kaplan–Meier analysis and tumor-free-survivor reporting.
8. Endpoint Analysis and Reporting: At termination, tumors are excised, photographed for pigmentation, and weighed; lungs and draining lymph nodes are screened for metastatic spread; tissues are processed for H&E and tyrosinase/gp100 immunohistochemistry, tumor-infiltrating immune populations are profiled by flow cytometry using the published CompLeukocyte-style panel (CD45, CD11b, MDSC, M1/M2 macrophage, NK, T-cell subsets), ex vivo bioluminescence maps signal distribution in luciferase studies, and tumor-growth, time-to-progression, tumor-free-survivor, and survival data are compiled into the final report.

Fig 2. Cloudman S91 / S91-luc orthotopic mouse model construction workflow.

Case Study-Cloudman S91 / S91-luc Orthotopic Mouse Model Development

Cloudman S91 is the reference responsive syngeneic melanoma in industry pharmacology, and the platform has carried a broad range of Alfa Cytology client programs — checkpoint inhibitor single agents and rational combinations, radiation–immunotherapy pairings evaluated with image-guided focal delivery, differentiation-antigen targeting, and receptor-engineered variants for ADC and nanotransporter evaluation. Across these programs, readouts have combined caliper or bioluminescence kinetics in vivo, pigmentation documentation, and immune-profile flow cytometry matched to the model's myeloid-dominated microenvironment. Anonymized case summaries and representative deliverable formats are available on request.

Why Choose Alfa Cytology?

S91's value is its responsiveness — and responsiveness means results live or die by site selection, pigmentation control, and reference-arm discipline. Alfa Cytology has operationalized all three.

• A melanoma that responds: quantified checkpoint, radiation, and chemotherapy benchmarks where B16-F10 is refractory, including regulatory-pedigree anti-PD-L1 data.
• True orthotopic capability: intradermal implantation with documented, design-relevant kinetics distinct from subcutaneous growth.
• Pigmentation as a built-in biomarker, verified per batch to protect differentiation-antigen biology.
• A characterized immune landscape — M-MDSC-dominated, T-cell-poor — informing combination strategies and immune-profiling endpoints.
• A quantified benchmark matrix (ITP and tumor-free-survivor endpoints across PD-1, PD-L1, CTLA-4, radiation, cisplatin, and paclitaxel) available as reference arms.
• Engineered variant compatibility: human EGFR preservation in vivo, HER3 benchmarking, and metastatic subline options.
• Monoclonal, high-signal luciferase banks with quantitative imaging in vivo for disseminated and combination designs.

Contact Us

If your melanoma program needs a syngeneic model that actually responds to checkpoint blockade, radiation, and chemotherapy — with orthotopic intradermal kinetics and a quantified benchmark matrix behind it — the Cloudman S91 / S91-luc model is the proven alternative to refractory B16 systems. Alfa Cytology is ready to configure your study. Contact us to review implantation sites, reference-arm designs, and immune-profiling endpoints, and receive a customized study quotation today.

For research use only. Not intended for any clinical use.