Drug-Induced Partial Immunosuppression for Preclinical Human Tumor Xenograft Models

With the rising incidence of cancer, there is a growing need for improved preclinical models to test new therapies. While patient-derived xenografts (PDX) in immunodeficient mice are the gold standard, they are costly and result in a complete absence of a functional immune system, limiting their utility for studying tumor-immune interactions. This study characterizes a pharmacological partial immunosuppression protocol in immunocompetent mice as a promising alternative, evaluating its impact on the immune system and demonstrating its efficacy for growing human tumor xenografts.

Mice received a regimen of cyclosporine (20 mg/kg, i.p., every 48 h for 12 days), cyclophosphamide (60 mg/kg, i.p., every 48 h for 8 days), and ketoconazole (10 mg/kg, p.o., for 12 days). The dynamics of CD3⁺, CD4⁺, CD8⁺, and CD19⁺ lymphocyte subpopulations and the CD4/CD8 index were monitored via flow cytometry on days 1, 5, 8, 12, 16, and 21. The protocol's utility was tested by orthotopic transplantation of human glioma and lung cancer cells, and subcutaneous transplantation of breast cancer cells (MCF7). Tumor engraftment and growth were assessed using in vivo microscopy, MRI, and histology.

The immunosuppressive protocol induced a significant but partial reduction in CD3⁺ T-cells and CD19⁺ B-cells by day 8 (p = 0.0277). A profound and progressive decrease in the CD4/CD8 index was observed, indicating a shift towards immunosuppression. Crucially, CD8⁺ and CD4⁺ T-cells populations recovered rapidly post-therapy, demonstrating that the protocol creates a temporary and modifiable immune window rather than inducing complete ablation. The protocol enabled successful engraftment and growth of all three tested tumors in a residual immune microenvironment, confirmed by in vivo imaging and histopathological analysis.

This drug-induced partial immunosuppression protocol effectively creates a reproducible state of transient immunodeficiency in outbred mice, suitable for various human tumor xenograft models. It represents a cost-effective and flexible alternative to genetic models, with the distinct advantage of preserving a residual immune microenvironment, making it particularly valuable for preclinical studies that require a partially intact host immune system.