Patient-Derived Xenograft Preparation: A Comprehensive Guide
Patient-Derived Xenografts (PDXs) have become a cornerstone in cancer research, offering a more faithful model of human tumors compared to traditional cell lines. These models involve transplanting tumor tissue directly from a patient into immunodeficient mice, preserving the tumor’s original architecture, genetic heterogeneity, and microenvironment. The preparation of PDX models requires careful planning, precision, and adherence to ethical and biosafety standards.
Tissue Collection and Handling
The first step in PDX preparation begins with the collection of tumor tissue from surgical resections or biopsies. Maintaining tissue viability is critical, so samples are typically placed in cold, sterile transport medium enriched with nutrients and antibiotics to prevent contamination. The time from excision to implantation should be minimized, ideally within a few hours, to preserve cell viability and the tumor’s histological characteristics.
Once in the laboratory, the tissue is carefully dissected to remove necrotic regions and excess fat. It is then divided into small fragments, usually 2–3 mm in diameter, suitable for implantation. For some protocols, enzymatic digestion is performed to create a single-cell suspension, which can facilitate engraftment and expansion. Throughout this process, sterility and gentle handling are emphasized to avoid compromising the tissue’s integrity.
Selection of Host Models
Immunodeficient mice, such as NOD-SCID or NSG strains, are the most common hosts for PDX models because their compromised immune systems do not reject human tissue. The site of implantation depends on the tumor type and research goals. Subcutaneous implantation is often preferred for ease of monitoring tumor growth, while orthotopic implantation—placing tissue in the tissue of origin—better replicates the tumor microenvironment and metastatic behavior.
Implantation and Monitoring
During implantation, the tumor fragment is placed into a small incision or a pre-prepared pocket in the mouse. Surgical procedures are performed under anesthesia, and postoperative care ensures minimal stress and infection risk. After implantation, mice are closely monitored for tumor growth, typically assessed via caliper measurements, imaging techniques, or biomarker analysis. Engraftment success rates vary depending on tumor type, tissue quality, and host strain, with some tumors requiring multiple passages to establish a stable PDX line.