Patient-derived Xenograft Modeling: A Technique to Generate Melanoma Mouse Models

- In patient-derived xenograft or PDX models, tumor cells or fragments from human patients get implanted into immunodeficient recipient mice. PDX models simulate the biological and molecular characteristics of the human tumor microenvironment. To develop a melanoma PDX model, first, harvest tumor tissue from a melanoma patient. Remove the necrotic tissue from the tumor. Mince the tumor to obtain a slurry. Next, prep an anesthetized recipient mouse in a prone position. Make a small surgical incision on the dorsal skin. Gently cut the fascial membrane or the layer of loose connective tissue just underneath the skin. This separates the skin from the underlying muscle layers and helps create a pocket for tumor implantation.

Gently transfer the tumor slurry into the pocket. Now, administer an artificial extracellular matrix into the pocket to stabilize and secure the implanted tumor cells. Surgically staple the wound and allow the mouse to recover. Monitor the recipient mouse weekly to observe the growth of xenograft tumor. In the following protocol, we will demonstrate the subcutaneous implantation of patient-derived melanoma tumor cells into an immunodeficient NSG mouse to generate melanoma patient-derived xenograft models.

- To implant surgical excision or surgical biopsy tissue, first, shave hair from the lower back of NSG six to eight-week old anesthetized mice leaving an approximately 1.5 centimeters to 3 centimeters area without hair. Prepare tumor chunks and divide tumor slurry in a Petri dish into individual mounds for surgical implantation. Using a scalpel blade, make an approximately 5 millimeter long incision on the center of the back of the mouse. With one pair of forceps, lift up the skin on the side of the incision opposite the operator. With scissors in the other hand, separate the skin from the muscle layer by gently cutting the fascial membrane with small scissor cuts, thereby creating a pocket for the tumor tissue.

Use a scalpel blade to pick up one tumor chunk as well as one individual mound of tumor slurry tissue and gently place the tissue into the created pocket. Then, add 100 microliters of artificial extracellular matrix on the tumor tissue mound in the pocket. Using two pairs of forceps, pull up the incision on both ends so that the wound edges come close together. Then, apply one or two wound clips to close the wound. Subcutaneously inject 1-5 milligrams per kilogram of analgesic. When healing is complete, after approximately 7 days, remove the wound clips.