Casper zebrafish support MM cell growth. (A) Schematic chart depicting the procedures used to establish the zebrafish MM xenograft model (hpf, hours postfertilization; hpi, hours postinjection; hpt, hours posttreatment). (B) Fluorescence microscopy images of the CM-Dil–stained MM cells injected into the perivitelline area of Casper zebrafish larvae. Bright field of whole Casper zebrafish 24 hours after injection with human MM cells (top). Red fluorescence protein (RFP) channel of whole Casper zebrafish; the red fluorescence color under the microscope shows CM-Dil–stained MM cells (middle). Merged image from bright field and RFP field (bottom). All cells are located in the perivitelline area after mixing with Matrigel. (C) Whole-mount immunohistochemistry staining. Bright field of whole zebrafish 24 hpi with human multiple MM cells (top). RFP field shows red fluorescence from CM-Dil–stained MM cells (middle). GFP field showing the EGFP-labeled anti–human λ light-chain antibody colocalizing with CM-Dil–labeled MM1S cells (bottom). (D) Typical fluorescence microscopy images of the CM-Dil–stained MM cells xenograft growth of MM1S, INA-6, and primary patient MM cells without drug treatment in the perivitelline area of Casper zebrafish larvae at 24, 48, and 72 hpi. (E) Tumor growth curves of xenografts with these 3 cell types in Casper zebrafish larvae (n = 30 for each group).