VSV(Δ51)-NIS replicates in subcutaneous 5TGM1 tumors. (A) Histologic analysis and immunohistochemical staining for VSV-G antigen of representative sections of 5TGM1 myeloma tumors 4 days after initiation of therapy for groups receiving no virus or VSV(Δ51)-NIS (IT or IV). Paraffin-embedded tissues were sectioned at 4-μm thickness and incubated with polyclonal anti-VSV-G antibody, which was detected with biotinylated antirabbit secondary antibody and the avidin:biotin complexing system. Sections were counterstained with hematoxylin and viewed with an Olympus BX45 microscope (Olympus, Center Valley, PA) at 40×/0.9 NA magnification. (B) 5TGM1 tumors were treated with VSV(Δ51)-NIS IT or IV, excised on days 1 and 3 after therapy, and viral titers determined by Vero cell titration. The data are expressed as log TCID₅₀/mg of tumor and are averaged for 3 tumors/time point. (C) Tumor-free bg/nu/xid mice received a single intravenous administration of 10⁸ TCID₅₀ of VSV-GFP, VSV(Δ51)-NIS, or VSV(Δ51)-GFP, and were monitored for toxicity and survival (n = 5/group). Experiments were performed in triplicate (mean ± SEM).