3-4 week-old male nude/NMRI mice (Taconic) bearing HER2-expressing N87 gastric cancer xenografts were treated in a mechanism of action experiment as in figure 4, but with adjusted doses: 3Ã-108 VP/tumor or saline on days 0, 4, 8, and 15, while one saline-treated group also received 5.0 µg/g of systemic commercial trastuzumab intraperitoneally (tras). On day 20, tumors, draining lymph nodes (DLNs) and spleens were collected, homogenized and analyzed by flow cytometry with CD49b NK-cell marker. Overall absolute levels of NK-cells did not differ between groups in any compartment. However, when distribution of NK cells into draining lymph nodes (left panel) and tumors (right panel) over the spleens of the animals was assessed, the oncolytic trastuzumab-coding virus (OV-tras) showed the highest ratio of NK cells in both target tissues; In particular, NK-cells showed homing towards the draining lymph nodes where they have been reported to e.g. mediate DC-editing and polarize activated CD4+ T-cells into T-helper 1 phenotype (36). Ratio of NK cells between compartments was calculated by dividing the average NK-cell frequency in tumors/lymph nodes by the average of NK-cells in spleens, each per 5Ã-104 cells. n=3 mice per group. Mock, animals treated with intratumoral saline injections; DLN, draining lymph node; OV-tras, oncolytic adenovirus coding for trastuzumab; OV, oncolytic control virus; tras, systemic trastuzumab therapy.