ULBP-expressing tumors resected after subcutaneous implantation contain higher percentages of NK cells, NK1.1⁺Tcells, and T cells. EL4 cells (1 × 10⁷) transduced with vector alone (A,D), ULBP1 (B,E), or ULBP3 (C,F) were injected subcutaneously into C57BL/6 mice (n = 3; a representative experiment is shown). Two days (A-C) or 4 days (D-F) after implantation, tumors were resected, dispersed, and stained for the presence of T cells, NK cells, and NK1.1⁺ T cells. Dot plots portray NK1.1 expression versus TCR-β expression on lymphocytes that were gated based on forward and side scatter. Increased percentages of infiltrating NK cells, NK1.1⁺ T cells, and T cells were observed on day 4 when EL4 cells expressed either ULBP1 or ULBP3 compared with mock. When the percentage of NK cells (□), NK1.1⁺ T cells (▦), and T cells (▪) was adjusted to compensate for the relative percentage of infiltrating lymphocytes on days 2 (G) and 4 (H), the expression of ULBP1 or ULBP3 on EL4 cells resulted in approximately a 3- to 5-fold increase in infiltration of T cells and NK cells to the tumor relative to the EL4 mock tumors on day 4. NK1.1⁺ T-cell infiltration was augmented by as much as 5- to 6-fold.