NK cells and naive CD4 T cells are weak in mediating tumor rejection. Percentage of tumor-free mice (A) or tumor volume (B) is shown for mice with neither T cells nor NK cells (gc^–/–Rag^–/–; ▪), or lacking T cells but having NK cells (Rag^–/–; •), or mice with naive transgenic C5-specific T cells (A18 TCR transgenic mice; ▴) following subcutaneous inoculation with 5 × 10⁵ C5-transfected LK35 tumor cells. Symbols represent individual animals in groups of 5 mice (A) or mean data for groups of 5 mice (B). (C) IL-2 secretion by naive CD4 A18 TCR transgenic T cells after stimulation with C5-transfected LK35 tumor cells with 1 × 10⁴ DCs (○) or without DCs (•). Mean cpm of [³H] thymidine incorporation by triplicate cultures of IL-2—dependent CTLL cells are shown.