Immunofluorescence studies of frozen sections of tissue taken from the injection sites of patients 3 and 7 one week after injection of IL-2-transduced autologous tumor cells. The figures show a moderate infiltration with T cells (A), and scanty surviving neuroblasts (B). (A,B) Patient 3 (A) and 7 (B) CD4⁺ T cells are green, and CD8⁺ T cells red; there is a preponderance of CD4⁺ cells. (C,D) Patient 3 (C) and 7 (D) CD4⁺ T cells are green, GD2⁺neuroblasts are red.