T cells need to home to the regional LN to mediate tumor growth inhibition. (a) Melanoma growth inhibition is less efficient in sublethally irradiated, LN cell–transfused LTα-deficient B6 mice (triangles) than in LTα+/+ mice (inverted triangles) (both groups n = 6). Homeostatic proliferation characteristics of CFSE-labeled B6.PL (Thy1.1+) CD4+ and CD8+ T cells in the spleen of an irradiated B6.LTα–/– host is intact, as measured by flow cytometry on day 7 after transfer (inset). (b) Adoptive transfer of β7/CD62L–/– spleen cells into irradiated C57BL/6 mice (triangles) does not lead to enhanced tumor growth inhibition compared with irradiated, nontransfused C57BL/6 controls (squares). Homeostatic proliferation of CFSE-labeled B6.β7/CD62L–/– (Thy1.2+) CD4+ and CD8+ T cells in the spleen of an irradiated B6.PL host (Thy1.1+) is intact, as measured by flow cytometry on day 7 after transfer (inset). Controls included nonirradiated, nontransfused (circles), and irradiated C57BL/6 mice transfused with 5 × 106 B6 LN cells (inverted triangles).