We established a CD4+ T-cell clone specific for syngeneic methylcholanthrene-induced sarcoma, S1509a raised in an A/J mouse, involved in tumor regression. The phenotype of the T-cell clone was CD3+, TCR-β+, CD4+, CD45RB+, LFA-1+, ICAM-1+, CD44+, and VLA-4+. The CD4+ T-cell clone specifically proliferated through antigen stimulation with attenuated S1509a in the presence of syngeneic accessory cells, and this antigen-induced proliferation was inhibited with anti-CD4 and anti-I-Ek monoclonal antibodies. The CD4+ T-cell clone designated YS1093 secreted interleukin (IL) 4, IL-5, and IL-6, but not IFN-γ, tumor necrosis factor α, or IL-2, thus indicating that the clone belongs to the Th2 type. YS1093 cells and their culture supernatant after antigen stimulation augmented the primed cytotoxic T lymphocyte killing activity at the effector phase. YS1093 cells having Th2-type characteristics made the homologous growing tumor regress in the tumor-bearing syngeneic mice when YS1093 cells were transferred into the tumor-bearing mice i.v.

The in vivo tumor regression initiated by YS1093 cell transfer essentially required the presence of CD8+ T cells in the tumor-bearing hosts, thus suggesting that some specific Th2 cells are positively involved in tumor regression by activating primed CD8+ cytotoxic T lymphocytes against the homologous tumor in situ.

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