The Roles of CD8⁺ and CD4⁺ Cells in Tumor Rejection

In vivo administrations of anti‐Lyt‐2.2 (CDS) mAb and anti‐L3T4 (CD4) mAb selectively eliminated CD8⁺ cells amd CD4⁺ cells, respectively. The relative potencies of CD8⁺ cells and CD4⁺ cells and their roles in primary tumor rejections were studied by investigating the effects of these mAbs on tumor growth. CD8⁺ cells were themselves fully capable of mediating rejection in 5 different tumor rejection systems: two radiation leukemia virus (RadLV)‐induced leukemias, B6RV2 and BALBRVD, a radiation‐induced leukemia BALBRL♂1, and a plasmacytoma BALBMOPC‐70A in CB6F₁ mice, and a Friend virus‐induced leukemia B6FBL‐3 in B6 mice. On the other hand, CD4⁺ cells were capable of resisting tumor growth of B6FBL‐3, but not of the other four tumors. Furthermore, for efficient rejection of CB6F₁UV+^˚l sarcoma by CB6F₁ mice, synergy of CDS⁺ and CD4⁺ cells was necessary. Blocking of UV+^˚ 1 rejection was abrogated by delayed administration of anti‐L3T4 (CD4) mAb but not anti‐Lyt‐2.2 (CDS) mAb, indicating the involvement of CD4⁺ cells in only the initial phase of rejection.