Phenotype Analyses and Cellular Mechanisms of the Pre-effector T-Lymphocyte Response to a Progressive Syngeneic Murine Sarcoma

Abstract

Lymph nodes draining the progressively growing, weakly immunogenic, MCA 105 sarcoma contained tumor-sensitized but not fully functional pre-effector T-cells. These cells could further differentiate to acquire full antitumor effector function for adoptive therapy in an established in vitro sensitization (IVS) procedure. In this study, we utilized selective depletion with antibodies of lymphocyte subsets bearing the L3T4 (CD4) or Lyt-2 (Cd8) antigen and of cells bearing the asialo-GM₁ (ASGM-1) glycosphingolipid to identify the phenotype of pre-effector cells elicited during progressive tumor growth. Cells from lymph nodes draining a progressive MCA 105 tumor in the footpad were treated with antibodies plus complement prior to IVS. The antitumor efficacy of resulting IVS cells was assessed in adoptive therapy of 3-day established pulmonary MCA 105 metastases. Depletion of Lyt-2⁺ cells eliminated in vivo antitumor reactivity with concurrent elimination of in vitro cytotoxic activity against the MCA 105 tumor, whereas depletion of L3T4⁺ cells did not have an impact on either in vivo or in vitro antitumor reactivities. Treatment with ASGM-1 antiserum plus complement was also found to abrogate therapeutic efficacy. However, the in vitro cytotoxic activity was not affected. These results indicate that the pre-effector cells were Lyt-2⁺, L3T4⁻, and ASGM-1⁺. We next examined whether the sensitization of pre-effector cells in vivo required the participation of L3T4⁺ helper cells. To approach this, mice were depleted of L3T4⁺, Lyt-2⁺, or ASGM-1⁺ cells by antibody injections before tumor inoculation. Treatment with Lyt-2 monoclonal antibody abrogated the pre-effector cell response in the draining lymph nodes, as evidenced by failure to generate therapeutically effective cells following IVS. On the other hand, neither L3T4 nor ASGM-1 antibody treatment affected the generation of pre-effector cells. Thus, sensitization of Lyt-2⁺ pre-effector cells in response to progressive tumor occurred in the absence of L3T4⁺ helper cells.