Adoptive therapy of established syngeneic leukemia by cells primarily sensitized in vitro

The aim of the current studies was to determine whether cells primarily sensitized in vitro are effective in adoptive therapy of established tumors. Spleen cells from normal BALB/c mice were cultured for 5 days at variable responder:stimulator ratios with an X-irradiated syngeneic Moloney virus-induced leukemia (LSTRA), denoted as BALB/c.(LSTRA)x, or with X-irradiated normal BALB/c spleen cells, denoted as BALB/c. (BALB/C)x, and tested for ability to eradicate an established lethal inoculum of LSTRA in adaptive chemoimmunotherapy. BALB/c mice inoculated with 2 X 10(3) LSTRA i.p. on Day 0 were treated on Day 5 with cyclophosphamide (180 mg/kg) plus 1 X 10(7) cultured cells. Treatment with cyclophosphamide alone cured only 3% of mice. As an adjunct to cyclophosphamide, therapy with BALB/c.(BALB/c)x cultured at responder:stimulator ratios of 8:1, 32:1, and 128:1 cured 29%, 37%, and 33% of mice, respectively; and BALB/c.(LSTRA)x cultured at the same responder:stimulator ratios cured 54, 83, and 29% of mice, respectively. Furthermore, the therapeutic efficacy of BALB/c.(LSTRA)x was abrogated by treatment with anti-Thy 1.2 + complement. Thus, culture of normal lymphoid cells with tumor at optimal responder:stimulator ratios substantially enhanced their ability to eradicate established tumor, and the enhanced therapeutic efficacy was mediated by a T-cell generated during culture. The specificity of primary in vitro sensitization in generating cells effective in the therapy of established tumors was confirmed by treating BALB/CH-2d X C57BL/6H-2b F1 (hereafter called B6F1) mice bearing either LSTRAH-2d or an antigenically distinct chemically induced leukemia, EL-4(G-)H-2b, with CB6F1 spleen cells sensitized in vitro to either of the parental tumors.