Bryostatin/ionomycin-activated T cells mediate regression of established tumors

We have shown that adoptive transfer of tumor-sensitized lymphocytes activa ted in vitro with bryostatin-l and ionomycin (Bn), and expanded in culture, can induce regression of small established tumors. We set out to determine whether similar treatment would be effective against larger tumors and wha t cells mediate this effect. We also attempted to shorten the ex vivo cultu re period with the ultimate aim of developing a more clinically useful prot ocol. BALB/c mice were injected in one footpad with IL-2-transfected 4T07 mammary tumor cells. Ten days later, popliteal draining lymph nodes (DLN) were har vested and activated with B/I for 18 h. Mice with either 3-day or 10-day 4T 07 flank tumors were treated with cyclophosphamide (100 mg/ kg ip, CYP) alo ne or CYP followed the next day by infusion of either B/I-activated lymphoc ytes transferred immediately or activated cells that had been expanded in v itro for 3 or 10 days. In some experiments, mice were also treated with rat anti-mouse CD4 monoclonal antibody (GK1.5) or anti-CDS antibody (2.43). All mice receiving CYP alone or CYP + sensitized, nonactivated DLN cells de monstrated progressive tumor growth. One hundred percent (6/6) of mice trea ted with CYP + AIT with B/I-activated,10-day expanded cells had complete re gression of 3-day flank tumors. Treatment with activated, nonexpanded cells , induced tumor regression in a majority of mice, but was not as reliable a s AIT with expanded cells. We developed a protocol with a shortened expansi on period (3-day) that was efficacious for treatment of 4T07 when adoptivel y transferred to either 3 or 10 day tumor-bearing mice. In vivo depletion o f CD4(+) cells had no effect on regression of 3-day tumors, but treatment w ith anti-CD8 antibody abrogated the effect of immunotherapy. Adoptive trans fer of B/I-activated cells, with or without long-term expansion, induced re gression of early and late stage 4T07 tumors and is dependent on CD8(+) but not CD4(+) T cells. (C) 2001 Academic Press.