Influence of estradiol and tamoxifen on susceptibility of human breast cancer cell lines to lysis by lymphokine-activated killer cells

The design of combination hormonal and immunotherapeutic protocols for breast cancer patients may be facilitated by analysis of preclinical in vitro model systems. Estrogen receptor positive (ER⁺: MCF—7) and negative (^{ER −}: MDA—MB—231) human breast cancer cell lines were utilized to evaluate the effects of tamoxifen (TAM) and estradiol (E₂) on modulation of breast cancer target susceptibility to lysis by lymphokine—activated killer (LAK) cells. E₂—stimulated ER⁺cells were more susceptible to lysis by LAK cells than corresponding TAM—treated or control cells, while treatment of ER⁻cells with either E₂or TAM alone did not alter from control their susceptibility to this immune—mediated lysis. All ER⁺and ER⁻cells tested remained sensitive after treatment with TAM to lysis by LAK cells. In addition, an adenocarcinoma reactive human—mouse chimeric monoclonal antibody (ING—1) was able to significantly boost in vivo generated LAK cell—mediated lysis of control, E₂—treated, and TAM—treated ER–⁺and ER⁻cells. These in vitro results provide a preclinical rationale for in vivo testing of TAM, interleukin—2 (IL—2), and breast cancer reactive antibody—dependent cellular cytotoxicity facilitating antibody in patients with refractory or high risk breast cancer.