Cell-mediated immune response to breast tumor has only been marginally investigated. To gain insight into this issue we have developed two clones of distinct phenotype, CD3+ alpha/beta, CD4+, CD8-, CD16-, and CD3+ alpha/beta, CD4-, CD8+, CD16-, respectively, from peripheral blood lymphocytes (PBL) of a breast cancer patient. These effectors, selected on the basis of their cytolytic activity against autologous tumor cells and lack of lysis on NK-sensitive cell lines, preferentially recognize autologous tumor cells. The two clones' cytotoxic activity, while inhibited by anti-LFA-1 mAb, could not be abolished by mAbs to CD3, to class I and class II MHC molecules, and by mAbs to molecules involved in T cell function (i.e., CD4, CD8, CD2). The molecular structure of the alpha and beta T cell receptor chains of the two effector cells, confirmed their clonality and showed that, despite an overlapping killing pattern, they possess distinct TCR alpha and beta chains. These findings demonstrate that breast tumor-specific CTL clones can be generated through current technology and that a alpha/beta effector cell population operating through a HLA-unrestricted and TCR/CD3-independent pathway may be involved in the identification and killing of this tumor.