CD4 and breast cancer: Vβ6+ CD4+ T cells interacted exclusively with MMTV(SW) SAg (Held et al., 1993; Ardavin et al., 1997) and MMTV(C3H, a kind mouse strain with spontaneous breast cancer) only influenced the activation of CD4+ T cells bearing Vβ14+ and Vβ15+ TCRs (Choi et al., 1991; Held et al., 1993).