No abstract

The presence of HER-2/neu antibodies in breast cancer patients and the correlation with HER-2/neu-positive cancer implies that immunity to HER-2/neu develops as a result of exposure of patients to HER-2/neu protein expressed by their own cancer. These findings should stimulate further studies to develop the detection of immunity to oncogenic proteins as tumor markers, as well as the development and testing of vaccine strategies to induce and augment immunity to HER-2/neu for the treatment of breast cancer or prevention of recurrent disease.

c-erbB-2, a member of the tyrosine kinase oncogene family, is overexpressed in about 30% of human breast tumors where it correlates with poor prognosis. In vitro studies have suggested that increased expression of the receptor plays an important role in malignant progression. To better understand the direct e ects of p185 HER2 overexpression, a human c-erbB-2 expression vector was transfected into the hormone-dependent MCF-7 human breast carcinoma cell line and cell growth was analysed. Unexpectedly, colony formation assay revealed a reduction in the number and size of colonies as compared with mock-transfected cells. In hormone-deprived medium, c-erbB-2 transfected cells acquired growth capability, consistent with previous reports. By contrast, two c-erbB-2-transfected clones grown in complete medium showed a reduced proliferation rate despite the activation of a fully functional oncoprotein capable of autophosphorylation and induction of the MAPK pathway. The number of c-erbB-2-overexpressing cells in the S phase of the cell cycle was about one-half the number of control and mock-transfected cells. Also, overexpression of c-erbB-2 induced overexpression of p21 WAF1 , pRB hypophosphorylation and a mature di erentiated cell phenotype with production of lipid droplets. Functional inactivation of p185 HER2 by means of a speci®c single chain antibody indicated the c-erbB-2-dependence of the observed alterations. These data show that the exogenous overexpression of the c-erbB-2 gene in hormonedependent breast cancer cells inhibits proliferation and induces di erentiation.

Transgenic FVB-NeuN mice (N202) bearing the rat neu protooncogene driven by the mouse mammary tumor virus promoter/enhancer develop focal mammary carcinomas overexpressing the neu-encoded p185 neu protein. In vitro expression of p185 neu among mammary carcinoma cultures was heterogeneous, and we could establish some cell lines and clones displaying a complete loss of p185 neu expression, along with others with very high p185 neu protein level. Upon in vivo injection, p185 neu-positive cells gave rise to fast-growing tumors with a short latency, while p185 neu-negative cells required a very long latency time, and the resulting tumors were invariably p185 neu-positive. The lower growth ability of p185 neu-negative cells in vivo was also confirmed in athymic nude mice. In vitro, analysis of anchorage-independent growth in soft agar revealed colony formation from p185 neu-positive but not p185 neu-negative cells. The direct involvement of p185 neu in clonogenicity was demonstrated by the inhibition of p185 neu-positive colony growth in soft agar in the presence of an anti-p185 neu monoclonal antibody. By contrast , a higher level of anchorage-dependent clonogenic growth and proliferation was observed in p185 neu-negative cells as compared to p185 neu-positive cells, thus explaining the relative ease with which p185 neu-negative cell lines and clones were established in vitro. Together, the results indicate that p185 neu expression can lead to tumor formation and metastasis through the modification of intrinsic properties of cells related to anchorage-independent growth ability rather than to proliferation or host-dependent mechanisms.

Our data demonstrate different leukocytic types in the infiltrate of breast tumors with different prognostic significance.