Immunosurveillance of<i>Erbb2</i>Carcinogenesis in Transgenic Mice Is Concealed by a Dominant Regulatory T-Cell Self-Tolerance

AbstractTo assess the role of CD4+CD25+Foxp3+ regulatory T (Treg) cells in overcoming immunosurveillance of Erbb2 (HER-2/neu) mammary lesions, we studied the effects of their sustained removal in BALB/c female mice made transgenic for the rat Erbb2 (r-Erbb2) oncogene (BALB-neuT mice), which develop multiple mammary carcinomas. During the progression of these lesions, Treg cells expand in the spleen, tumor draining lymph nodes, and tumors. Repeated administration of anti-CD25 antibodies extends tumor-free survival, reduces carcinoma multiplicity, and leads to the manifestation of a natural antibody and CTL-mediated reactivity against r-Erbb2. Loss of Foxp3+ Treg cells during anti-CD25 treatment remarkably caused the disappearance of Gr1+ immature myeloid cells, suggesting a cross-talk between these two inhibitory immune cell types. Treg cell expansion associated with r-Erbb2 overexpression may be seen as a physiologic response to dampen the immune reaction elicited by local anomalous overexpression of a self-antigen. (Cancer Res 2006; 66(15): 7734-40)