Does HER‐2/neu antigen loss in metastatic breast tumors occur under immune pressure?

Abstract

Tumor immune editing has been demonstrated in the preclinical studies that underscore counter-regulatory function of antitumor immune responses in both tumor rejection and tumor escape or recurrence. We were greatly interested in the article by Santinelli et al.1 in this journal on discrepancy between primary breast tumors and their metastatic lesions on the status of HER-2/neu expression. Their work clearly demonstrates that a fraction of patients with HER-2/neu positive primary tumors appeared to lose HER-2/neu expression in their distant metastatic lesions. However, there was a concordance in HER-2/neu expression between primary tumors and metachronous lymph node metastasis. Similar observations were made by Lower et al.,2 where 382 patients with metastatic breast cancer were studied. A fraction of patients with HER-2/neu positive primary lesions also had HER-2/neu negative metastatic lesions. These observations suggest that breast tumors are not stable in the expression of HER-2/neu in vivo. Therefore, it is important to understand the mechanisms by which tumors lose or gain HER-2/neu expression in vivo. Our preclinical results complement their findings by demonstrating that HER-2/neu antigen loss occurred under the immune pressure in vivo and in vitro.3 Our studies underscored the role of HER-2/neu-specific IFN-γ-secreting T cells in the induction of HER-2/neu antigen loss or downregulation, which facilitated emergence of an invasive HER-2/neu negative tumor variant. Interestingly, microarray analysis showed that expression of IFN-γ Rα in the relapsed tumor lesion, which had lost HER-2/neu expression under immune pressure, was higher than that in the regressing tumor lesion.4 We also showed that presence of the inflammatory cytokine, IL-6, would upregulate expression of IFN-γ Rα in human breast tumor line, SKBR3, rendering it more susceptible to the IFN-γ-induced downregulation of HER-2/neu expression (Fig. 1). Based on these preclinical studies and other reports emphasizing on counter-regulatory role of IFN-γ in tumor rejection and antigen loss,5-7 and the fact that breast tumors are heterogeneous in the expression of receptors, we suggest that IFN-γ Rα positive tumor clones had lost HER-2/neu expression in the presence of HER-2/neu-specific immune responses, IFN-γ-producing T cells in particular, and became metastatic. On the other hand, IFN-γ Rα negative tumor clones continued to express HER-2/neu antigen in primary tumor lesions. Availability of tumor samples from the patients studied by Santinelli et al.1 would allow them to determine whether such discordance between primary and metastatic breast tumors in the expression of HER-2/neu may be correlated with the status of IFN-γ Rα expression in the tumors. Further studies are required to determine whether expression of HER-2/neu in primary tumors and loss of this antigen in metastatic lesions may also be associated with the preexisting HER-2/neu-specific T-cell responses in these patients. IL-6 renders SKBR3 tumors sensitive to the IFN-γ-induced downregulation of HER-2/neu. The HER-2/neu positive human SKBR3 cells were cultured in the presence or absence of IFN-γ (50 ng/ml) for 5 days (a), or cultured with IL-6 for 16 hr and then cultured in the presence or absence of IFN-γ for 5 days (b). Expression of HER-2/neu was evaluated using flow cytometry analysis on the indicated cells (a, b) and RT-PCR analysis of mRNA extracted from the IL-6-pretreated SKBR3 cells that were cultured in the presence or absence of IFN-γfor 5 days (c). The authors gratefully acknowledge the support of VCU Massey Cancer Centre and the Commonwealth Foundation for Cancer Research. Yours sincerely, Masoud H. Manjili*, Maciej Kmieciak*, * Department of Microbiology and Immunology, VCU School of Medicine, Massey Cancer Center, Richmond, VA.