Myeloid tumor infiltrating cells in a mouse model of prostate cancer progression

Introduction About 50% of human prostate cancers (PC) overexpress an ETS gene due to a translocation downstream of promoters of genes highly expressed in prostate. Half of 10 month-old transgenic mice with prostate overexpression of the ETS gene ETV4 (ETV4 mice) develop low-grade prostatic intraepithelial neoplasia. In comparison, almost all mice carrying both ETV4 overexpression and heterozygote Pten deletion (ETV4-Pten+/- mice) develop PC at 7 months, suggesting an oncogenic cooperation between these two common genetic alterations. Inflammatory and immune tumor-infiltrating cells may have a major role in tumor development. We are investigating if differences in the subsets of tumor-infiltrating cells may have a role in the above model of PC progression. Material and Methods ETV4 mice and mice with heterozygote Pten deletion were crossed to obtain mice with 4 different genotypes: WT, ETV4, Pten+/-, ETV4-Pten+/-. Tumor-infiltrating cells were characterized in 10 and 14 month-old mice. A single-cell suspension was obtained from shredded prostate tissues by using collagenase/hyaluronidase enzymes: inflammatory and immune infiltrating cells were identified by flow cytometry using an anti-CD45+ moAb, and further subtyped by appropriate antibodies in lymphoid (B-, T-, T-helper, T-suppressor lymphocytes and dendritic cells) and in myeloid (macrophages and neutrophils) cells. ? Results and discussion We analyzed 28 ten-month-old mice (>=6 for genotype) and 61 fourteen-month-old mice (>=13 for genotype). We found no differences in the frequency of prostate lymphoid infiltrating-cells at any age. In contrast, at any ages we found an increase of neutrophils in Pten-deleted mice, increase that was particularly high and significant in ETV4-Pten+/- mice. Furthermore, we investigated pro-inflammatory (M1) and anti-inflammatory (M2) activated macrophages. We found a higher percentage of M2 macrophages in both Pten+/- and ETV4-Pten+/- compared to WT and ETV4 mice. ? Conclusion The high frequency of anti-inflammatory activated macrophages (M2) in mice with Pten deletion suggests a role of Pten in macrophage regulation. The particularly high increase of neutrophils in mice with both ETV4 overexpression and Pten deletion (ETV4-Pten+/- mice) developing early PC, is in keeping with the high neutrophil/lymphocyte ratio found associated with poor prognosis in several cancers. The direct or indirect role of these genetic alterations in the increase of neutrophils needs to be investigated.