Prevalence of FoxP3+ Cells in Canine Tumours and Lymph Nodes Correlates Positively with Glucose Transporter 1 Expression

Hypoxia and regulatory T cells (Tregs) in tumours are both known to be negative prognostic factors in cancer, and this study demonstrated a correlation between the two factors in canine neoplasia. Samples of 57 canine tumours and 29 canine lymph nodes categorized as tumour-draining, with or without metastasis, or reactive and not tumour-associated, were examined. Sequential sections were labelled by immunohistochemistry for glucose transporter 1 (Glut1) and FoxP3 as markers of hypoxia and Tregs, respectively. Up to 21 regions of interest (ROI) were selected in each section in a representative pattern and were assigned a semiquantitative score based on Glut1 labelling. The number of FoxP3+ cells within each ROI was counted. A generalized estimating equation with negative binomial log link function was used to determine an association between Glut1 expression and FoxP3+ cell count. Higher Glut1 immunoreactivity was correlated with significantly higher numbers of FoxP3+ cells in the total tumour sample pool and total lymph node sample pool. Analysis of various subcategories of tumours and lymph nodes showed that this correlation was also present within samples characterized as malignant, haemopoietic mesenchymal tumours, non-haemopoietic mesenchymal tumours, epithelial tumours, lymphoma, lymph nodes containing metastases and reactive lymph nodes. These results indicate that hypoxia in canine tumours may result in an increased infiltration by Tregs.