Peripheral lymphocyte subpopulations in prostate cancer - data from an animal model

Abstract

Introduction: Prostate cancer (PCa) is one of the most common cancers among men worldwide. The presence of immune cells in human cancer raises a fundamental question in oncology. The interaction between immune system and PCa is an important field for translational research. This work aimed to characterize the peripheral lymphocyte subpopulations in a PCa animal model. Methods: Twenty-five male Wistar Unilever rats (Rattus norvegicus) with twelve weeks of age were randomly divided into two groups: Control (n=10) and Induced (n=15). All procedures were approved by the Portuguese Competent Authority (DGAV no. 021326). Prostate lesions were induced through the administration of flutamide (50 mg/kg, TCI Chemicals, USA), testosterone propionate (100 mg/kg, TCI Chemicals, USA) and N-methyl-N-nitrosourea (30 mg/kg, Sigma Chemical Co., Spain), and crystalline testosterone implants. Animals were humanely sacrificed at 61 weeks of age. Peripheral blood of all animals was collected by intracardiac puncture and transferred into tubes containing EDTA salt as an anticoagulant for flow cytometry analysis. The following conjugated monoclonal antibodies were used: cyCD3-BV421, CD3-FITC, CD25-APC, CD45-BV510, CD127-PE, CD161-FITC, CD4-PE/Cy7, CD45RA-APC/Cy7, OX-82-PE and CD8a-PerCP. The flow cytometry immunophenotyping was performed in a BD FACSCantoTM II cytometer (BD Biosciences, USA) and data were analysed with InfinicytTM, flow cytometry software 1.7 version. Statistical analysis was performed using SPSS 25. The differences were considered statistically significant at p<0.05. Results: Although differences did not reach the level of statistical significance, the populations of CD3+ and CD4+ lymphocytes were higher in control group when compared with induced group (p>0.05). Similarly, CD8+ lymphocyte population was higher in control group than in induced group (9.56±0.74 vs 6.38±0.32) (p<0.05). Inversely, the population of regulatory T cells (TRegs) (2.99±0.46 vs 4.630±0.35), the TRegs/CD8 ratio (0.35±0.09 vs 0.45±0.08) and the TRegs/Natural Killer ratio (0.52±0.05 vs 1.03±0.13) were higher in induced group when compared with control one (p<0.05). Conclusion: The population of Tregs increased in induced animals, while the population of NK decreased in these animals, which is in accordance with data previously published by other authors reporting the increase of Tregs and decrease of NK cells in animals with cancer. The characterization of these immune system subpopulation can be important for other studies such as preclinical cancer models.