Effetto della chemioterapia metronomica sul sistema immunitario e sulla prognosi di cani affetti da neoplasia

Immunosuppressive regulatory T cells (Tregs) are part of the tumor microenvironment and contribute to the establishment of neoplastic tolerance, promoting tumor development and progression by dampening antitumor immune responses. Metronomic chemotherapy (MC) is defined as the oral administration of low doses of chemotherapy on a continuous schedule of treatment, without extended drug-free breaks. MC has been shown to be a multitarget therapy and to act not only on neovascularization, cancer stem cells and tumor quiescence but also being able to interact with the patient's immune response to cancer, reversing the state of immune tolerance by selectively depleting the number of Tregs and impairing their functions. The aim of this study was to evaluate the effects of MC consisting of daily administration of cyclophosphamide, meloxicam and thalidomide, on the absolute number of circulating Tregs in a population of patients with different cancer diseases, over the medium/long term. It was hypothesized that during metronomic chemotherapy, the absolute number of circulating Tregs would progressively decrease; furthermore, good tolerability with few adverse effects was expected. This prospective study included 29 canine cancer patients. To determine circulating Tregs we performed a complete blood count (CBC) and a cytofluorimetric examination of the lymphocytes. A blood sample was collected before and 15, 30, 90 and 180 days after the start of metronomic treatment (cyclophosphamide at 12,5 mg/m2, meloxicam at 0,1 mg/kg and thalidomide at 3-6 mg/kg). The percentage of circulating CD4+CD25+Foxp3+ Tregs obtained by cytofluorimetry was then related to the absolute number of circulating lymphocytes to obtain the absolute number of circulating Tregs of each sample. We found that the duration of MC administration has a statistically significant influence on the reduction of circulating Tregs absolute number, but not on the circulating Tregs percentage. Furthermore, in our cohort, tumor type or previous surgery did not seem to have any effect on the circulating Tregs absolute number. Our patients did not develop any moderate or severe adverse effects, and long-term treatment was well tolerated. This is the first time that the effect of the metronomic combination of cyclophosphamide, meloxicam, and thalidomide on circulating Tregs is evaluated in a canine population with cancer, showing a reduction in their absolute number over time. This is an interesting result that should motivate to gather more knowledge about the interactions between immune system and different tumor types, in order to be able to use MC in a more targeted way. Furthermore, flow cytometry is a readily available tool that could be of great value in daily clinical practice to analyze the pattern of circulating Tregs during MC to detect early tumor progression.