Milk fermented by Lactobacillus casei CRL431 modifies cytokine profiles associated to different stages of breast cancer development in mice

Breast cancer is one of the leading causes of death worldwide. It is recognised that immune system influences its promotion, progression, and metastasis, as well as their responsiveness to therapies. Previously, it was reported that milk fermented by Lactobacillus casei CRL431 decreased tumour growth and metastasis in a mouse breast cancer model, through the modulation of the host immune response. The aim of the present work was to analyse the systemic immune response induced by the administration of probiotic fermented milk (PFM) at different stages of cancer development, evaluating cytokines produced by splenocytes stimulated in vitro with 4T1 tumour cells, or its conditioned medium (CM). Groups of healthy mice and mice bearing 4T1 tumour or suffering metastasis after tumour surgery were studied. Results showed that at the early stages, PFM maintained pro-inflammatory response associated to the delay or the inhibition of tumour growth. PFM administration to mice bearing tumour maintained an important inflammatory response; however, in contrast to the milk group, this response was regulated to avoid exacerbation of inflammation. In the metastasis model, the benefits of PFM were associated to avoid the immunosuppression associated to high interleukin-10 levels. In conclusion, as cancer cells induce modifications of the immune response to favour their own growth at each stage of cancer development, PFM administration stimulated different profile of cytokines to respond to these modifications and fight against cancer cells.