Effects of exercise and anti-PD-1 on the tumour microenvironment

Immune checkpoint inhibition is highly effective in treating a subset of patients with certain cancers, such as malignant melanoma. However, a large proportion of patients will experience treatment resistance, and other tumour types, such as breast cancer, have thus far proven largely refractory to immune checkpoint inhibitors as single agents. Exercise has been associated with improved cancer patient survival, has known immune-modulatory effects, may improve anti-tumour immunity and may normalise tumour blood vessels. Therefore, we hypothesised that post-implant exercise would boost the effect of concurrent immunotherapy by enhancing anti-tumour immune responses and improving tumour blood flow. To investigate this, mice with EO771 breast tumours or B16-F10 melanomas received anti-PD-1, an isotype control antibody or no treatment. Mice were randomised to exercise (voluntary wheel running) or no exercise at tumour implant. Exercise reduced the number of CD8⁺T cells in EO771 (p = 0.0011) but not B16-F10 tumours (p = 0.312), and reduced the percentage of CD8⁺T cells within the total T cell population in both tumour types (B16-F10: p = 0.0389; EO771: p = 0.0015). In contrast, the combination of exercise and anti-PD-1 increased the percentage of CD8⁺T cells in EO771 (p = 0.0339) but not B16-F10 tumours. Taken together, our results show that exercise and anti-PD-1 induce changes in the tumour immune microenvironment which are dependant on tumour type.