Abstract
CD8+ T cells are crucial immune cells for protection against cancers. Recent studies have shown that microbial metabolite butyrate boosts CD8+ T cell effector function in viral infection models and may protect from cancer. This study used in vitro culture, immune cell therapy, and flow cytometry to explore the effect of butyrate on CD8+ T cells and their anti-tumour responses in mice. It was hypothesised that butyrate would enhance the effector function of CD8+ T cells in vitro and reduce tumour growth in vivo when these cells are adoptively transferred.
CD8+ T cells were activated in vitro using anti-CD3 and anti-CD28 beads, in the presence of 1mM butyrate then analysed using flow cytometry for immune function. To investigate anti-tumour immunity, 5 x 105 in vitro activated cells treated with or without butyrate, were adoptively transferred into tumour-bearing mice. A control group (which did not receive activated cells) was included, n = 17-19 mice per group.
In vitro, butyrate increased the frequency of IFN-γ+ CD8+ T cells compared to control cells activated without butyrate (87% vs 25% P = 0.0004, Friedman test), and the median fluorescence intensity (MFI) of anti-tumour molecule IFN-γ (9206 vs 48374 fluorescent units, P = 0.0052, Friedman test). When adoptively transferred into tumour-bearing mice, butyrate-activated cells caused only a 3-fold increase in tumour area compared to 9-fold in control activated cells. Butyrate activated cells were also present at a higher frequency within tumours than non-butyrate activated cells (26.7% vs 6.67%, P = 0.0010, Mann-Whitney test).
Overall, exposure to butyrate during CD8+ T cell activation increased effector functions and boosted anti-tumour immunity when cells were adoptively transferred into tumour bearing mice. Thus, treating cells with butyrate may be a powerful method to enhance T cell-based therapies and antitumour responses with the goal of improving outcomes for cancer patients.