There is indirect evidence that T cell responses can control the metastatic spread of colorectal cancer (CRC). However, an enrichment of CD4⁺Foxp3⁺ regulatory T cells (Tregs) has also been documented.

To evaluate whether CRC promotes Treg activity and how this influences anti-tumour immune responses and disease progression.

A longitudinal study of Treg activity on a cohort of patients was performed before and after tumour resection. Specific CD4⁺ T cell responses were also measured to the tumour associated antigens carcinoembryonic antigen (CEA) and 5T4.

Tregs from 62 preoperative CRC patients expressed a highly significant increase in levels of Foxp3 compared to healthy age-matched controls (p=0.007), which returned to normal after surgery (p=0.0075). CD4⁺ T cell responses to one or both of the tumour associated antigens, CEA and 5T4, were observed in approximately two-thirds of patients and one third of these responses were suppressed by Tregs. Strikingly, in all patients with tumour recurrence at 12 months, significant preoperative suppression was observed of tumour-specific (p=0.003) but not control CD4⁺ T cell responses.

These findings demonstrate that the presence of CRC drives the activity of Tregs and accompanying suppression of CD4⁺ T cell responses to tumour-associated antigens. Suppression is associated with recurrence of tumour at 12 months, implying that Tregs contribute to disease progression. These findings offer a rationale for the manipulation of Tregs for therapeutic intervention.