Survival in rectal cancer is predicted by T cell infiltration of tumour-associated lymphoid nodules.

Lymphoid nodules are a normal component of the mucosa of the rectum, but little is known about their function and whether they contribute to the host immune response in malignancy. In rectal cancer specimens from patients with local (n=18), regional (n=12) and distant (n=10) disease, we quantified T cell (CD3, CD25) and dendritic cell (CD1a, CD83) levels at the tumour margin as well as within tumour-associated lymphoid nodules. In normal tissue CD3+, but not CD25+, T cells are concentrated at high levels within lymphoid nodules, with significantly fewer cells found in surrounding normal mucosa (P=0.001). Mature (CD83), but not immature (CD1a), dendritic cells in normal tissue are also found clustered almost exclusively within lymphoid nodules (P=<0.0001). In rectal tumours, both CD3+ T cells (P=0.004) and CD83+ dendritic cells (P=0.0001) are also localized preferentially within tumour-associated lymphoid nodules. However, when comparing tumour specimens to normal rectal tissue, the average density of CD3+ T cells (P=0.0005) and CD83+ dendritic cells (P=0.0006) in tumour-associated lymphoid nodules was significantly less than that seen in lymphoid nodules in normal mucosa. Interestingly, regardless of where quantified, T cell and dendritic cell levels did not depend upon the stage of disease. Increased CD3+ T cell infiltration of tumour-associated lymphoid nodules predicted improved survival, independent of stage (P=0.05). Other T cell (CD25) markers and different levels of CD1a+ or CD83+ dendritic cells did not predict survival. Tumour-associated lymphoid nodules, enriched in dendritic cells and T cells, may be an important site for antigen presentation and increased T cell infiltration may be a marker for improved survival.