Purpose: Human invariant natural killer T (NKT) cells are novel, distinct lymphocyte populations with a restricted T-cell receptor repertoire (Vα24-Vβ11). They play a pivotal role in immunoregulation and in antitumor activities. This study focused on Vα24⁺ NKT cells in colorectal carcinomas and their clinicopathologic significance.

Experimental Design: Vα24⁺ NKT-cell infiltration immunohistochemistry was studied in a total of 103 colorectal carcinoma cases. The degree of NKT-cell infiltration in tumors was evaluated as low (<7 NKT cells/5 HPF) or high (≥7 NKT cells/5 HPF). The correlation between the degree of infiltrated Vα24⁺ NKT cells and clinicopathologic variables was studied statistically.

Results: A small number of Vα24⁺ NKT cells were found in the normal colorectal mucosa (2.6 ± 3.7 cells/5 HPF); however, their number increased remarkably in colorectal carcinomas (15.2 ± 16.3 cells/5 HPF; P = 0.0003) and a majority showed phenotype of activation. Higher NKT-cell infiltration was more frequent in women than in men (P = 0.034) and correlated with fewer lymph node metastases (P = 0.042). Patients with high NKT-cell infiltration showed higher overall (P = 0.018) as well as disease-free (P = 0.0006) survival rates. Intratumor NKT-cell infiltration was an independent prognostic factor for the overall (P = 0.033) and disease-free (P = 0.0064) survival rates.

Conclusions: Increased infiltration of Vα24⁺ NKT cells was observed in colorectal carcinomas. Higher Vα24⁺ NKT-cell infiltration in colorectal carcinomas was an independent prognostic factor for favorable prognosis.