Purpose: To determine if melanoma within the tumor microenvironment will result in immunosuppression within the draining lymph node as measured by down-regulation of T-cell receptor zeta (TCR zeta) expression.
Experimental design: Patients with clinical stage I to III melanoma undergoing wide local excision and sentinel lymph node biopsy or therapeutic lymph node dissection were consented to have a portion of their lymph node sampled. Lymph nodes were classified as macroscopically involved (TI), microscopically involved (MI), noninvolved with positive wide excision (NI+), or noninvolved with negative wide excision (NI-). Lymphocytes were stained using antibodies to TCR zeta and other immune cells and analyzed via flow cytometer. Reverse transcription-PCR was used to assess for mediators of immunosuppression.
Results: Fifty patient lymph node samples (15 TI, 7 MI, 9 NI+, and 19 NI-) were evaluated. Increasing involvement of tumor in the lymph node was associated with decreasing TCR zeta chain expression (TI 56%, MI 76%, and NI- 89%). Differences between TI and MI (P = 0.005), TI and NI- (P = 0.0001), and MI and NI- (P = 0.019) were statistically significant. There was also a significant difference between TCR zeta chain expression of NI+ and NI- (73% versus 89%; P = 0.0016). A trend toward increased arginase expression in tumor-involved lymph nodes was detected by reverse transcription-PCR.
Conclusions: Melanoma involvement of regional nodes is associated with loss of TCR zeta expression that is inversely related to tumor burden. Residual melanoma within the wide local excision specimen is associated with TCR zeta loss in noninvolved sentinel lymph nodes, suggesting that immune modulation precedes tumor spread.