Expression of programmed death-1 (CD279) in primary cutaneous B-cell lymphomas with correlation to lymphoma entities and biological behaviour.

BACKGROUND: Programmed death-1 (PD-1/CD279) is a cell-surface protein expressed in activated T cells and a subset of T lymphocytes including follicular helper T cells (TFH ). The interaction between PD-1 and its ligands plays a role in immune response and evasion of malignancies. In nodal follicular lymphoma, the number of intratumoral PD-1-positive lymphocytes is associated with overall survival.

OBJECTIVES: To investigate 28 cases of primary cutaneous B-cell lymphoma, including the subtypes PCFCL (n = 10), PCMZL (n = 10) and DLBCL-LT (n = 8) for the number and density of PD-1-positive cells.

METHODS: Immunohistochemical staining and a computerized morphometric analysis for evaluation were applied. The results were correlated with the clinical outcome. To distinguish between activated T cells and TFH we performed PD-1/bcl-6 double staining and compared these results with CXCL-13 staining. Double staining for PD-1 and PAX-5 was used to investigate whether tumour cells were positive for PD-1.

RESULTS: The PD-1-positive cells represented tumour-infiltrating T cells (TILs). Only a minor subset was represented by TFH . Patients with DLBCL-LT had a significantly lower number of PD-1-positive TILs than those with PCMZL (P = 0·012) and PCFCL (P = 0·002) or both (P = 0·001). The difference between PCMZL and PCFCL did not reach significance (P = 0·074). The tumour cells were negative for PD-1.

CONCLUSIONS: A higher number of PD-1-expressing cells was found in indolent PCMZL and PCFCL than in high-malignant DLBCL-LT. The PD-1-positive cells represented not only TFH , but also other activated T cells as a part of the tumour microenvironment. The tumour cells in all investigated types of PCBCL did not show aberrant PD-1 expression.