Background and objectives: A distinct subset of T helper cells, named follicular helper T- (TFH) cells, have been recently described. The TFH-cells can be identified on the basis of the expression of several markers including: the chemokine CXCL13; the costimulatory molecules PD-1 and inducible costimulator (ICOS); and the transcription factor Bcl-6. The TFH-cells appeared to be localized in several subsets of T-cell lymphomas. However, their localization in cutaneous T-cell lymphomas has been rarely described. In this study, the clinical features, histopathological morphology, and expression of TFH markers in cutaneous T-cell lymphomas were investigated.
Materials and methods: Forty-nine Korean patients (24 men, 25 women) diagnosed with cutaneous T-cell lymphoma were examined: 25 patients with mycosis fungoides (MF), 9 with lymphomatoid papulosis, 8 with anaplastic large cell lymphoma, 4 with subcutaneous panniculitis-like T-cell lymphoma, 2 with peripheral T-cell lymphoma, and 1 with NK/T-cell lymphoma. Chart review was performed to evaluate the clinical features. Hematoxylin and eosin (H&E) staining was used to study the general histopathological changes. Additionally, immunohistochemical staining for CD10, Bcl-6, ICOS, CXCL13, and PD-1 were performed. The extent of staining was scored from 0 to 3 by 2 independent observers.
Results: PD-1 was frequently expressed in most of the MF cases, but was rarely expressed in other cutaneous T-cell lymphomas. Bcl-6, CXCL13, ICOS, and CD10 were scantly expressed in most T-cell lymphomas, including MF. Interestingly, the staining for PD-1 was negative in all the MF cases with large-cell transformation. No correlation was observed among clinical morphology, disease course, and PD-1 expression rate in the MF cases.
Conclusions: Most of the MF samples expressed TFH-cell markers. This finding suggests that some MF tumor cells might consist of TFH-cells. In addition, higher PD-1 expression rates in MF than in other cutaneous T-cell lymphomas implies that PD-1 can be an MF-sensitive marker, and it might be useful in differentiating MF from other cutaneous T-cell lymphoma. The loss of PD-1 expression in large-cell–transformed MF suggests that PD-1 downregulation may be related to the processes responsible for large-cell transformation.
