Immunophenotypic Characterization of Neoplastic T Follicular Helper Cells by Flow Cytometry.

Background: T follicular helper (TFH) cell lymphoma is complex, and we hope to provide a new perspective for its diagnosis.

Methods: We analysed the immunophenotypes of 89 mature T-cell lymphomas, including 52 nodal lymphomas of TFH origin, as well as 32 benign lymph node samples and 30 healthy bone marrow samples, by flow cytometry (FCM).

Results: Among pan-T cell markers, CD4⁺CD5⁺CD3^- is the typical pattern that distinguishes TFH lymphoma from other T-cell lymphomas. Specific markers with high sensitivity for the diagnosis of TFH lymphoma include programmed cell death protein 1 (PD-1) and inducible synergistic co-stimulation molecules (ICOS), which are expressed at lower levels in neoplastic TFH cells than in benign TFH cells. In contrast, the specificity of C-X-C chemokine receptor type 5 (CXCR5) and CD10 is high, and the proportion of CD10-positive cells in neoplastic TFH samples is greater than that in benign TFH samples. Of the 52 TFH lymphoma samples in our study, 7 presented with abnormalities in B cells or plasmablast cells; we considered these to indicate B-cell proliferation rather than composite lymphoma.

Conclusion: Immunophenotypic characterization of neoplastic TFH cells by FCM is unique and has diagnostic value. Each specimen of suspected TFH lymphoma should be analyzed for the presence of specific markers, such as PD-1, ICOS, CXCR5, and CD10, and the clonality of B cells and plasmablast cells should be assessed.