T-cell subset analysis of peripheral T-cell lymphomas by paraffin section immunohistology and correlation of CD4/CD8 results with flow cytometry

Peripheral T-cell lymphomas (PTCLs) are often diagnosed after demonstration of T-lineage-related antigen expression on neoplastic lymphocytes by paraffin immunoperoxidase (PIP). However, complete T-cell subset analysis for helper, suppressor/cytotoxic, αβ, and γδ phenotypes has not been examined by PIP. Therefore, PIP was performed for CD4, CD8, T- cell intracellular antigen (TIA)-1, and βF1 expression in 31 PTCLs previously studied for CD4 and CD8 by flow cytometry. The CD4 and CD8 results from both methods were compared. All βF1^- PTCLs were studied for T-cell receptor (TCR)γδ by PIP. PIP showed 71% correlation with the 21 PTCLs that had distinct CD4⁺CD8^- or CD4^-CD8⁺ phenotypes by flow cytometry, with 64% and 90% sensitivity for CD4 and CD8 expression, respectively. Tumor cells in four of six PTCLs that had no clear CD4 or CD8 predominance or coexpression of these antigens by flow cytometry were shown to be CD4⁺CD8^- or CD4^- CD8⁺ by PIP. Twelve (39%) PTCLs demonstrated a cytotoxic (TIA-1⁺) phenotype by PIP, including eight CD4^-CD8⁺, one CD4⁺CD8^- and three CD4^-CD8^- cases. Of 30 immunoreactive PTCLs, 26 (87%) were αβ (βF1⁺) by PIP. Both large cell cases among four βF1^- PTCLs were TCRγδ⁺ by PIP, including one γδ⁺ case confirmed by flow cytometry. We conclude that CD4 and CD8 T-cell subsets can be assigned for most PTCLs by PIP, with CD4 showing moderate and CD8 showing strong correlation with flow cytometric results. PIP can also define CD4 or CD8 expression on tumor cells in the PTCLs in which flow cytometry produces inconclusive results. Cytotoxic PTCLs can be identified easily with TIA-1, which can also distinguish cytotoxic from 'suppressor' CD8⁺ PTCLs. Most PTCLs are derived from αβ T-cells, however some large cell γδ PTCLs may be identified by PIP.