Immune Correlates of Denileukin Diftitox Treatment in TFH-Type Lymphoma.

Background/Objectives: Follicular helper T-cell (TFH)-type lymphomas, including angioimmunoblastic T-cell lymphoma (AITL) and TFH lymphoma, not otherwise specified (TFH-NOS), are characterized by marked immune dysregulation in the tumor microenvironment. We investigated whether TFH-type lymphomas are enriched in immunosuppressive cells and explored immunologic changes associated with denileukin diftitox (DD) treatment. Methods: FOXP3-positive mononuclear cells were quantified by immunohistochemistry in lymph node specimens from 10 patients with TFH-type lymphoma and six with non-TFH-type T-cell lymphoma. Paired skin biopsy specimens obtained before and after DD treatment from two patients with AITL were evaluated for CD4, CD8, CD68, CD163, and FOXP3 expression. Longitudinal flow cytometric T-cell receptor Vβ repertoire analysis of CD8-positive T-cell subsets was performed in three patients with AITL treated with DD. Clinical responses were retrospectively assessed in seven patients with relapsed or refractory TFH-type lymphoma treated with DD. Results: TFH-type lymphomas showed significantly higher intra-tumoral FOXP3-positive cell densities than non-TFH-type lymphomas (p = 0.0024). In paired skin biopsies, DD treatment was associated with reductions in CD68- and CD163-positive macrophage-rich infiltrates and a suggested decrease in FOXP3-positive cells. Among seven patients treated with DD, the overall response rate was 86%, including one complete response and five partial responses. Responders showed selective Vβ over-representation patterns in effector and/or memory CD8-positive T-cell subsets, whereas such findings were not convincing in the non-responder. Conclusions: TFH-type lymphomas were associated with higher FOXP3-positive cell density than selected non-TFH-type comparators. DD treatment may be associated with changes in tissue immune infiltrates and peripheral CD8/TCR Vβ skewing in responding cases, although these findings remain exploratory and do not establish causality.