Tnfrsf4-expressing regulatory T cells promote immune escape of chronic myeloid leukemia stem cells
Magdalena Hinterbrandner, Viviana Rubino, Carina Stoll, Stefan Forster, Noah Schnüriger, Ramin Radpour, Gabriela M. Baerlocher, Adrian F. Ochsenbein, Carsten Riether
Magdalena Hinterbrandner, Viviana Rubino, Carina Stoll, Stefan Forster, Noah Schnüriger, Ramin Radpour, Gabriela M. Baerlocher, Adrian F. Ochsenbein, Carsten Riether
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Research Article Hematology Stem cells

Tnfrsf4-expressing regulatory T cells promote immune escape of chronic myeloid leukemia stem cells

Abstract

Leukemia stem cells (LSCs) promote the disease and seem resistant to therapy and immune control. Why LSCs are selectively resistant against elimination by CD8+ cytotoxic T cells (CTLs) is still unknown. In this study, we demonstrate that LSCs in chronic myeloid leukemia (CML) can be recognized and killed by CD8+ CTLs in vitro. However, Tregs, which preferentially localized close to CD8+ CTLs in CML BM, protected LSCs from MHC class I–dependent CD8+ CTL–mediated elimination in vivo. BM Tregs in CML were characterized by the selective expression of tumor necrosis factor receptor 4 (Tnfrsf4). Stimulation of Tnfrsf4 signaling did not deplete Tregs but reduced the capacity of Tregs to protect LSCs from CD8+ CTL–mediated killing. In the BM of newly diagnosed CML patients, TNFRSF4 mRNA levels were significantly increased and correlated with the expression of the Treg-restricted transcription factor FOXP3. Overall, these results identify Tregs as key regulators of immune escape of LSCs and TNFRSF4 as a potential target to reduce the function of Tregs and boost antileukemic immunity in CML.

Authors

Magdalena Hinterbrandner, Viviana Rubino, Carina Stoll, Stefan Forster, Noah Schnüriger, Ramin Radpour, Gabriela M. Baerlocher, Adrian F. Ochsenbein, Carsten Riether

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Figure 8

Tregs protect human CD34+CD38– CML stem/progenitor cells from elimination by CD8+ CTLs.

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Tregs protect human CD34+CD38– CML stem/progenitor cells from eliminatio...
(A) Colony forming and replating capacity of CD34+CD38– LSCs (CML 1–3) cultured overnight in the presence and absence of CD8+ CTLs of the same CML patients at a ratio of 1:1; t test. (B) Colony forming and replating capacity of LSCs (CML 4–7) pretreated with the granzyme B inhibitor I (100 μM) and cultured in the presence and absence of CD8+ CTLs at a ratio of 1:1 overnight; t test. (C) Colony forming and replating capacity of LSCs (CML 4–6) cultured in the presence and absence of CD8+ CTLs and/or CD25+CD127lo CD4+ Tregs at a ratio of 1:1:1. One-way ANOVA followed by Tukey’s post hoc test. (D) Numbers of BM Tregs in CML patients and healthy donors (CML, n = 10; healthy donors [HD], n = 4). Tregs per 1.2 mm2 field were determined; t tests. (E) Distribution of BM FOXP3+ Tregs (scale bar: 200 μm; n = 10 CML patients). (F and G) Spatial localization of BM FOXP3+ Tregs in respect to (F) CD8+ CTLs and (G) CD34+ CML stem/progenitor cells (LSPCs) (scale bar: 50 μm; n = 10 CML patients; FOXP3, brown; CD8+ CTLs and LSPCs, red). FOXP3+ cells, black; CD8+ CTLs and LSPCs, red circles. (H) Frequency of BM Tregs located near CD8+ CTLs and LSPCs (n = 10 CML patients). Close proximity was defined as a distance of ≤ 2 cell nuclei; t tests. (I–K) TNFRSF4, FOXP3, and TGFB1 mRNA expression in CML patients and HD (n = 73; CML: n = 76; GSE13159); t test. (L and M) Correlation of FOXP3 with (L) TNFRSF4 and (M) TGFB1 mRNA expression in BM of CML patients (n = 76; GSE13159); Spearman correlations. (N) Frequency of CD25+CD127lo CD4+ Tregs, CD8+ CTLs, and LSPCs expressing TNFRSF4 on the cell surface in CML patients (CML 2, 5, 7) analyzed by FACS. Data are displayed as mean. *P < 0.05, **P < 0.01, ***P < 0.001 and ****P < 0.0001.