Page 67 - Haematologica Vol. 109 - July 2024

ARTICLE - Leukemia-induced interferon signature in stroma M.W.E. Smeets et al.
B-cell precursor acute lymphoblastic leukemia cells trigger an IFNα/b but not IFNγ response in mesenchymal stromal cells
Remarkably, the amount of secreted IFNα (and IFNb) was decreased in the co-culture setting compared with the levels detected in mono-culture of BCP-ALL cells and MSC, an effect unrelated to ETV6-RUNX1 status (Figure 6A and Online Supplementary Figure S13A, left). This is remarkable since the ETV6-RUNX1-positive cells clearly induced the expression of IFN-related genes in MSC (Figures 1 and 2). The expression level of the IFNα/b-binding IFNAR1, but not IFNAR2 receptor, was often decreased in MSC after co-cul- ture with BCP-ALL, independently of ETV6-RUNX1 status (Figure 6B). Secreted levels of IFNγ were below the level of quantifiable detection in virtually all samples and (mono/ co)-culture conditions (Online Supplementary Figure S13A, right). Expression levels of the IFNγ receptor genes IFNGR1 and IFNGR2 were variable and not related to ETV6-RUNX1 status (Online Supplementary Figure S13C).
The gene regulation in MSC is sensitive to IFNα/b since addition of recombinant IFNα and IFNb to mono-cultures of MSC for 40 and 120 hours clearly induced the expression of the (most significantly upregulated) IFN-index gene IFI6 in MSC. In correspondence, the ETV6-RUNX1-mediated in- duction of IFI6 expression was prevented by simultaneous addition of inhibitors of IFNα/b signaling, resulting in 56-fold
and 27-fold reductions, respectively, after 40 hours of in- cubation and 35-fold and 12-fold reductions, respectively, after 120 hours of incubation (Figure 7A). The ETV6-RUNX1 BCP-ALL-induced expression of IFN-related genes in MSC was also reduced upon exposure to inhibitors of IFNα/b but not to inhibitors of IFNγ (Figure 7B). However, addition of these inhibitors did not affect the viability of BCP-ALL cells in co-culture with MSC, after either 40 hours or 120 hours of incubation, whereas MSC clearly provided a survival benefit to ETV6-RUNX1 BCP-ALL cells at a prolonged incubation of 120 hours (Figure 7C). This MSC-induced survival benefit for ETV6-RUNX1 BCP-ALL was not sensitive to IFNα/b inhibition (Figure 7C, right). Furthermore, inhibitors of IFNα/b did not modulate MSC-induced resistance of ETV6-RUNX1 BCP-ALL cells to L-asparaginase, daunorubicin and prednisolone (Figure 8). In conclusion, the level of resistance of BCP-ALL cells to three chemotherapeutic agents was unaffected by blockade of IFN signaling in MSC.
Discussion
Leukemic cells communicate with components of the bone marrow microenvironment in such a way that protection against chemotherapy and survival of leukemic cells is stim- ulated.9-13,21 In this study, we showed that ETV6-RUNX1 BCP-
AB
Figure 8. The interferon-mediated response in mesenchymal C stromal cells does not affect the sensitivity of primary ETV6- RUNX1 B-cell precursor acute lymphoblastic leukemia cells to drugs. Fold change in percentages of viable ETV6-RUNX1 B-cell precursor acute lymphoblastic leukemia cells in 120-hour mo- no-culture or mesenchymal stromal cell co-culture upon expo- sure to (A) L-asparaginase, (B) daunorubicin, or (C) prednisolone (concentration as determined in Online Supplementary Figure S2) and/or inhibitors of interferon α/b (1.8 ng/mL), normalized to values in mono-culture without drug exposure or interferon inhibitors. Bars represent means ± standard error of mean of triplicate measurements for three independent experiments. i-IFNα/b: inhibitors of interferon α/b; BCP-ALL: B-cell precursor acute lymphoblastic leukemia; MSC: mesenchymal stromal cells;
ASP: L-asparaginase; DNR: daunorubicin; PRED: prednisolone.
Haematologica | 109 July 2024
2081