CD40L induces proliferation, self-renewal, rescue from apoptosis, and production of cytokines by CD40-expressing AML blasts

Objective Conflicting experimental and clinical results have been reported regarding the role of CD40 in acute myeloid leukemia (AML). In the present study, we analyzed the capability of CD40L/CD154 to modulate several functional aspects of CD40-expressing AML blasts. Methods After defining the constitutive expression levels of CD40 in a wide panel (n = 67) of AMLs and evaluating the capability of cytokines to modulate its expression, we investigated the effects of CD40 engagement by soluble (s) CD40L on proliferation, self-renewal capacity, apoptosis, homotypic adhesion, and cytokine production of leukemia cells. Results CD40 was detected in blast cells from about 37% of AMLs, the highest frequency being documented in monocytic subtypes, and its expression was upregulated or de novo induced by treatment with interleukin (IL)-1α, IL-3, IL-4, granulocyte-macrophage colony-stimulating factor (GM-CSF), interferon-γ, and tumor necrosis factor-α. Exposure of CD40+ AML blasts to sCD40L resulted in a dose-dependent proliferative response, enhancement of clonogenic growth and self-renewal capacity, and a striking increase in colony size. CD40 engagement was able to rescue AML blasts from apoptosis induced by serum deprivation, as demonstrated by reduced expression of APO2.7 and annexin-V binding, as well as upregulation of the anti-apoptotic protein bcl-xL. CD40 triggering upregulated cell surface expression of the adhesion molecules CD54, CD58, and CD15 and resulted in homotypic aggregation of leukemia cells at least in part CD54-dependent. An increased production of IL-6 and GM-CSF by CD40+ AML blasts was also documented upon sCD40L exposure. Conclusions This study indicates a possible involvement of CD40 in the interactions of AML blasts with other growth-sustaining microenvironmental accessory cells and immune effectors, in turn expressing CD40L. Caution in the use of CD40 triggering in immunotherapy of AMLs is also suggested.