Ad-CD154 gene therapy causes rapid reductions in cell counts and lymph node size

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Accepted May 9, 2005

Inhibitors of XIAP sensitize CD40-activated chronic lymphocytic

leukemia cells to CD95-mediated apoptosis

Arnon P Kater, Dicker, Massimo Mangiola, Kate Welsh,

Houghten, Ostresh, Adel Nefzi, C , Clemencia Pinilla,

and J Kipps*

s Cancer Center, University of California, San Diego, La Jolla,

CA, USA; Department of Hematology, Academic Medical Center,

University of Amsterdam, Amsterdam, The Netherlands; Chronic

Lymphocytic Leukemia Research Consortium, La Jolla, CA, USA

s Cancer Center, University of California, San Diego, La Jolla,

CA, USA; Chronic Lymphocytic Leukemia Research Consortium, La Jolla,

CA, USA

Burnham Institute, La Jolla, CA, USA; Chronic Lymphocytic Leukemia

Research Consortium, La Jolla, CA, USA

Burnham Institute, La Jolla, CA, USA

Torrey Pines Institute for Molecular Sciences, San Diego, CA, USA

* Corresponding author; email: tkipps@....

Chronic lymphocytic leukemia (CLL) patients treated with adenovirus

(Ad)-CD154 (CD40L) gene therapy experienced rapid reductions in

leukemia-cell counts and lymph-node size associated with the induced

expression Fas (CD95). However, CLL cells initially resist CD95-

mediated apoptosis within the first 3 days after CD40-ligation in

vitro. Thereafter, they become sensitive, which is associated with

the CD40-induced expression of the pro-apoptotic protein BH3

interacting domain death agonist (Bid). We hypothesized the initial

resistance to CD95-mediated apoptosis may be due to the high-level

expression of X-linked inhibitor of apoptosis protein (XIAP) by CLL

cells. Consistent with this, CLL cells from patients one day after

treatment with autologous Ad-CD154-transduced CLL cells became

sensitive to CD95-mediated apoptosis following treatment with a novel

XIAP inhibitor, 1540-14. Similarly, 1540-14 specifically enhanced

CD95-mediated apoptosis of CLL cells following CD40-ligation in

vitro. Immunoblot analyses demonstrated that treatment with 1540-14

allowed CD40-stimulated CLL cells to experience high-level activation

of caspases 8 and 3 and cleavage of poly(ADP-ribose) polymerase

following CD95-ligation. This study demonstrates that distal

apoptosis regulators contribute to the initial resistance of CD40-

activated CLL cells to CD95-mediated apoptosis and suggests that XIAP

inhibitors might enhance the effectiveness of immune-based treatment

strategies that target CD40, such as CD154 gene therapy.