CD40 stimulation of B‐cell chronic lymphocytic leukaemia cells enhances the anti‐apoptotic profile, but also Bid expression and cells remain susceptible to autologous cytotoxic T‐lymphocyte attack

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Abstract
Summary: To enhance the poor antigen‐presenting capacity of B‐cell chronic lymphocytic leukaemia (B‐CLL), CD40 triggering has been considered as an active immunotherapy. However, CD40 stimulation also has an anti‐apoptotic effect and may further impair the dysregulated response of B‐CLL to apoptotic stimuli. Therefore, we measured the expression of virtually all regulators of apoptosis before and after CD40 stimulation. These findings were correlated with sensitivity for chemotherapy‐ and death‐receptor‐induced apoptosis and T‐cell‐mediated killing. CD40 stimulation enhanced the constitutive anti‐apoptotic profile of B‐CLL cells by upregulation of Bcl‐xL and Bfl‐1 and downregulation of the BH3‐only protein Harakiri. Unexpectedly, the BH3‐only protein Bid was strongly induced. Functionally, CD40‐stimulated B‐CLL cells became resistant to drug‐induced apoptosis and, despite upregulation of CD95 and Bid, were not sensitive to CD95L. In contrast, autologous T cell killing, triggered by loading CLL cells with viral (CMV) peptides, was very efficient both before and after CD40 stimulation. Upon CTL interaction, CLL targets underwent mitochondrial depolarization and caspase‐3 activation. Thus, despite an increased anti‐apoptotic profile, CD40 triggered B‐CLL cells remain excellent targets for resident cytotoxic T cells. These data support therapeutic exploitation of CD40 stimulation in B‐CLL, provided that a strong CTL component is induced.