Purpose:
CD38 has emerged as a high-impact therapeutic target in multiple myeloma, with the approval of daratumumab (anti-CD38 monoclonal antibody). The clinical importance of CD38 in chronic lymphocytic leukemia (CLL) patients has been known for over two decades, though it’s relevance as a therapeutic target in CLL remains understudied.
Experimental Design:
We investigated the biological effects and anti-tumor mechanisms engaged by daratumumab in primary CLL cells. Besides its known immune-effector mechanisms (ADCC, CDC and ADCP), we also measured direct apoptotic effects of daratumumab alone or in combination with ibrutinib. In vivo anti-leukemic activity was assessed in a partially-humanized xenograft model. The influence of CD38 on BCR signaling was measured via immunoblotting of Lyn, Syk, BTK, PLCγ2, ERK1/2 and AKT.
Results:
In addition to immune-effector mechanisms; daratumumab also induced direct apoptosis of primary CLL cells, which was partially dependent on FcγR crosslinking. For the first time, we demonstrated the influence of CD38 on BCR signaling where interference of CD38 downregulated Syk, BTK, PLCγ2, ERK1/2 and AKT; effects that were further enhanced by addition of ibrutinib. In comparison to single agent treatment, the combination of ibrutinib and daratumumab resulted in significantly enhanced anti-CLL activity in vitro and significantly decreased tumor growth and prolonged survival in the in vivo CLL xenograft model.
Conclusions:
Overall, our data demonstrate the anti-tumor mechanisms of daratumumab in CLL; furthermore, we show how co-targeting BTK and CD38 lead to a robust anti-CLL effect, which has clinical implications.