The presence of BM-MSCs rescues chronic lymphocytic leukaemia (CLL) cells from apoptosis both spontaneously and following induction with various drugs, including fludarabine, cyclophosphamide, bendamustine, prednisone, and hydrocortisone. The treatment with a combination of anti-Notch-1, Notch-2, and Notch-4 antibodies or γ-secretase inhibitor XIIreverts this protective effect by day 3, even in the presence of the above-mentioned drugs. The gene discussed is NOTCH4; the disease is B-cell chronic lymphocytic leukemia.