Disclosed herein are compositions and methods of use comprising hexavalent DNL complexes. Preferably, the complexes comprise anti-CD20 and/or anti-CD22 antibodies or fragments thereof. More preferably, the anti-CD20 antibody is veltuzumab and the anti-CD22 antibody is epratuzumab. Administration of the subject hexavalent DNL complexes induces apoptosis and cell death of target cells in diseases such as B-cell lymphomas or leukemias, autoimmune disease or immune dysfunction disease. In most preferred embodiments, the DNL complexes increase levels of phosphorylated p38 and PTEN, decrease levels of phosphorylated Lyn, Akt, ERK, IKKα/β and IκBα, increase expression of RKIP and Bax and decrease expression of Mcl-1, Bcl-xL, Bcl-2, and phospho-BAD in target cells. The subject DNL complexes show EC50 values for inhibiting tumor cell growth in the low nanomolar or even sub-nanomolar concentration range.