The CLL cells in microwells had a proliferation rate and viability identical to standard co-cultures (Fig. 1I, Supplementary Fig. 1L, M), showing similar signs of CD40L/IL4 interaction: elevated surface FAS expression induced by CD40L, down-modulated CXCR4 surface levels by IL4, and increased cell size (Supplementary Fig. 1N–P). Here, IL4 is linked to B-cell chronic lymphocytic leukemia.