TNF and B-cell chronic lymphocytic leukemia: In addition, paraformaldehyde fixed instead of alive HUVEC monolayers lacked any prosurvival effects in the cocultured CLL cells and, more importantly, emphasized the proapoptotic ones onto TNF-HUVEC even at 2 or 5 days (Figure 1B-i) pointing to the release of prosurvival soluble factors in the alive conditions.