Movement is indicated by tracking lines (red to yellow) from the original position of U-937 cells at t = 0 to t = 2 hours (magnification 20x, Scale bar: 50 mm). doi:10.1371/journal.pone.0019330.g007 -ESO-1 in patients who responded to the antibody therapy [56] . It is therefore conceivable that the mature B cell compartment could be enhanced with immunotherapeutic approaches, and that monitoring humoral responses to therapeutics may have clinical relevance.