An important question therefore relates to whether patientderived mature B cell responses have any functional capability to potently activate immune effector cells against cancer. For this, we measured the capacity of one antibody clone to kill tumor cells. Antibody clone 6_2G3 derived from a patient with stage III disease (Patient 6, Table 1 ) was not observed to bind to fibroblasts or melanocytes, but bound to a proportion of melanoma cell lines tested ( Figure 5 ). Antibodies against tumor-associated antigens can attack tumor cells via a number of mechanisms including induction of apoptosis in tumor cells and engaging Fc receptors on immune cells [50, 51, 52, 53] . Antibodies approved for the treatment of cancer have been shown to function through one or more of these mechanisms [54, 55] . While our strategy yields fully human monoclonal antibodies in a matter of a few months, we were limited in the amount of antibody we could produce from the B cells to perform functional studies and evaluate reactivity to patient-derived melanoma tumors. However, we had sufficient quantity to evaluate whether a patient-derived melanoma tumorspecific monoclonal antibody could mediate antibody dependent cellular cytotoxicity (ADCC) in the presence of monocytic effector cells and tumor cells using a real-time live cell imaging assay. We show that the tumor-specific 6_2G3 clone is capable of mediating ADCC in vitro and additionally measured the restricted movement of monocytic effector cells once in contact with tumor-specific antibody-coated tumor cells, providing further evidence of ADCC ( Figure 6 ). These preliminary assessments provide a promising clue that a potentially active mature B cell response against melanoma may be present in patients. An example of this possibility was recently reported by Yuan et al. who demonstrated that administration of the anti-CTLA-4 antibody ipilimumab led to serological enhancement of antibodies to the testis antigen NY human U-937 monocytic cells was compared between samples treated with 6_2G3 or 6_2D10 antibody after 2 hours at 37uC (*** = P,0.001) (left). Error bars represent 95% confidence intervals. Mean fluorescence intensity of A-375 tumor cells pre-labeled with the live cell dye Calcein AM, and incubated with U-937 cells and antibody 6_2G3 or 6_2D10 was measured at 0 and 120 min time points (right). (B) Fluorescent images of the live cell cytotoxicity assays at 30 minute intervals. Live Calcein AM-labeled melanoma tumor cells (green) were incubated with 6_2G3 or 6_2D10 antibody and U-937 cells (blue) and cell death was evaluated (red). Incorporation of Ethidium homodimer-1 (incorporation of red into tumor cells) was observed with 6_2G3 but not 6_2D10 (magnification 20x, Scale bar: 100 mm). (C) Movement of U-937 cells tracked and measured over two hours was compared for cells in contact and those not in contact with tumor cells (*** = P,0.001for 6_2G3 and P = 0. 3 