Since it is established that trAb-dependent vaccination induces tumor-specific humoral immune responses , which correlate with tumor protection in vivo, we then measured the titers of melanoma-directed antibodies in sera of vaccinated mice. While specific antibodies of the IgG1 subclass were not significantly affected by any vaccination protocol, immunization with Surek induced elevated levels of the IgG2a subclass (Figure 4B). HB304 induced anti-melanoma antibody titers that were not significantly different from untreated controls. However, combining Surek with HB304 strongly enhanced the IgG2a induction effected by Surek monotherapy (Figure 4B).