Ganglioside GD2-specific trifunctional surrogate antibody Surek demonstrates therapeutic activity in a mouse melanoma model.

BACKGROUND: Trifunctional bispecific antibodies (trAb) are a special class of bispecific molecules recruiting and activating T cells and accessory immune cells simultaneously at the targeted tumor. The new trAb Ektomab that targets the melanoma-associated ganglioside antigen GD2 and the signaling molecule human CD3 (hCD3) on T cells demonstrated potent T-cell activation and tumor cell destruction in vitro. However, the relatively low affinity for the GD2 antigen raised the question of its therapeutic capability. To further evaluate its efficacy in vivo it was necessary to establish a mouse model. METHODS: We generated the surrogate trAb Surek, which possesses the identical anti-GD2 binding arm as Ektomab, but targets mouse CD3 (mCD3) instead of hCD3, and evaluated its chemical and functional quality as a therapeutic antibody homologue. The therapeutic and immunizing potential of Surek was investigated using B78-D14, a B16 melanoma transfected with GD2 and GD3 synthases and showing strong GD2 surface expression. The induction of tumor-associated and autoreactive antibodies was evaluated. RESULTS: Despite its low affinity of approximately 10(7) M(-1) for GD2, Surek exerted efficient tumor cell destruction in vitro at an EC(50) of 70 ng/ml [0.47 nM]. Furthermore, Surek showed strong therapeutic efficacy in a dose-dependent manner and is superior to the parental GD2 mono-specific antibody, while the use of a control trAb with irrelevant target specificity had no effect. The therapeutic activity of Surek was strictly dependent on CD4(+) and CD8(+) T cells, and cured mice developed a long-term memory response against a second challenge even with GD2-negative B16 melanoma cells. Moreover, tumor protection was associated with humoral immune responses dominated by IgG2a and IgG3 tumor-reactive antibodies indicating a Th1-biased immune response. Autoreactive antibodies against the GD2 target antigen were not induced. CONCLUSION: Our data suggest that Surek revealed strong tumor elimination and anti-tumor immunization capabilities. The results warrant further clinical development of the human therapeutic equivalent antibody Ektomab.

Two new trifunctional antibodies for the therapy of human malignant melanoma.

Trifunctional antibodies are able to redirect T cells and Fcgamma receptor(+) accessory immune cells to tumor targets. The simultaneous activation of these different classes of effector cells results in efficient killing of the tumor cells by different mechanisms such as phagocytosis and perforin-mediated cytotoxicity. Here, we introduce 2 new trifunctional antibodies specific for human melanoma. These trifunctional antibodies recognize with one binding arm CD3 on human T cells. The other binding arm is directed against melanoma-associated proteoglycans or melanoma-associated gangliosides (GD2 as well as GD3). They mediate specific lysis of various melanoma cell lines in correlation with the level of antigen expression in short-term cytotoxicity experiments. A combination of the 2 trifunctional antibodies was equally or even more efficient. Moreover, they induced a strong Th1 cytokine pattern with high amounts of IFN-gamma and low or no IL-4. Accordingly, CD4(+) and especially CD8(+) T cells expanded, whereas B cells, NK cells and monocytes decreased. The cytokine response was up to 16-fold higher when tumor cells were present. IFN-gamma reached cytotoxic concentrations for SK-MEL-23 melanoma cells. The induction of a T-cell-activatory and melanoma cell-inhibitory cytokine milieu together with the redirection of T-cell- and accessory cell-mediated cytotoxicity are interesting features of these trifunctional antibodies. They may be a new option for the therapy of human malignant melanoma.