Trispecific antibodies for CD16A-directed NK cell engagement and dual-targeting of tumor cells.

Bispecific antibodies that redirect the lytic activity of cytotoxic immune effector cells, such as T- and NK cells, onto tumor cells have emerged as a highly attractive and clinically validated treatment modality for hematological malignancies. Advancement of this therapeutic concept into solid tumor indications, however, is hampered by the scarcity of targetable antigens that are surface-expressed on tumor cells but demonstrate only limited expression on healthy tissues. To overcome this limitation, the concept of dual-targeting, i.e. the simultaneous targeting of two tumor-expressed surface antigens with limited co-expression on non-malignant cells, with multispecific antibodies has been proposed to increase tumor selectivity of antibody-induced effector cell cytotoxicity. Here, a novel CD16A (FcγRIIIa)-directed trispecific, tetravalent antibody format, termed aTriFlex, is described, that is capable of redirecting NK cell cytotoxicity to two surface-expressed antigens. Using a BCMA/CD200-based in vitro model system, the potential use of aTriFlex antibodies for dual-targeting and selective induction of NK cell-mediated target cell lysis was investigated. Bivalent bispecific target cell binding was found to result in significant avidity gains and up to 17-fold increased in vitro potency. These data suggest trispecific aTriFlex antibodies may support dual-targeting strategies to redirect NK cell cytotoxicity with increased selectivity to enable targeting of solid tumor antigens.

A tetravalent bispecific TandAb (CD19/CD3), AFM11, efficiently recruits T cells for the potent lysis of CD19(+) tumor cells.

To harness the potent tumor-killing capacity of T cells for the treatment of CD19(+) malignancies, we constructed AFM11, a humanized tetravalent bispecific CD19/CD3 tandem diabody (TandAb) consisting solely of Fv domains. The molecule exhibits good manufacturability and stability properties. AFM11 has 2 binding sites for CD3 and 2 for CD19, an antigen that is expressed from early B cell development through differentiation into plasma cells, and is an attractive alternative to CD20 as a target for the development of therapeutic antibodies to treat B cell malignancies. Comparison of the binding and cytotoxicity of AFM11 with those of a tandem scFv bispecific T cell engager (BiTE) molecule targeting the same antigens revealed that AFM11 elicited more potent in vitro B cell lysis. Though possessing high affinity to CD3, the TandAb mediates serial-killing of CD19(+) cells with little dependence of potency or efficacy upon effector:target ratio, unlike the BiTE. The advantage of the TandAb over the BiTE was most pronounced at lower effector:target ratios. AFM11 mediated strictly target-dependent T cell activation evidenced by CD25 and CD69 induction, proliferation, and cytokine release, notwithstanding bivalent CD3 engagement. In a NOD/scid xenograft model, AFM11 induced dose-dependent growth inhibition of Raji tumors in vivo, and radiolabeled TandAb exhibited excellent localization to tumor but not to normal tissue. After intravenous administration in mice, half-life ranged from 18.4 to 22.9 h. In a human ex vivo B-cell chronic lymphocytic leukemia study, AFM11 exhibited substantial cytotoxic activity in an autologous setting. Thus, AFM11 may represent a promising therapeutic for treatment of CD19(+) malignancies with an advantageous safety risk profile and anticipated dosing regimen.