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

作者：Reusch Uwe; Duell Johannes; Ellwanger Kristina; Herbrecht Carmen; Knackmuss Stefan H J; Fucek Ivica; Eser Markus; McAleese Fionnuala; Molkenthin Vera; Le Gall Fabrice; Topp Max; Little Melvyn; Zhukovsky Eugene A^*

来源：mAbs, 2015, 7(3): 584-604.

DOI：10.1080/19420862.2015.1029216

• SD, standard deviation
• PBS, phosphate buffered saline
• His, histidine
• kd, dissociation rate constant
• CCS, cell culture supernatant
• i.v., intravenous
• HMF, high molecular weight forms
• Fc, fragment crystallizable
• ka, association rate constant
• BiTE, bispecific T cell engager
• CAR, chimeric antigen receptor
• Vss, volume of distribution at steady state
• EC50, half maximal effective concentration
• DMSO, dimethyl sulfoxide
• ctrl., control
• SABC, standardized antibody binding capacity

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.

• 出版日期2015-5-4