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.
Keywords: ALL; AUCtot, total area under the curve; B-ALL, B-precursor acute lymphoblastic leukemia; BBB, blood-brain barrier; BiTE, bispecific T cell engager; CAR, chimeric antigen receptor; CCS, cell culture supernatant; CD, cluster of differentiation; CD3; CDR, complementarity determining region; CHO, Chinese hamster ovary; CL, clearance; CLL, chronic lymphocytic leukemia; CNS, central nervous system; Cmax, maximal concentration; DMSO, dimethyl sulfoxide; E:T, effector:target; EC50, half maximal effective concentration; ECL, electrochemiluminescence; F, fluorescence; FACS, fluorescence-activated cell sorting; FCS, fetal calf serum; FR, framework region; Fab, fragment antigen-binding; Fc, fragment crystallizable; FcRn, neonatal Fc receptor; FcgR, Fc gamma receptor; Fv, variable fragment; HMF, high molecular weight forms; HSA, human serum albumin; His, histidine; IFN, interferon; IL, interleukin; IgG, immunoglobulin G; KD, dissociation constant; LMF, low molecular weight forms; MSD, MesoScale Discovery; MWCO, molecular weight cut-off; NHL, non-Hodgkin lymphoma; NK, natural killer; NOD/scid, nonobese diabetic/severe combined immunodeficiency; Non-Hodgkin lymphoma; ORR, overall response rate; PBMC, peripheral blood mononuclear cell; PBS, phosphate buffered saline; PES, polyethersulfone; PHA, phytohemagglutinin; PI, propidium iodide; SABC, standardized antibody binding capacity; SD, standard deviation; SDS-PAGE, sodium dodecyl sulfate polyacrylamide gel electrophoresis; SE-HPLC, size exclusion high-pressure liquid chromatography; SEC, size exclusion chromatography; SPR, surface plasmon resonance; T cells; TNF, tumor necrosis factor; TandAb, tandem diabody; VH, variable heavy; VL, variable light; Vss, volume of distribution at steady state; WBA, whole body autoradiography; bispecific antibodies; ctrl., control; i.v., intravenous; ka, association rate constant; kd, dissociation rate constant; s.c., subcutaneous; scFv, single-chain variable fragment; t1/2, terminal elimination half-life; w/o, without.