Combination of rituximab with blinatumomab (MT103/MEDI-538), a T cell-engaging CD19-/CD3-bispecific antibody, for highly efficient lysis of human B lymphoma cells

Development of a Target cell-Biologics-Effector cell (TBE) complex-based cell killing model to characterize target cell depletion by T cell redirecting bispecific agents

“…These cell lines have varied CD19 receptor expression levels and different sensitivities to T cells. 33 In this step, some of the model parameters (e.g., EC 50 , γ and τ Reference ) that are associated with the sensitivity of individual B-cell lines to T cell killing were re-estimated, while other parameter values (e.g., K max , E max , k τ1 , k τ2 , K g and K out ) were fixed to the ones established with blinatumomab and Nalm-6 cells using human T cell clone (Table 1). Using the established concentration-response relationships from Nalm-6, Karpas-422, MEC-1 and Raji cells (Tables 1 and 2), the TBE model was used to predict blinatumomab-mediated B cell depletion in human blood and bone marrow by replacing system-specific parameters, such as concentrations of the drug, effector cells, and target cells, with values obtained from patients with leukemia.…”

“…The effect of T cell proliferation was not considered in the current simulation since it was reported that, on average, blinatumomab caused approximately a two-fold expansion of T cells in patients, 41 which would only lead to minor changes in τ. CD19 expression level on B cells was assigned at 20,000 receptors per cell based on literature report, 42 and this value was 2- to 5-fold lower than that of B cell lines used in vitro cytotoxicity assays (20,000 vs. 40,000 – 100,000 receptors per cell). 22,33,43–45 The blood and bone marrow blinatumomab concentration-response curves predicted by the TBE model are shown in Figure 5. Blinatumomab plasma drug concentration information following the approved dosing regimen, i.e., continuous intravenous infusion at a 9 µg/day priming dose for 7 days and then 28 µg/day full dose treatments, was obtained from multiple clinical PK studies in patients with either ALL or non-Hodgkin’s lymphoma.…”

“…The EC 50 for a T-cell redirecting bsAb is expected to be determined by CD3 and target receptor binding epitopes, 53,54 the bsAb architecture, 31 and the sensitivity of individual target cells to T cell killing (Tables 1 and 2, Figure 2 and S2) . 2,33,53 The exact mechanism for how T-cell redirecting bsAbs trigger T cell activation and subsequent target cell killing has yet to be elucidated, but some bsAb architectures and epitopes appear to be more potent than others. 31,53,54 Taken together, these findings support the mechanistic nature and biological relevance of our TBE model.…”

“…However, the standard error values (SE%) for some model estimated parameters were found to be 0 in several cases (Tables S2, S3 and 2); these estimates appear to be associated with the limited number of observations and the fixation of most model parameters. 23,25,26,33,48 …”

“…In vitro cytotoxicity assay data used for model development and evaluation was digitized from the literature; data included: depletion of CD19+ Nalm-6 target cells (150 – 1500 cells per µL) by a human T cell clone (150 – 1500 cells per µL) in the presence of blinatumomab, an anti-CD19xCD3 BiTE, after 4 and 24 hours of incubation; 19 depletion of CD19+ Blin-1 cells (50 cells per µL) by human PBLs (100 – 850 T cells per µL) in the presence of blinatumomab after 4 hours of incubation; 27 depletion of CD19+ Nalm-6 cells (250 cells per µL) by purified human peripheral T cells (625 – 5000 cells per µL) in the presence of blinatumomab after 24 hours of incubation; 23 depletion of CD19+ MEC-1, Nalm-6 and Raji cells (75 – 150 cells per µL) by un-stimulated or pre-stimulated isolated T cells (750 cells per µL) in the presence of blinatumomab after 18 hours of incubation; 48 depletion of P-cadherin+ HCT116 cells (15,000 – 80,000 cells per well, 75 – 400 cells per µL) by PBMCs (15,000 – 400,000 cells per well, 75 – 2000 cells per µL) in the presence of P-cadherin LP-DART after 24 – 96 hours of incubation; 16 depletion of CD33+ OCI-AML3 target cells (22.2 cells per µL) by purified human T cells (22.2 – 222 cells per µL) in the presence of AMG 330, an anti-CD33xCD3 BiTE, after 48 hours of incubation; 3 depletion of FLT3+ REH target cells (100 cells per µL) by activated CD8 + T cells (1000 cells per µL) in the presence of a series of anti-FLT3xCD3 Fabsc bsAbs after 8 hours of incubation; 25 depletion of CD20 + B cells (230 cells per µL) by human T cells (650 cells per µL) in the presence of a series of anti-CD20xCD3 bsAbs after 24 hours of incubation; 26 depletion of Karpas-422, MEC-1, or Raji target cells (150 cells per µL) by PBMCs (1500 cells per µL) in the presence of blinatumomab after 24 hours of incubation 33 . The experimental condition associated parameters were either obtained from literature or leveraged from other studies.…”