Extremely potent, rapid and costimulation‐independent cytotoxic T‐cell response against lymphoma cells catalyzed by a single‐chain bispecific antibody

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

“…19 Meanwhile, instead of increasing the killing potency of T cells, higher E:T ratios appeared to only accelerate the T cell killing process. 19,23,49–52 Consistently, the data we analyzed also suggested that the higher E:T ratios only accelerate the T cell killing process (τ), but do not affect the intrinsic potency value (EC 50 ). Our model used two exponential functions to correlate both effector cell concentrations (k τ1 ) and target-to-effector cell ratios (k τ2 ) to τ.…”

“…Similarly, the TBE model was first established with purified human T cell-mediated Nalm-6 cell depletion profiles after 24 hours of incubation with blinatumomab (Figure 3f) at the highest tested E:T ratio of 20:1 (solid line), and the model was then used to simulate the cytotoxicity profiles Nalm-6 cells at lower E:T ratios (e.g., 2.5:1 to 10:1) from the same assay. 23  The results showed that the simulations (dashed lines) agreed reasonably well with the observed data. The model estimated EC 50 , γ, k max , and τ reference values are also summarized in Table S2.…”

“…The low EC 50 value likely reflects the extremely high potency of blinatumomab. 19 Of note, TBEPC R was calculated based on the experimentally determined expression values of T cell CD3 and Nalm-6 cell CD19 and the reported blinatumomab binding affinities to CD3 and CD19 on cell surfaces following 45-minute incubations; 22,23 any potential divergence between the assay measurements and true values of receptor density and binding affinity would affect the derivation of TBEPC R values and the estimation of EC 50 . The baseline killing in the absence of the drug (Base) was fixed at 0, based on the observed data.…”

“…The impact of binding affinity was evaluated with cytotoxicity profiles of FLT3+ REH cells by CD8 + T cells in the presence of FLT3xCD3 bsAbs with differentiated binding affinity to FLT3 after 8 hours of incubation (c), 25 and that of CD20 + B cells by CD3 + T cells in the presence of CD20xCD3 bsAbs with differentiated binding affinity to CD3 after 24 hours of incubation (d) 26 . The impact of effector-to-target (E:T) ratio was evaluated with CD19+ Blin-1 cell cytotoxicity profiles by PBLs in the presence of blinatumomab after 4 hours of incubation (e), 27 and CD19+ Nalm-6 cell cytotoxicity profiles by purified human peripheral T cells in the presence blinatumomab after 24 hours of incubation (f) 23 . Symbols represent observed in vitro cytotoxicity data; solid lines with corresponding color represent model estimation results; dashed lines with corresponding color represent model simulation results.…”

“…23,27,28 The established relationships between τ and T cell concentration and τ and E:T ratio were kept the same as those derived above using blinatumomab in vitro cytotoxicity data with human T cell clones and Nalm-6 target cells (Table 1). Since the sources of effector cells in these two datasets differed (human peripheral blood lymphocytes (PBLs) or purified human T cells vs. human T cell clone), the other parameters (e.g., k max , EC 50 , γ and τ reference ) were re-estimated.…”