Preclinical Study of a Novel Tri-Specific Anti-CD3/CD19/CD20 T Cell-Engaging Antibody As a Potentially Better Treatment for NHL

CD20 targeted therapy by means of anti-CD20 mAb is currently the most important regimen for treating B cells malignancies. However, 1-2% of B-cell lymphoma patients test negative for CD20. Besides, it has been reported in several studies that CD20 expression was down-regulated in over 20% of CD20-positive DLBCL patients that had relapsed/progressed after R-CHOP regimen. The limited prognosis for these patients poses a substantial unmet medical need. A new class of "1:2" format CD3 x CD20 bispecific antibodies emerged aiming for increased tumor antigen avidity and enhanced tumor cell killing, however, its advantages over conventional "1:1" format CD3 x CD20 antibodies have yet to be revealed in clinical trials. CMG1A46 is a 151 KD IgG-like "1:(1+1)" tri-specific antibody constructed on Chimagen's TRIAD platform. It simultaneously targets CD3 on T cell and two different biomarkers - CD20 and CD19 (abundancy of which proven to be intact post CD20-targeted treatment) - on tumor cells, recruiting T cells to kill tumor cells expressing CD19 and/or CD20. CMG1A46 is designed to target not only conventional CD19+CD20+ DLBCL, but also CD20-CD19+ DLBCL and DLBCL with trace to low expression of CD20 owing to its high avidity for tumor cells from 2 binders for CD19 and CD20 respectively. In vitro, CMG1A46 was shown to mediate tumor cell lysis by human PBMCs in a dose-dependent manner with EC50 around 0.3 pM. CMG1A46 was shown to have superior potency and safety (based on target-independent T cell activation) when compared to CD3 x CD20 bispecific antibodies with the conventional "1:1" IgG-based format. The antibody was able to induce potent tumor lysis in cells expressing both CD19 and CD20, and in cells expressing CD19 or CD20 alone. In vivo, 1A46 displayed potent tumor-suppressing activity in human PBMC-engrafted NOD mouse models and induced fast regression of large (CD19+CD20+) Jeko-1 lymphoma and (CD19+CD20-) A20-hCD19 tumors of ~100mm3. Remarkably, CMG1A46 can be administrated at the dosage 6 times as high as conventional CD3 x CD20 bispecific antibodies (3mg/kg for CMG1A46, 0.5mg/kg for conventional) and conferred even higher anti-tumor potency without any noticeable increase in toxicity (as evidenced by body weight of the animals and cytokine levels/T cell counts in serum post last administration). Pharmacokinetic studies in cyno monkeys show that when administrated at 1mpk CMG1A46 has a half-life that is over 70 hours in serum. After initial induction doses, weekly administration is able to maintain high circulating levels of the molecule. Dosages up to 10mpk do not lead to significant adverse effects. CMG1A46 treatment resulted in fast and complete elimination of B cells in peripheral blood within 24 hours after the first administration. Peripheral B cell elimination sustained for at least 28 days after last administration at 1mpk. B cell depletion was paralleled by transient decrease of T-cell counts in the peripheral blood and by the peak of cytokine release 4-8 hours after the first administration, followed by rapid recovery and return to baseline levels at 24 hours post treatment. Accordingly, CD3 receptor occupancy (RO) transiently increased during the induction phase and fell back to and sustained at a low level of around 20-30%. These studies show that CMG1A46 is a novel CD19/CD20-targeting T cell-engaging tri-specific antibody with very promising anti-tumor activity. In both in vitro and in vivo experiments, CMG1A46 demonstrated superior potency and safety compared to other CD3 x CD20 bispecific antibodies with the conventional "1:1" IgG format. Preliminary study in cyno monkeys suggested IgG-like half-life in serum and manageable toxicity. Taken together, the preclinical data strongly support for clinical testing of CMG1A46 in patients with CD20+ cancers. Phase 1 trial of the molecule is scheduled to start by April 2021. Disclosures No relevant conflicts of interest to declare.