A NOVEL B7H3/NKP30 BISPECIFIC NK CELL ENGAGER FOR CANCER IMMUNOTHERAPY
Authors: Jiang Xiaoling , Wu Chongbing , Chen Zi , Yin Liusong 
Published: July 2023

Abstract

Background and Significance
Biological therapies harnessing the adaptive immune system have achieved a great success, given the clinical efficacy of CAR-T therapies and CD3 based T cell engagers in treating hematologic tumors, and the application of T cell immune checkpoint inhibitors in various indications. However, the challenges still exist due to the limitation of CAR-T therapies and T cell engagers in treating solid tumors. Side effects such as cytokine release storm and neurotoxicity remain a concern in the selection of CAR-T therapies and CD3-based T cell engagers as therapeutics. For PD1/L1-based immunotherapy, the relatively low objective response rate (ORR), short progression-free survival (PFS) of patients, and drug resistance and recurrence especially for solid malignancy, are the major clinical challenges. In contrast, innate effector cells such as NK cells and macrophages are naturally existing in human body as front line to defeat general pathogens and cancers，which will have a better safety profile. Also, NK cell activation is not limited by the antigen presentation of the MHC on the cell surface which makes it has broader anti-tumor effects. However, the innate effector cell based therapy is facing the limitation of low cell number, poor in vitro activation, and short effective duration in vivo.
SunHo has generated a B7H3/NKp30 NK cell engager bispecific antibody which can directly activate and enrich NK cells to the TME when used alone or enhance the efficacy when used in combination NK cell therapy. NKp30 is a potent NK cell activation receptor with wide and persistent expression compared with other NK markers. B7H3 as a tumor associate antigen is also widely expressed on many kinds of tumor cells with great potential for multiple indications, especially for solid tumors.

Methods
Three anti-NKp30 VHHs were identified from Alpaca immunized library. The VHHs were fused to the N-terminus or C-terminus of an anti-B7H3 mAb heavy chain with different IgG isotypes (IgG1 or IgG4). The binding activity to NK cells was evaluated by FACS. IFNγ level was detected in the NK cell activation assay. The NK cell mediated target cell killing was evaluated using either NK92MI-cd16a or Primary NK cells as effector cells. To evaluate the non-specific self-killing of NK cell without target cell, the B7H3/NKp30 candidates were incubated with NK92MI-cd16a and cell lysis percentage were calculated. NSG mice bearing Hs.746T tumors were used to evaluate the in vivo efficacy of B7H3/NKp30 candidates.

Results
The B7H3/NKp30 candidates showed good binding activity and better activation to NK cells compared with benchmarks. Notably, the B7H3/NKp30 candidate IAN0982-VHH25 with NKp30 fused to the C-terminal with an IgG1 isotype showed lowest risk of non-specific NK cell killing. In the in vivo study, B7H3/NKp30 candidates in combination with 1x106 NK cells showed excellent anti-tumor activity with TGI over 95%. And we didn’t observe any significant change in body weight of the animals demonstrating good safety profile of the candidates. Moreover, even with lower NK cell amount (5x105), IAN0982-VHH25 showed great anti-tumor efficacy. We have also generated three mini pools of stably transfected cells for IAN0982-VHH25 for the commercial stable cell line development.

Conclusion
IAN0982-VHH25 is a first-in-class B7H3/NKp30 bispecific NK cell engager for cancer immunotherapy with excellent NK cell activation and in vivo anti-tumor efficacy, and also low risk of non-specific NK cell killing. It is expected to lift the limitations of current adaptive and innate effector cells-based therapies.