Preclinical Research Shows B Cell Medicines Durably Produce Functional Biologics and Engraft without Preconditioning

Platform Modularity Drives Creation of B Cell Medicines Across Multiple Diseases

Be Biopharma, Inc. (“Be Bio”), a company pioneering the discovery and development of Engineered B Cell Medicines (BeCMs), will present preclinical research today showing the precise genome engineering of human B cells to express diverse therapeutic proteins using the company’s proprietary platform. The findings will be presented during an oral session at the American Society of Gene & Cell Therapy (ASGCT) 26^th Annual Meeting at 2:15-2:30 p.m. PST with additional data in poster presentation 1453 on Friday, May 19^th from 12:00-2:00 p.m. PST.

Plasma cells are terminally differentiated B cells, which can live for decades¹ and have the capacity to secrete extremely high levels of protein² making them attractive for the sustained delivery of biologics to treat a wide range of diseases. However, it has historically been challenging to genetically engineer B cells efficiently, precisely, and in a manner that could produce proteins at therapeutic levels over long durations. Leveraging the convergence of advanced gene editing, deep insights into B cell biology and cell therapy technologies, Be Bio has designed a versatile CRISPR/Cas9 engineering platform capable of delivering a gene of interest via homology-directed repair (HDR) to produce stable BeCMs.

“In a short two years, Be Bio has validated key concepts of our B cell medicine platform including editing precision and efficiency, reproducible engraftment, and durable functional protein expression with the goal of creating a new class of cellular medicines with broad therapeutic utility,” said Dr. Rick Morgan, Chief Scientific Officer, Be Bio. “B cell medicines have the potential to transform the lives of patients – they can be redosed when required, delivered autologously and allogeneically, and can be administered without preconditioning – offering distinct advantages over other advanced therapies.”

Be Bio Platform Attributes

• Engineering Precision and Efficiency:

Depending on the desired therapeutic protein expression level, the platform can target gene insertions to safe harbor sites as well as sites transcriptionally active in B cells. Across transgenes, targeting a transcriptionally active B cell site can enable up to a tenfold increase in protein secretion compared to insertion at the CCR5 safe harbor site. In addition, precisely targeted integration significantly reduces the risk of random gene insertion.

Using optimized cell culture and engineering conditions, the platform achieves gene knockouts with greater than 90% efficiency, stable gene insertion via precise HDR with up to 60% efficiency as measured by digital droplet PCR, and multiplexed expression of two genes with efficiencies above 20% as measured by flow cytometry.

• Durable and Functional Protein Expression:

We observed the robustness of the platform through the expression of multiple therapeutic proteins such as Factor IX (FIX) for hemophilia B, acid sphingomyelinase (ASM) for Niemann-Pick Diseases (NPD) and an anti-CD19/CD3 bispecific T cell engager for acute lymphoblastic leukemia (ALL).

In each of two donors, FIX was detected in mouse plasma and lasted for greater than 18 weeks post BeCM transfer demonstrating persistence. In a separate experiment, BeCM-secreted ASM corrected the disease phenotype in NPD (SMPD1) gene knock-out cells.

In addition, in vitro and in vivo anti-tumor activity was observed. Potent in vitro anti-tumor activity was shown when supernatant from bispecific T cell engager-producing BeCMs directed primary human T cells to kill Raji tumor cells (CD19+). In a study conducted by Be Bio’s scientific co-founders and collaborators from the Seattle Children’s Research Institute, engineered B cells produced bispecific T cell engagers in vivo that mediated T cell activation and showed anti-tumor efficacy in a patient-derived xenograft mouse model³.

• Rapid Screening:

To supplement adeno-associated virus (AAV) vector-mediated HDR, a rapid plasmid-based screening protocol was developed. The plasmid-based platform efficiently identifies the appropriate parameters for the secretion of a given protein of interest in primary B cells enabling rapid development from idea to prototype. The screening protocol assesses gene and protein design parameters for optimal transgene expression levels.

• Engraftment without Preconditioning:

Rapid homing (within one day) and engraftment without preconditioning were shown in two models. In immunodeficient (NOG-hIL6) mice, BeCMs engrafted and persisted for greater than 100 days. In non-human primates with intact immune systems, BeCMs administered by intravenous infusion homed to and engrafted in the bone marrow and spleen.

These fundamental platform attributes overcome historical challenges for scalable and effective B cell engineering. The platform has the potential to transform the power of B cells into the development of autologous and allogeneic B cell medicines and unlock a pipeline of product candidates for broad and meaningful therapeutic utility in rare disease, cancer and beyond.

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About B Cells – A New Class of Cellular Medicines

Imagine what could “Be?” In nature, a single B cell engrafts in the bone marrow and can produce thousands of proteins per second at constant levels over decades. B cells are nature’s exquisite medicine factories, manufacturing proteins to fight disease and maintain health. Unleashing the power of B cells is driving a new class of cellular medicines – Engineered B Cell Medicines (BeCMs). BeCMs have the potential to be durable, allogeneic, redosable and administered without toxic conditioning. The promise of BeCMs could transform therapeutic biologics with broad application — across protein classes, patient populations and therapeutic areas.

About Be Biopharma

Be Biopharma (“Be Bio”) is pioneering Engineered B Cell Medicines (BeCMs) to dramatically improve the lives of patients who are living with cancer, rare diseases and other serious conditions. With eyes locked on the patient, our team of purpose-driven scientists, technologists, manufacturing experts and business builders collaborate to create a bold new class of cell therapies. Be Bio was founded in October 2020 by Longwood Fund and B cell engineering pioneers David Rawlings, M.D., and Richard James, Ph.D., from Seattle Children’s Research Institute. Be Bio is backed by ARCH Venture Partners, Atlas Venture, RA Capital Management, Alta Partners, Longwood Fund, Bristol Myers Squibb, Takeda Ventures, Seattle Children’s Research Institute and others. Since our founding, Be Bio’s investors have committed over $180 million to enable the Company to re-imagine medicine based on the power of B cell therapy. For more information, please visit us at Be.Bio and our LinkedIn page.

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1</sup> Landsverk et al (2017) J Exp Med

² Hibi and Dosch (1986) J Immunol; Eyer et al (2017) Nat Biotech

³ Hill et al (2023, May 16-19) Human Plasma Cells Engineered to Produce Bi-Specific T cell Engagers Show In Vivo Anti-Tumor Efficacy [Conference Abstract]. American Society of Gene & Cell Therapy 26 Annual Meeting.

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