OR36-08 Long-Term in Vivo Expression of Tissue Nonspecific Alkaline Phosphatase by Ex Vivo Gene Edited B Cells as a Potential Treatment of Hypophosphatasia

Abstract Disclosure: P. Pierog: None. M. Brophy: None. W. Wong: None. X. Zhang: None. L. Li: None. J. Hickey: None. A. Lundberg: None. W. Bainter: None. C. Bullock: None. S. Keegan: None. S. Bedard-Shurtleff: None. T. Mullen: None. J. Edelstein: None. S. Bhawsar: None. G. Adekanye: None. E. Liberzon: None. S. Singh: None. M. Musial-Siwek: None. A. Hohmann: None. S. Arlauckas: None. A. Lazorchak: None. H. Liu: None. R. Morgan: None. Hypophosphatasia (HPP) is a rare metabolic disorder that causes skeletal abnormalities, chronic pain, and systemic complications. The condition arises from loss-of-function mutations in the ALPL gene that encodes the tissue-nonspecific alkaline phosphatase (TNSALP) enzyme. Deficient TNSALP activity leads to the accumulation of inorganic pyrophosphate (PPi), an inhibitor of bone mineralization, and pyridoxal 5’-phosphate responsible for disease manifestation. To address limitations of current therapies, we have developed a B cell-based cell therapy, termed BE-102. BE-102 is manufactured from primary human B cells by isolating, activating, and precision engineering with CRISPR/Cas9 followed by AAV and homology directed repair mediated insertion of human ALPL gene into CCR5 locus. Engineered TNSALP-producing cells, have properties of long-lived plasma cells and are expected to reduce elevated levels of substrates PPi and PLP, that accumulate in patients with HPP. BE-102 cells were manufactured from six healthy donors and were characterized for viability (84.9 ± 3.5%), CD38+ expression (93.3 ± 4.3%), ALPL transgene integration (45.1 ± 7.2%) and TNSALP secretion rate (9.5 ± 10.2 ng/mL/hour). In vitro pharmacology results demonstrate that BE-102 secretes active TNSALP (409.7 ± 10.2 µUnits/mL), which is capable of rescuing calcium deposition inhibited by PPi in a cell-based in vitro test system. Having demonstrated the in vitro function of BE-102, in vivo studies (N=3) were conducted in immune-deficient NOG-hIL6 mice. The animals received a single intravenous (IV) injection of 2 x107 viable cells. Human TNSALP was detected in serum at every time point starting at Day 1 and up to 6 months following a single dose of BE-102 using a human specific immunocapture assay. Consistent with BE-102 pharmacology, serum ALP activity showed statistically significant increase in BE-102 treated animals as compared to vehicle-treated animals. The in vivo data confirm long-term engraftment and continuous production of active TNSALP. Consistent with the expected pharmacology of BE-102 and construct design of ALPL transgene, human TNSALP activity was detected at day 90 in the bones of animals treated with BE-102 surrogate construct secreting TNSALP. These data confirm the delivery of functional TNSALP secreted by the surrogate construct to the bone, one of the main HPP disease target organs. Finally, clinical chemistry and hematology results from the end of the studies were all within acceptable ranges. Safety data together with the absence of adverse clinical observations and no unscheduled animal deaths support that BE-102 was well-tolerated in vivo. In summary, pharmacology and safety data establish non-clinical proof of concept that BE-102, has the potential to be a disease-modifying therapy by providing sustained level of active TNSALP following a single IV infusion for patients with HPP. Presentation: Monday, July 14, 2025