cGMP production of astatine-211-labeled anti-CD45 antibodies for use in allogeneic hematopoietic cell transplantation for treatment of advanced hematopoietic malignancies

The objective of this study was to translate reaction conditions and quality control methods used for production of an astatine-211((211)At)-labeled anti-CD45 monoclonal antibody (MAb) conjugate, (211)At-BC8-B10, from the laboratory setting to cGMP production. Five separate materials were produced in the preparation of (211)At-BC8-B10: (1) p-isothiocyanato-phenethyl-closo-decaborate(2-) (B10-NCS), (2) anti-CD45 MAb, BC8, (3) BC8-B10 MAb conjugate, (4) [(211)At]NaAt, and (5) (211)At-BC8-B10. The (211)At-labeling reagent, B10-NCS, was synthesized as previously reported. BC8 was produced, then conjugated with B10-NCS under cGMP conditions to form BC8-B10. [(211)At]NaAt was produced by α-irradiation of Bi targets, followed by isolation of the (211)At using a “wet chemistry” method. The clinical product, (211)At-BC8-B10, was prepared by reacting [(211)At]NaAt with BC8-B10 in NH(4)OAc buffer (pH 5.5) for 2 min at room temperature, followed by size-exclusion chromatography purification. Quality control tests conducted on the (211)At-BC8-B10 included evaluations for purity and identity, as well as pyrogen and sterility tests. Stability of the (211)At-BC8-B10 in 25 mg/mL sodium ascorbate solution was evaluated at 1, 2, 4, 6 and 21 h post isolation. For qualification, three consecutive (211)At-BC8-B10 clinical preparations were successfully conducted in the cGMP suite, and an additional cGMP clinical preparation was carried out to validate each step required to deliver (211)At-BC8-B10 to a patient. These cGMP preparations provided 0.80–1.28 Gbq (21.5–34.5 mCi) of (211)At-BC8-B10 with radiochemical purity of >97%. The preparations were found to be sterile and have a pyrogen level <0.50 EU/mL. Cell binding was retained by the (211)At-BC8-B10. (211)At-BC8-B10 in ascorbic acid solution demonstrated a radiochemical stability of >95% for up to 21 h at room temperature. The experiments conducted have defined conditions for translation of (211)At-BC8-B10 production from the laboratory to cGMP suite. This study has allowed the initiation of a phase I/II clinical trial using (211)At-BC8-B10 (NCT03128034).