Genetically engineered radiolabeled
antibody fragments have shown great promise for the radioimmunoscintigraphy of
cancer. Retaining the exquisite specificity of
monoclonal antibodies yet smaller in molecular size,
antibody fragments display rapid
tumor targeting and blood clearance, a more uniform distribution in the
tumor, and present a lower potential to elicit an immune response. However, one of the factors that has limited clinical evaluation of these antibody-derived
proteins has been the difficulty in expressing and purifying the quantities necessary for clinical trials. This study outlines the capability of mammalian expression for the production of recombinant
antibody fragments intended for clinical use. Two anti-
carcinoembryonic antigen antibody fragments, the T84.66/212 Flex minibody (scFv-C(H)3) and the T84.66 diabody (scFv dimer) have been previously expressed and have shown excellent radioimaging properties in
tumor bearing animals. To proceed toward human studies, these high affinity recombinant fragments and a second minibody version, the T84.66/GS18 Flex minibody, were expressed using a high-level mammalian expression system. Production of all three
antibody fragments in a small-scale hollow fiber
bioreactor resulted in 137-307 mg of crude antibody harvest. A purification protocol that employed ceramic
hydroxyapatite and
anion exchange chromatography resulted in 50-150 mg of purified T84.66 diabody and T84.66 minibody. The development of this level of research grade material established conditions for clinical production as well as provided material to complete pre-clinical studies and undertake
protein crystallization studies. Scale-up for clinical studies produced 3.4 g of the T84.66 minibody in the harvest. A portion of this material was purified yielding 180 mg of highly purified T84.66 minibody intended for pilot radioimmunoscintigraphy studies of
carcinoembryonic antigen (CEA) positive disease.