Radiotherapy of CD19 Expressing Daudi Tumors in Nude Mice with Yttrium-90-Labeled Anti-CD19 Antibody

Studies were performed to determine the suitability of using two different anti-CD19 monoclonal antibodies to deliver the high energy beta-particle emitting isotope ⁹⁰Y to B-cell lymphoma grown as flank tumors in athymic nude mice. The antibodies BU12 and HD37, both of the IgG1 subclass, recognize CD19, an internalizing B-lineage-specific membrane glycoprotein and member of the Ig supergene family. The antibodies were readily labeled with ⁹⁰Y using the highly stable chelate, 1B4M-MX-DTPA. The radioimmunoconjugates selectively bound to the CD19 expressing B cell line Daudi, but not to CD19 negative control cells. Significantly more ⁹⁰Y anti-CD19 bound to Daudi tumors growing in nude mice than did a control non-binding antibody (p = 0.001). The biodistribution data correlated with an anti-tumor effect. Anti-tumor activity was dose dependent and the best results were observed in mice receiving a single dose of approximately 300 uCi. The anti-CD19 antibody had significantly better anti-tumor activity as compared to a control ⁹⁰Y-labeled antibody and most mice survived over 119 days with no evidence of tumor (p < 0.003). Histology studies showed no significant injury to the kidney, liver, or small intestine. Because radiolabeled anti-CD19 antibody can be used to deliver radiation selectively to lymphohematopoietic tissue, these data support the use of ⁹⁰Y anti-CD19 antibodies in treating B-cell malignancies.