IRTA2 Protein on Lymphoma Cell Lines and Hairy Cell Leukemia Cells Detected by Novel Monoclonal Antibodies.

The immunoglobulin superfamily receptor translocation associated 2 (IRTA2) gene encodes a cell surface receptor homologous to the family of Fc receptors. Because of the restricted expression of the mRNA in B cell-linage cells, IRTA2 is a new potential target for the immunotherapy of B cell malignancies. To study the function and expression of the IRTA2 gene product, we produced monoclonal antibodies (MAbs) specific to IRTA2. We successfully made 36 MAbs from a mouse immunized with IRTA2-encoding plasmid DNA. All the MAbs reacted with IRTA2-extracellular domain-Fc fusion protein in ELISA and 293T cells expressing IRTA2 in a fluorescence-activated cell sorter (FACS) analysis. Binding of each MAb to a series of deletion mutants of IRTA2-Fc fusion protein and mutual competition of the MAbs to the binding to the whole extracellular domain of IRTA2-Fc fusion protein revealed that the panel of MAbs recognizes more than 10 epitopes on IRTA2. There are at least 1, 1, 2, 4, and 2 epitopes on extracellular domain 1 (ED1), ED3, ED1-3, ED4-9, and whole extracellular domain, respectively. Twenty five out of the 36 MAbs are specific to IRTA2 but 11 others showed cross reactivity to other members of the IRTA family. Among 36 MAbs produced, 3 MAbs (F25, F56 and F119) were used for further analysis based on their specific reactivity with recombinant IRTA2 expressed on 293T cells and lack of cross reactivity with other IRTA family members. In a FACS analysis, MAbs F56 and F119 detected IRTA2 expression on 6/7 B-cell non-Hodgkin’s lymphoma and 1/6 Burkitt’s lymphoma cell lines. Reverse transcriptase-polymerase chain reaction experiments and Western blotting using MAb F25 confirmed the expression profile. We also analyzed blood samples of 11 patients with hairy cell leukemia (HCL), 11 patients with chronic lymphocytic leukemia (CLL), and 4 patients with follicular lymphomas (FL) by FACS. We detected IRTA2 expression on 100% HCL (11/11), 55% CLL (6/11) and 0% of FL cells (0/4). Our results provide the first evidence that the IRTA2 is expressed on the surface of HCL and CLL cells as well as some human lymphoma cell lines. We expect IRTA2 will be established as a new target for immunotherapy.