Production and characterization of a new specific monoclonal antibody against A‐isoform of SALL4: A novel emerging testicular cancer marker

SALL4 transcription factor plays an important role to maintain the pluripotent and self‐renewal of embryonic stem cells. It contributes to the growth of many cancers and embryonic development. With the exception of spermatogonia, SALL4 expression is silenced in most adult tissues after birth; nevertheless, it is re‐expressed in a subset of different solid malignancies. SALL4 is a new, precise biomarker for testicular germ cell cancers that was just introduced. The whole isoform of SALL4 is called SALL4‐A. Regarding the lack of antibody against human SALL4 isoforms, the pattern of expression, the role of each isoform remain unknown. Furthermore, in isoform specific evaluations, we aimed, for the first time, to produce and characterize mAb against human SALL4‐A. Immunization of mice were performed with a selected 33‐mer synthetic peptide of SALL4‐A conjugated with KLH. Hybridoma cells were screened by ELISA for positive reactivity with SALL4‐A peptide. From the ascites fluid of mice that had been injected with hybridoma cells, anti‐SALL4‐A mAbs were isolated using a protein G column. Reactivity of the mAbs was evaluated using the peptide and SALL4‐A recombinant protein by ELISA and IHC on testicular cancer tissue as positive control, and normal kidney, stomach and prostate tissues as negative control. The produced mAb could well detect SALL4‐A in testicular cancer tissues using IHC, while the reactivity was negative in normal kidney, stomach and prostate tissues. Using ELISA, the mAb affinity for the peptide and SALL4‐A recombinant protein was assessed, and it was shown to be reasonably high. The mAb detected SALL4‐A in nucleus and cytoplasm of several cancer cells and spermatogonia in testicular cancer tissue. In addition, it could recognize SALL4‐A recombinant protein. Our produced monoclonal antibody against isoform‐A of human SALL4 can specifically recognize SALL4‐A using either IHC or ELISA. We hope that this mAb could help researchers in isoform‐specific study of human SALL4.