Identification of a novel single chain fragment variable antibody targeting CD24-expressing cancer cells

- A stable transgenic CHO cell line expressing recombinant CD24 was developed.
- High-affinity binding scFv-conjugated phage (Jd3) against CD24 was enriched during bio-pannings.
- Soluble Jd3 scFv was expressed and purified successfully.
- Jd3 scFv showed appropriate affinity to CD24 in ELISA and immunocytochemistry analysis.
- The novel anti-CD24 scFv can be used in delivery of diagnostic and therapeutic agents to CD24-expressing cells.

CD24 is a heavy glycosylated protein that is overexpressed in numerous cancer and cancer stem cells. It is involved in the development, invasion, and metastasis of the cancer cells. CD24 can be considered in targeted cancer therapy as a new target. Here, phage display technology was used for the identification of novel scFv antibodies against CD24. To do so, the CD24 protein was expressed and purified from a stable transgenic CHO cell line. The cells were developed by using a CD24 encoding construct, which targets the 18S rRNA gene. The recombinant CD24 was used in the biopanning process. Four rounds of biopanning were performed with the Tomlinson J library. The polyclonal phage ELISA and DNA sequencing of the selected colonies confirmed that specific binders have been enriched during the biopanning process. Based on the DNA sequencing results, three phage-displaying scFv were obtained and their specificity to CD24 was verified in the monoclonal phage ELISA. The results showed that clone 3 (called Jd3) has the highest affinity to CD24 and also is the most abundant clone (80%) among the three clones. Therefore, Jd3 was selected for further analyses. In order to produce soluble Jd3-scFv, the phage was transfected to E. coli BL21 pLysS. Soluble Jd3 scFv was expressed and purified successfully. The soluble Jd3 scFv showed appropriate affinity to recombinant CD24 in the ELISA analysis. Also, the immunocytochemistry experiment showed that the purified Jd3 scFv can bind to the CD24 expressing A549 cells. So, the scFv may be useful in the targeted delivery of drugs or diagnostic nanoparticles to the CD24 expressing cancer cells. To the best of our knowledge, this study is the first report to identify an scFv antibody against CD24, using the phage display method.