In vivo Characterization of Fusion Protein Comprising of A1 Subunit of Shiga Toxin and Human GM-CSF: Assessment of Its Immunogenicity and Toxicity

Background: Most cancer cells become resistant to anti-cancer agents. In the last few years, a new approach for targeted therapy of human cancer has been developed using immunotoxins which comprise both the cell targeting and the cell killing moieties. Methods: In the present study, the recombinant Shiga toxin A1 subunit fused to human granulocyte-macrophage colony stimulating factor (A1-GM-CSF), previously produced in E. coli, was further characterized. Results: The recombinant protein could cause 50% cytotoxicity and induced apoptosis in cells bearing GM-CSF receptors. The non-specific toxicity of the fusion protein was assessed in C57BL/6 and BALB/c mice. No mortality was observed in either group of mice, with different concentration of fusion protein. Conclusion: The lymphocyte proliferation assay, induction of specific IgG response and a mixed (Th1/Th2) response were observed only in BALB/c mice. The mixed response in BALB/c mice (Th1/Th2) could be explained on the basis of the two components of the fusion protein i.e. A1 and GM-CSF.