Characterization of dendritic cells generated in vivo by an E. coli derived chimeric dual receptor agonist

Background: Progenipoietin-4 (ProGP-4) is an E. coli derived chimeric growth factor that activates the human Flt3 and G-CSF receptors. ProGP-4 possesses cross-species activity and treatment of mice with ProGP-4 results in increases in the number of WBC and Class II⁺/CD11c⁺ cells in both spleen and peripheral blood. Herein, we report morphologic, phenotypic and functional evaluation of Class II⁺/CD11c⁺ cells generated by in vivo administration of ProGP-4. Material/Methods: C57BL/6 mice were injected daily with ProGP for 7 to 18 days. Leukocytes from spleen and peripheral blood were analyzed by flow cytometry to enumerate and characterize changes in DC populations. Spleens from ProGP treated mice were evaluated by immunocytochemistry and enriched CD11c⁺ populations were functionally assessed in a mixed lymphocyte assay and in an antigen dependent CTL assay. Results: Administration of this dual receptor agonist to mice resulted in dose-dependent increases in the numbers of total white blood cells and Class II⁺/CD11c⁺ cells in spleen and peripheral blood. CD11c⁺ cells from ProGP-4 treated mice co-expressed DEC205 and also expressed CD80, CD86 and CD40, albeit at lower levels as compared to Class 11⁺/CD11c⁺ cells from untreated animals. Despite lower co-stimulatory molecule expression, ProGP-4-generated Class 11⁺/CD11c⁺ cells stimulated proliferation of allogeneic T cells and an antigen-specific T cell hybridoma as efficiently as bone marrow derived dendritic cells from untreated mice. Conclusion: The data presented in this report highlight the ability of E. coli derived ProGP-4 to expand large numbers of functional DC in the peripheral blood and lymphoid organs in vivo using a rodent model of hematopoiesis. E. coli derived chimeric receptor agonists such as ProGP-4 may enable further investigations of imnmnotherapeutic approaches to the treatment of diseases such as cancer and autoimmunity.