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 II+/CD11c+ cells from untreated animals. Despite lower co-stimulatory molecule expression, ProGP-4-generated Class II+/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. CONCLUSIONS: 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 immunotherapeutic approaches to the treatment of diseases such as cancer and autoimmunity.

Enhanced ability of the progenipoietin-1 to suppress apoptosis in human hematopoietic cells.

Repopulating hematopoietic cell compartments after myeloablative chemotherapy remains a key factor in a successful chemotherapy program. Modified and chimeric cytokines have been developed to help reduce inflammation, fever and hospitalization time for patients. A chimeric cytokine, progenipoietin-1 (ProGP-1), containing the G-CSF and FL receptor agonists binds both the G-CSF receptor and FLT-3. It also stimulates the growth of dendritic cells, which play an important role in immunotherapy. While in vivo effects of ProGP-1 are well described, the mechanisms by which it stimulates growth are not well understood. We have investigated the effects of ProGP-1 on prevention of apoptosis in the human hematopoietic cell line OCI-AML.5. ProGP-1 promoted cellular proliferation better than G-CSF or FL separately but stimulated proliferation similar to their co-addition as demonstrated by growth curves and [3H]-thymidine incorporation. ProGP-1 prevented apoptosis to a greater degree than G-CSF or FL alone as determined by annexin V/propidium iodide binding and TUNEL assays. ProGP-1 promoted maintenance of the mitochondrial membrane potential better than G-CSF or FL alone. In addition, Pro-GP promoted a lower redox potential as higher levels of free radicals were detected after cytokine treatment than in cytokine-deprived cells implying increased respiration. These data indicate that ProGP-1 promotes the proliferation and prevents the apoptosis of human hematopoietic cells better than FL or G-CSF alone, and to a similar extent as their co-addition. Thus, ProGP-1 can be used to repopulate certain hematopoietic cells as a single entity rather than the introduction of two different cytokines.