Platelet factor 4 and other CXC chemokines support the survival of normal hematopoietic cells and reduce the chemosensitivity of cells to cytotoxic agents.

The effects of platelet factor 4 (PF4) on the viability and chemosensitivity of normal hematopoietic cells and cancer cell lines were studied to determine the mechanisms whereby PF4 functions as either an inhibitor or a protector and to evaluate its clinical significance. Two other chemokines, interleukin-8 (IL-8) and neutrophil-activating peptide-2 (NAP-2), were also studied in comparison to PF4. Using a tetrazolium salt assay for cell viability, we observed that PF4 at 1 to 50 microg/mL supported the viability of normal human bone marrow cells. Approximately 45% of cells cultured for 48 hours survived, whereas 80% or more survived in the presence of PF4 5 microg/mL. PF4 also supported the viability of CD34+ cord blood (CB) cells and protected them from apoptosis induced by transforming growth factor beta1 (TGFbeta1) and cytotoxic drugs. Pretreatment of CD34+ cells by PF4, but not by TGFbeta1, caused an increase in the number of megakaryocyte colonies after these cells were replated in secondary cultures. Flow cytometry analysis showed that when CD34+ cells were preincubated with PF4 or TGFbeta1 for 12 days in hematopoietic growth factor-rich medium, an increased number of remaining CD34+ cells was observed only for PF4-treated cells. Furthermore, PF4 significantly reduced the chemosensitivity of bone marrow cells, as shown by its ability to increase the 50% inhibition concentration (IC50) of several cytotoxic agents. Like PF4, IL-8 and NAP-2 at 0.1, 0.6, and 1 microg/mL supported the survival of myeloid progenitors, including colony-forming units granulocyte, erythroblast, monocyte, megakaryocyte (CFU-GEMM), CFU-megakaryocyte (CFU-MK), CFU-granulocyte/macrophage (CFU-GM), and burst-forming units-erythroblast (BFU-E), and reduced their sensitivity to the toxicity of etoposide (ETP). Protamine sulfate at 1 to 100 microg/mL showed no such activity of PF4. Interestingly, the three chemokines failed to affect significantly the viability and chemosensitivity of three leukemic and two other tumor cell lines. Based on these results, we conclude for the first time that PF4 and IL-8 and NAP-2 support the survival of normal hematopoietic precursors and protect them from the toxicity of chemotherapeutic agents. Because such activities are unique to normal hematopoietic cells but not to the cancer cell lines evaluated, a potential clinical application of these molecules in the treatment of cancer is suggested.

[Transgenic human thymopoiesis from retrovirally transduced umbilical cord blood hematopoietic stem cells: experimental studies in the SCID-hu mouse]. / Thymopoïèse humaine transgénique à partir des cellules souches hématopoïétiques du sang de cordon ombilical génétiquement modifiées par voie rétrovirale: étude expérimentale dans la souris SCID-hu.

The gene encoding the CD2 mouse cell surface antigen was retrovirally transduced into cord blood CD34+ cells. On infection by culture at the contact of retrovirus-packaging cells, the mCD2 marker was expressed by 30-40% CD34+ cells, that included the most primitive stem cell-enriched Thy-1+ and CD38- subsets. Accordingly, sorted cord blood CD34+Thy-1+ cells could be directly infected in the same conditions. mCD2- transgenic cord blood CD34+ cells were then used to reconstitute human fetal thymus implanted in SCID mice. Five to 8 weeks later, the mCD2 antigen was detected on approximately 10% of the human thymocytes repopulating the thymus grafts and the transgene genome was detected in graft cell DNA by Southern blot. These results demonstrate efficient gene transfer into primitive cord blood hematopoietic cells endowed with lymphoid potential and suggest gene therapy schemes in neonates suffering inherited or acquired-such as HIV infection-disorders of the T-cell lineage.

Comparison of the effects of AcSDKP, thymosin beta4, macrophage inflammatory protein 1alpha and transforming growth factor beta on human leukemic cells.

We have compared the effects of AcSDKP, Thymosin beta4 (Tbeta4), MIP1alpha and TGFbeta on acute myeloid leukemia (AML) and B-lineage acute lymphoid leukemia (B-ALL) cells using liquid cultures in the presence of GM-CSF, IL-3 and SCF for AML cells and IL-3 and IL-7 for ALL cells. Each molecule was added daily and cell proliferation was evaluated on day 3 by thymidine incorporation. Whereas TGFbeta was found inhibitory in all the AML and B-ALL cases studied, MIP1alpha was inhibitory in 6/12 AML cases and had no effect on B-ALL cells. AcSDKP and Tbeta4 showed an inhibitory effect in a few cases but only at high doses which were inactive on normal cells. Thus, our study not only confirms the effect of TGFbeta, MIP1alpha and AcSDKP on AML cells but also provides new data concerning their effect on B-ALL and the possible inhibitory effect of AcSDKP at high doses. Furthermore, we show for the first time the effect of Tbeta4 on leukemic cells. Altogether, our data indicate differences of sensitivity of leukemic cells to negative regulators, some leukemias being inhibited by one or several of these molecules whereas others were unresponsive to all used. The clinical relevance of these observations still remains to be determined.