ABSTRACT
Bone marrow mesenchymal stem cells (MSCs) are multipotential progenitors of connective tissues and bone marrow stroma as well, which implies the modulatory function of MSCs in hematopoiesis. To clarify the contributions of MSCs to hematopoiesis, the methods for isolation and expansion of MSCs were established and long-term bone marrow cultures were performed using irradiated MSCs as the feeder layer. The results here showed that CD34(+) cells from cord blood formed hematopoietic foci adherent to the monolayer. Furthermore, colony-forming cells remained in the coculture of 5 weeks, indicating the maintenance of long-term culture-initiating cells (LTC-IC). Flow cytometry analysis showed that about 1% of the hematopoietic cells in the culture were positive for CD34 and around 15% were CD41a-positive. It is clear that MSCs maintain LTC-IC in vitro and promote differentiation of hematopoietic progenitors especially into megakaryocytic lineage. The preliminary results here demonstrate that MSCs residing in the bone marrow might be a crucial cellular component in the hematopoietic microenvironment.
ABSTRACT
Objective: This study was aimed to explore antitumor responses induced by recombinant vaccinia viruses expressing a point mutant p53 (rVV-p53FL) and enhancive effects of recombinant vaccinia viruses expressing costimulatory molecule B7 (rVV-B7). Methods: A 135 Cys to Tyr point mutant p53 protein was used as the model of tumor associated antigen. rVV-of3FL and rVV-B7 were used as vaccines to test their induction of CTLs and antitumor immunity. Results: Immunization BABL/c mice with rVV-p53FL could elicited specific CD8+ CTLs that could effecively lyse P815-mp53 cells, a transfectant of the murine P815 mastocytoma containing the mutant p53 gene. Treatment with rVV-p53FL could survive a part of mice challenged with 1 ? 106 P815-mp53. Treatment with rVV-p53FL could significantly prolong survival of tumor-bearing force. Admixture at 1: 1 ratio of rVV-p53FL and rVV-B7 could enhance therapeutic antitumor effects of rVV-p53FL. ~Conclusion: Mutant P53 over-expressed in tumor cells can render cells targets for specific CTLs generated by immunization with mutant p53 protein based vaccine. Costimulatory molecule H7 can enhance tumor-associated antigen inducing antitumor responses.