Bioactivities of Culture Supernatants from Retroviral Packaging Cells Carrying the Mouse Fas Ligand Gene

The bioactivities of culture supernatants from retroviral packaging cells carrying the mouse Fas ligand (mFasL) gene was investigated. FasLcDNA was cloned into PLXIN with an internal ribosome entry site to link two cistrons through gene recombination technology, PLXIN and the recombinant vector PLFIN were separately transfected into PA317 retrovirus packing cell line by lipofectamine 2000, and the resistant clones were selected with G418 selective medium. The integration of genome DNA was assayed by genomic DNA PCR. NIH3T3 cells were transduced by the culture supernatants from PA317 carrying the mFasLcDNA gene, and were selected with G418 selective medium, so as to select the PLFIN-PA317 clone capable of producing higher titer of supernatants. The levels of mFasL protein on NIH3T3 cells membrane were assayed by flow cytometry (FCM). The biological activity of mFasL on NIH3T3 cells membrane was investigated by the inducing apoptosis of Fas + Yac-1 cells co-cultured with NIH3T3 cells expressing Fas ligand. To explore the direct mFasL cytotoxicity of culture supernatants from retroviral packaging cells carrying the mFasL gene, the culture supernatants from PLFIN-PA317 and PLXIN-PA317 were separately co-cultured with Yac-1 cells in parallel. The recombinant PLFIN was successfully constructed. The highest titer of supernatants from twelve resistant clones was 8.5×10 5 colony-forming-unit (CFU)/ml. The NIH3T3 cells transfected by above supernatants had a higher level of mFasL (53.81±6.9 %), and significantly induced the apoptosis of Fas + Yac-1 cells (56.78±4.5 %), as both were cocultured for 5 h at 1∶1 ratio, whereas it is 7.08±3.4 % in control group (P<0.01). Supernatant from PLFIN-PA317 could also directly induce the apoptosis of Yac-1 within 5 h of incubation. Thus, the culture supernatants from PLFIN-PA317 possessed both infectivity and cytotoxicity of mFasL.

PROLIFERATION OF ANTI－CD_3 McAb AND IL－2 INDUCED SPLENOCYTES AND ANTITUMOR EFFECT OF THEIR CULTURE SUPERNATANTS

The proliferation of splenocytes from health adults was induced by anti-CD3 McAb and IL-2.The proliferative potential of the splenocytes and antitumor activity of their culture supernatants of splenocytes were studied.The results showed that anti-CD3 McAb not only enhanced the proliferation of the splenocytes directly,but also enhanceil that of induced by IL-2.Their enhancing effect was more significant when the incubation time in vitro was prolonged.The culture supernatants of anti-CD3 and IL-2 induced splenocytes also had the antitumor activity and enhancing capability to the antitumor activity of LAK tells.The results suggested that LAK cells could secret lymphokine,and this effect would be synergically promoted when anti-CD3 and IL-2 were simultaneously used.

Acute myeloid leukemia cells inhibit the differentiation and maturation of dendritic cells and induce the generation of regulatory T cells

Objective： To investigate the effects of soluble factors secreted by acute myeloid leukemia （AML） cells on the phenotypical and functional properties of DCs derived from normal mononuclear cells. Methods： Mononuclear cells were cultured with interleukin-4 （IL-4） and granulocyte-macrophage colony-stimulating factor （GM-CSF）, in the presence or absence of 24 h culture supematants from fresh pdmary AML cells, to generate immature DCs. The maturation of DCs was induced by cytokines IL-lbeta, IL-6, tumor necrosis factor-alpha （TNF-alpha）, and prostaglandin-2 （PGE-2）. The phenotypic alterations of DCs and DCs-primed CD4＋ T cells were evaluated using flow cytometry. Precursor frequency （PF） was calculated to monitor the allostimulatory effects of DCs on CD4^＋ and CD8^＋ T cells. Results：AML cell supernatant-treated DCs showed significantly lower expression of co-stimulatory molecules CDS0 and CD86, and reduced response to cytokines IL-1beta, IL-6, TNF-alpha, and PGE-2. The allostimulatory effects of AML cell supematant-treated DCs on CD4^＋ and CD8^＋ T cells were significantly lower than those of normal mature DCs [PF： （1.8 ±0.5）% vs. （5.2 ± 1.6）% for CD4^＋ T cells, （2.1 ±0.6）% vs. （6.5 ± 2.0）% for CD8^＋ T cells, P 〈 0.01]. These AML supernatantoinduced DCs could also induce allogeneic CD4^＋ T cells to differentiate into CD4^＋CD25high T cells, which had immunophenotyping characteristics of regulatory T cells, i.e. they expressed Foxp3 but not active maker CD69. Conclusion： This study demonstrates that soluble factors secreted by AML cells can inhibit development and functions of DCs. In addition, AML supernatant-induced DCs can induce the generation of CD4^＋CD25^high T cells from CD4^＋ T cells, which may be a mechanism of increased prevalence of CD4^＋CD25^high regulatory T cells and immune dysfunction in AML patients.