Determination of the precursor frequency and the reaction intensity of xenoreactive human T lymphocytes.
ABSTRACT It is acknowledged that the response of human T cells to xenogeneic targets is more potent than that to allogeneic targets. However, it is not clear whether the more vigorous T cell response to xenoantigens than to alloantigens is attributable to a higher frequency or stronger reaction of xenoreactive T cells.
We determined the precursor frequencies (PFs) and stimulation indexes (SIs) of xenoreactive human T cells by performing a mixed lymphocyte reaction (MLR) assay using a carboxyfluorescein diacetate succinimidyl ester (CFSE)-labeling technique. Irradiated porcine or human peripheral blood mononuclear cells (PBMCs)used as stimulator cells--were cultured with CFSE-labeled human PBMCs--used as responder cells.
The SIs of the xenoreactive CD4(+) T cells were significantly higher than those of the alloreactive CD4(+) T cells, whereas the PFs of the alloreactive and xenoreactive CD4(+) T cell precursors were almost identical, suggesting a stronger reaction by a single xenoreactive CD4(+) T cell. In contrast, the SIs of the xenoreactive CD8(+) T cells did not differ from those of the alloreactive CD4(+) T cells, and the PFs of the allo- and xenoreactive CD8(+) T cell precursors were also identical. Addition of a soluble human CD47-Fc fusion protein in the porcine-to-human MLR assay caused a statistically significant reduction of the SIs of the xenoreactive CD4(+) T cells. Such an alteration was abrogated by further addition of blocking antibodies (Abs) against either human CD47 or signal regulatory protein-alpha in the porcine-to-human MLR assay. Addition of human CD47-Fc after the depletion of non-T cells from the population of human responder PBMCs in this MLR assay did not influence the SIs of the xenoreactive CD4(+) T cells.
The more vigorous T cell response to xenoantigens than to alloantigens is possibly attributable to a stronger reaction of xenoreactive T cells; the interspecies incompatibility of CD47 may contribute to such xenoreactive CD4(+) T cell responses via an indirect pathway.
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ABSTRACT: Human immunodeficiency virus (HIV)-1 protease is a known target of CD8+ T cell responses, but it is the only HIV-1 protein in which no fully characterized HIV-1 protease CD4 epitopes have been identified to date. We investigated the recognition of HIV-1 protease by CD4+ T cells from 75 HIV-1-infected, protease inhibitor (PI)-treated patients, using the 5,6-carboxyfluorescein diacetate succinimidyl ester-based proliferation assay. In order to identify putative promiscuous CD4+ T cell epitopes, we used the TEPITOPE algorithm to scan the sequence of the HXB2 HIV-1 protease. Protease regions 4-23, 45-64 and 73-95 were identified; 32 sequence variants of the mentioned regions, encoding frequent PI-induced mutations and polymorphisms, were also tested. On average, each peptide bound to five of 15 tested common human leucocyte antigen D-related (HLA-DR) molecules. More than 80% of the patients displayed CD4+ as well as CD8+ T cell recognition of at least one of the protease peptides. All 35 peptides were recognized. The response was not associated with particular HLA-DR or -DQ alleles. Our results thus indicate that protease is a frequent target of CD4+ along with CD8+ proliferative T cell responses by the majority of HIV-1-infected patients under PI therapy. The frequent finding of matching CD4(+) and CD8+ T cell responses to the same peptides may indicate that CD4+ T cells provide cognate T cell help for the maintenance of long-living protease-specific functional CD8+ T cells.Clinical & Experimental Immunology 02/2011; 164(1):90-9. · 3.41 Impact Factor
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ABSTRACT: Schneider MKJ, Seebach JD. Xenotransplantation literature update June – October 2010. Xenotransplantation 2010; 17: 481–488. © 2010 John Wiley & Sons A/S.Xenotransplantation 01/2010; 17(6):481-8. · 2.57 Impact Factor
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ABSTRACT: We have previously proven that the interspecies incompatibility of CD47 is responsible for phagocytosis of xenogeneic cells by host macrophages. Utilizing an model in the present study, we investigated whether genetically engineered expression of mouse CD47 in rat insulinoma cells (INS-1E) could inhibit macrophage-mediated xenograft rejection. INS-1E cells transfected with the pRc/CMV-mouse CD47 vector (mCD47-INS-1E) induced SIRPα-tyrosine phosphorylation in mouse macrophages in vitro, whereas cells transfected with the control vector (cont-INS-1E) did not. When these cells were injected into the peritoneal cavity of streptozotocin-induced diabetic Rag2γ chain mice, which lack T, B, and NK cells, the expression of mouse CD47 on the INS-1E cells markedly reduced the susceptibility of these cells to phagocytosis by macrophages. Moreover, these mice became normoglycemic after receiving mCD47-INS-1E, whereas the mice that received cont-INS-1E failed to achieve normoglycemia. Furthermore, injection of an anti-mouse SIRPα blocking monoclonal antibody into the mouse recipients of mCD47-INS-1E cells prevented achievement of normoglycemia. These results demonstrate that interspecies incompatibility of CD47 significantly contributes to rejection of xenogeneic cells by macrophages. Thus, genetic induction of the expression of recipient CD47 on xenogeneic donor cells could provide inhibitory signals to recipient macrophages via SIPRα; this constitutes a novel approach for preventing macrophage-mediated xenograft rejection.PLoS ONE 01/2013; 8(3):e58359. · 3.73 Impact Factor