Determination of the precursor frequency and the reaction intensity of xenoreactive human T lymphocytes

Department of Surgery, Division of Frontier Medical Science, Programs for Biomedical Research, Graduate School of Biomedical Sciences, Hiroshima University, Hiroshima, Japan.
Xenotransplantation (Impact Factor: 2.84). 05/2010; 17(3):188-96. DOI: 10.1111/j.1399-3089.2010.00575.x
Source: PubMed


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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    • "not due to a higher frequency of human xenoreactive CD4 þ T cells than in the allogeneic counterpart , and there was no evidence of any differences in CD8 þ T-cell content between allo-and xeno-related direct reactions (Tahara et al. 2010). These studies also suggest that the CD4 þ helper function is needed for xenoreactive CD8 þ T cells to proliferate (Tahara et al. 2010). Indirect anti-pig T-cell responses appear to be mediated primarily by CD4 þ T cells (Dorling et al. 1996). "
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    Cold Spring Harbor Perspectives in Medicine 03/2014; 4(4). DOI:10.1101/cshperspect.a015578 · 9.47 Impact Factor
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    • "These observations raise a question as to whether interspecies incompatibility of CD47 affects CD4+ T cell-mediated responses to xenoantigens positively or negatively. In our previous study, recombinant human CD47-Fc fusion protein (which contains the extracellular domain of human CD47 fused to the Fc portion of human immunoglobulin) significantly reduced the indirect response of human CD4+ T cells to porcine antigens, but did not affect the direct response of these cells in in vitro pig-to-human mixed lymphocyte reaction assays [27]. Inhibition of the phagocytic activity of human APCs toward porcine cells by interaction between the human CD47-Fc fusion protein and the corresponding ligand, probably SIRPα, might might attenuate subsequent CD4+ T cell immune responses against porcine antigens. "
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