M. Kozik

Recipient-Specific Tolerance after HLA-Mismatched Umbilical Cord Blood Stem Cell Transplantation

Background. Lower incidence and severity of acute graft versus host disease (GVHD) has been observed in leukemia patients receiving HLA-mismatched umbilical cord (UCB) transplants. However, despite the increased use of UCB in stem cell transplantation, the mechanisms underlying these favorable outcomes are not well delineated. Methods. We analyzed antigen specific lymphocyte responses after transplant to determine whether the decreased allogeneic responsiveness of UCB lymphocytes is attributable to pan-unresponsiveness, lymphocyte repressive or recipient-specific tolerance. Results. Circulating lymphocytes collected early (3 months) after UCB transplant demonstrate a less naïve phenotype compared with that in the infused graft. Additionally, after transplant, circulating peripheral blood UCB-derived lymphocytes produced normal levels of interferon-&ggr; and proliferated normally when stimulated with mitogen or third party alloantigen. In contrast, when stimulated with recipient antigen, circulating lymphocytes emerging posttransplant did not proliferate nor produce interferon-&ggr;. Moreover, analysis of interleukin-4 production revealed a Th2 response to recipient antigens. These data indicate early induction of immune tolerance of naïve UCB graft lymphocytes with skewing of transplant recipient-specific immune response towards Th2 cytokine profile. Conclusions. UCB graft lymphocyte immune naivety and observed early tolerance induction may contribute to the observed favorable GVHD incidence, despite infusion of HLA mismatch grafts in the unrelated allogeneic setting.

Cyclosporin A effects during primary and secondary activation of human umbilical cord blood T lymphocytes

OBJECTIVE Cyclosporin A (CsA), effective in prophylaxis and treatment of graft-vs-host disease (GVHD) after human allogeneic transplantation, blunts T-cell responses by inhibiting nuclear factor of activated T cells-1 (NFAT1) activation. This laboratory has shown that NFAT1 protein expression is severely reduced in human UCB (umbilical cord blood) T cells. Since UCB is increasingly used as a hematopoietic stem cell source in allogeneic transplantation, it is important to determine whether CsA sensitivity in UCB differs from that of adult T cells. METHODS Surface flow cytometric analysis, intracellular cytokine staining, flow cytometric analysis of cell death, and thymidine incorporation were used in this study to determine T-cell activation and effector functions during primary and secondary stimulation in the presence of CsA. RESULTS Although we observed differential CsA sensitivity of T-cell activation marker (CD69, CD45RO, CD25) upregulation comparing UCB and adult, we did not observe any significant difference in CsA sensitivity of T-cell effector functions. Importantly, we observed reduced IFN-gamma and TNF-alpha expression in UCB T cells both in primary and secondary stimulation, as well as increased rates of activation-induced cell death (AICD). CONCLUSION Thus, our studies do not support the previous hypothesis that reduced GVHD observed after UCB transplantation is attributable to increased CsA sensitivity of UCB T cells. Rather, reduced UCB T-cell cytokine production and increased AICD may be important cellular mechanisms underlying these favorable rates of GVHD in UCB transplant recipients.

Allogeneic transplantation of multiple umbilical cord blood units in adults: role of pretransplant-mixed lymphocyte reaction to predict host-vs-graft rejection.

Allogeneic transplantation of multiple umbilical cord blood units in adults: role of pretransplant-mixed lymphocyte reaction to predict host-vs-graft rejection

Regulation of IL-2 expression by transcription factor BACH2 in umbilical cord blood CD4+ T cells

On activation, umbilical cord blood (UCB) CD4+ T cells demonstrate reduced expression of tumor necrosis factor-α (TNF-α) and interferon-γ (IFN-γ), whereas maintaining equivalent interleukin-2 (IL-2) levels, as compared with adult peripheral blood (PB) CD4+ T cells. Nuclear factor of activated T cells (NFAT1) protein, a transcription factor known to regulate the expression of IL-2, TNF-α and IFN-γ, is reduced in resting and activated UCB CD4+ T cells. In contrast, expression of Broad-complex-Tramtrack-Bric-a-Brac and Cap‘n’collar homology 1 bZip transcription factor 2 (BACH2) was shown by gene array analyses to be increased in UCB CD4+ T cells and was validated by qRT-PCR. Using chromatin immunoprecipitation, BACH2 was shown binding to the human IL-2 proximal promoter. Knockdown experiments of BACH2 by transient transfection of UCB CD4+ T cells with BACH2 siRNA resulted in significant reductions in stimulated IL-2 production. Decreased IL-2 gene transcription in UCB CD4+ T cells transfected with BACH2 siRNA was confirmed by a human IL-2 luciferase assay. In summary, BACH2 maintains IL-2 expression in UCB CD4+ T cells at levels equivalent to adult PB CD4+ T cells despite reduced NFAT1 protein expression. Thus, BACH2 expression is necessary to maintain IL-2 production when NFAT1 protein is reduced, potentially impacting UCB graft CD4+ T-cell allogeneic responses.

Deficient IFN-γ Expression in Umbilical Cord Blood (UCB) T Cells Can Be Rescued by IFN-γ -Mediated Increase in NFATc2 Expression

Regulation of nuclear factor of activated T cells-c2 (NFATc2) gene expression is not clearly defined. We previously reported reduced NFATc2 protein expression in cord blood T lymphocytes. Here we show that NFATc2 expression in T cells is dependent in part on the presence of IFN-γ during primary stimulation, as blocking of IFN-γ blunted NFATc2 protein and mRNA upregulation. Conversely, addition of exogenous IFN-γ during stimulation resulted in increased expression of NFATc2 in cord blood T lymphocytes. This correlated with rescue of deficient IFN-γ expression by cord blood T cells. Rescue of IFN-γ expression in cord blood T cells was dependent on the presence of antigen-presenting cells, as addition of IFN-γ during stimulation of purified cord blood T cells did not result in an increase of IFN-γ expression, and depletion of monocytes ablated the rescue of IFN-γ expression. Our results point to impaired function in the antigen-presenting cell population of cord blood, playing a role in the hyporesponsiveness of T cells.