CD8 blockade promotes the expansion of antigen-specific CD4+ FOXP3+ regulatory T cells in vivo

Abstract

Treatment with a cocktail of CD4 and CD8-specific monoclonal antibodies (mAb) induces long-term transplantation tolerance and regulatory CD4 + T cells that induce tolerance in non-tolerant T cells. In contrast, treatment with a CD4-specific mAb alone fails to induce long-term tolerance. The current study was designed to test the hypothesis that CD8 blockade plays a role in promoting the development of CD4 + regulatory T cells.Using the DO11.10 CD4 + TCR transgenic mouse model we show that treatment with a CD4/CD8-specific mAb cocktail induces antigen-specific tolerance to OVA, measured by a significant decrease in OVA-specific IgG, on challenge with antigen. Although treatment with OVA and the CD4-specific mAb alone also induces a significant decrease in OVA-specific antibody, the number of DO11.10 cells is significantly greater in mice treated with the CD4/CD8-specific mAb cocktail, and this is associated with a significant increase in proliferation of DO11.10 cells in response to specific antigen. DO11.10 cells sorted from mice made tolerant to OVA with the CD4/CD8-specific mAb cocktail promote an OVA-specific IgG1 (Th2-type) response but not an OVA-specific IgG3 (Th1-type) response on transfer into new syngeneic recipients, suggesting their ability to regulate the type of antigen-specific immune response that ensues after priming with antigen. In addition, DO11.10 cells from tolerant mice express markers that are characteristic of CD4 + regulatory cells, including FOXP3, GITR and CTLA4, but not CD25. Taken as a whole, these data suggest that CD8 blockade promotes CD4 + FOXP3 + regulatory CD4 + T cells by promoting their proliferation in tolerant mice.

CD8 Blockade Promotes Antigen Responsiveness to Nontolerizing Antigen in Tolerant Mice by Inhibiting Apoptosis of CD4+ T Cells

“…Using a wellestablished model for the study of Ag responsiveness and tolerance, we show that while CD8 blockade is not necessary to induce Ag-specific regulatory CD4 ϩ FOXP3 ϩ T cells, it is essential for the maintenance of Ag responsiveness to irrelevant Ag in tolerant mice. In this model, the effect of CD8 blockade is to prevent the loss of nontransgenic CD4 ϩ T cells in mice treated with OVA and anti-CD4 mAb and this is consistent with previous findings indicating that CD8 blockade also prevents the loss of TCR-transgenic CD4 ϩ T cells in mice treated with anti-CD4 mAb (12). However, the mechanism for this effect on transgenic and nontransgenic CD4 ϩ T cells is not the same.…”

“…It has been suggested that effector CD8 ϩ T cell function is less affected by CD40-CD40L, CD28-B7, and CD4 blockade than CD4 ϩ T cell function (5-7, 10, 11); therefore, an additional CD8-directed approach is necessary to control CD8 effector function. However, we have recently shown that blockade of CD8 promotes CD4 ϩ T cell-mediated immune regulation by promoting proliferation of Ag-specific CD4 ϩ regulatory T cells (12), suggesting an additional role of CD8 blockade in the development of long-term tolerance. The model used in this study involves the well-characterized nondepleting CD4-specific mAb, YTS 177, and the CD8-specific mAb, YTS 105.…”

“…The model used in this study involves the well-characterized nondepleting CD4-specific mAb, YTS 177, and the CD8-specific mAb, YTS 105. These mAbs induce Ag-specific tolerance to skin (4,13), bone marrow (3), and cardiac allografts (14), and OVA (12). Transplantation tolerance is associated with the development of FOXP3 ϩ CD4 ϩ regulatory cells (15) that are capable of preventing (suppressing) nontolerant cells from rejecting the allograft (10,16).…”

“…Transplantation tolerance is associated with the development of FOXP3 ϩ CD4 ϩ regulatory cells (15) that are capable of preventing (suppressing) nontolerant cells from rejecting the allograft (10,16). Using the OVA-specific CD4 ϩ TCR-transgenic system, DO11.10 (17), we have recently shown that treatment with the anti-CD4/anti-CD8 mAb mixture promotes an increase in the number of CD4 ϩ TCR-transgenic cells compared with treatment with OVA and the anti-CD4 mAb without the anti-CD8 mAb and that these cells show regulatory activity on transfer into new recipients (12). Moreover, in the absence of anti-CD8 mAb, Ag-specific CD4 ϩ T cells in anti-CD4 mAb-treated mice fail to proliferate in response to Ag in vivo but proliferation is significantly increased in mice cotreated with the anti-CD8 mAb (12).…”

“…Using the OVA-specific CD4 ϩ TCR-transgenic system, DO11.10 (17), we have recently shown that treatment with the anti-CD4/anti-CD8 mAb mixture promotes an increase in the number of CD4 ϩ TCR-transgenic cells compared with treatment with OVA and the anti-CD4 mAb without the anti-CD8 mAb and that these cells show regulatory activity on transfer into new recipients (12). Moreover, in the absence of anti-CD8 mAb, Ag-specific CD4 ϩ T cells in anti-CD4 mAb-treated mice fail to proliferate in response to Ag in vivo but proliferation is significantly increased in mice cotreated with the anti-CD8 mAb (12). Using the same model system, the current study was set up to determine whether CD8 blockade also promotes the proliferation of non-TCR-transgenic CD4 ϩ T cells in tolerant mice or whether the effect is restricted to Ag-specific regulatory cells.…”