In Vitro Induction of Regulatory CD4+CD8α+ T Cells by TGF-β, IL-7 and IFN-γ

Abstract

In vitro CD4+ T cell differentiation systems have made important contributions to understanding the mechanisms underlying the differentiation of naive CD4+ T cells into effector cells with distinct biological functions. Mature CD4+ T cells expressing CD8αα homodimers are primarily found in the intestinal mucosa of men and mice, and to a lesser extent in other tissues such as peripheral blood. Although CD4+CD8α+ T cells are easily identified, very little is known about their development and immunological functions. It has been reported, however, that CD4+CD8α+ T cells possess regulatory properties. In this report, we present a novel in vitro differentiation system where CD4+ T cells are stimulated to become CD4+CD8α+ T cells in the presence of TGF-β, IL-7 and IFN-γ, resulting in cells with very similar features as CD4+CD8α+ intraepithelial lymphocytes. This novel in vitro differentiation culture should provide a powerful and tractable tool for dissecting the differentiation and biological functions of CD4+CD8α+ T cells.

CD4+/CD8+ double-positive T cells: more than just a developmental stage?

“…Mature T cells, expressing CD4 and CD8 coreceptors, have been observed in the periphery, hence, bringing into question the mutually exclusive expression of ThPOK and Runx3. Interestingly, when CD4/CD8a + DP T cells are generated in vitro by coculturing mature CD4 + T cells with TGF-b, IL-7, and IFN-g, Runx3 expression is increased, along with ThPOK being reduced [38], thus providing support for the idea that ThPOK and Runx3 expression may, in fact, be more plastic outside of the thymus in mature T cells than thought previously. In vivo, it was reported recently that mature CD4 + intraepithelial lymphocytes in the intestine concurrently express ThPOK and Runx3 [39].…”

“…The underlying mechanism of this regulatory phenotype was IL-10 dependent, although the cells also expressed IFN-g but not IL-4. The ability of CD4/CD8 DP T cells to produce IL-10 and IFN-g but not IL-4 has been confirmed by another group, who likewise showed that mouse splenic CD4/CD8 DP T cells can exhibit a suppressive phenotype [38] and reduce T cell proliferation when cocultured with CD4 + T cells. In contrast, a study focusing on human skin biopsies from a GVHD patient reported the ability of CD4/CD8 DP T cells to produce IL-4 [37]; however, a possible regulatory function for these cells was upheld, based on their cytokine-secretion profile, which included IL-10, IFN-g, and TGF-b.…”

“…However, differences in lineage of origin, tissue location, function, and disease association, as well as species, may all influence the form of CD8 expressed. For example, in mice, rats, and chickens, CD4/CD8 DP T cells derived from the CD4 lineage have been reported to express the CD8aa homodimer exclusively [38,44,52,69]. In humans, within the CD4/CD8 DP T cell population, ;99% express the CD8ab heterodimer in human blood, indicating that they are thymically derived and not gut derived, as the latter principally expresses the CD8aa homodimer [67].…”

“…With the acceptance of CD4/CD8 DP T cells as a distinct lymphocyte population, the question of functionality arises. However, little is currently known about their development or function [38]. This research area appears to be very controversial, and several conflicting papers exist.…”

Intestinal CD4-CD8αβ-TCRαβ+ T cells function as tolerogenic antigen presenting cells

“…4). In addition, some papers suggest that CD8αα can be transiently expressed 31,32 In some papers, CD4 -CD8α -TCRαβ + T cells are defined as DNT cells 33 . This fraction is not same as DNT cells in the current study, because considerable part of DNTs expresses CD8αα.…”