Overexpression Of FOXP3 Research Articles

The role of 2 FOXP3 isoforms in the generation of human CD4+ Tregs.

Little is known about the molecules that control the development and function of CD4+ CD25+ Tregs. Recently, it was shown that the transcription factor FOXP3 is necessary and sufficient for the generation of CD4+ CD25+ Tregs in mice. We investigated the capacity of FOXP3 to drive the generation of suppressive CD4+ CD25+ Tregs in humans. Surprisingly, although ectopic expression of FOXP3 in human CD4+ T cells resulted in induction of hyporesponsiveness and suppression of IL-2 production, it did not lead to acquisition of significant suppressor activity in vitro. Similarly, ectopic expression of FOXP3delta2, an isoform found in human CD4+ CD25+ Tregs that lacks exon 2, also failed to induce the development of suppressor T cells. Moreover, when FOXP3 and FOXP3delta2 were simultaneously overexpressed, although the expression of several Treg-associated cell surface markers was significantly increased, only a modest suppressive activity was induced. These data indicate that in humans, overexpression of FOXP3 alone or together with FOXP3delta2 is not an effective method to generate potent suppressor T cells in vitro and suggest that factors in addition to FOXP3 are required during the process of activation and/or differentiation for the development of bona fide Tregs.

HIV infection of naturally occurring and genetically reprogrammed human regulatory T-cells.

A T-cell subset, defined as CD4+CD25hi (regulatory T-cells [Treg cells]), was recently shown to suppress T-cell activation. We demonstrate that human Treg cells isolated from healthy donors express the HIV-coreceptor CCR5 and are highly susceptible to HIV infection and replication. Because Treg cells are present in very few numbers and are difficult to expand in vitro, we genetically modified conventional human T-cells to generate Treg cells in vitro by ectopic expression of FoxP3, a transcription factor associated with reprogramming T-cells into a Treg subset. Overexpression of FoxP3 in naïve human CD4+ T-cells recapitulated the hyporesponsiveness and suppressive function of naturally occurring Treg cells. However, FoxP3 was less efficient in reprogramming memory T-cell subset into regulatory cells. In addition, FoxP3-transduced T-cells also became more susceptible to HIV infection. Remarkably, a portion of HIV-positive individuals with a low percentage of CD4+ and higher levels of activated T-cells have greatly reduced levels of FoxP3+CD4+CD25hi T-cells, suggesting disruption of the Treg cells during HIV infection. Targeting and disruption of the T-cell regulatory system by HIV may contribute to hyperactivation of conventional T-cells, a characteristic of HIV disease progression. Moreover, the ability to reprogram human T-cells into Treg cells in vitro will greatly aid in decoding their mechanism of suppression, their enhanced susceptibility to HIV infection, and the unique markers expressed by this subset.

THE AMOUNT OF SCURFIN PROTEIN DETERMINES PERIPHERAL T CELL NUMBER AND RESPONSIVENESS

Khattri R, Kasprowicz D, Cox T, et al. J Immunol. 2002;167:6312–6320The disorder IPEX (immunodysregulation, polyendocrinopathy, enteropathy, X-linked syndrome) is characterized by enlargement of secondary lymphoid structures, diabetes mellitus beginning in early infancy, and chronic enteropathy. The gene defect was identified in 2001 as FOXP3 on the X chromosome. The FOXP3 gene is a member of the forkhead family of transcription factors, however, the basis for IPEX has remained poorly characterized. Previous groups have shown that the immune system is in a state of chronic activation in these patients with overproduction of cytokines and immunoglobulins, but the relationship of these problems to the FOXP3 mutations has been unclear. This article describes work defining the role of the FOXP3 protein product, scurfin, to the manifestation of T cell expansion.The authors use mouse models including the scurfy mouse, which has an inactive FOXP3 gene and mice transgenic for overexpression of FOXP3. Flow cytometry and histology are used to characterize changes in peripheral T cells and the T cell compartments in secondary lymphoid structures.The scurfin protein is expressed in the thymus but had no demonstrable affect on the phenotype of the scurfy mouse. Overexpression of scurfin in the thymus in a normal mouse had modest affects on various thymic subsets but did not induce any changes in the periphery. Overexpression of scurfin globally in normal mice caused decreased T cell proliferation and interleukin (IL)-2 production. Similarly, overexpression of scurfin inhibited cytolytic T cell activity.The function of scurfin appears to regulate the function and size of the peripheral T cell compartment.IPEX is an uncommon but nearly always fatal immunodeficiency. Affected boys are often total parenteral nutrition-dependent because of their enteropathy and require very stringent immunosuppression for even short-term survival. Stem cell transplantation may be effective. The importance of this article is in its description of a global overactivity of the T cell compartment. This contributes to our understanding of the pathogenesis of this disorder and reinforces the growing belief that the best management option may be early stem cell transplantation.