IL-7 promotes long-term in vitro survival of unique long-lived memory subset generated from mucosal effector memory CD4⁺ T cells in chronic colitis mice

Colitogenic memory CD4⁺ T cells are important in the pathogenesis of inflammatory bowel disease (IBD). Although memory stem cells with high survival and self-renewal capacity were recently identified in both mice and humans, it is unclear whether a similar subset is present in chronic colitis mice. We sought to identify and purify a long-lived subset of colitogenic memory CD4⁺ T cells, which may be targets for treatment of IBD. A long-lived subset of colitogenic memory CD4⁺ T cells was purified using a long-term culture system. The characteristics of these cells were assessed. Interleukin (IL)-7 promoted the in vitro survival for >8 weeks of lamina propria (LP) CD4⁺ T cells from colitic SCID mice previously injected with CD4⁺CD45RB^high T cells. These cells were in a quiescent state and divided a maximum of 5 times in 4 weeks. LP CD4⁺ T cells expressed higher levels of Bcl-2, integrin-α4β7, CXCR3 and CD25 after than before culture, as well as secreting high concentrations of IL-2 and low concentrations of IFN-γ and IL-17 in response to intestinal bacterial antigens. LP CD4⁺ T cells from colitic mice cultured with IL-7 for 8 weeks induced more severe colitis than LP CD4⁺ T cells cultured for 4 weeks. We developed a novel culture system to purify a long-lived, highly pathogenic memory subset from activated LP CD4⁺ T cells. IL-7 promoted long-term in vitro survival of this subset in a quiescent state. This subset will be a novel, effective target for the treatment of IBD.