Peripheral T-cell expansion is of major relevance for immune function after lymphopenia. In order to promote regeneration, the process should result in a peripheral T-cell pool with a similar subpopulation structure as before lymphopenia. We investigated the repopulation of the CD8+ central-memory T cells (TCM) and effector-memory T cells (TEM) pools after adoptive transfer of sorted CD8+ T cells from naïve, TCM and TEM subsets into T-cell-deficient hosts. We show that the initial kinetics of expansion are distinct for each subset and that the contribution to the repopulation of the CD81+ T-cell pool by the progeny of each subset is not a mere function of its initial expansion. We demonstrate that CD4+ CD25+ Treg play a major role in the repopulation of the CD8+ T-cell pool and that CD8+ T-cell subsets impact on each other. In the absence of CD4+ CD25+ Treg, a small fraction of naïve CD81 T cells strongly proliferates, correlating with further expansion and differentiation of co-expanding CD8+ T cells. CD4+ CD25+ Treg suppress these responses and lead to controlled repopulation, contributing decisively to the maintenance of recovered TCM and TEM fractions, and leading to repopulation of each pool with progeny of its own kind.

Interleukin-7 receptor α (encoded by IL7R) is essential for lymphoid development. Whether acute lymphoblastic leukemia (ALL)-related IL7R gain-of-function mutations can trigger leukemogenesis remains unclear. Here, we demonstrate that lymphoid-restricted mutant IL7R, expressed at physiological levels in conditional knock-in mice, establishes a pre-leukemic stage in which B-cell precursors display self-renewal ability, initiating leukemia resembling PAX5 P80R or Ph-like human B-ALL. Full transformation associates with transcriptional upregulation of oncogenes such as Myc or Bcl2, downregulation of tumor suppressors such as Ikzf1 or Arid2, and major IL-7R signaling upregulation (involving JAK/STAT5 and PI3K/mTOR), required for leukemia cell viability. Accordingly, maximal signaling drives full penetrance and early leukemia onset in homozygous IL7R mutant animals. Notably, we identify 2 transcriptional subgroups in mouse and human Ph-like ALL, and show that dactolisib and sphingosine-kinase inhibitors are potential treatment avenues for IL-7R-related cases. Our model, a resource to explore the pathophysiology and therapeutic vulnerabilities of B-ALL, demonstrates that IL7R can initiate this malignancy.

Tight regulation of IL-7Rα expression is essential for normal T-cell development. IL-7Rα gain-of-function mutations are known drivers of T-cell acute lymphoblastic leukemia (T-ALL). Although a subset of patients with T-ALL display high IL7R messenger RNA levels and cases with IL7R gains have been reported, the impact of IL-7Rα overexpression, rather than mutational activation, during leukemogenesis remains unclear. In this study, overexpressed IL-7Rα in tetracycline-inducible Il7r transgenic and Rosa26 IL7R knockin mice drove potential thymocyte self-renewal, and thymus hyperplasia related to increased proliferation of T-cell precursors, which subsequently infiltrated lymph nodes, spleen, and bone marrow, ultimately leading to fatal leukemia. The tumors mimicked key features of human T-ALL, including heterogeneity in immunophenotype and genetic subtype between cases, frequent hyperactivation of the PI3K/Akt pathway paralleled by downregulation of p27Kip1 and upregulation of Bcl-2, and gene expression signatures evidencing activation of JAK/STAT, PI3K/Akt/mTOR and Notch signaling. Notably, we also found that established tumors may no longer require high levels of IL-7R expression upon secondary transplantation and progressed in the absence of IL-7, but remain sensitive to inhibitors of IL-7R–mediated signaling ruxolitinib (Jak1), AZD1208 (Pim), dactolisib (PI3K/mTOR), palbociclib (Cdk4/6), and venetoclax (Bcl-2). The relevance of these findings for human disease are highlighted by the fact that samples from patients with T-ALL with high wild-type IL7R expression display a transcriptional signature resembling that of IL-7–stimulated pro-T cells and, critically, of IL7R-mutant cases of T-ALL. Overall, our study demonstrates that high expression of IL-7Rα can promote T-cell tumorigenesis, even in the absence of IL-7Rα mutational activation.

Naïve CD4 T cells harbour functional subsets that influence the quality of immune reconstitution and the persistent viral reservoirs in people with HIV (PWH) under antiretroviral therapy (ART). Here, we profiled the circulating naïve CD4 T cells from PWH under effective ART with distinct past histories of viral burden, namely starting treatment early in acute or late in chronic stage HIV-1 infection, and people with HIV-2 (PWH2), who feature low to undetectable viremia before ART and slow disease progression. Spectral flow cytometry enabled us to capture the heterogeneity of this overlooked T cell compartment. Early-treated PWH1 maintained a naïve CD4 T cell profile comparable to that of age-matched seronegative individuals. Late-treated PWH1 and PWH2 showed distinct imbalances in conventional and regulatory subpopulations, yet both exhibited a relative expansion of CD31-expressing naïve cells, consistent with an IL-7-mediated homeostatic response. The ability of purified naïve CD4 T cells to respond to IL-7 was evaluated in additional cohorts of untreated PWH, revealing reduced proliferation and increased p21 transcription in PWH1 elite controllers. Additionally, a significant decline in proviral DNA was found in PWH2, suggesting an impact of IL-7 on HIV-2-infected naïve CD4 T cells that was not observed in the case of HIV-1 infection. Unravelling the homeostatic pathways and functional implications of naïve CD4 T cell heterogeneity will help clarify viral reservoir dynamics and inflammation in PWH and define strategies to prevent immune senescence.