Interleukin 7

Structure

The three-dimensional structure of IL-7 in complex with the ectodomain of IL-7 receptor has been determined using X-ray diffraction.

Function

Lymphocyte maturation

IL-7 stimulates the differentiation of multipotent (pluripotent) hematopoietic stem cells into lymphoid progenitor cells (as opposed to myeloid progenitor cells where differentiation is stimulated by IL-3). It also stimulates proliferation of all cells in the lymphoid lineage (B cells, T cells and NK cells). It is important for proliferation during certain stages of B-cell maturation, T and NK cell survival, development and homeostasis.

IL-7 is a cytokine important for B and T cell development. This cytokine and the hepatocyte growth factor (HGF) form a heterodimer that functions as a pre-pro-B cell growth-stimulating factor. This cytokine is found to be a cofactor for V(D)J rearrangement of the T cell receptor beta (TCRß) during early T cell development. This cytokine can be produced locally by intestinal epithelial and epithelial goblet cells, and may serve as a regulatory factor for intestinal mucosal lymphocytes. Knockout studies in mice suggested that this cytokine plays an essential role in lymphoid cell survival.

IL-7 signaling

IL-7 binds to the IL-7 receptor, a heterodimer consisting of Interleukin-7 receptor alpha and common gamma chain receptor. Binding results in a cascade of signals important for T-cell development within the thymus and survival within the periphery. Knockout mice which genetically lack IL-7 receptor exhibit thymic atrophy, arrest of T-cell development at the double positive stage, and severe lymphopenia. Administration of IL-7 to mice results in an increase in recent thymic emigrants, increases in B and T cells, and increased recovery of T cells after cyclophosphamide administration or after bone marrow transplantation.

Disease

Cancer

IL-7 promotes hematological malignancies (acute lymphoblastic leukemia, T cell lymphoma).

Viral Infections

Elevated levels of IL-7 have also been detected in the plasma of HIV-infected patients.

Clinical application

IL-7 as an immunotherapy agent has been examined in many pre-clinical animal studies and more recently in human clinical trials for various malignancies and during HIV infection.

Cancer

Recombinant IL-7 has been safely administered to patients in several phase I and II clinical trials. A human study of IL-7 in patients with cancer demonstrated that administration of this cytokine can transiently disrupt the homeostasis of both CD8+ and CD4+ T cells with a commensurate decrease in the percentage of CD4+CD25+Foxp3+ T regulatory cells. No objective cancer regression was observed, however a dose limiting toxicity (DLT) was not reached in this study due to the development of neutralizing antibodies against the recombinant cytokine.

HIV infection

Associated with antiretroviral therapy, IL-7 administration decreased local and systemic inflammations in patients that had incomplete T-cell reconstitution. These results suggest that IL-7 therapy can possibly improve the quality of life of those patients.

Transplantation

IL-7 could also be beneficial in improving immune recovery after allogenic stem cell transplant.

References

References

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16. (January 2001). "Increased production of IL-7 accompanies HIV-1-mediated T-cell depletion: implications for T-cell homeostasis". Nat. Med..
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