Reviewing the potential utility of interleukin-7 as a promoter of thymopoiesis and immune recovery.

The identification of interleukin-7 (IL-7) as a critical cytokine in early B- and T-cell development, combined with the discovery that it acts on mature T cells, opens new avenues for investigating the thymopoietic machinery and manipulation of the immune system. Initially, IL-7 was thought to be a growth factor in the context of the B-cell lineage in that it stimulates proliferation of early B-cell progenitors. However, it appears that this cytokine has a much broader field of activity within the network of signal transduction. Indeed, evidence exists to support the pivotal involvement of IL-7 in the gene rearrangement of the T-cell receptor repertoire that ultimately leads to thymocyte commitment. The finding that IL-7 is an inducer of both cytotoxic T-cell- and lymphocyte-activated killer cells is one of the significant recent developments in the field of tumor immunology. Lately, it has been demonstrated that administration of IL-7 to mice after myeloablative treatment accelerates immune recovery via a unique pathway. This review of the literature dealing with IL-7 in the realm of immune function shows, inter alia, the value of the cytokine in immunosuppressed animals. The collection of findings noted in this paper may be considered the forerunner for clinical application of IL-7 in a variety of conditions of hematolymphopoietic failure.