Human γ-chain genes are rearranged in leukaemic T cells and map to the short arm of chromosome 7

Abstract

Three gene families that rearrange during the somatic development of T cells have been identified in the murine genome. Two of these gene families (α and β) encode subunits of the antigen-specific T-cell receptor and are also present in the human genome^1–5. The third gene family, designated here as the γ-chain gene family, is rearranged in murine cytolytic T cells but not in most helper T cells^6–8. Here we present evidence that the human genome also contains γ-chain genes that undergo somatic rearrangement in leukaemia-derived T cells. Murine γ-chain genes appear to be encoded in gene segments that are analogous to the immunoglobulin gene variable, constant and joining segments⁸. There are two closely related constant-region gene segments in the human genome. One of the constant-region genes is deleted in all three T-cell leukaemias that we have studied. The two constant-region γ-chain genes reside on the short arm of chromosome 7 (7p15); this region is involved in chromosomal rearrangements identified in T cells from individuals with the immunodeficiency syndrome ataxia telangiectasia^9–12 and observed only rarely in routine cytogenetic analyses of normal individuals^13–16. This region is also a secondary site of β-chain gene hybridization¹⁷.