Kathleen F. Bongiovanni

Rearrangements of Genes for the Antigen Receptor on T Cells as Markers of Lineage and Clonality in Human Lymphoid Neoplasms

The T alpha and T beta chains of the heterodimeric T-lymphocyte antigen receptor are encoded by separated DNA segments that recombine during T-cell development. We have used rearrangements of the T beta gene as a widely applicable marker of clonality in the T-cell lineage. We show that the T beta genes are used in both the T8 and T4 subpopulations of normal T cells and that Sézary leukemia, adult T-cell leukemia, and the non-B-lineage acute lymphoblastic leukemias are clonal expansions of T cells. Furthermore, circulating T cells from a patient with the T8-cell-predominantly lymphocytosis associated with granulocytopenia are shown to be monoclonal. Finally, the sensitivity and specificity of this tumor-associated marker have been exploited to monitor the therapy of a patient with adult T-cell leukemia. These unique DNA rearrangements provide insights into the cellular origin, clonality, and natural history of T-cell neoplasia.

Functional and phenotypic comparison of human T cell leukemia/lymphoma virus positive adult T cell leukemia with human T cell leukemia/lymphoma virus negative Sézary leukemia, and their distinction using anti-Tac. Monoclonal antibody identifying the human receptor for T cell growth factor.

Adult T cell leukemia (ATL) and Sézary leukemia are malignant proliferations of T lymphocytes that share similar cell morphology and clinical features. ATL is associated with HTLV (human T cell leukemia/lymphoma virus), a unique human type C retrovirus, whereas most patients with the Sézary syndrome do not have antibodies to this virus. Leukemic cells of both groups were of the T3, T4-positive, T8-negative phenotype. Despite the similar phenotype, HTLV-negative Sézary leukemic cells frequently functioned as helper cells, whereas some HTLV-positive ATL and HTLV-positive Sézary cells appeared to function as suppressors of immunoglobulin synthesis. One can distinguish the HTLV-positive from the HTLV-negative leukemias using a monoclonal antibody (anti-Tac) that appears to identify the human receptor for T cell growth factor (TCGF). Resting normal T cells and most HTLV-negative Sézary cells were Tac-negative, whereas all ATL cell populations were Tac-positive. The observation that ATL cells manifest TCGF receptors suggests the possibility that an abnormality of the TCGF-TCGF receptor system may partially explain the uncontrolled growth of these cells.

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

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 genome1–5. 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 cells6–8. 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 telangiectasia9–12 and observed only rarely in routine cytogenetic analyses of normal individuals13–16. This region is also a secondary site of β-chain gene hybridization17.

IL-2 receptors in adult T-cell leukemia: a target for immunotherapy.

The induction of a T-cell immune response to a foreign antigen requires the activation of T-lymphocytes that is initiated by the interaction of the T-cell antigen receptor with antigen presented in the context of products of the major histocompatibility locus and the macrophage-derived interleukin-1. Following this interaction, T cells express the gene encoding the lymphokine interleukin-2 (IL-2) [1,2]. To exert its biological effect, IL-2 must interact with specific high-affinity membrane receptors. Resting T cells do not express IL-2 receptors, but receptors are rapidly expressed on T cells after activation with an antigen or mitogen [3–5]. Thus, the growth factor IL-2 and its receptor are absent in resting T cells, but after activation the genes for both proteins become expressed.

Role and Molecular Biology of the Interleukin–2-Interleukin-2 Receptor System in Health and Disease

Interleukin-2 (IL-2) is a lymphokine synthesized by T cells following activation. Resting T cells do not express IL-2 receptors, but receptors are rapidly expressed on T cells following interaction of the antigen-specific T cell receptor complex with appropriately processed and presented antigens. AntiTac, a monoclonal antibody that recognizes the IL-2 receptor, has been used to purify the receptor. The receptor is a 55-kDa glycoprotein comprised of 251 amino acids as well as a single 19-amino acid transmembrane domain and a short intra-cytoplasmic domain composed of 13 amino acids at the carboxy-terminus. Normal resting T cells and most leukemic T cell populations examined did not express IL-2 receptors; however, the leukemic cells of all patients with HTLV-I-associated adult T cell leukemia (ATL) expressed the Tac antigen. In HTLV-I-infected cells, the 42-kDa tat protein encoded in part by the tat region of HTLV-I may act as a transacting activator that induces transcription of the IL-2 receptor gene, thus providing an explanation for the constant association of HTLV-I infection of lymphoid cells and IL-2 receptor expression. The constant display of large numbers of IL-2 receptors which may be aberrant in the ATL cells may play a role in the uncontrolled growth of these leukemic T cells. Patients with the Tac-positive ATL are being treated with both unmodified and toxin-conjugated forms of anti-Tac monoclonal antibody directed toward this growth factor receptor.

Interleukin-2 Receptors

Interleukin-2 (IL-2) is a lymphokine synthesized by some T-cells following activation. Resting T-cells do not express IL-2 receptors but receptors are rapidly expressed on T-cells following the interaction of antigens, mitogens, or monoclonal antibodies with the antigen specific T-cell receptor complex. Using anti-Tac a monoclonal antibody that recognizes the IL-2 receptor, the receptor has been purified. The receptor is a 33kd peptide that is posttranslationally glycosylated to a 55kd mature form. Mature receptors contain both N-linked and O-linked sugars and are both sulfated and phosphorylated. Using an oligonucleotide probe, based on the N-terminal amino acid sequence, cDNAs encoding this receptor have been cloned, sequenced and expressed. The addition of anti-Tac to in vitro culture systems blocks the IL-2 induced DNA synthesis of IL-2 dependent T-cell lines and inhibits soluble auto- and alloantigen induced T-cell proliferation. Furthermore, it prevents the generation of cytotoxic and suppressor effector T cells. The anti-receptor antibody also inhibits lectin stimulated immunoglobulin synthesis and the sequential expression of late appearing activation antigens on T-cells. Normal resting T-cells and most leukemic T-cell populations do not express IL2 receptors however the leukemic cells of all patients with human T-cell leukemia/lymphoma virus (HTLV-1) associated, adult T-cell leukemia (ATL) examined expressed the Tac antigen. In HTLV-I infected cells the 42kd LOR protein encoded in part, by the pX region of HTLV-I may act as a transacting transcriptional activator that induces transcription of the IL-2 receptor gene thus providing an explanation for the constant association of HTLV-I infection of lymphoid cells and IL-2 receptor expression. The constant display of large numbers of IL-2 receptors which may be aberrant in the ATL cells may play a role in the uncontrolled growth of these leukemic T-cells. Patients with the Tac positive adult T-cell leukemia are being treated with the anti-Tac monoclonal antibody directed towards this growth factor receptor.