Several antigen-nonspecific, genetically unrestricted factors derived from T cells have been shown to play a role in the regulation of B cell responses (1-9). One such factor, designated B cell growth factor (BCGF-1 or BSF-1), ~ appears to be required for the proliferation of a subset of B cells after interaction with antigen or antiimmunoglobulin molecules. A second series of factors, called B cell differentiation (BCDF) or T cell-replacing factors (TRF), is involved in the terminal maturation of proliferating B cells into immunoglobulin-secreting cells. There has been controversy regarding the possible involvement of T cell growth factor or interleukin 2 (IL-2) in B cell responses and specifically the ability of this growth factor to act directly on B lymphocytes. The proponents of a direct action of IL-2 on B cells showed that depletion of IL-2 from cofactor-rich supernatants by absorption on IL-2-dependent T cell lines also removed a factor required for B cell differentiation (4, 5, 10). Furthermore, there was a strict correlation between the levels of IL-2 and one of the B cell-specific factors required for antibody production (4). This view that IL-2 acts directly on B cells has been challenged, since both mouse and human IL-2 have been distinguished from B cell growth and differentiation factors (7-11). The IL-2-containing supernatants generally used in the previous studies (the supernatant of the FS6-14.13 line) also contained BCGF and one or more TRFs (9). Furthermore, IL-2 was not absorbed from cofactor-rich supernatants by incubation with lipopolysaccharide (LPS)-stimulated splenic lymphoblasts (4). Finally, radiolabeled IL-2 did not bind to LPS-stimulated B cells or to either of the two Burkitt's lymphoma B cell lines examined (Raji and Daudi) suggesting that B cells do not manifest receptors for IL-2 (12).We have reexplored the possibility that certain activated B cells display receptors for IL-2 using the anti-Tac monoclonal antibody produced in our laboratory (13,14). This monoclonal antibody identifies the human membrane receptor for 16,17). The observations that led to this conclusion include: (a) antiAbbreviations used in this paper: BCDF, B cell differentiation factor; BCGF, B cell growth factor; EBV, Epstein-Barr virus; IL-2, interleukin 2; LPS, lipopolysaccharide; NWSM, Nocardia watersoluble mitogen; PWM, pokeweed mitogen; SDS, sodium dodecyl sulfate; SLO, Streptolysin-O; WGA, wheat germ agglutinin.

There are at least two interleukin 2 (IL-2) binding peptides: one is the Mr 55,000 peptide (p55) reactive with the anti-Tac monoclonal antibody, and the other is a Mr 75,000 non-Tac IL-2 binding peptide (p75). Independently existing Tac or p75 peptides represent low-affinity IL-2 receptors, whereas high-affinity IL-2 receptors are expressed when both peptides are present and associated in a receptor complex. It has long been known that normal large granular lymphocytes (LGL) or leukemic cells from the patients with abnormal expansions of LGL can be activated by IL-2 not only to more-potent natural killer cells but also to effectors of lymphokine-activated killer (LAK) activity, although they do not express the Tac peptide. In the present study, using crosslinking methodology, we found that normal LGL and leukemic LGL from all individuals tested expressed the p75 IL-2 binding peptide but did not express the Tac peptide. These LGL leukemia cells made proliferative responses to IL-2 but required a much higher concentration than that required for the proliferation of normal phytohemagglutinin-stimulated T lymphoblasts that express high-affinity receptors. Furthermore, the addition of IL-2 to Tac-negative LGL leukemic cells augmented transcription of the Tac gene and induced the Tac peptide. Neither the IL-2-induced proliferation nor the upregulation of Tac gene expression was inhibited by the addition of anti-Tac. These results strongly suggest that the p75 peptide is responsible for IL-2-induced activation of LGL and that the p75 peptide alone can mediate an IL-2 signal. Thus, the p75 peptide may play an important role in the IL-2-mediated immune response not only by participating with the Tac peptide in the formation of the high-affinity receptor complex on T cells but also by contributing to the initial triggering of LGL activation so that these cells become efficient natural killer and lymphokine-activated killer cells.

Three gene families that rearrange during the somatic development of T cells have been identified in the murine genome. Two of these gene families (alpha and beta) encode subunits of the antigen-specific T-cell receptor and are also present in the human genome. The third gene family, designated here as the gamma-chain gene family, is rearranged in murine cytolytic T cells but not in most helper T cells. Here we present evidence that the human genome also contains gamma-chain genes that undergo somatic rearrangement in leukaemia-derived T cells. Murine gamma-chain genes appear to be encoded in gene segments that are analogous to the immunoglobulin gene variable, constant and joining segments. 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 gamma-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 and observed only rarely in routine cytogenetic analyses of normal individuals. This region is also a secondary site of beta-chain gene hybridization.

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.

As bstract. Adult T cell leukemia (ATL) and Sezary 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 Sezary syndrome do not have antibodies to this virus. Leukemic cells of both groups were ofthe T3, T4-positive, T8-negative phenotype. Despite the similar phenotype, HTLV-negative S&ary leukemic cells frequently functioned as helper cells, whereas some HTLV-positive ATL and HTLV-positive Sezary cells appeared to function as suppressors of immunoglobulin synthesis. One can distinguish the HTLVpositive 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 Sezary 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 T-cell lymphotropic virus I (HTLV-I)-induced adult T-cell leukemia (ATL) cells constitutively express interleukin-2 (IL-2) receptors identified by the anti-Tac monoclonal antibody (MoAb), whereas normal resting cells do not. This observation provided the scientific basis for a trial of intravenous anti-Tac in the treatment of nine patients with ATL. The patients did not suffer untoward reactions and did not have a reduction in the normal formed elements of the blood, and only one of the nine produced antibodies to the anti-Tac MoAb. Three patients had transient mixed, partial, or complete remissions lasting from 1 to more than 8 months after anti-Tac therapy, as assessed by routine hematologic tests, immunofluorescence analysis of circulating cells, and molecular genetic analysis of HTLV-I provirus integration and of the T-cell receptor gene rearrangement. The precise mechanism of the antitumor effects is unclear; however, the use of a MoAb that prevents the interaction of IL-2 with its receptor on ATL cells provides a rational approach for the treatment of this malignancy.

The use of probes to genes (IG and TCRB) encoding immunoglobulins (IG) and the ,3 chain of the T-cell antigen receptor (TCRB), respectively, have become a sensitive means to assess clonality and lineage in lymphoid malignancies. It has become apparent that some individual cases show rearrangements of both IG and TCRB genes. In an attempt to more accurately define cell lineage we have analyzed cells from patients with B-or T-cell leukemia (n = 26) at various stages of maturation with probes to two additional TCR genes, TCRG and TCRA (encoding the TCR y and a chains, respectively), as well as the IG heavy chain joining region (IGHJ) and TCRB genes. On Southern blot analysis, the mature T-cell leukemia cells studied had rearranged TCRG and TCRB while IGHJ remained as in the germ line. The mature B-cell leukemia cells studied had rearranged IGHJ with germ-line TCRG and TCRB. These data suggest that, in the majority of more mature leukemias, cells have rearranged IG or TCR genes but not both. In contrast, cells from five of nine precursor B-cell leukemia patients and cell lines from one of four precursor T-cell leukemia patients had rearranged both IGHJ and TCR genes. TCRG and TCRB mRNAs were expressed in the cells of precursor T-but not B-cell leukemia patients studied. The spectrum of leukemia cells studied within the T-cell series permitted an assessment of the order of TCR gene rearrangements. Two of 13 patients had cells with germ-line TCRG and TCRB, 2 patients had cells with rearranged TCRG alone, and the remainder had cells with rearranged TCRG and TCRB. TCRG and TCRB mRNAs were expressed in precursor T-cell leukemia cells, whereas TCRB and TCRA were expressed in mature T-cell leukemia cells. These results parallel observations from mouse studies on gene expression and support the view of a hierarchy of TCR gene rearrangements in Tlymphocyte ontogeny. TCRG genes are rearranged first, subsequently TCRB genes are rearranged, followed by TCRA gene activation.The T-cell antigen receptor (TCR) is a 90-kDa heterodimer consisting of 40-to 50-kDa a and A3 subunits (TCRA and

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