In the murine thymus, the stroma forms microenvironments that control different steps in T cell development. To study the architecture of such microenvironments and more particularly the nature of communicative signals in lympho-stromal interaction during T cell development, we have employed the phage antibody display technology, with the specific aim of isolating thymic stromal cellspecific single-chain antibodies from a semisynthetic phage library. A subtractive approach using intact, mildly fixed thymic fragments as target tissue and lymphocytes as absorber cells generated monoclonal phages (MoPhabs) detecting subsets of murine thymic stromal cells. In the present paper we report on the reactivity of single-chain antibodies derived from three MoPhabs, TB4-4, TB4-20, and TB4-28. While TB4-4 and TB4-20 are both epithelium specific, TB4-28 detects an epitope expressed on both epithelial-and mesenchymal-derived stromal cells. TB4-4 reacts with all cortical epithelial cells and with other endoderm-derived epithelia, but this reagent leaves the majority of medullary epithelial cells unstained. In contrast, MoPhab TB4-20 detects both cortical and medullary thymic epithelial cells, as well as other endoderm-and ectoderm-derived epithelial cells. Cross-reaction of single-chain antibodies to human thymic stromal cells shows that our semisynthetic phage antibody display library, in combination with the present subtractive approach, permits detection of evolutionary conserved epitopes expressed on subsets of thymic stromal cells.
Approximately 25 ± 30% of childhood pre-B cell acute lymphoblastic leukemias (pre-B ALL) is characterized by the presence of a (1;19)(q23;p13.3) translocation. The presence of this translocation is generally accompanied by a poor prognosis. The chimeric gene resulting from this chromosomal rearrangement encodes a hybrid transcription factor, E2A-Pbx1. In an attempt to delineate the genetic cascade initiated by E2A-Pbx1, we sought to identify genes that are deregulated by this transcription factor in t(1;19) pre-B ALL. We show here that the gene encoding the granulocyte colonystimulating factor receptor (G-CSFr) is speci®cally upregulated in pre-B cells expressing E2A-Pbx1. GCSFr is also expressed in cell lines established from t(1;19) pre-B cell leukemia and on primary t(1;19) tumor cells, but not on control cells. These data indicate that G-CSFr gene is a target for deregulation by E2A-Pbx1.
In chronic myeloid leukemia (CML) and acute lymphoblastic leukemia (ALL) the Ph1 chromosome (22q-) is the most frequent chromosomal aberration encountered. At the molecular level the c-abl gene from chr. 9 is translocated to the bcr gene on chr. 22. As a result, a chimeric bcr-abl gene is generated, which encodes chimeric proteins. Since these proteins are only expressed in Ph1 positive cells, they are per definition tumor-specific. In this report we describe the reactivity of polyvalent antisera raised against synthetic peptides corresponding to the tumor-specific bcr-abl junctions. Native chimeric proteins were specifically recognized by these junction-specific antisera. Therefore we conclude that the bcr-abl junctions are antigenically exposed on the chimeric proteins. We discuss the relevance of these antisera for CML and ALL diagnosis.
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