A phage antibody identifying an 80-kDa membrane glycoprotein exclusively expressed on a subpopulation of activated B cells and hairy cell leukemia B cells

Evolving concepts in the pathogenesis of hairy-cell leukaemia

Hairy-cell leukaemia (HCL) has long been recognized as distinct from other chronic B-cell malignancies, but several questions remain unanswered. What is the HCL cell of origin? Why does HCL lack the hallmarks of most mature B-cell tumours (for example, chromosomal translocations and consistent lymph node involvement) and show unique features like 'hairy' morphology and bone-marrow fibrosis? Gene-expression profiling and other studies have recently provided new insights into HCL biology and have the potential to affect clinical practice.

New insights into the phenotype and cell derivation of B cell chronic lymphocytic leukemia

For many decades, B cell chronic lymphocytic leukemia (B-CLL) stood out as a B cell-derived malignancy that was difficult to position within the framework of the available B cell differentiation scheme: First, the histology as well as the immunophenotype did not quite resemble that of any normal lymphocyte; second, in contrast to almost all other B cell tumor subtypes, the immunoglobulin variable region (IgV) genes of B-CLL cases could be either unmutated or somatically mutated; third, the genomic lesions observed in B-CLL were markedly distinct from those of the other major B cell malignancies, which typically exhibit balanced chromosome translocations. Recent advances in the characterization of both B-CLL and normal B cell subpopulations by phenotypic analysis, global gene expression profiling, as well as extensive IgV gene repertoire analyses have shed new light on the phenotype and the cell derivation of B-CLL and provided novel hypotheses concerning its pathogenesis. Here we summarize recent work relevant to these issues and conclude that B-CLL may be derived from a cell that can be referred to as a marginal zone B cell. Moreover, we propose that the lack of chromosomal translocations in B-CLL may be related to their derivation from marginal zone B cells, since somatic hypermutation and Ig class switch, the processes that generate chromosome translocations in most germinal center (GC)-derived malignancies, are no longer active in marginal zone B cells. Also, we discuss similarities and differences between B-CLL and hairy cell leukemia (HCL) and suggest that also HCL may be derived from a post-GC memory or marginal zone B cell.

Nectin-like protein 2 defines a subset of T-cell zone dendritic cells and is a ligand for class-I-restricted T-cell-associated molecule

Dendritic cells (DCs) are a phenotypically and functionally heterogenous population of leukocytes with distinct subsets serving a different set of specialized immune functions. Here we applied an in vitro whole cell panning approach using antibody phage display technology to identify cell-surface epitopes specifically expressed on human blood BDCA3(+) DCs. A single-chain antibody fragment (anti-1F12 scFv) was isolated that recognizes a conserved surface antigen expressed on both human BDCA3(+) DCs and mouse CD8alpha(+) DCs. We demonstrate that anti-1F12 scFv binds Nectin-like protein 2 (Necl2, Tslc1, SynCaM, SgIGSF, or Igsf4), an adhesion molecule involved in tumor suppression, synapse formation, and spermatogenesis. Thus, Necl2 defines a specialized subset of DCs in both mouse and human. We further show that Necl2 binds Class-I-restricted T-cell-associated molecule (CRTAM), a receptor primarily expressed on activated cytotoxic lymphocytes. When present on antigen presenting cells, Necl2 regulates IL-22 expression by activated CD8(+) T-cells. We propose that Necl2/CRTAM molecular pair could regulate a large panel of cell/cell interactions both within and outside of the immune system.

Gene expression profiling of hairy cell leukemia reveals a phenotype related to memory B cells with altered expression of chemokine and adhesion receptors

Hairy cell leukemia (HCL) is a chronic B cell malignancy characterized by the diffuse infiltration of bone marrow and spleen by cells displaying a typical "hairy" morphology. However, the nature of the HCL phenotype and its relationship to normal B cells and to other lymphoma subtypes remains unclear. Using gene expression profiling, we show here that HCL displays a homogeneous pattern of gene expression, which is clearly distinct from that of other B cell non-Hodgkin lymphomas. Comparison with the gene expression profiles of purified normal B cell subpopulations, including germinal center (GC), pre-GC (naive), and post-GC (memory) B cells, shows that HCL cells are more related to memory cells, suggesting a derivation from this B cell population. Notably, when compared with memory cells, HCL cells displayed a remarkable conservation in proliferation, apoptosis, and DNA metabolism programs, whereas they appeared significantly altered in the expression of genes controlling cell adhesion and response to chemokines. Finally, these analyses have identified several genes that are specifically expressed in HCL and whose expression was confirmed at the protein level by immunocytochemical analysis of primary HCL cases. These results have biological implications relevant to the pathogenesis of this malignancy as well as clinical implications for its diagnosis and therapy.

The biology of hairy cells

The evidence that hairy cells are activated clonal late B cells is presented. The largely non-specific (i.e. not confined to hairy-cell leukaemia) chromosome and genetic abnormalities are then described. Next, the features of malignant-cell activation are considered, including the distinctive morphology of hairy cells and their expression of activation-related antigens and activated adhesion receptors. Also, signalling and cytokine production are discussed in the context of malignant-cell activation. It is then demonstrated that many of the distinctive clinicopathological features of hairy-cell leukaemia can be explained in terms of the interaction of the activated malignant cells with other types of cell and tissue matrix. Finally, the biological basis of the hairy cell's unusually high sensitivity to IFN-alpha and nucleoside analogues is discussed.

Gene expression profiling of B cell chronic lymphocytic leukemia reveals a homogeneous phenotype related to memory B cells

B cell-derived chronic lymphocytic leukemia (B-CLL) represents a common malignancy whose cell derivation and pathogenesis are unknown. Recent studies have shown that >50% of CLLs display hypermutated immunoglobulin variable region (IgV) sequences and a more favorable prognosis, suggesting that they may represent a distinct subset of CLLs which have transited through germinal centers (GCs), the physiologic site of IgV hypermutation. To further investigate the phenotype of CLLs, their cellular derivation and their relationship to normal B cells, we have analyzed their gene expression profiles using oligonucleotide-based DNA chip microarrays representative of approximately 12,000 genes. The results show that CLLs display a common and characteristic gene expression profile that is largely independent of their IgV genotype. Nevertheless, a restricted number of genes (<30) have been identified whose differential expression can distinguish IgV mutated versus unmutated cases and identify them in independent panels of cases. Comparison of CLL profiles with those of purified normal B cell subpopulations indicates that the common CLL profile is more related to memory B cells than to those derived from naive B cells, CD5(+) B cells, and GC centroblasts and centrocytes. Finally, this analysis has identified a subset of genes specifically expressed by CLL cells of potential pathogenetic and clinical relevance.

Protein-protein interactions in hematology and phage display

Phage display, which exploits fundamental tools and principles of immune repertoire diversity, antigen-antibody interactions, and clonal and immunologic selection, is used increasingly to advance experimental and clinical hematology. Phage display is based on the ability of bacteriophage to present engineered proteins on their surface coat. Diverse libraries of proteins such as peptides, antibody fragments, and protein domains corresponding to gene fragments or cDNAs may be displayed. Interactions between phage-displayed proteins and target antigens can be identified rapidly and characterized using high throughput methodologies. Peptide and gene fragment libraries are particularly useful to characterize binding interactions between proteins, such as ligand-receptor interactions. This approach allows rapid generation of human antibodies, often against nonimmunogenic, conserved proteins. Phage antibodies against surface and intracellular antigens are used as reagents for flow cytometry, in vivo imaging, and therapeutic targeting. Phage-derived antibodies also facilitate analyses of the humoral antibody response. Finally, cellular delivery of phage-displayed peptides and gene fragments can be used to modulate functional pathways and molecules in vitro and in vivo. The combinatorial power of phage display enables identification of candidate epitopes without knowledge of the protein interaction, a priori. Overall, these capabilities provide a versatile, high-throughput approach to develop tools and reagents useful for a plethora of experimental hematology applications. This paper focuses on current and future applications of antibody and epitope phage display technology in hematology.

The use of recombinant antibodies in proteomics

Recombinant antibodies are becoming increasingly important in the field of proteomics. Recent advances include the development of large phage-antibody libraries that contain high-affinity binders to almost any target protein, and new methods for high-throughput selection of antibody-antigen interactions. Coupled with a range of new screening technologies that use high-density antibody arrays to identify differentially expressed proteins, these antibody libraries can be applied to whole proteome analysis.