ABSTRACT
Anaplastic lymphoma kinase-positive anaplastic large cell lymphoma (ALK+ ALCL) originates from the T-lineage and is marked by rearrangements of the ALK gene. More than 10 fusion partners with the ALK gene are known, with the most common being the t(2;5)(p23;q35) translocation resulting in the NPM1::ALK fusion. In 10% to 20% of the ALK+ ALCL cases, the ALK gene fuses with various other partners. Modern molecular techniques, especially next-generation sequencing (NGS), have eased the identification of ALK gene fusion partners and have allowed in-depth characterization of the T-cell receptor (TCR) repertoire. We devised a real-time quantitative reverse-transcription polymerase chain reaction to measure the expression of the translocated portion of the ALK gene. Fusion partners for the ALK gene were analyzed using rapid amplification of 5'cDNA ends (RACE) method or NGS. TCR immunoprofiling was performed by amplicon NGS. We studied 96 ALK+ ALCL patients. NPM1::ALK fusion gene was observed in 71 patients, ATIC::ALK in 9, and TPM3::ALK in 3. CLTC::ALK, MYH9::ALK, and RNF213::ALK fusions were identified in 2 patients each. We also discovered the TPM4::ALK and SATB1::ALK fusion genes, plus the following 2 previously unidentified ALK+ ALCL fusions: SQSTM1::ALK and CAPRIN1::ALK. High expression of the translocated ALK gene segment was observed in all 93 analyzed samples. TCR testing was conducted on 23 patients with available DNA. In 18 (78%) patients, we discerned at least one (ranging from 1 to 4) clonal TCR rearrangement. In 59% of the patients, clonal TCR beta junctions corresponded with sequences previously observed in both healthy donors and under various pathological conditions. Reverse-transcriptase quantitative detection of ALK expression is a fast and reliable method for both diagnosing and monitoring treatment response in ALK+ ALCL patients, irrespective of the ALK gene translocation. NGS reveals new ALK translocation partners. Both malignant and reactive TCR repertoires in ALK+ ALCL patients are unique and do not consistently occur among different patients.
Subject(s)
Lymphoma, Large-Cell, Anaplastic , Matrix Attachment Region Binding Proteins , Ubiquitin-Protein Ligases , Humans , Anaplastic Lymphoma Kinase/genetics , Lymphoma, Large-Cell, Anaplastic/genetics , Lymphoma, Large-Cell, Anaplastic/pathology , Receptor Protein-Tyrosine Kinases/genetics , Protein-Tyrosine Kinases/genetics , Translocation, Genetic , Transcription Factors/genetics , Nuclear Proteins/genetics , Receptors, Antigen, T-Cell/genetics , High-Throughput Nucleotide Sequencing , Cell Cycle Proteins/genetics , Adenosine Triphosphatases/geneticsABSTRACT
Follicular lymphoma (FL) is a common indolent B-cell malignancy with a variable clinical course. An unfavorable event in its course is histological transformation to a high-grade lymphoma, typically diffuse large B-cell lymphoma. Recent studies show that genetic aberrations of MYC or its overexpression are associated with FL transformation (tFL). However, the precise molecular mechanisms underlying tFL are unclear. Here we performed the first profiling of expression of microRNAs (miRNAs) in paired samples of FL and tFL and identified 5 miRNAs as being differentially expressed. We focused on one of these miRNAs, namely miR-150, which was uniformly downmodulated in all examined tFLs (â¼3.5-fold), and observed that high levels of MYC are responsible for repressing miR-150 in tFL by binding in its upstream region. This MYC-mediated repression of miR-150 in B cells is not dependent on LIN28A/B proteins, which influence the maturation of miR-150 precursor (pri-miR-150) in myeloid cells. We also demonstrated that low miR-150 levels in tFL lead to upregulation of its target, namely FOXP1 protein, which is a known positive regulator of cell survival, as well as B-cell receptor and NF-κB signaling in malignant B cells. We revealed that low levels of miR-150 and high levels of its target, FOXP1, are associated with shorter overall survival in FL and suggest that miR-150 could serve as a good biomarker measurable in formalin-fixed paraffin-embedded tissue. Overall, our study demonstrates the role of the MYC/miR-150/FOXP1 axis in malignant B cells as a determinant of FL aggressiveness and its high-grade transformation.
Subject(s)
Forkhead Transcription Factors/genetics , Gene Expression Regulation, Neoplastic , Lymphoma, Follicular/genetics , MicroRNAs/genetics , Repressor Proteins/genetics , Cell Transformation, Neoplastic/genetics , Cell Transformation, Neoplastic/pathology , Down-Regulation , Humans , Lymphoma, Follicular/diagnosis , Lymphoma, Follicular/pathology , Lymphoma, Large B-Cell, Diffuse/genetics , Lymphoma, Large B-Cell, Diffuse/pathology , Prognosis , Proto-Oncogene Proteins c-myc/genetics , Transcriptional Activation , Up-RegulationABSTRACT
Hodgkin's lymphoma is unusual among B cell lymphomas, in so far as the malignant Hodgkin/Reed-Sternberg (HRS) cells lack a functional B cell receptor (BCR), as well as many of the required downstream signalling components. In Epstein-Barr virus (EBV)-positive cases of Hodgkin's lymphoma, HRS cells express the viral latent membrane proteins (LMP)-1 and -2A. LMP2A is thought to contribute to the pathogenesis of Hodgkin's lymphoma by providing a surrogate BCR-like survival signal. However, LMP2A has also been shown to induce the virus-replicative cycle in B cells, an event presumably incompatible with lymphomagenesis. In an attempt to resolve this apparent paradox, we compared the transcriptional changes observed in primary HRS cells with those induced by LMP2A and by BCR activation in primary human germinal centre (GC) B cells, the presumed progenitors of HRS cells. We found a subset of genes that were up-regulated by both LMP2A expression and BCR activation but which were down-regulated in primary HRS cells. These genes included EGR1, an immediate-early gene that is required for BCR-induced entry to the virus-replicative cycle. We present data supporting a model for the pathogenesis of EBV-positive Hodgkin's lymphoma in which LMP2A-expressing HRS cells lacking BCR signalling functions cannot induce EGR1 and are consequently protected from entry to the virus lytic cycle. The primary microarray data are available from GEO (http://www.ncbi.nlm.nih.gov/geo/) under series Accession No 46143.
Subject(s)
Early Growth Response Protein 1/metabolism , Herpesvirus 4, Human/metabolism , Hodgkin Disease/metabolism , Reed-Sternberg Cells/metabolism , Viral Matrix Proteins/metabolism , B-Lymphocytes/metabolism , Burkitt Lymphoma/metabolism , Burkitt Lymphoma/pathology , Burkitt Lymphoma/virology , Cell Line, Tumor , Cytopathogenic Effect, Viral , Early Growth Response Protein 1/genetics , Enzyme Activation , Extracellular Signal-Regulated MAP Kinases/metabolism , Gene Expression Profiling/methods , Gene Expression Regulation, Neoplastic , Herpesvirus 4, Human/genetics , Herpesvirus 4, Human/pathogenicity , Hodgkin Disease/genetics , Hodgkin Disease/pathology , Hodgkin Disease/virology , Humans , Oligonucleotide Array Sequence Analysis , Receptors, Antigen, B-Cell/metabolism , Reed-Sternberg Cells/pathology , Reed-Sternberg Cells/virology , Trans-Activators/metabolism , Transfection , Up-Regulation , Viral Matrix Proteins/geneticsABSTRACT
Penile squamous cell carcinoma (pSCC) is a rare tumour with a variable prognosis. More prognostic markers linked to mutational signatures and the tumour immune microenvironment are needed. A cohort made up of 165 invasive pSCC was retrospectively analysed using formalin-fixed, paraffin-embedded tumour tissue, focusing on tumour mutational burden (TMB), programmed death ligand 1 (PD-L1) expression, microsatellite instability (MSI), the number of tumour infiltrating lymphocytes (TILs) expressing cytotoxic T-lymphocyte-associated protein 4 (CTLA4), HPV status determined by p16 immunohistochemistry, and several traditional histopathological variables. High TMB (>10 mut/Mb) was associated with high PD-L1 expression (TPS 50-100%), and HPV-negative status. High PD-L1 expression was linked to HPV negativity, a high number of intratumoural CTLA4+ cells, and brisk lymphocytic infiltrate. High TMB was a significant predictor of shorter overall survival (OS) in both univariate and multivariate analysis when using a median cut-off value of 4.3 mut/Mb, but not when using an arbitrary cut-off of 10 mut/Mb. Low CTLA4+ cell infiltration at the tumour invasion front was a marker of shorter OS and cancer-specific survival in both univariate and multivariate analysis. PD-L1 expression had no significant impact on prognosis. Only two cases were MSI high. The results support the hypothesis of two aetiological pathways in pSCC cancerogenesis: (1) SCC linked to HPV infection characterised by low TMB, less common PD-L1 expression, and a lower number of TILs; and (2) SCC linked to chronic inflammation leading to a high number of acquired mutations (high TMB), HPV negativity, increased neoantigen production (i.e., PD-L1), and high immune cell infiltration.
Subject(s)
Carcinoma, Squamous Cell , Papillomavirus Infections , Penile Neoplasms , Male , Humans , B7-H1 Antigen/metabolism , CTLA-4 Antigen , Papillomavirus Infections/complications , Retrospective Studies , Penile Neoplasms/genetics , Tumor MicroenvironmentABSTRACT
Penile squamous cell carcinoma (pSCC) is a rare malignancy with a slowly increasing incidence and variable prognosis. Regional lymph node involvement signifies poor prognosis but represents a late sign, and more prognostic markers for effective patient risk stratification are urgently needed. In this retrospective study, 152 tumour samples with formalin-fixed, paraffin-embedded tissue were analysed for traditional pathological variables, tumour budding, p53, p16, and mismatch repair proteins (MMR) immunohistochemistry. The density of tumour lymphocytic infiltrate was also determined, using subjective evaluation by two pathologists (brisk/non-brisk/absent) and also using the immunoscore method, which categorised the cohort into five immunoscore groups according to the number of CD3+ and CD8+ T-cells in both the tumour centre and tumour invasion front. Only one case (0.6%) was MMR-deficient. Tumour budding count ≥5 tumour buds/20× power field and non-brisk/absent lymphocytic infiltrate were significant negative predictors of both the overall survival (OS) and cancer-specific survival (CSS), whereas a low immunoscore was a significant marker of shorter OS but not CSS. Advanced pT stage (3+4) was a significant marker of shorter CSS but not OS. In the multivariate analysis, high-grade budding was a significant parameter if adjusted for the patient's age and associated variables, except for the pN stage. The lymphocytic infiltrate retained its prognostic significance if adjusted for age and associated variables. The negative prognostic significance of the previously described parameters (lymphatic, venous, and perineural invasion, regional lymph node metastasis, and p53 mutated profile) were confirmed in our study. Grade, histological subtype, and HPV status (as determined by p16 immunohistochemistry) showed, surprisingly, little or no prognostic significance.
Subject(s)
Carcinoma, Squamous Cell , Penile Neoplasms , Male , Humans , Retrospective Studies , Tumor Suppressor Protein p53/metabolism , Carcinoma, Squamous Cell/pathology , Prognosis , Penile Neoplasms/pathology , InflammationABSTRACT
Cholangiocarcinoma (CCA) is a liver malignancy associated with a poor prognosis. Its main subtypes are peripheral/intrahepatic and hilar/extrahepatic CCA. Several molecular, morphological and clinical similarities between hilar/extrahepatic CCA and pancreatic ductal adenocarcinoma (PDAC) have been described. FOXF1 is a transcription factor which has been described to have prognostic significance in various tumors and it is involved in the development of bile ducts. The aim of this study is to determine occurrence of nuclear expression of FOXF1 in both subtypes of CCA and metastatic PDAC and assess its potential usefulness as a diagnostic marker. Secondary aims were to investigate the use of C-reactive protein (CRP) immunohistochemistry for diagnosing intrahepatic peripheral CCA and the significance of histological features in CCA subtypes. 32 archive specimens of CCA, combined hepatocellular carcinoma-CCA (HCC-CCA) and liver metastasis of PDAC were stained by FOXF1 and CRP immunohistochemistry and evaluated to determine histological pattern. The CCAs were classified radiologically into peripheral/intrahepatic and hilar subtype. Using Fisher exact test, we identified nuclear FOXF1 as a fairly specific (87%) but insensitive (65%) marker of hilar and extrahepatic CCA and metastatic PDAC (p = 0.005). CRP immunohistochemistry was characterized by a high sensitivity and specificity, of 79% and 88%, respectively (p = 0.001). We did not identify any histomorphological features associated with either types of CCA or metastatic PDAC. As a conclusion of novel finding, FOXF1 immunohistochemistry may be regarded as a specific but insensitive marker of hilar/extrahepatic CCA and metastatic PDAC and it may help distinguish them from peripheral CCA.
Subject(s)
Biomarkers, Tumor/metabolism , Carcinoma, Hepatocellular/pathology , Carcinoma, Pancreatic Ductal/secondary , Forkhead Transcription Factors/metabolism , Klatskin Tumor/pathology , Liver Neoplasms/secondary , Pancreatic Neoplasms/pathology , Adult , Aged , Aged, 80 and over , Bile Duct Neoplasms/metabolism , Bile Duct Neoplasms/pathology , Carcinoma, Hepatocellular/metabolism , Carcinoma, Pancreatic Ductal/metabolism , Female , Follow-Up Studies , Humans , Immunohistochemistry , Klatskin Tumor/metabolism , Liver Neoplasms/metabolism , Male , Middle Aged , Pancreatic Neoplasms/metabolism , Prognosis , Survival Rate , Pancreatic NeoplasmsABSTRACT
BACKGROUND: Panniculitis-like T-cell lymphoma is an uncommon type of non-Hodgkin lymphoma, occurring usually in the form of nodules within the subcutaneous fat tissue of the extremities or trunk. In the literature, subcutaneous panniculitis-like T-cell lymphoma (SPTCL) is described as a distinct type of T-cell lymphoma with a variable clinical behavior, depending on molecular phenotype of T-cell receptor (TCR) and on the presence or absence of hemophagocytic syndrome. CASE PRESENTATION: We present a bioptic and autoptic case of a 65-years old Caucasian man with panniculitic T-cell lymphoma with morphological and immunohistochemical features of SPTCL, limited to the retroperitoneal and mesenteric mass, i.e. without any cutaneous involvement, and associated with severe hemophagocytic lymphohistiocytosis. CONCLUSION: A panniculitic T-cell lymphoma with morphological and molecular features of SPTCL, which is limited to mesentery, i.e. does not involve subcutaneous fat, seems to be exceedingly rare.
Subject(s)
Lymphohistiocytosis, Hemophagocytic/pathology , Lymphoma, T-Cell/pathology , Panniculitis/pathology , T-Lymphocytes/pathology , Aged , Autopsy , Diagnosis, Differential , Humans , Lymphohistiocytosis, Hemophagocytic/diagnosis , Lymphoma, T-Cell/diagnosis , Lymphoma, T-Cell, Cutaneous/diagnosis , Lymphoma, T-Cell, Cutaneous/pathology , Male , Panniculitis/diagnosis , Skin Neoplasms/diagnosis , Skin Neoplasms/pathologyABSTRACT
BACKGROUND: Despite the relatively high rate of curability, approximately 20% to 30% of patients with classic Hodgkin lymphoma relapse. Hodgkin-Reed-Sternberg (HRS) cells:lymphoma-associated macrophages (LAMs) cross talk promotes tumor growth and resistance to therapy. The aim of the study was to assess the prognostic role of the LAM to HRS ratio (LHR) in lymph node biopsies using a novel automated system for scanning large sample areas. PATIENTS AND METHODS: High-quality tissue samples obtained from 71 patients and stained with anti-CD30 and anti-CD68 were analyzed using the TissueFAXS (TissueGnostics). RESULTS: A high LHR was associated with inferior 5-year progression-free survival (PFS; 50.0% vs. 79.3%; P = .032) and overall survival (OS; 65.4% vs. 92.3%; P = .012). Multivariate Cox regression identified the high LHR as an unfavorable prognostic factor for PFS (hazard ratio [HR], 3.07; P = .029) and OS (HR, 4.56; P = .025). CONCLUSION: A high LHR at diagnosis is associated with a higher risk of lymphoma progression or death. Automated image analysis is a new tool that can overcome technical limitations of by microarray samples in lymphomas with high intratumor heterogeneity.
Subject(s)
Hodgkin Disease/pathology , Lymph Nodes/pathology , Macrophages/pathology , Reed-Sternberg Cells/pathology , Adolescent , Adult , Aged , Aged, 80 and over , Antigens, CD/metabolism , Antigens, Differentiation, Myelomonocytic/metabolism , Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Biopsy/methods , Disease-Free Survival , Female , Hodgkin Disease/drug therapy , Hodgkin Disease/metabolism , Humans , Ki-1 Antigen/metabolism , Male , Middle Aged , Neoplasm Recurrence, Local , Prognosis , Young AdultABSTRACT
Our article reports a case of a 35-year-old man with cardiac mass, who underwent a wide range of imaging methods, including cardiac magnetic resonance imaging (MRI) and positron emission tomography/computed tomography (PET/CT). Contrast-enhanced MRI images revealed "sun ray" pattern in the mass. Final histopathological diagnosis of angiosarcoma was confirmed during autopsy. To our knowledge, our case is the second direct observation of this MRI diagnostic pattern and the first one that allows a comparison with PET/CT findings.
Subject(s)
Heart Neoplasms/diagnostic imaging , Hemangiosarcoma/diagnostic imaging , Magnetic Resonance Imaging/methods , Positron Emission Tomography Computed Tomography/methods , Adult , Fatal Outcome , Heart/diagnostic imaging , Humans , MaleABSTRACT
Matrix-assisted laser desorption/ionization coupled with Orbitrap mass spectrometry (MALDI-Orbitrap-MS) is used for the clinical study of patients with renal cell carcinoma (RCC), as the most common type of kidney cancer. Significant changes in sulfoglycosphingolipid abundances between tumor and autologous normal kidney tissues are observed. First, sulfoglycosphingolipid species in studied RCC samples are identified using high mass accuracy full scan and tandem mass spectra. Subsequently, optimization, method validation, and statistical evaluation of MALDI-MS data for 158 tissues of 80 patients are discussed. More than 120 sulfoglycosphingolipids containing one to five hexosyl units are identified in human RCC samples based on the systematic study of their fragmentation behavior. Many of them are recorded here for the first time. Multivariate data analysis (MDA) methods, i.e., unsupervised principal component analysis (PCA) and supervised orthogonal partial least square discriminant analysis (OPLS-DA), are used for the visualization of differences between normal and tumor samples to reveal the most up- and downregulated lipids in tumor tissues. Obtained results are closely correlated with MALDI mass spectrometry imaging (MSI) and histologic staining. Important steps of the present MALDI-Orbitrap-MS approach are also discussed, such as the selection of best matrix, correct normalization, validation for semiquantitative study, and problems with possible isobaric interferences on closed masses in full scan mass spectra. Graphical Abstract á .
Subject(s)
Carcinoma, Renal Cell/pathology , Kidney Neoplasms/pathology , Kidney/pathology , Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization/methods , Sulfoglycosphingolipids/analysis , Biomarkers, Tumor/analysis , Carcinoma, Renal Cell/chemistry , Carcinoma, Renal Cell/diagnosis , Humans , Kidney/chemistry , Kidney Neoplasms/chemistry , Kidney Neoplasms/diagnosis , Least-Squares Analysis , Multivariate Analysis , Principal Component Analysis , Sensitivity and SpecificityABSTRACT
This study analyzed the prognostic significance of soluble interleukin-2 receptor α (sIL-2Rα) levels in 100 prospectively enrolled patients with previously untreated follicular lymphoma. It showed that sIL-2Rα level ≥ 115 pmol/L at the time of treatment initiation correlated with a high Follicular Lymphoma International Prognostic Index-2 (FLIPI-2), bulky disease, advanced clinical stage, number of involved lymph nodes, bone marrow involvement and elevated ß2-microglobulin (B2M) level. When testing all patients, sIL-2Rα ≥ 115 pmol/L was associated with significantly shorter progression-free (PFS; p < 0.03, hazard ratio [HR] 2.04) but not overall (OS; p = 0.06, HR 2.36) survival rates. Subanalysis of patients receiving cyclophosphamide, doxorubicin, vincristine and prednisone (CHOP) ± rituximab showed higher predictive power for both PFS (HR 2.75, 95% confidence interval [CI] 1.24-6.11, p = 0.01) and OS (HR 3.33, 95% CI 1.15-9.63, p = 0.02). In the whole population (n = 100), only B2M proved a significant univariate predictor (p = 0.007, HR = 2.8) of PFS. When testing patients treated with CHOP ± rituximab, sIL-2Rα was found to be the best univariate predictor for PFS among all FLIPI-2 factors (HR = 2.68, p = 0.015). Serum IL-2Rα levels may help to refine risk assessment in the modern immunotherapy era complementary to FLIPI-2 factors.
Subject(s)
Antineoplastic Combined Chemotherapy Protocols/therapeutic use , Lymphoma, Follicular/blood , Lymphoma, Follicular/mortality , Receptors, Interleukin-2/blood , Adult , Aged , Cyclophosphamide/administration & dosage , Doxorubicin/administration & dosage , Female , Humans , Lymphoma, Follicular/diagnosis , Lymphoma, Follicular/drug therapy , Male , Middle Aged , Neoplasm Staging , Prednisone/administration & dosage , Prognosis , Rituximab/administration & dosage , Treatment Outcome , Vincristine/administration & dosageABSTRACT
INTRODUCTION: Breast cancer treatment currently represents one of the biggest challenges in clinical oncology. The gold standard for axillary lymph node management is to perform sentinel node biopsy to avoid axillary dissection and its sequelae. The detection of radiocolloid flow outside the axillary nodes is a diagnostic and therapeutic challenge. METHODS: A database search at the Department of Oncology of Palacky University, Olomouc, Czech Republic, identified 127 patients who underwent breast cancer resection with a sentinel node procedure and had radiocolloid flow into the internal mammary nodes. Sentinel node lymphoscintigraphy was performed after intraparenchymal injection. Clinical and pathological data were collected to identify possible risk factors. RESULTS: Ten clinical and pathological parameters including age, tumor histology, axillary lymph node status, estrogen receptor expression, progesterone receptor expression, tumor grade, Ki-67 expression, Her-2 status, tumor size and tumor location were analyzed with regard to internal mammary node drainage. A cohort of 127 patients with detected drainage into the internal mammary nodes was compared with 135 patients without such drainage. Six significant risk factors, including age <50 years ( P <0.0313), tumor location in central and inner quadrants (P <0.012), larger tumor size (P <0.017), positive Her-2 status (P <0.025), progesterone receptor expression (P <10-4) and axillary lymph node involvement (P <0.01) were found to predict radiocolloid flow into the internal mammary nodes. CONCLUSION: Six parameters (patient age, tumor location, hormone receptor status, tumor size, Her-2 status and axillary lymph node status) should be considered in the management of breast cancer patients and help in the selection of patients for locoregional procedures encompassing the internal mammary nodes.
Subject(s)
Biomarkers, Tumor/analysis , Breast Neoplasms/chemistry , Breast Neoplasms/pathology , Drainage , Lymph Nodes/pathology , Sentinel Lymph Node Biopsy , Adult , Age Factors , Aged , Axilla , Breast Neoplasms/epidemiology , Breast Neoplasms/surgery , Czech Republic/epidemiology , Databases, Factual , Female , Humans , Ki-67 Antigen/analysis , Lymph Node Excision , Lymphatic Metastasis , Lymphoscintigraphy/methods , Middle Aged , Neoplasm Grading , Neoplasm Staging , Receptor, ErbB-2/analysis , Receptors, Estrogen/analysis , Receptors, Progesterone/analysis , Retrospective Studies , Risk Assessment , Risk FactorsABSTRACT
TCR gene rearrangement generates diversity of T lymphocytes by V(D)J recombination. Ig genes are rearranged in B cells using the same enzyme machinery. Physiologically, TCR gene is postulated to rearrange exclusively in T lineage, but malignant B precursor lymphoblasts contain rearranged TCR genes in most patients. Several mechanisms by which malignant cells break the regulation of V(D)J recombination have been proposed. In this study we show that incomplete TCR delta rearrangements V2-D3 and D2-D3 occur each in up to 16% alleles in B lymphocytes of all healthy donors studied, but complete VDJ rearrangement was negative at the sensitivity limit of 1%. Data are based on real-time quantitative PCR validated by PAGE and sequencing of the cloned products. Therefore, TCR genes rearrange not exclusively in T lineage. This study opens up further questions regarding the exact extent of the "cross-lineage" TCR or Ig rearrangements in normal lymphocytes, specific subsets in which the cross-lineage rearrangements occur, and the physiological importance of these rearrangements.