Modulated expression of notch1 during thymocyte development

The Notch gene family encodes transmembrane proteins that have been implicated in control of diverse cellular differentiation events in the fly, frog, and mouse. Mammalian Notch1 is expressed at high levels in thymus and is mutated in a subset of human T-cell acute lymphoblastic neoplasms, suggesting a role in T-cell differentiation. To investigate the patterns of expression of NOTCH1 protein in thymocytes of the developing and mature thymus, antibodies raised against NOTCH1 were used to perform immunohistochemical and flow cytometric analyses. Strong staining for NOTCH1 within the fetal murine thymus was observed as early as 13.5 days postcoitum. By 17.5 days postcoitum, preferential staining of superficial cortical thymocytes was observed, with weak staining of developing medulla. Flow cytometric analysis and immunohistochemical staining of flow-sorted cells confirmed that the highest levels of NOTCH1 expression in adult murine thymus were present in immature cortical thymocytes (CD24high, CD4-CD8-). In contrast, NOTCH1 expression was low or absent in more mature cortical thymocytes (CD24low, CD4+CD8+), whereas intermediate levels of expression were observed in CD4+CD8- and CD4-CD8+ cells. These data indicate a dynamic pattern of NOTCH1 expression during T-cell differentiation and suggest that downregulation of NOTCH1 may be required for maturation of cortical thymocytes.

Lymphocytic progenitor cell origin and clonal evolution of human B-lineage acute lymphoblastic leukemia

At presentation, bone marrow specimens from over 25% of B-lineage acute lymphoblastic leukemias (ALL) display more than two clonal rearrangements of immunoglobulin heavy chain (IgH) genes in Southern blot analyses. Nucleotide sequence analysis has shown predominantly different V(H)DJ(H) junctions among these genes, leading to the frequent description of such cases as oligoclonal leukemias. In the present study, we have analyzed the lgH genes from four patients whose leukemic cells contained different patterns of lgH gene rearrangements between presentation and relapse. Nucleotide sequence analysis of the lgH genes showed that three mechanisms could account for these differences: de novo V(H)DJ(H) rearrangement, V(H) to DJ(H) recombination, and V(H) replacement. In all cases, more than two totally different V(H)DJ(H) rearrangements appeared during evolution of the disease, formally consistent with the conclusion that these tumors were composed of apparently unrelated clones. However, the retention of some of the antigen receptor gene rearrangements, as well as the persistence of a chromosomal marker in two cases, indicated that these leukemias had a monoclonal origin. These findings support the hypothesis that some ALLs arise from a lymphoid progenitor cell at a stage of lymphocyte development before the onset of IgH gene rearrangement. These leukemic lymphocyte progenitors generate malignant daughter cells capable of an in vivo maturation that involves the completion of multiple different lgH rearrangements as well as the modification of preexisting rearrangements by V(H) to DJ(H) recombination or by a V(H) replacement.

Complete nucleotide sequence of Ig V genes in three cases of Burkitt lymphoma associated with AIDS

To investigate the role of polyclonal stimulation and antigen driven selection in the pathogenesis of acquired immunodeficiency syndrome (AIDS) related lymphomas, we studied the variable region nucleotide sequence of heavy (VH) and light (VL) chains expressed by 3 Burkitt lymphomas (BL) associated with HIV infection. Two cases expressed the VH3-30P1 gene with 88.6% and 86.7% homology when compared to their germinal counterpart, whereas the VH4-18 was rearranged in the third one (89% identity). All these genes displayed high numbers of mutations (27, 22, 28 respectively), predominating in CDR regions. The encoded light chain genes determined for cases 1 and 2 expressed the same V kappa I-018 gene. These results indicate that: 1) Although, it is difficult to address the issue of VH usage based on the limited number of cases studied, Burkitt's lymphoma associated with AIDS may use a restricted repertoire of Ig genes. 2) Mutations and/or replacements predominated in CDR regions, which might suggest the occurrence of an antigen driven selection process, at least in some AIDS associated lymphomas. However, the high ratio of mutations observed in framework (FW) regions also favors the possibility that the antigen selection process is associated with polyclonal B cell stimulation.

Analysis of VH gene expression in CD5+ and CD5- B-cell chronic lymphocytic leukemia

In contrast to highly mutated follicular lymphomas and multiple myelomas, chronic lymphocytic leukemias (CLLs) frequently express VH genes in germline configuration. It is currently unclear whether this difference is related to the expression of CD5 or to the differentiation stage of the B cell when malignant transformation occurs. We have studied the VH sequence of 11 cases of CD5- B-CLL to address the question whether CD5- B-CLL are derived from naive pregerminal B cells (low mutation pattern) or from germinal center-derived memory B cells (high mutation pattern). Among the 12 detected rearrangements (2 distinct rearrangements in 1 case) VH1 family was found in 2, VH2 in 2, VH3 in 4, and VH4 in 4. Nine different VH genes were detected among the 12 rearrangements, including 2 cases expressing V1-69 (51p1) and 1 case expressing V4-39 (VH4.18), previously reported to be overexpressed in CD5+ B-CLL. A higher mutation pattern, following a random distribution, was observed when compared with classical CD5+ B-CLL. However, as reported in normal B cells, these results appeared to be related to membrane Ig phenotype (less mutations in membrane mu delta-expressing forms in leukemias expressing exclusively membrane mu). Overall, the differences found when comparing the mutational profile with classical CD5+ B-CLL were not clearcut and might be explained more by the membrane isotype (mu v mu delta) than by CD5 expression.

High expression of latent membrane protein 1 of Epstein-Barr virus and BCL-2 oncoprotein in acquired immunodeficiency syndrome-related primary brain lymphomas

Nearly all primary brain lymphomas in acquired immunodeficiency syndrome (AIDS) patients are associated withEpstein-Barr virus (EBV). The role of EBV in lymphomagenesis is not totally elucidated. One possible mechanism is the overexpression of the BCL-2 oncoprotein, because the latent membrane protein 1 (LMP1) has been reported to transactivate the bcl-2 gene in vitro. To study the interrelationship beetween LMP1 and BCL-2 in vivo, we have analyzed and compared their expression in 11 AIDS-related primary brain lymphomas and 57 AIDS-related systemic lymphomas by immunoperoxidase technique on frozen sections. In AIDS-related primary brain lymphoma, LMP1 and BCL-2 were expressed in all cases but 1. All positive cases exhibited morphologic immunoblastic features. In contrast, the only negative case was histologically close to Burkitt's lymphoma. In systemic lymphomas, LMP1 was expressed in 21 cases, whereas BCL-2 was positive in only 3 cases, all of which were extranodal. These results indicate that, in addition to the histologic type, the role of EBV genes and BCL-2 expression in lymphomatous cells differ as a function of their localization. In AIDS-related primary brain lymphomas, this correlation between LMP1 and BCL-2 overexpression may have a major implication in lymphomagenesis.

Lymphoproliferative disorders after organ transplantation: a report of 24 cases observed in a single center

PURPOSE

Organ recipients are at a high risk of post-transplant lymphoproliferative disorders (PTLDs) as a complication of immunosuppressive therapy. We report the incidence, clinical presentation, pathologic findings, treatment, and outcome for 24 cases of PTLD observed at our institution.

PATIENTS AND METHODS

Twenty-four (1.7%) of 1,385 organ transplant recipients developed PTLDs. Dosages of immunosuppressive drugs were reduced in 19 patients. Treatment consisted of anti-B-cell monoclonal antibodies (12 patients), and/or chemotherapy (eight patients), or surgery (two patients).

RESULTS

The median time between grafting and the onset of PTLD was 210 days. Tumors were classified as monomorphic and polymorphic in nine and 15 cases, respectively. Three of 24 cases were of T-cell origin. Genotypic studies confirmed the monoclonality of the tumors in 11 cases among 14 PTLDs tested. Epstein-Barr virus (EBV) infection was associated with 70% of B-cell PTLDs tested. The overall survival duration was 5 months. Ten patients are alive and disease-free with a median follow-up time of 37 months; most were treated with anti-B-cell antibodies. Two other patients died in complete remission of unrelated causes at 33 and 38 months.

CONCLUSION

Anti-B-cell monoclonal antibody therapy seems to be effective in PTLD, even in monoclonal B-cell forms, but other approaches will be necessary to improve survival further.

Description of a novel FR1 IgH PCR strategy and its comparison with three other strategies for the detection of clonality in B cell malignancies

PCR amplification of IgH gene V-D-J junctional variability (IgH PCR) is increasingly replacing Southern analysis for the detection of clonal lymphoid populations in cases presenting diagnostic difficulties. In order to determine the most efficient strategy, we have compared three known methods, using consensus primers against the VH FR3 or FR2 (FR256) regions, or a mix of six primers against the FR1 region (FR1f), with a new approach using a consensus primer against FR1 (FR1c), never previously described for diagnostic purposes, on DNA from 89 monoclonal B-cell proliferations (16 ALL, 28 CLL/PLL, 15 myelomas, 30 NHL). We obtained a detection rate of 70% for FR3, 64% for FR1f and 77% and 78% for FR256 and FR1c, respectively. Polyclonal lymphocytes and mature T cell malignancies tested negative for all systems. Differences in the detection rate were related not only to the choice of VH primer but also the JH primer(s) used and the pathological subtype. All strategies led to adequate detection of leukaemic DNA, whereas the detection rate in myeloma varied between strategies from 47 to 80% and that of follicular lymphoma from 13 to 63%. The lowest detection rates were observed in follicular lymphoma and in mature CD5 negative proliferations, reflecting the probable correlation between somatic mutation and PCR false-negativity. The combined use of FR1c and FR256 allowed detection in at least one system of 92% of cases overall and at least 75% in all pathological subtypes, thus providing a simple, reliable and rapid non-radioactive system for the detection of B cell clonality.

Growth arrest and terminal differentiation of leukemic myelomonocytic cells induced through ligation of surface CD23 antigen

Acute myelogenous leukemia (AML) cells express CD23 surface antigen after in vitro treatment with various cytokines, including interleukin-4 (IL-4) and interferon gamma. Subsequent ligation of CD23 by specific monoclonal antibody (MoAb) induces substantial morphologic and functional modifications in these cells. In the present study, we investigated the role of CD23 in the proliferation and the maturation of leukemic cells from AML patients or the U937 cell line. CD23+ cell treatment with CD23 MoAb inhibited the proliferation of leukemic cells. This correlated with their terminal differentiation after 7 to 9 days incubation because they (1) definitively lost their growth capacity; (2) adhered to culture flasks and became monocyte/macrophage-like; and (3) expressed mature monocyte markers including nonspecific esterases. Intracellular mechanism of this antitumoral effect was then analyzed in U937 cells. Induction of high-density surface CD23 expression by IL-4 or granulocyte-macrophage colony-stimulating factor coincided with a transient decrease of U937 cell proliferation. CD23 ligation during this low-proliferative phase induced a rapid activation of L-arginine-dependent pathway and the intracellular accumulation of cyclic guanosine monophosphate and cyclic adenosine monophosphate (cAMP). Induction of these early messengers was followed by the activation of nuclear factor-kB transcription factor and the modulation of proto-oncogene expression by U937 cells. Whereas U937 cell treatment with IL-4 decreased c-fos/c-jun expression, CD23 MoAb reinduced c-fos/c-jun and promoted the expression of cell maturation-associated proto-oncogenes junB and c-fms, during the first 24 hours. Both IL-4 and CD23 MoAb downregulated the expression of c-myb. CD23 ligation also induced the production of TNF alpha by U937 cells. Inhibitors of cAMP and nitric oxide reversed CD23-mediated modification in U937 cells. These data evidence the ability of CD23 surface antigen to mediate terminal differentiation of early leukemic myelomonocytic cells.

Expression of a novel type of immunoglobulin C lambda transcripts in human mature B lymphocytes producing kappa light chains

Ordered rearrangement of immunoglobulin genes (heavy chain then kappa and eventually lambda genes) is observed during B lymphocyte ontogeny. Unexpectedly, we found that human mature B cells producing kappa chains and having germ-line lambda genes contain lambda mRNA consisting of an invariant 5' region (herein termed X) and of one of the classical C lambda exons. The X region of these transcripts originates from a unique exon located 5 kb upstream of the J-C lambda 1 gene segment. X-C lambda mRNA expression occurs without somatic DNA rearrangement. The use of the X DNA fragment as a probe allows definition of a family of human genes that comprises at least four members and includes the first exon of the lambda 14.1 gene. The latter is selectively transcribed in pre-B lymphocytes and directs the synthesis of a lambda-like chain. In contrast, the X-C lambda transcripts do not appear to encode a C lambda-related polypeptide in mature B cells. Thus, despite a 73% homology extending far beyond the exon sequences, the X and lambda 14.1 genes are expressed at different stages of B cell development and might serve different functions.

Detection of a T cell receptor delta chain with an anti-TCR alpha chain serum

Two types of T cell antigen-specific receptors have been described. Most peripheral blood T lymphocytes express, at their surface, an antigen receptor consisting of alpha and beta subunits, while a small subset of thymocytes and a minority of mature T lymphocytes express a heterodimeric receptor termed gamma delta. Whereas the gene segments localization corresponding to the TCR gamma and beta chains are separate, genes encoding the joining and the constant regions of TCR delta chain are located between the TCR V alpha region and the J alpha-C alpha gene cluster. To determine whether V alpha gene segments are used by delta chains, immunoprecipitations from human TCR gamma delta expressing cell clones were performed with an anti-alpha serum. The results show that a rabbit antiserum raised against the purified REX TCR alpha subunit immunoprecipitates a TCR delta chain from the cell surface of only one human T cell clone termed SO1. However, since no SO1 RNA hybridization is observed with REX TCR V alpha probe and SO1 cloned cells do react with an anti-V delta 2 monoclonal antibody, we conclude that TCR delta and alpha chains expressed a limited structural homology and that REX TCR V alpha gene do not seem to be frequently used in a functional delta chain.

Prevalence of monoclonal Ig with lambda light chains in chronic myelocytic leukaemia

Light chains from seven of eight monoclonal Ig detected in the serum of patients with chronic myelocytic leukaemia (CML) were of the lambda isotype. Although the presence of monoclonal Ig in CML is distinctly unusual, this prevalence of lambda chains is unlikely to be a mere coincidence. All patients had otherwise typical clinical, chromosomal and molecular (bcr rearrangements) features of classical CML. The lambda locus appeared unaltered. Only two patients had an excess of dystrophic plasma cells suggestive of multiple myeloma.

Tumoral nasopharyngeal lymphoid hyperplasia in human immunodeficiency virus-infected patients

Two patients presented with a large tumoral nasopharyngeal lesion with obstructive symptoms, which suggested a malignant tumor. They were black men of Caribbean origin who were infected with human immunodeficiency virus 1. In both cases, histologic examination revealed intense but benign lymphoid follicular hyperplasia, and immunohistochemical studies were consistent with its polyclonal nature. DNA studies performed on tumoral tissue failed to disclose immunoglobulin or T-cell receptor gene rearrangements. In one biopsy specimen, DNA hybridization using Epstein-Barr virus-specific probes showed no evidence of Epstein-Barr virus-DNA sequences. The nasopharynx can be involved in the diffuse extranodal lymphoid hyperplasia associated with human immunodeficiency virus infection.

Use of a variable alpha region to create a functional T-cell receptor delta chain

Two categories of T-cell antigen-specific receptor have been described. Most mature T lymphocytes have, on their membrane, an antigen receptor consisting of alpha and beta subunits, while early T cells and thymocytes possess a heterodimeric receptor termed gamma-delta. The DS6 clone, isolated from the peripheral blood of a patient with immunodeficiency, is a CD3+, CD4-, CD8- human T-cell line that expresses the disulfide-linked form of the gamma-delta antigen receptor. The nucleotide sequence analysis of DS6 cDNA makes clear that its variable region is a member of an alpha variable-region gene family. We have cloned and sequenced the germ-line joining and variable regions used to create the DS6 delta mRNA. Comparison of these sequences does not show evidence of extensive somatic mutations. The major difference between the germ-line and the T-cell antigen receptor delta cDNA sequence is an insertion of three consecutive nucleotides between the variable and joining segments and is evocative of somatic diversification rather than of the use of a germ-line-encoded diversity region.