Kaiss Lassoued

Expression of surrogate light chain receptors is restricted to a late stage in pre-B cell differentiation

Surrogate light chain (psi LC) genes are transcriptionally active in progenitor B (pro-B) cells before immunoglobulin genes are rearranged. Current hypothetical models suggest that the psi LC proteins may couple with surrogate or conventional heavy chain proteins to form cell surface receptors that signal the progressive differentiation of pro-B, precursor B (pre-B), and immature B cells. Monoclonal antibodies were produced and used to examine the synthesis, expression, intermolecular interaction, and function of psi LC during B cell differentiation. The results indicate that, while psi LC production spans several developmental stages, cell surface expression is confined to a relatively late stage in normal pre-B cell differentiation, during which receptor cross-linkage does not impede cell growth or B cell differentiation.

STAT3 transcription factor is constitutively activated and is oncogenic in nasal-type NK/T-cell lymphoma

Nasal-type natural killer (NK) cell lymphoma is an infrequent aggressive malignant disease with very poor prognosis. We aimed to explore the possible role of the transcription factor STAT3 in the pathophysiology of this malignancy, as it was involved in oncogenesis and chemoresistance. For this, we established and characterized a continuous interleukin 2-dependent NK cell line (MEC04) from a patient with a fatal nasal-type NK-cell lymphoma. Cells harbored poor cytotoxic activity against K562 cells, and spontaneously secreted interferon-γ, interleukin-10 and vascular-endothelium growth factor in vitro. STAT3 was phosphorylated in Y705 dimerization residue in MEC04 cells and restricted to the nucleus. Y705 STAT3 phosphorylation involved JAK2, as exposure of cells to AG490 inhibitor inhibited Y705 STAT3 phosphorylation. By using recombinant transducible TAT-STAT3-β (β isoform), TAT-STAT3Y705F (a STAT3 protein mutated on Y705 residue, which prevents STAT3 dimerization) and peptides inhibiting specifically STAT3 dimerization, we inhibited STAT3 phosphorylation and cell growth, with cell death induction. Finally, STAT3 was phosphorylated in Y705 residue in the nuclei of lymphoma cells in eight/nine patients with nasal-type NK/T-cell lymphoma and in YT, another NK cell line. Our results suggest that STAT3 protein has a major role in the oncogenic process of nasal-type NK-cell lymphomas, and may represent a promising therapeutical target.

Iron overload in HFE C282Y heterozygotes at first genetic testing: a strategy for identifying rare HFE variants

Background Heterozygotes for the p.Cys282Tyr (C282Y) mutation of the HFE gene do not usually express a hemochromatosis phenotype. Apart from the compound heterozygous state for C282Y and the widespread p.His63Asp (H63D) variant allele, other rare HFE mutations can be found in trans on chromosome 6. Design and Methods We performed molecular investigation of the genes implicated in hereditary hemochromatosis in six patients who presented with iron overload but were simple heterozygotes for the HFE C282Y mutation at first genetic testing. Functional impairment of new variants was deduced from computational methods including molecular modeling studies. Results We identified four rare HFE mutant alleles, three of which have not been previously described. One mutation is a 13-nucleotide deletion in exon 6 (c.1022_1034del13, p.His341_Ala345>LeufsX119), which is predicted to lead to an elongated and unstable protein. The second one is a substitution of the last nucleotide of exon 2 (c.340G>A, p.Glu114Lys) which modifies the relative solvent accessibility in a loop interface. The third mutation, p.Arg67Cys, also lies in exon 2 and introduces a destabilization of the secondary structure within a loop of the α1 domain. We also found the previously reported c.548T>C (p.Leu183Pro) missense mutation in exon 3. No other known iron genes were mutated. We present an algorithm at the clinical and genetic levels for identifying patients deserving further investigation. Conclusions Our results suggest that additional mutations in HFE may have a clinical impact in C282Y carriers. In conjunction with results from previously described cases we conclude that an elevated transferrin saturation level and elevated hepatic iron index should indicate the utility of searching for further HFE mutations in C282Y heterozygotes prior to other iron gene studies.

Astrovirus enteritis in a chronic lymphocytic leukemia patient treated with fludarabine monophosphate.

Abstract We report on a case of severe astrovirus gastroenteritis in a chronic lymphocytic leukemia (CLL) patient treated with fludarabine monophosphate (FAMP). Astrovirus was detected in stools using both an immunoenzymatic assay and an electronic microscopy analysis. Treatment consisted in symptomatic care and the outcome was favorable. Astrovirus infection might constitute a common etiology of gastroenteritis in patients with hematologic malignancies that have been severely immunocompromised with FAMP or other purine analogues, and therefore should be more systematically investigated.

TGF‐β1 modulates Fas (APO‐1/CD95)‐mediated apoptosis of human pre‐B cell lines

We have previously shown that Fas‐induced apoptosis is markedly enhanced by IL‐7 in human pre‐B but not pro‐B cell lines. In addition, pre‐B cell receptor (pre‐BCR) ligation significantly potentiates the IL‐7 effects on Fas‐triggered pre‐B cell death. We show herein that transforming growth factor (TGF)‐β1 sharply reduces Fas‐induced death rate of pre‐B but not pro‐B cells. TGF‐β1 causes inhibition of Fas‐mediated disruption of mitochondrial transmembrane potential and cleavage of caspase 8, Bid and caspase 3. Bcl2 expression is markedly increased in TGF‐β1‐treated pre‐B cells, whereas cellular FLICE‐like inhibitory protein long (c‐FLIPL), Bcl‐XL, Bax, and Bad expression remains unchanged. TGF‐β1 causes a selective growth arrest of pre‐B cells in G0/G1 phase of the cell cycle and induces a partial down‐modulation of both Fas and pre‐BCR expression. All TGF‐β1‐mediated effects, but Bcl2 up‐regulation, can be reproduced by the LY294002 phosphatidylinositol 3‐kinase (PI3K)/Akt inhibitor but not by inhibitors of the MAPK/ERK (MEK) and Janus kinase (Jak)/STAT pathways, which promote cell death. Akt phosphorylation is strongly inhibited by TGF‐β1 in pre‐B but not pro‐B cells and is not modified by Fas engagement. Altogether, our findings suggest that TGF‐β1 prevents Fas‐induced apoptosis of pre‐B lines by inhibiting PI3K pathway and by enhancing expression of Bcl2. They also suggest that the PI3K/Akt pathway is involved in the control of Fas and pre‐BCR expression, a checkpoint in B cell development.

Interleukin-7 induces apoptosis of 697 pre-B cells expressing dominant-negative forms of STAT5: evidence for caspase-dependent and -independent mechanisms

The transcription factors STAT5A and STAT5B (STAT: signal transducer and activator of transcription) play a major role in the signaling events elicited by a number of growth factor and cytokine receptors. In this work, we aimed to investigate the role of STAT5 in human precursor B cell survival by introducing dominant-negative (DN) forms of STAT5A or STAT5B in the 697 pre-B cell line. All clones expressing DN forms of either transcription factor exhibited a higher spontaneous apoptotic rate that was massively enhanced upon interleukin-7 (IL-7) stimulation. This was associated with caspase 8 cleavage, mitochondrial transmembrane potential disruption and caspase 3 activation. However, the DN forms of STAT5 did not alter the expression of Bcl-2, Bax, Bcl-x, Bim, A1 and Mcl1 proteins in IL-7-stimulated cells. The pancaspase inhibitor Z-Val-Ala-Asp-fluoromylmethyl ketone partially suppressed IL-7-mediated mitochondrial transmembrane potential disruption and cell death, suggesting that IL-7 induced the death of DN STAT5 expressing 697 cells through caspase-dependent and -independent mechanisms that both require mitochondrial activation.

Polyclonal IgG4 hypergammaglobulinemia associated with plasmacytic lymphadenopathy, anemia and nephropathy.

Marked polyclonal immunoglobulin (Ig)G4 hypergammaglobulinemia has exceptionally been reported. Here we report on two Algerian patients who presented a syndrome characterized by anemia, plasmacytic lymphadenopathy, renal manifestations, and a marked polyclonal IgG4 hypergammaglobulinemia leading to a hyperviscosity syndrome in one case. The IgG4-expressing cell percentage was significantly increased in the peripheral blood lymphocytes collected from the two patients upon diagnosis. Moreover, in contrast with normal sera, both patients’ sera significantly increased the percentage of IgG4-expressing cells when incubated with CD40-stimulated normal B lymphocytes. Similar effects were obtained with the culture supernatants of the patients’ activated T cells. Anti-interleukin (IL) 4 and/or anti-IL-13 antibodies were unable to antagonize the IgG4 production. IL-4 and IL-13 serum concentrations were found to be normal in the two patients. The increased IgG4 production was found to be mediated by soluble factor(s), most probably secreted by activated T cells, which did not require the signal transducer and activator of transcription 6 signaling pathway.

Severe respiratory syncytial virus pulmonary infection in a patient treated with fludarabine for chronic lymphocytic leukemia

Abstract Fludarabine phosphate is currently proposed for the treatment of refractory chronic lymphocytic leukemia (CLL). CD4 T-lymphocyte depletion, myelosuppression, and subsequent severe infections are the major side effects of fludarabine phosphate therapy. We report here on a heretofore undescribed respiratory syncytial virus (RSV) infection in a patient with a long-standing history of refractory CLL that was treated with fludarabine phosphate. The patient developed a severe infection of the upper and lower respiratory tract with bilateral pulmonary infiltrates and severe hypoxemia. RSV was the only infectious agent that could be isolated, and treatment with aerosolized ribavirin lead to prompt improvement of all symptoms.

The Tumor Suppressor hTid1 Inhibits STAT5b Activity via Functional Interaction

STAT5a and -5b (signal transducers and activators of transcription 5a and 5b) proteins play an essential role in hematopoietic cell proliferation and survival and are frequently constitutively active in hematologic neoplasms and solid tumors. Because STAT5a and STAT5b differ mainly in the carboxyl-terminal transactivation domain, we sought to identify new proteins that bind specifically to this domain by using a bacterial two-hybrid screening. We isolated hTid1, a human DnaJ protein that acts as a tumor suppressor in various solid tumors. hTid1 interacts specifically with STAT5b but not with STAT5a in hematopoietic cell lines. This interaction involves the cysteine-rich region of the hTid1 DnaJ domain. We also demonstrated that hTid1 negatively regulates the expression and transcriptional activity of STAT5b and suppresses the growth of hematopoietic cells transformed by an oncogenic form of STAT5b. Our findings define hTid1 as a novel partner and negative regulator of STAT5b.

Epstein–Barr virus-driven B Cell Proliferation with CD4+ T Cell Expansion: A Lymphomatoid Granulomatosis-like Disease Related to Hyperinterleukin-10 Secretion of Remarkably Favourable Outcome with Rituximab

Granulomatous lymphomatosis is an Epstein–Barr virus (EBV)‐driven B cell proliferation associated with an exuberant CD4+ T cell reaction with usually histopathological pictures of angiocentrism. So far, the characteristics of CD4+ T cells in granulomatous lymphomatosis and the mechanism leading to their expansion remain poorly explored. We report a 56‐year‐old female with a past history of cold agglutinin disease, which was successfully treated with 4 weekly infusions of rituximab. She presented one year later with features of granulomatous lymphomatosis that resulted in severe lung and bone marrow infiltration. We provide evidence that CD4+ T cell expansion was oligoclonal, involved anergic cells and did not result from an EBV‐driven stimulation. Rather, it resulted possibly from a high production of interleukin‐10 by immunoblastic EBV‐positive B cells. The outcome was remarkably favourable with rituximab and steroids. Our results suggest that an EBV‐driven B cell proliferation should be investigated in patients presenting with a CD4+ T cells alveolitis or other systemic manifestations resulting from a CD4+ T cell expansion. These features should prompt to introduce an immunosuppressive therapy including steroids and rituximab. Our results deserve further investigations to confirm our pathophysiological hypotheses in CD4+ T cell expansions associated with EBV‐driven B cell proliferations and to assess whether granulomatous lymphomatosis could result from comparable mechanisms.