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CD20 est une cible thérapeutique validée pour l’immunothérapie des néoplasmes lymphoïdesdes cellules B, incluant la Leucémie Lymphoïde Chronique (LLC). Nous avons comparé les effets de rituximab et de GA101 (nouvel anticorps anti-CD20) contre les cellules LLC fraiches in vitro. Le marquage avec Annexine V a démontré une induction de l’apoptose après l’exposition au rituximab et GA101.Contrairement au rituximab, GA101 induisait une réduction du potentiel transmembranaire mitochondrial, uneffet qui peut être partiellement inhibé par la cyclosporine A et qui est partiellement caspase-dépendant. GA101induisait aussi la production des espèces d’oxygènes réactives. L’analyse du niveau d’expression des protéinespro- et anti-apoptotiques après exposition aux anticorps a démontré une forte hétérogénéité entre les échantillons.Bax subissait une activation de conformation et une translocation mitochondriale suite à l’exposition aux anticorps d’une manière caspase-indépendante. GA101, mais pas rituximab, induisait le clivage des caspase-8, -9et -3. En transfectant les cellules LLC avec un siRNA ciblant Bcl-xL utilisant la sonoporation, nous avons trouvéque la réduction du niveau d’expression de Bcl-xL est associée à une augmentation de la sensibilité aux anticorps. Nos résultats suggèrent que les voies de signalisation apoptotiques diffèrent entre rituximab et GA101avec une implication de la voie mitochondriale avec le GA101. L’inhibition de Bcl-xL peut constituer une façon pour sensibiliser les cellules LLC aux effets apoptotiques des anticorps anti-CD20. / CD20 is a validated target for the immunotherapy of B lymphoid neoplasms, including ChronicLymphocytic Leukemia (CLL). We compared the activities of rituximab and GA101 (novel anti-CD20 antibody)on fresh human CLL cells in vitro. AnnexinV staining demonstrated induction of apoptosis after exposure torituximab or GA101. Unlike rituximab, GA101 induced a reduction of the mitochondrial transmembranepotential, an effect which could be partially inhibited by cyclosporin A and which was partially caspasedependent.GA101 was also found to induce the production of Reactive Oxygen Species. Analysis of pro- andanti-apoptotic protein content after exposure to antibodies demonstrated a strong degree of heterogeneity between samples. Bax underwent conformational activation and mitochondrial translocation upon exposure toantibodies in a caspase-independent manner. GA101 but not rituximab induced cleavage of caspase-8, -9 and -3.By transfecting CLL cells with anti-Bcl-xL siRNA using a sonoporation method, we found that reduction of BclxLcontent was associated with increased sensitivity to these antibodies. Our results suggest that apoptoticsignalization pathways differ between rituximab and GA101 with a greater involvement of the mitochondrialpathway for GA101. Inhibition of Bcl-xL could constitute an approach to sensitize CLL cells to the apoptoticeffects of anti-CD20 antibodies.

Chronic Lymphocytic Leukemia (CLL) is defined by the accumulation of clonally expanded CD5+ and CD19+ B lymphocytes in blood and secondary lymphoid organs with impaired apoptotic mechanisms. CLL represents one third of all leukemia cases with an average age of 72 years at diagnosis making it the most common adult leukemia. The Eµ-Tcl1 mouse serves as an excellent model to study the development of CLL as they progress to a CLL like disease by 9-14 months of age, due to overexpression of an oncogene, T cell Leukemia 1(Tcl1), specifically in B cells through the Ig VH promoter and Eµ enhancer (Bichi et al. PNAS. 2002). In an adoptive transfer model, intravenous or intraperitoneal injection of primary CD5+CD19+ CLL cells from the Eµ-Tcl1 CLL mouse into recipient syngeneic mice leads to the development of a CLL like disease within 3-8 weeks of transfer. We have characterized the growth of CLL cells in these mice by periodic submandibular bleeding, spleen ultrasonography and flow cytometry. We find that Eµ-Tcl1 CLL cells express more Prostate apoptosis response-4 protein (Par-4), a known pro-apoptotic tumor suppressor protein, than normal B-1 or B-2 cells in mice. Par-4 is silenced by promoter methylation in more than 30% of all cancers and has been shown to be secreted and to induce apoptosis selectively in various types of cancer cells but not in normal cells. We found that CLL cells have constitutively active B-cell receptor signaling (BCR) and that inhibition of BCR signaling with FDA approved drugs causes a decrease in Par-4 protein, mRNA levels, and an increase in apoptosis. In particular, activities of Src family kinases, spleen tyrosine kinase and Bruton’s tyrosine kinase are required for Par-4 expression in CLL cells, suggesting a novel regulation of Par-4 through BCR signaling in both Eµ-Tcl1 CLL cells and primary human CLL samples. Consistent with this, lenti-viral shRNA mediated knockdown of Lyn kinase leads to a decrease in Par-4 expression in MEC-1 cells, a human CLL derived cell line. Igα (CD79a) silencing in primary human CLL cells also results in down regulation of Par-4 expression. Additionally, we knocked down expression of Par-4 in MEC-1 cells which resulted in a decrease in cell growth that could be attributed to an increase in p21 expression and a reduction in the G1/S cell cycle transition. We have also observed this phenomenon by crossing mice deficient in Par-4 with the Eµ-Tcl1 mouse where lack of Par-4 delays CLL growth in the mouse significantly (time to euthanization due to poor body condition - Eµ-Tcl1: 8.9mo vs Par4-/-EµTcl1: 11.97 mo, p = 0.0472) and splenic B-CLL cells from these mice also have increased expression of p21. Since mice in this cohort are whole body knockout for Par-4, the difference in survival times between the Par-4 +ve and Par-4 –ve EµTcl1 mice could be due to the influence of Par-4 on CLL cells as well as the effect of Par-4 secreted by the CLL cells on the microenvironment. There could be other potential roles for Par-4 in the context of CLL which are under further investigation. We have also investigated the site of CLL growth in mouse models to determine that the spleen is the primary organ to accumulate the CLL tumor burden. We have found that splenectomy significantly delays the development of CLL in the primary Eμ-Tcl1 mouse model and prevents growth and development in the adoptive transfer model. Interestingly, splenectomy did not delay CLL development as significantly in animals deficient for Par-4 compared to C57BL/6 wild type mice. Par-4 appears to regulate a specific microenvironment required for CLL growth. Current studies are investigating the role of Par-4 in the microenvironment and the cell types that are critical for CLL growth within the splenic niche.

Lymphocytes from normal subjects and patients with B-chronic lymphocytic leukemia (B-CLL) show functional responses to extracellular ATP characteristic of the P2X7 receptor. These responses include opening of a cation selective channel/pore which allows entry of the fluorescent dye, ethidium+ and activation of a membrane metalloprotease which sheds the adhesion molecule L-selectin. In this thesis, the surface expression of P2X7 receptors was measured in normal leucocytes, platelets and B-CLL lymphocytes and compared with their functional responses. Monocytes showed 4-5 fold greater expression of P2X7 than B-, T- and NK- lymphocytes, while P2X7 expression on neutrophils and platelets was weak. All cell types demonstrated abundant intracellular expression of this receptor. All 12 subjects with B-CLL expressed surface P2X7 at about the same level as for B-lymphocytes from normal subjects. P2X7 function, measured by ATP-induced uptake of ethidium, correlated closely with surface expression of this receptor in normal and B-CLL lymphocytes and monocytes. However, the ATP-induced uptake of ethidium into the malignant B-lymphocytes in 3 patients was low or absent. The lack of P2X7 function in these B-lymphocytes was confirmed by the failure of ATP to induce Ba2+ uptake into their lymphocytes. This lack of function of the P2X7 receptor resulted in a failure of ATP-induced shedding of L-selectin, an adhesion molecule which directs the recirculation of lymphocytes from blood into the lymph node. To study a possible genetic basis of non-functional P2X7 receptor, we sequenced DNA coding for the carboxyl terminal tail of P2X7. In 33 of 130 normal subjects a heterozygous nucleotide substitution (1513A--C) was found while 3 subject carried the homozygous substitution which codes for glutamic acid to alanine at amino acid position 496. Surface expression of P2X7 on lymphocytes was not affected by this 496Glu--Ala polymorphism demonstrated both by confocal microscopy and immunofluorescent staining. Monocytes and lymphocytes from the 496Glu--Ala homozygote subject expressed non-functional receptor while heterozygotes showed P2X7 function which was half that of wild type P2X7. Results of transfection experiments showed the mutant P2X7 receptor was non-functional when expressed at low receptor density but regained function at a high receptor density. This density-dependence of mutant P2X7 function was also seen on differentiation of fresh monocytes to macrophages with interferon-gamma which upregulated mutant P2X7 and partially restored its function. P2X7-mediated apoptosis of lymphocytes was impaired in homozygous mutant P2X7 compared with wild type. The data suggest that the glutamic acid at position 496 is required for optimal assembly of the P2X7 receptor. Apart from the 496Glu--Ala polymorphism, three other single nucleotide polymorphisms, 155His--Tyr, 348Ala--Thr and 568Ile--Asn were also found in the P2X7 receptor. The site directed mutant cDNA were generated for all 3 polymorphisms and transfected into HEK293 cells to study the impact of these polymorphisms on P2X7 function. Results suggested that Ile568 is important for P2X7 protein trafficking to cell surface. Further study of these two loss-of-function polymorphisms (496Glu--Ala and 568Ile--Asn) may help better understanding of the functional domains in the P2X7 receptor and its role in CLL, lymphoma and infectious diseases. Conclusions: 1.P2X7 receptor is expressed in human leukocytes, including lymphocytes, natural killer cells as well as monocytes, on both surface and intracellular locations. 2.Both the expression and function of P2X7 are highly variable between in human individuals. Non-functional P2X7 receptors are found in some subjects, including both normal subjects and CLL patients, and are often associated with defects in ATP-induced cytotoxicity and L-selectin shedding. 3.Two single nucleotide polymorphisms (SNPs), 496Glu--Ala and 568Ile--Asn, are found at low frequency in the human population and lead to the loss-of-function of P2X7. Both permeabllity function and the downstream effects mediated by P2X7 are affected by these two SNPs. The mechanisms for the loss-of-function differs between the two polymorphisms.

<p>Recent studies have shown that the somatic mutation status of the immunoglobulin (Ig) V_H genes can divide chronic lymphocytic leukemia (CLL) into two prognostic subsets, since cases with mutated V_H genes display superior survival compared to unmutated cases. Biased V_H gene usage has also been reported in CLL which may reflect antigen selection.</p><p>We performed V_H gene analysis in 265 CLL cases and confirmed the prognostic impact of the V_H mutation status. Preferential V_H gene usage was also demonstrated in both the mutated and unmutated subset. Interestingly, CLL cases rearranging one particular V_H gene, V_H3-21, displayed poor outcome despite that two-thirds showed mutated V_H genes. Many of the V_H3-21 cases expressed λ light chains, rearranged a V_λ2-14 gene, and had homologous complementarity determining region 3s (CDR3s), implying recognition of a common antigen epitope. We believe that the V_H3-21 subset comprises an additional CLL entity.</p><p>To further explore the B-cell receptors in CLL, we analyzed the V_H gene rearrangements and, specifically, the heavy chain CDR3 sequences in 346 CLL cases. We identified six new subgroups with similar HCDR3 features and restricted V_L gene usage as in the V_H3-21-using group. Our data indicate a limited number of antigen recognition sites in these subgroups and give further evidence for antigen selection in the development of CLL.</p><p>Different cutoffs have been suggested to distinguish mutated CLL in addition to the 2% cutoff. Using three levels of somatic mutations, i.e. <2%, 2-5% and >5%, we divided 323 CLLs into subsets with divergent survival. This division revealed a low-mutated subgroup (2-5%) with inferior outcome that would have been masked using the traditional 2% cutoff. </p><p>A 1513A/C polymorphism in the P2X₇ receptor gene was reported to be more frequent in CLL, but no difference in genotype frequencies was revealed in our 170 CLL cases and 200 controls. However, CLL cases with the 1513AC genotype showed superior survival than 1513AA cases and this was in particular confined to CLL with mutated V_H genes.</p><p> In summary, we could define new prognostic subgroups in CLL using Ig gene rearrangement analysis. This also allowed us to gain insights in the biology and potential role of antigen involvement in the pathogenesis of CLL.</p>