Mouse models of CLL
| Mouse model . | Key findings . |
|---|---|
| mir-15a/16-1−/− and mir-15a/16-1floxedCD19-Cre mice26 | Germ-line mutations interfering with the normal expression of mir-15a/16-1 are observed in a small fraction of CLL patients.115 The first indication that a disruption of the physiological expression of mir-15a/16-1 favors CLL development stemmed from the analysis of the NZB strain which is characterized by a germ-line mutation in the 3′ flanking region of pre-mir-16-1, resulting in decreased expression of mature mir-16-1.116 The targeted genetic inactivation of mir-15a/16-1 in mice provided conclusive evidence for a tumor-suppressor role of these microRNAs in CLL development,26 as proposed.25 25-30% of mir-15a/16-1−/− and mir-15a/16fl/–CD19-Cre mice developed, late in life, MBL and CLL, and less frequently CD5-negative NHLs in a B-cell autonomous fashion.26 The loss of the mir-15a/16-1 cluster led to an earlier entry into the cell cycle and an up-regulation of BCL2 protein levels compared with wild-type B cells,26 as previously described.117 |
| 14qC3 minimal deleted region (MDR)−/− and MDRfloxedCD19-Cre mice26 | MDR-deleted mice that in addition to mir-15a/16-1 lack the dleu2 and dleu5 genes show a higher penetrance of the phenotype and a more aggressive disease course compared with mir-15a/16-1-deleted mice,26 although the pathogenetic mechanism remains to be elucidated. 40-45% of MDR−/− and MDRfl/–CD19-Cre mice developed MBL, CLL and CD5-negative NHLs in a B-cell autonomous fashion. MDR−/− mice, in contrast to mir-15a/16-1−/− mice, succumbed to the lymphoproliferations earlier than their wild-type littermates. |
| 14qC3 common deleted region (CDR)floxedCD19-Cre mice27 | Homozygous deletion of the CDR in the germ-line causes embryonic lethality.27 Mice with deletion of the CDR in B cells develop lymphoproliferations at a similar frequency (40-45%) as MDR-deleted mice.27 However, the mice are characterized by a different spectrum of lymphoproliferations, as they mostly develop CLL with rare instances of MBL and NHLs. In addition, CDR-deleted mice presented with tumor cell infiltrates in spleen, bone marrow and non-lymphoid organs that were generally larger than those observed in the mir-15a/16-1 and MDR-deleted mice presenting with CLL. CDR+/− mice developed mainly CD5-positive lymphoproliferations at a penetrance of about 25%,27 which is similar to that observed in MDR+/− mice.26 While both CDR+/− and MDR+/− mice have a similar disease onset, once the lymphoproliferations develop, deletion of the CDR leads to a more aggressive disease.27 DLEU7 has been suggested to be a negative regulator of NF-κB activity.118 |
| Eμ-TCL1 transgenic mice28,29 | Exogenous expression of the human TCL1 gene under the control of the IGHV promoter and IGH enhancer (Eμ) in vivo (Eμ-TCL1) results in the clonal expansion of CD5+IgM+ B cells.28,29 Between 13 and 18 mo of age, virtually all Eμ-TCL1 mice develop an overt leukemia and massive infiltrations of monoclonal CD5+ B cells in both lymphoid and non-lymphoid tissues. TCL1 is a co-activator of the serine/threonine kinase AKT,38,39 activates the NF-κB pathway in CLL cells,40 and inhibits DNMT3A and DNMT3B activity.41 Leukemia development is at least partially dependent on enhanced AKT activity.90 |
| APRIL transgenic mice31,32 | Based on the finding of elevated levels of tumor necrosis factor (TNF) family member APRIL in sera of CLL patients,119 APRIL transgenic mice have been generated that accumulate increased levels of the molecule in the sera.31,32 APRIL induces proliferation of B cells. APRIL transgenic mice develop clonal lymphoproliferations originating from peritoneal CD5+ B1 cells between 9 and 12 mo of age with a penetrance of 40%.32 |
| BCL2 × traf2dn transgenic mice42 | Mice transgenic for the anti-apoptotic gene BCL2,120 which is expressed at high levels in human CLL cells, and a dominant negative form of the adaptor protein TNF receptor-associated factor 2 (traf2dn), the latter being structurally similar to TRAF1 which is overexpressed in CLL,33 have been generated to study the synergistic effects of these molecules in CLL pathogenesis.42 By 14 mo, ∼80% of BCL2 × traf2dn double-transgenic mice had died of a CLL-like disease showing lymphocytosis, lymphoadenopathy, spleen enlargement and involvement of bone marrow and non-lymphoid organs. |
| ROR1 transgenic mice34 | Receptor tyrosine kinase-like orphan receptor 1 (ROR1) is highly expressed on CLL cells in humans.13,14 This oncoembryonic antigen is considered a potential target for CLL therapy as it is virtually absent from adult tissues. Transgenic mice with the human ROR1 gene which is controlled by the murine Ig enhancer/promoter to ascertain B cell-restricted expression develop, late in life (≥ 15 mo), clonal lymphoproliferations resembling CLL at a very low penetrance (∼5%).34 However, ROR1 x TCL1 double-transgenic mice succumbed to CLL more rapidly than single Eμ-TCL1 or ROR1-tg mice,34 demonstrating that ROR1 expression accelerates disease progression in Eμ-TCL1 mice. |
| Eμ-mir-29 transgenic mice35 | Eμ-mir-29 transgenic mice that overexpress the microRNA cluster miR-29a/b in B cells present with expanded CD5+ B-cell populations and late in life develop an indolent CLL-like leukemia at a penetrance of ∼20%.35 Overexpression of miR-29 in myeloid cells promotes leukemogenesis.121 By analogy, it is possible that miR-29 may have oncogenic functions in the precursor cells of murine CLL. However, since in human CLL, miR-29 expression is downregulated and thought to exert tumor-suppressor functions,122 the implications of the findings from the Eμ-mir-29 model regarding a role of this microRNA cluster in human CLL development are presently unclear.123 |
| Vh11 × irf4−/− mice36 | To elucidate the proposed role of reduced IRF4 expression in CLL development16 in a mouse model, IRF4-deficient mice were crossed to mice transgenic for the Vh11 heavy chain gene which develop expansions of peritoneal CD5+ B cells.36 Vh11 × irf4−/− mice presents with a CLL-like disease in the majority of mice by 12 mo. Since irf4−/− mice are severely immunodeficient due to critical functions of IRF4 in various immune cell types,17 the conclusive determination of a B cell-intrinsic role of IRF4 deficiency in CLL pathogenesis needs to await results from Vh11 × irf4 conditional mice crossed to a B cell-specific deletor mouse. With regard to a possible leukemogenic function of altered IRF4 levels, a recent study demonstrated that reduced IRF4 expression altered the migration properties of B cells, most likely by upregulating NOTCH2 activity.43 |
| IgH.T and IgH.TEμ mice37 | The SV40 T antigen was suggested to exert an oncogenic function in B-cell malignancies.124 Sporadic SV40 T antigen expression in mature B cells has been achieved by insertion of a SV40 T antigen gene in opposite transcriptional orientation in the IGH chain locus between the D and JH segments, in presence (IgH.TEμ) or absence (IgH.T) of an extra copy of the Eμ enhancer. Virtually all aging IgH.TEμ and 13% of IgH.T mice developed an expansion of CD5+ B cells carrying either unmutated IGHV genes with preferential usage of the Vh11 family, or highly mutated IGHV genes. |
| Mouse model . | Key findings . |
|---|---|
| mir-15a/16-1−/− and mir-15a/16-1floxedCD19-Cre mice26 | Germ-line mutations interfering with the normal expression of mir-15a/16-1 are observed in a small fraction of CLL patients.115 The first indication that a disruption of the physiological expression of mir-15a/16-1 favors CLL development stemmed from the analysis of the NZB strain which is characterized by a germ-line mutation in the 3′ flanking region of pre-mir-16-1, resulting in decreased expression of mature mir-16-1.116 The targeted genetic inactivation of mir-15a/16-1 in mice provided conclusive evidence for a tumor-suppressor role of these microRNAs in CLL development,26 as proposed.25 25-30% of mir-15a/16-1−/− and mir-15a/16fl/–CD19-Cre mice developed, late in life, MBL and CLL, and less frequently CD5-negative NHLs in a B-cell autonomous fashion.26 The loss of the mir-15a/16-1 cluster led to an earlier entry into the cell cycle and an up-regulation of BCL2 protein levels compared with wild-type B cells,26 as previously described.117 |
| 14qC3 minimal deleted region (MDR)−/− and MDRfloxedCD19-Cre mice26 | MDR-deleted mice that in addition to mir-15a/16-1 lack the dleu2 and dleu5 genes show a higher penetrance of the phenotype and a more aggressive disease course compared with mir-15a/16-1-deleted mice,26 although the pathogenetic mechanism remains to be elucidated. 40-45% of MDR−/− and MDRfl/–CD19-Cre mice developed MBL, CLL and CD5-negative NHLs in a B-cell autonomous fashion. MDR−/− mice, in contrast to mir-15a/16-1−/− mice, succumbed to the lymphoproliferations earlier than their wild-type littermates. |
| 14qC3 common deleted region (CDR)floxedCD19-Cre mice27 | Homozygous deletion of the CDR in the germ-line causes embryonic lethality.27 Mice with deletion of the CDR in B cells develop lymphoproliferations at a similar frequency (40-45%) as MDR-deleted mice.27 However, the mice are characterized by a different spectrum of lymphoproliferations, as they mostly develop CLL with rare instances of MBL and NHLs. In addition, CDR-deleted mice presented with tumor cell infiltrates in spleen, bone marrow and non-lymphoid organs that were generally larger than those observed in the mir-15a/16-1 and MDR-deleted mice presenting with CLL. CDR+/− mice developed mainly CD5-positive lymphoproliferations at a penetrance of about 25%,27 which is similar to that observed in MDR+/− mice.26 While both CDR+/− and MDR+/− mice have a similar disease onset, once the lymphoproliferations develop, deletion of the CDR leads to a more aggressive disease.27 DLEU7 has been suggested to be a negative regulator of NF-κB activity.118 |
| Eμ-TCL1 transgenic mice28,29 | Exogenous expression of the human TCL1 gene under the control of the IGHV promoter and IGH enhancer (Eμ) in vivo (Eμ-TCL1) results in the clonal expansion of CD5+IgM+ B cells.28,29 Between 13 and 18 mo of age, virtually all Eμ-TCL1 mice develop an overt leukemia and massive infiltrations of monoclonal CD5+ B cells in both lymphoid and non-lymphoid tissues. TCL1 is a co-activator of the serine/threonine kinase AKT,38,39 activates the NF-κB pathway in CLL cells,40 and inhibits DNMT3A and DNMT3B activity.41 Leukemia development is at least partially dependent on enhanced AKT activity.90 |
| APRIL transgenic mice31,32 | Based on the finding of elevated levels of tumor necrosis factor (TNF) family member APRIL in sera of CLL patients,119 APRIL transgenic mice have been generated that accumulate increased levels of the molecule in the sera.31,32 APRIL induces proliferation of B cells. APRIL transgenic mice develop clonal lymphoproliferations originating from peritoneal CD5+ B1 cells between 9 and 12 mo of age with a penetrance of 40%.32 |
| BCL2 × traf2dn transgenic mice42 | Mice transgenic for the anti-apoptotic gene BCL2,120 which is expressed at high levels in human CLL cells, and a dominant negative form of the adaptor protein TNF receptor-associated factor 2 (traf2dn), the latter being structurally similar to TRAF1 which is overexpressed in CLL,33 have been generated to study the synergistic effects of these molecules in CLL pathogenesis.42 By 14 mo, ∼80% of BCL2 × traf2dn double-transgenic mice had died of a CLL-like disease showing lymphocytosis, lymphoadenopathy, spleen enlargement and involvement of bone marrow and non-lymphoid organs. |
| ROR1 transgenic mice34 | Receptor tyrosine kinase-like orphan receptor 1 (ROR1) is highly expressed on CLL cells in humans.13,14 This oncoembryonic antigen is considered a potential target for CLL therapy as it is virtually absent from adult tissues. Transgenic mice with the human ROR1 gene which is controlled by the murine Ig enhancer/promoter to ascertain B cell-restricted expression develop, late in life (≥ 15 mo), clonal lymphoproliferations resembling CLL at a very low penetrance (∼5%).34 However, ROR1 x TCL1 double-transgenic mice succumbed to CLL more rapidly than single Eμ-TCL1 or ROR1-tg mice,34 demonstrating that ROR1 expression accelerates disease progression in Eμ-TCL1 mice. |
| Eμ-mir-29 transgenic mice35 | Eμ-mir-29 transgenic mice that overexpress the microRNA cluster miR-29a/b in B cells present with expanded CD5+ B-cell populations and late in life develop an indolent CLL-like leukemia at a penetrance of ∼20%.35 Overexpression of miR-29 in myeloid cells promotes leukemogenesis.121 By analogy, it is possible that miR-29 may have oncogenic functions in the precursor cells of murine CLL. However, since in human CLL, miR-29 expression is downregulated and thought to exert tumor-suppressor functions,122 the implications of the findings from the Eμ-mir-29 model regarding a role of this microRNA cluster in human CLL development are presently unclear.123 |
| Vh11 × irf4−/− mice36 | To elucidate the proposed role of reduced IRF4 expression in CLL development16 in a mouse model, IRF4-deficient mice were crossed to mice transgenic for the Vh11 heavy chain gene which develop expansions of peritoneal CD5+ B cells.36 Vh11 × irf4−/− mice presents with a CLL-like disease in the majority of mice by 12 mo. Since irf4−/− mice are severely immunodeficient due to critical functions of IRF4 in various immune cell types,17 the conclusive determination of a B cell-intrinsic role of IRF4 deficiency in CLL pathogenesis needs to await results from Vh11 × irf4 conditional mice crossed to a B cell-specific deletor mouse. With regard to a possible leukemogenic function of altered IRF4 levels, a recent study demonstrated that reduced IRF4 expression altered the migration properties of B cells, most likely by upregulating NOTCH2 activity.43 |
| IgH.T and IgH.TEμ mice37 | The SV40 T antigen was suggested to exert an oncogenic function in B-cell malignancies.124 Sporadic SV40 T antigen expression in mature B cells has been achieved by insertion of a SV40 T antigen gene in opposite transcriptional orientation in the IGH chain locus between the D and JH segments, in presence (IgH.TEμ) or absence (IgH.T) of an extra copy of the Eμ enhancer. Virtually all aging IgH.TEμ and 13% of IgH.T mice developed an expansion of CD5+ B cells carrying either unmutated IGHV genes with preferential usage of the Vh11 family, or highly mutated IGHV genes. |
AKT, protein kinase B/v-AKT murine thymoma viral oncogene; DNMT, DNA methyltransferase; NF-κB, nuclear factor κB; SV40, simian virus 40; TNF, tumor necrosis factor.