Genetically Engineered Mouse Models Support a Major Role of Immune Checkpoint-Dependent Immunosurveillance Escape in B-Cell Lymphomas.

These last 20 years, research on immune tumor microenvironment led to identify some critical recurrent mechanisms used in cancer to escape immune response. Through immune checkpoints, which are cell surface molecules involved in the immune system control, it is now established that tumor cells are able to shutdown the immune response. Due to the complexity and heterogeneity of Non Hodgkin B-cell Lymphomas (NHBLs), it is difficult to understand the precise mechanisms of immune escape and to explain the mitigated effect of immune checkpoints blockade for their treatment.

Pre-clinical blocking of PD-L1 molecule, which expression is down regulated by NF-κB, JAK1/JAK2 and BTK inhibitors, induces regression of activated B-cell lymphoma.

Escape from immune control must be important in the natural course of B-cell lymphomas, especially for those with activation of NF-κB. The pre-clinical LMP1/CD40-expressing transgenic mouse model is characterized by B-cell specific CD40 signaling responsible for NF-κB continuous activation with a spleen monoclonal B-cell tumor after 1 year in 60% of cases. LMP1/CD40 tumors B-cells expressed high levels of PD-L1.

TP53INP1 deficiency maintains murine B lymphopoiesis in aged bone marrow through redox-controlled IL-7R/STAT5 signaling.

Bone marrow (BM) produces all blood and immune cells deriving from hematopoietic stem cells (HSCs). The decrease of immune cell production during aging is one of the features of immunosenescence. The impact of redox dysregulation in BM aging is still poorly understood.

The IgH 3' regulatory region and c-myc-induced B-cell lymphomagenesis.

Deregulation and mutations of c-myc have been reported in multiple mature B-cell malignancies such as Burkitt lymphoma, myeloma and plasma cell lymphoma. After translocation into the immunoglobulin heavy chain (IgH) locus, c-myc is constitutively expressed under the control of active IgH cis-regulatory enhancers. Those located in the IgH 3' regulatory region (3'RR) are master control elements of transcription.

PLZF mutation alters mouse hematopoietic stem cell function and cell cycle progression.

Hematopoietic stem cells (HSCs) give rise to all blood populations due to their long-term self-renewal and multipotent differentiation capacities. Because they have to persist throughout an organism's life span, HSCs tightly regulate the balance between proliferation and quiescence. Here, we investigated the role of the transcription factor promyelocytic leukemia zinc finger (plzf) in HSC fate using the Zbtb16(lu/lu)mouse model, which harbors a natural spontaneous mutation that inactivates plzf.

Deciphering the importance of the palindromic architecture of the immunoglobulin heavy-chain 3' regulatory region.

The IgH 3' regulatory region (3'RR) controls class switch recombination (CSR) and somatic hypermutation (SHM) in B cells. The mouse 3'RR contains four enhancer elements with hs1,2 flanked by inverted repeated sequences and the centre of a 25-kb palindrome bounded by two hs3 enhancer inverted copies (hs3a and hs3b). hs4 lies downstream of the palindrome.

The IgH 3' regulatory region controls somatic hypermutation in germinal center B cells.

Interactions with cognate antigens recruit activated B cells into germinal centers where they undergo somatic hypermutation (SHM) in V(D)J exons for the generation of high-affinity antibodies. The contribution of IgH transcriptional enhancers in SHM is unclear. The Eμ enhancer upstream of Cμ has a marginal role, whereas the influence of the IgH 3' regulatory region (3'RR) enhancers (hs3a, hs1,2, hs3b, and hs4) is controversial.

Mantle cell lymphoma-like lymphomas in c-myc-3'RR/p53+/- mice and c-myc-3'RR/Cdk4R24C mice: differential oncogenic mechanisms but similar cellular origin.

Mantle cell lymphoma (MCL) is a malignant lymphoproliferative B-cell disorder that does not occur spontaneously in mice but experimental mice model have been developed. Recently two different mice models prone to develop MCL-like lymphomas were generated: c-myc-3'RR/Cdk4(R24C) mice and c-myc-3'RR/p53+/- mice. Comparison of their gene expression profiles does not highlight specific differences other than those in relation with their specific mutational status (i.

A defect of the INK4-Cdk4 checkpoint and Myc collaborate in blastoid mantle cell lymphoma-like lymphoma formation in mice.

Mantle cell lymphoma (MCL) is a B-cell malignancy characterized by a monoclonal proliferation of lymphocytes with the co-expression of CD5 and CD43, but not of CD23. Typical MCL is associated with overexpression of cyclin D1, and blastoid MCL variants are associated with Myc (alias c-myc) translocations. In this study, we developed a murine model of MCL-like lymphoma by crossing Cdk4(R24C) mice with Myc-3'RR transgenic mice.

Enhancers located in heavy chain regulatory region (hs3a, hs1,2, hs3b, and hs4) are dispensable for diversity of VDJ recombination.

V(D)J recombination occurs during the antigen-independent early steps of B-cell ontogeny. Multiple IgH cis-regulatory elements control B-cell ontogeny. IGCR1 (intergenic control region 1), the DQ52 promoter/enhancer, and the intronic Emu enhancer, all three located upstream of Cmu, have important roles during V(D)J recombination, whereas there is no clue about a role of the IgH regulatory region (RR) encompassing the four transcriptional enhancers hs3a, hs1,2, hs3b, and hs4 during these early stages.

A p53 defect sensitizes various stages of B cell development to lymphomagenesis in mice carrying an IgH 3' regulatory region-driven c-myc transgene.

Although c-myc is classically described as the driving oncogene in Burkitt's lymphoma (BL), deregulation and mutations of c-myc have been reported in multiple solid tumors and in other mature B cell malignancies such as mantle cell lymphoma (MCL), myeloma, and plasma cell lymphoma (PCL). After translocation into the IgH locus, c-myc is constitutively expressed under the control of active IgH enhancers. Those located in the IgH 3' regulatory region (3'RR) are master control elements of class switch recombination and of the transcriptional burst associated with plasma cell differentiation.

Characterisation of genome-wide PLZF/RARA target genes.

The PLZF/RARA fusion protein generated by the t(11;17)(q23;q21) translocation in acute promyelocytic leukaemia (APL) is believed to act as an oncogenic transcriptional regulator recruiting epigenetic factors to genes important for its transforming potential. However, molecular mechanisms associated with PLZF/RARA-dependent leukaemogenesis still remain unclear.We searched for specific PLZF/RARA target genes by ChIP-on-chip in the haematopoietic cell line U937 conditionally expressing PLZF/RARA.

The IgH locus 3' regulatory region: pulling the strings from behind.

Antigen receptor gene loci are among the most complex in mammals. The IgH locus, encoding the immunoglobulin heavy chain (IgH) in B-lineage cells, undergoes major transcription-dependent DNA remodeling events, namely V(D)J recombination, Ig class-switch recombination (CSR), and somatic hypermutation (SHM). Various cis-regulatory elements (encompassing promoters, enhancers, and chromatin insulators) recruit multiple nuclear factors in order to ensure IgH locus regulation by tightly orchestrated physical and/or functional interactions.

The IgH 3' regulatory region and its implication in lymphomagenesis.

The 3' regulatory region (3'RR) located downstream of the IgH gene is the master element that controls class switch recombination and sustains high-level transcription at the plasma-cell stage. This latter role suggests that the 3'RR may be involved in oncogene deregulation during the frequent IgH translocation events associated with B-cell malignancies. A convincing demonstration of the essential contribution of 3'RR in lymphomagenesis has been provided by transgenic animal models.

Lipid mediators and human leukemic blasts.

Some of the most potent inflammatory mediators share a lipid origin. They regulate a wide spectrum of cellular processes including cell proliferation and apoptosis. However, the precise roles and ways (if any) in which these compounds impact the growth and apoptosis of leukemic blasts remain incompletely resolved.

Genomic deletion of the whole IgH 3' regulatory region (hs3a, hs1,2, hs3b, and hs4) dramatically affects class switch recombination and Ig secretion to all isotypes.

The immunoglobulin heavy chain locus (IgH) undergoes multiple changes along B-cell differentiation. In progenitor B cells, V(D)J assembly allows expression of μ heavy chains. In mature B cells, class switch recombination may replace the expressed constant (C)μ gene with a downstream C(H) gene.

A myeloma translocation-like model associating CCND1 with the immunoglobulin heavy-chain locus 3' enhancers does not promote by itself B-cell malignancies.

Cyclin D1 overexpression is associated with mantle cell lymphoma and multiple myeloma. In myeloma, it often results from chromosomal translocations linking the CCND1 gene to the 3' part of the IgH locus constant region. This region includes a single and potent transcriptional regulatory region (RR) 3' of the Calpha gene mostly active in mature B-cells.

Ig synthesis and class switching do not require the presence of the hs4 enhancer in the 3' IgH regulatory region.

Several studies have reported that regulatory elements located 3' of the IgH locus (namely hs3a, hs1,2, hs3b, and hs4) might play a role during class switch recombination (CSR) and Ig synthesis. While individual deletion of hs3a or hs1,2 had no effect, pairwise deletion of hs3b (an inverted copy of hs3a) and hs4 markedly affected CSR and Ig expression. Among these two elements, hs4 was tentatively presented with the master role due to its unique status within the 3' regulatory region: distal position outside repeated regions, early activation in pre-B cells, strong activity throughout B cell ontogeny.