Use of novel chemical supplements in the establishment of three human malignant lymphoma cell lines (NU-DHL-1, NU-DUL-1, and NU-AMB-1) with chromosome 14 translocations

A Humanized Lym-1 CAR with Novel DAP10/DAP12 Signaling Domains Demonstrates Reduced Tonic Signaling and Increased Antitumor Activity in B-Cell Lymphoma Models

PURPOSE

The murine Lym-1 mAb targets a discontinuous epitope (Lym-1 epitope) on several subtypes of HLA-DR, which is upregulated in a majority of human B-cell lymphomas and leukemias. Unlike CD19, the Lym-1 epitope does not downregulate upon crosslinking, which may provide an advantage as a target for CAR T-cell therapy. Lym-1 CAR T cells with a conventional 4-1BB and CD3ζ (BB3z) signaling domain exhibited impaired ex vivo expansion. This study aimed to identify the underlying mechanisms and develop strategies to overcome this effect.

EXPERIMENTAL DESIGN

A functional humanized Lym-1 antibody (huLym-1-B) was identified and its scFv form was used for CAR design. To overcome observed impaired expansion in vitro, a huLym-1-B CAR using DAP10 and DAP12 (DAP) signaling domains was evaluated for ex vivo expansion and in vivo function.

RESULTS

Impaired expansion in huLym-1-B-BB3z CAR T cells was shown to be due to ligand-dependent suboptimal CAR signaling caused by interaction of the CAR binding domain and the surface of human T cells. Using the novel DAP signaling domain construct, the effects of suboptimal CAR signaling were overcome to produce huLym-1-B CAR T cells with improved expansion ex vivo and function in vivo. In addition, the Lym-1 epitope does not significantly downregulate in response to huLym-1-B-DAP CAR T cells both ex vivo and in vivo.

CONCLUSIONS

DAP intracellular domains can serve as signaling motifs for CAR, and this new construct enables nonimpaired production of huLym-1-B CAR T cells with potent in vivo antitumor efficacy.

Specific interactions of BCL-2 family proteins mediate sensitivity to BH3-mimetics in diffuse large B-cell lymphoma

The BCL-2-specific inhibitor, ABT-199 (venetoclax) has exhibited remarkable clinical activity in nearly all cases of chronic lymphocytic leukemia. In contrast, responses are usually much less in diffuse large B-cell lymphoma (DLBCL), despite high level expression of BCL-2 in over 40% of cases, indicating that co-expression of related anti-apoptotic BCL-2 family proteins may limit the activity of ABT-199. We have investigated the roles of BCL-2 proteins in DLBCL cells using a panel of specific BCL-2 homology 3 (BH3)-mimetics and identified subgroups of these cells that exhibited marked and specific dependency on either BCL-2, BCL-X_L or MCL-1 for survival. Dependency was associated with selective sequestration of the pro-apoptotic proteins BIM, BAX and BAK by the specific anti-apoptotic BCL-2 protein which was important for cellular survival. Sensitivity to BH3-mimetics was independent of genetic alterations involving the BCL-2 family and only partially correlated with protein expression levels. Treatment with ABT-199 displaced BAX and BIM from BCL-2, subsequently leading to BAK activation and apoptosis. In contrast, apoptosis induced by inhibiting BCL-X_L with A1331852 was associated with a displacement of both BAX and BAK from BCL-X_L and occurred independently of BIM. Finally, the MCL-1 inhibitor S63845 induced mainly BAX-dependent apoptosis mediated by a displacement of BAK, BIM and NOXA from MCL-1. In conclusion, our study indicates that in DLBCL, the heterogeneous response to BH3-mimetics is mediated by selective interactions between BAX, BAK and anti-apoptotic BCL-2 proteins.

Malignant hematopoietic cell lines: in vitro models for double-hit B-cell lymphomas

Mature B-cell lymphomas with concurrent rearrangements of MYC and BCL2 (more rarely BCL6), "double-hit lymphomas" (DHLs), form a heterogeneous group. Recent studies have shown that DHLs often present with an aggressive clinical course and a poor prognosis with standard therapy. This distinct clinical entity would benefit from more detailed pathobiological characterization to develop improved treatment options. Lymphoma cell lines are important and informative research tools. Several cell lines have been established from B-cell lymphoma patients harboring MYC rearrangements combined with either (double-hit) or both (triple-hit) BCL2 or BCL6 translocations. All rearrangements have been detected by cytogenetics and validated by FISH. These cell lines provide preclinical models for basic and translational research which speed development of effective treatment strategies.

Apoptosis in Burkitt lymphoma cells is prevented by promotion of cysteine uptake

Burkitt lymphoma (BL) cells are highly sensitive to suboptimal growth conditions and undergo apoptosis when seeded at reduced serum concentration or low cell density. Irradiated fibroblasts can protect BL cells from apoptosis induced by lowering the serum concentration or cell density through secretion of a survival- and proliferation-promoting activity which is soluble and labile. Murine B cells have a restricted uptake capacity for cystine and require cysteine for proliferation, which can be supplied efficiently by feeder cells. Therefore, we have studied the role of cysteine and other compounds with free thiol groups for survival and proliferation of BL cells. Cysteine, when added alone, exerted strong toxicity on BL cells. This toxicity could be counteracted by the addition of catalase, pyruvate or bathocuproine disulfonate (BCS), all of which interfere with the production of hydrogen peroxide. Inhibition of the toxicity of cysteine was necessary to unravel the survival- and growth-promoting activity of cysteine at low cell density. Alpha-thioglycerol, beta-mercaptoethanol and dithiothreitol had similar toxic activity in the absence of catalase, pyruvate and BCS and, through stimulation of cysteine uptake and glutathione synthesis, displayed a similar survival- and growth-promoting activity in the presence of the protective agents. The survival- and proliferation-inducing activity of thiol compounds in the presence of catalase, pyruvate and BCS was not associated with induction of BCL-2 or BAX. Cysteine/cystine uptake and the intra/cellular glutathione level are thus important parameters, determining the susceptibility vs. resistance of BL cells to apoptosis.

A 1.5-megabase restriction map surrounding MYC does not include the translocation breakpoint in familial renal cell carcinoma

A constitutional translocation t(3;8)(p14.2;q24.1) segregates concordantly with a familial form of renal cell carcinoma (RCC). This translocation moves the MYC oncogene, located at 8q24.1, onto the short arm of chromosome 3. Chromosome rearrangements that break in or near MYC can result in altered expression of this gene and are thought to be a primary change leading to the transformed phenotype in certain neoplastic diseases, particularly Burkitt lymphoma. Possible rearrangements of this gene in familial RCC have so far not been detected using standard Southern blot analysis. We used pulsed field gel (PFG) analysis to construct a restriction map that covers a 1500-kb region surrounding MYC, including over 1000 kb to the 5' and 550 kb to the 3' side of this gene. The 5' end of MYC contains a cluster of cleavage sites for rare-cutting restriction endonucleases, indicating the presence of an HTF island. PFG analysis of DNA containing the t(3;8) rearrangement shows that the breakpoint is not located in the mapped region, making it unlikely that MYC is involved in this form of renal cell carcinoma. The map should facilitate study of other chromosome 8 rearrangements thought to break near MYC.

Cloning the chromosomal breakpoint of t(14;18) human lymphomas: clustering around JH on chromosome 14 and near a transcriptional unit on 18

Specific chromosomal translocations found in distinct neoplasms suggest that genes that flank such breakpoints play a critical role in transformation. We have characterized the t(14;18)(q32;q21) chromosomal translocation present in over 60% of human follicular lymphomas. We exploited an unexpected rearrangement of an Ig heavy-chain gene to clone the chromosomal breakpoint. An element isolated from 18q21 mediated translocations in all four t(14;18) bearing cell lines and in six of 11 follicular lymphomas, but did not normally rearrange in other B or non-B cells. The breakpoints clustered within a small 4.3 kb region on chromosome 18. The breakpoints on chromosome 14 were focused within or immediately 5' to JH. These breakpoints retained the Ig enhancer region close to a new transcriptional unit identified on chromosome segment 18q21. Since none of the cellular oncogenes are known to map to 18q21, cloning this element provides an opportunity to characterize a potentially new transforming gene.