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doi:10.1158/2643-3249.BCD-ITI1-2

DOI: 10.1158/2643-3249.BCD-ITI1-2 Published September 2020

Dual-specificity CAR T Cells Targeting BCMA and GPRC5D in Multiple Myeloma

See article, p. 146.

Dual BCMA/GPRC5D-specific CAR T cells confer long-term protection from BCMA-negative myeloma rechallenge.
Expressing two CAR specificities increases the T cell avidity for double antigen-positive target cells.
Bicistronic CAR performs better than other dual-CAR approaches.

CAR T cell (CART) therapy elicits clinical response in the majority of patients with multiple myeloma, but is often followed by a relapse. Loss of the CAR-targeted antigen expression by cancer cells is common at relapse and is considered among the main mechanisms limiting durability of response. Here Fernández de Larrea and colleagues develop approaches for simultaneously targeting BCMA and GPRC5D myeloma antigens by a single CART infusion. They demonstrate that BCMA/GPRC5D dual-specific CARTs eliminate myeloma cells positive for both antigens and protect mice from rechallenge with BCMA-negative myeloma cells. CART performance was best when BCMA/GPRC5D was introduced as a single bicistronic vector, as compared to pooled CARTs individually transduced with BCMA and GPRC5D, and with a vector encoding a bivalent CAR. If reproduced with other CARs, these findings suggest that bicistronic vectors are an optimal strategy to dual CART manufacture. It remains to be tested in a clinical setting whether BCMA/GPRC5D CAR T would prevent antigen escape and offer more durable remission than current mono-specific CARTs.

Transcriptional Features of Mediastinal Gray Zone Lymphoma and Related Diseases

See article, p. 155.

Mediastinal gray zone lymphomas (MGZL) gene expression is compared to related disorders.
MGZL transcriptional signatures display intermediate values between cHL and PMBL.

Mediastinal gray zone lymphoma (MGZL) is a rare cancer with features intermediate between classical Hodgkin lymphoma (cHL) and primary mediastinal large B-cell lymphoma (PMBL). More information on molecular and histopathological characteristics of MGZL is essential for clarifying diagnostic criteria and understanding its pathogenesis and responsiveness to therapies. Here Pittaluga and colleagues compare transcriptomic and histological patterns in a cohort of 20 MGZL, 18 cHL and 17 PMBL patients. The results further document intermediate and heterogeneous molecular phenotypes of MGZL and highlight features of potential relevance to diagnostics and therapy.

Structural and Functional Contributions of BCOR and CBX8 to MLL-AF9-Driven Leukemia

See article, p. 162.

Protein structures of CBX8-AF9 and BCOR-AF9 are solved.
Structure-guided mutagenesis pinpoints the oncogenic potential of BCOR-AF9 but not CBX8-AF9 interaction.
Eya1-dependent Myc stabilization is implicated in driving leukemic transformation downstream of MLL-AF9-BCOR interaction.

Schmidt et al. elucidate the structural basis of AF9 binding to AF4, DOT1L, BCOR, and CBX8, revealing their mutually exclusive interactions. By structure-guided mutagenesis, the authors create a series of point mutants of AF9 and its partners, selectively abrogating either BCOR or CBX8 interactions. Disrupting the interaction with CBX8 impairs MLL-AF9 effect on proliferation but not leukemic potential. In contrast, a mutation that disrupts BCOR-binding also diminishes MLL-AF9 leukemogenic potential. Cells transduced with this mutant display low expression of EYA1 phosphatase and Myc signature genes, as well as low Myc protein level, as compared to unmodified MLL-AF9. Eya1 overexpression can partially restore Myc-dependent transcription and leukemic potential of the MLL-AF9 mutant, connecting Eya1 known role in promoting c-Myc protein stability to AF9-MLL pathogenesis. The findings establish AF9-BCOR-Eya1-Myc axis as a major contributor to MLL-AF9-driven leukemogenesis and highlight Eya1 as a potential therapeutic target in this disease.

Ets1-Dependent Control of Notch Transcriptional Programs in T-Cell Leukemia

See article, p. 178.

Ets1 binds to Notch and co-occupies the majority of direct Notch target genes in T-ALL.
Notch-dependent normal and leukemic T-cell development requires Ets1.
Genetic Ets1 blockade stalls T-cell leukemia while minimally impacting intestinal homeostasis.

Notch hyperactivation is common in T-cell acute lymphoblastic leukemia (T-ALL). As Notch also plays essential roles in homeostasis of other tissues, toxicities of Notch inhibitors limiting their clinical use. Here McCarter and colleagues identify Ets1 transcription factor as a major coregulator of Notch transcription in T cells. Ets1 deficiency impedes normal T-cell development as well as Notch-mediated T-ALL. Ets1- and Notch-dependent genes show a large degree of overlap, including key oncogenic pathway components. Ets1 co-occupies most of Notch/RBPJ-bound genomic regions. H3K27ac deposition and binding to gene regulatory regions is impaired in the absence of Ets1, suggesting Ets1 may facilitate Notch transcriptional complex recruitment. Ets1 inhibition in Notch-induced transplanted model of T-ALL extend mouse survival and cooperates with low-dose Notch pharmacological blockade. At the same time, acute whole-body deletion of Ets1 gene causes less intestinal toxicity as compared to Notch inhibitor, raising hope that systemic Ets1 inhibition may have better safety profile as a T-ALL therapy.

Apolipoprotein C2 Promotes Leukemia Growth via CD36-ERK Signaling Pathways and Represents a Viable Therapeutic Target in Acute Myeloid Leukemia

See article, p. 198.

APOC2 is upregulated in MLL-rearranged AML and correlates with worse prognosis.
APOC2 levels define cultured AML cell growth rate through CD36-dependent metabolism.
Blocking APOC2 or CD36 in vivo slows down AML xenograft growth in mice.

APOC2 is a constituent of lipoproteins carrying lipids in circulation. It can interact with CD36, which mediates intracellular fatty acid uptake. In this report, Zhang et al. identify APOC2 as a gene associated with MLL rearrangements and poor outcome in AML. Noting that APOC2 expression is elevated in AML cells, the authors interrogate its cell-autonomous role in leukemic cells. Gain-of-function and loss-of-function experiments reveal that APOC2 levels define AML cell growth rate in culture through CD36-dependent effects on metabolism and survival. Abrogating the APOC2-CD36 axis in vivo by CD36 blocking antibody or by inducible APOC2 shRNA delays leukemia progression in a mouse xenograft model. These findings expand the current understanding of lipid metabolism fueling leukemic cell growth and identify APOC2 and CD36 as potential therapeutic targets in AML.