BCMA-Specific ADC MEDI2228 and Daratumumab Induce Synergistic Myeloma Cytotoxicity via IFN-Driven Immune Responses and Enhanced CD38 Expression.

PURPOSE: Efforts are required to improve the potency and durability of CD38- and BCMA-based immunotherapies in human multiple myeloma. We here delineated the molecular and cellular mechanisms underlying novel immunomodulatory effects triggered by BCMA pyrrolobenzodiazepine (PBD) antibody drug conjugate (ADC) MEDI2228 which can augment efficacy of these immunotherapies. EXPERIMENTAL DESIGN: MEDI2228-induced transcriptional and protein changes were investigated to define significantly impacted genes and signaling cascades in multiple myeloma cells. Mechanisms whereby MEDI2228 combination therapies can enhance cytotoxicity or overcome drug resistance in multiple myeloma cell lines and patient multiple myeloma cells were defined using in vitro models of tumor in the bone marrow (BM) microenvironment, as well as in human natural killer (NK)-reconstituted NOD/SCID gamma (NSG) mice bearing MM1S tumors. RESULTS: MEDI2228 enriched IFN I signaling and enhanced expression of IFN-stimulated genes in multiple myeloma cell lines following the induction of DNA damage-ATM/ATR-CHK1/2 pathways. It activated cGAS-STING-TBK1-IRF3 and STAT1-IRF1-signaling cascades and increased CD38 expression in multiple myeloma cells but did not increase CD38 expression in BCMA-negative NK effector cells. It overcame CD38 downregulation on multiple myeloma cells triggered by IL6 and patient BM stromal cell-culture supernatant via activation of STAT1-IRF1, even in immunomodulatory drug (IMiD)- and bortezomib-resistant multiple myeloma cells. In vitro and in vivo upregulation of NKG2D ligands and CD38 in MEDI2228-treated multiple myeloma cells was further associated with synergistic daratumumab (Dara) CD38 MoAb-triggered NK-mediated cytotoxicity of both cell lines and autologous drug-resistant patient multiple myeloma cells. CONCLUSIONS: These results provide the basis for clinical evaluation of combination MEDI2228 with Dara to further improve patient outcome in multiple myeloma.

Preclinical evaluation of CD8+ anti-BCMA mRNA CAR T cells for treatment of multiple myeloma.

Chimeric antigen receptor (CAR) T-cell therapy remains limited to select centers that can carefully monitor adverse events. To broaden use of CAR T cells in community clinics and in a frontline setting, we developed a novel CD8+ CAR T-cell product, Descartes-08, with predictable pharmacokinetics for treatment of multiple myeloma. Descartes-08 is engineered by mRNA transfection to express anti-BCMA CAR for a defined length of time. Descartes-08 expresses anti-BCMA CAR for 1 week, limiting risk of uncontrolled proliferation; produce inflammatory cytokines in response to myeloma target cells; and are highly cytolytic against myeloma cells regardless of the presence of myeloma-protecting bone marrow stromal cells, exogenous a proliferation-inducing ligand, or drug resistance including IMiDs. The magnitude of cytolysis correlates with anti-BCMA CAR expression duration, indicating a temporal limit in activity. In the mouse model of aggressive disseminated human myeloma, Descartes-08 induces BCMA CAR-specific myeloma growth inhibition and significantly prolongs host survival (p < 0.0001). These preclinical data, coupled with an ongoing clinical trial of Descartes-08 in relapsed/refractory myeloma (NCT03448978) showing preliminary durable responses and a favorable therapeutic index, have provided the framework for a recently initiated trial of an optimized/humanized version of Descartes-08 (i.e., Descartes-11) in newly diagnosed myeloma patients with residual disease after induction therapy.

VIS832, a novel CD138-targeting monoclonal antibody, potently induces killing of human multiple myeloma and further synergizes with IMiDs or bortezomib in vitro and in vivo.

Therapeutically targeting CD138, a define multiple myeloma (MM) antigen, is not yet approved for patients. We here developed and determined the preclinical efficacy of VIS832, a novel therapeutic monoclonal antibody (MoAb) with differentiated CD138 target binding to BB4 that is anti-CD138 MoAb scaffold for indatuximab ravtansine (BT062). VIS832 demonstrated enhanced CD138-binding avidity and significantly improved potency to kill MM cell lines and autologous patient MM cells regardless of resistance to current standard-of-care therapies, via robust antibody-dependent cellular cytotoxicity and phagocytosis mediated by NK and macrophage effector cells, respectively. Specifically, CD38-targeting daratumumab-resistant MM cells were highly susceptible to VIS832 which, unlike daratumumab, spares NK cells. Superior maximal cytolysis of VIS832 vs. daratumumab corresponded to higher CD138 vs. CD38 levels in MM cells. Furthermore, VIS832 acted synergistically with lenalidomide or bortezomib to deplete MM cells. Importantly, VIS832 at a sub-optimal dose inhibited disseminated MM1S tumors in vivo as monotherapy (P < 0.0001), and rapidly eradicated myeloma burden in all mice concomitantly receiving bortezomib, with 100% host survival. Taken together, these data strongly support clinical development of VIS832, alone and in combination, for the therapeutic treatment of MM in relapsed and refractory patients while pointing to its potential therapeutic use earlier in disease intervention.

The immunomodulatory drugs lenalidomide and pomalidomide enhance the potency of AMG 701 in multiple myeloma preclinical models.

We investigated here the novel immunomodulation and anti-multiple myeloma (MM) function of T cells engaged by the bispecific T-cell engager molecule AMG 701, and further examined the impact of AMG 701 in combination with immunomodulatory drugs (IMiDs; lenalidomide and pomalidomide). AMG 701 potently induced T-cell-dependent cellular cytotoxicity (TDCC) against MM cells expressing B-cell maturation antigen, including autologous cells from patients with relapsed and refractory MM (RRMM) (half maximal effective concentration, <46.6 pM). Besides inducing T-cell proliferation and cytolytic activity, AMG 701 also promoted differentiation of patient T cells to central memory, effector memory, and stem cell-like memory (scm) phenotypes, more so in CD8 vs CD4 T subsets, resulting in increased CD8/CD4 ratios in 7-day ex vivo cocultures. IMiDs and AMG 701 synergistically induced TDCC against MM cell lines and autologous RRMM patient cells, even in the presence of immunosuppressive bone marrow stromal cells or osteoclasts. IMiDs further upregulated AMG 701-induced patient T-cell differentiation toward memory phenotypes, associated with increased CD8/CD4 ratios, increased Tscm, and decreased interleukin 10-positive T and T regulatory cells (CD25highFOXP3high), which may downregulate T effector cells. Importantly, the combination of AMG 701 with lenalidomide induced sustained inhibition of MM cell growth in SCID mice reconstituted with human T cells; tumor regrowth was eventually observed in cohorts treated with either agent alone (P < .001). These results strongly support AMG 701 clinical studies as monotherapy in patients with RRMM (NCT03287908) and the combination with IMiDs to improve patient outcomes in MM.

A novel BCMA PBD-ADC with ATM/ATR/WEE1 inhibitors or bortezomib induce synergistic lethality in multiple myeloma.

To target mechanisms critical for multiple myeloma (MM) plasma cell adaptations to genomic instabilities and further sustain MM cell killing, we here specifically trigger DNA damage response (DDR) in MM cells by a novel BCMA antibody-drug conjugate (ADC) delivering the DNA cross-linking PBD dimer tesirine, MEDI2228. MEDI2228, more effectively than its anti-tubulin MMAF-ADC homolog, induces cytotoxicity against MM cells regardless of drug resistance, BCMA levels, p53 status, and the protection conferred by bone marrow stromal cells and IL-6. Distinctly, prior to apoptosis, MEDI2228 activates DDRs in MM cells via phosphorylation of ATM/ATR kinases, CHK1/2, CDK1/2, and H2AX, associated with expression of DDR-related genes. Significantly, MEDI2228 synergizes with DDR inhibitors (DDRi s) targeting ATM/ATR/WEE1 checkpoints to induce MM cell lethality. Moreover, suboptimal doses of MEDI2228 and bortezomib (btz) synergistically trigger apoptosis of even drug-resistant MM cells partly via modulation of RAD51 and accumulation of impaired DNA. Such combination further induces superior in vivo efficacy than monotherapy via increased nuclear γH2AX-expressing foci, irreversible DNA damages,  and tumor cell death, leading to significantly prolonged host survival. These results indicate leveraging MEDI2228 with DDRi s or btz as novel combination strategies, further supporting ongoing clinical development of MEDI2228 in patients with relapsed and refractory MM.

APRIL signaling via TACI mediates immunosuppression by T regulatory cells in multiple myeloma: therapeutic implications.

We investigate here how APRIL impacts immune regulatory T cells and directly contributes to the immunosuppressive multiple myeloma (MM) bone marrow (BM) microenvironment. First, APRIL receptor TACI expression is significantly higher in regulatory T cells (Tregs) than conventional T cells (Tcons) from the same patient, confirmed by upregulated Treg markers, i.e., Foxp3, CTLA-4. APRIL significantly stimulates proliferation and survival of Tregs, whereas neutralizing anti-APRIL monoclonal antibodies (mAbs) inhibit these effects. Besides TACI-dependent induction of cell cycle progression and anti-apoptosis genes, APRIL specifically augments Foxp3, IL-10, TGFß1, and PD-L1 in Tregs to further enhance Treg-inhibited Tcon proliferation. APRIL further increases MM cell-driven Treg (iTreg) via TACI-dependent proliferation associated with upregulated IL-10, TGFß1, and CD15s in iTreg, which further inhibits Tcons. Osteoclasts producing APRIL and PD-L1 significantly block Tcon expansion by iTreg generation, which is overcome by combined treatment with anti-APRIL and anti-PD1/PD-L1 mAbs. Finally, APRIL increases IL-10-producing B regulatory cells (Bregs) via TACI on BM Bregs of MM patients. Taken together, these results define novel APRIL actions via TACI on Tregs and Bregs to promote MM cell survival, providing the rationale for targeting APRIL/TACI system to alleviate the immunosuppressive BM milieu and improve patient outcome in MM.