Therapeutic Candidate Alpn-101, a Dual ICOS/CD28 Antagonist, Potently Suppresses Human/NSG Mouse Xenograft Graft Vs. Host Disease (GvHD) in a Dose Ranging Study and Reduces Disease Activity in a Mouse Model of Hemophagocytic Lymphohistiocytosis (HLH)

Abstract Background/Purpose: ALPN-101 is a potent dual inhibitor of the ICOS and CD28 T cell costimulatory pathways designed for therapeutic application in inflammatory diseases. CD28 and ICOS bind CD80/CD86 and ICOS ligand (ICOSL), respectively, and play critical roles in T cell activation and adaptive immunity. ALPN-101 has previously been demonstrated to have potent efficacy - superior to wild type ICOSL-Fc - in models of graft versus host disease (GvHD), a disease reflecting immune-mediated attack of recipient tissue by donor T cells. Here, we examined the efficacy of a single dose of ALPN-101 or repeat dosing with different dose levels in GvHD. We also explored the potential therapeutic benefit of ALPN-101 in another T cell-driven inflammatory disease, hemophagocytic lymphohistiocytosis (HLH), a spectrum of disorders of the immune system characterized by the excessive production of cytokines by activated T cells and macrophages accumulating in organs such as the liver, spleen, bone marrow, and brain, which mediate significant tissue damage. Methods: ALPN-101 was generated using our proprietary variant Ig domain (vIgD™) platform and is an effector-function negative Fc-fusion protein with an engineered variant Ig ICOSL domain capable of binding both ICOS and CD28 with high affinity. ALPN-101 blocks the interaction of these T cell costimulatory molecules with their respective receptors, downregulating T cell activation. The dose ranging GvHD study was executed with ALPN-101 (3x weekly/4 weeks, 20 ug - 500 ug) treatment of NSGTM mice engrafted with human peripheral blood mononuclear cells (PBMC) in comparison to belatacept, a CTLA-4-Fc fusion protein CD28 pathway inhibitor. Mice were monitored daily for clinical signs of GvHD. In a model of primary (inherited) HLH in which perforin-deficient (Prf1(-∕-)) mice are infected with lymphocytic choriomeningitis virus (LCMV), we evaluated both prophylactic (days 0, 3, and 6 post LCMV infection) and delayed (days 3, 5, and 7) treatment with ALPN-101 (400ug/dose). Results: ALPN-101 significantly attenuated T cell activation in the human PBMC-NSG GvHD model at a single 100ug dose and at all multiple doses tested, protecting mice from the effects of xenogeneic T cell activation in vivo. Treated animals exhibited enhanced survival and reduced disease scores compared to control mice treated with saline or belatacept. Flow cytometric analyses of blood collected at 1-2 weeks post cell transfer demonstrated ALPN-101 reduced both the number and activation state of the transferred human CD4+ and CD8+ T cells. In the HLH model, ALPN-101 lessened several of the clinical and laboratory manifestations of HLH, including organomegaly, anemia, CD8+ T cell expansion, and liver inflammation. Conclusion: ALPN-101 is a potent T cell inhibitor capable, even with a single dose, of preventing T cell activation, such as that observed in the huPBMC-NSGTM GvHD and the LCMV-induced HLH models, and thus is a promising novel therapeutic candidate for GvHD and other inflammatory diseases. Preclinical development is underway to support clinical studies of this potentially first-in-class dual ICOS and CD28 inhibitor. Disclosures Dillon: Alpine Immune Sciences: Employment, Equity Ownership. Lewis:Alpine Immune Sciences: Employment, Equity Ownership. Swanson:Alpine Immune Sciences: Employment, Equity Ownership. Evans:Alpine Immune Sciences: Employment, Equity Ownership. Levin:Alpine Immune Sciences: Employment, Equity Ownership. Rixon:Alpine Immune Sciences: Employment, Equity Ownership. Peng:Alpine Immune Sciences: Employment, Equity Ownership. Nichols:Incyte: Research Funding; Alpine Immune Sciences: Research Funding. Swiderek:Alpine Immune Sciences: Employment, Equity Ownership.

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CD20-TCB, a Novel T-Cell-Engaging Bispecific Antibody, Induces T-Cell-Mediated Killing in Relapsed or Refractory Non-Hodgkin Lymphoma: Biomarker Results From a Phase I Dose-Escalation Trial

Blood ◽

10.1182/blood-2019-123979 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 5319-5319 ◽

Cited By ~ 2

Author(s):

Ann-Marie E Bröske ◽

Ian James ◽

Anton Belousov ◽

Enrique Gomez ◽

Marta Canamero ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

B Cells ◽

Board Of Directors ◽

T Cell Activation ◽

Research Funding ◽

Cell Activation ◽

Employment Equity ◽

Advisory Committees ◽

Equity Ownership

Introduction: CD20-TCB (RG6026) is a novel T-cell-engaging bispecific (TCB) antibody with a '2:1' molecular format that comprises two fragment antigen binding regions that bind CD20 (on the surface of B cells) and one that binds CD3 (on the surface of T cells). CD20-TCB offers the potential for increased tumor antigen avidity, rapid T-cell activation, and enhanced tumor cell killing versus other bispecific formats. The safety, tolerability, pharmacokinetics, biomarkers, and antitumor activity of CD20-TCB are currently being investigated in a multicenter Phase I dose-escalation trial (NP30179; NCT03075696). We recently presented preliminary clinical data demonstrating promising clinical activity in relapsed or refractory (R/R) non-Hodgkin lymphoma (NHL) patients with indolent or aggressive disease (Dickinson et al. ICML 2019). Here, we present preliminary blood and tissue biomarker analyses to explore modes of action, support optimal biological dose selection, and identify potential outcome predictors. Methods: For biomarker analyses, we performed immune profiling of peripheral blood by flow cytometry, analyzed plasma cytokine levels by ELISA, and characterized baseline and on-treatment tumor biopsies by immunohistochemistry/immunofluorescence assays and RNA sequencing. Biomarker data were obtained from 122 patients dosed with 0.005-25mg CD20-TCB. Results: CD20-TCB infusion led to a rapid and transient reduction in T cells in the peripheral circulation (T-cell margination) in all patients. T-cell margination reached nadir 6 hours after the first CD20-TCB infusion, and showed a strong association with CD20-TCB dose and receptor occupancy (RO%; as determined by Djebli et al. ASH 2019). Interestingly, rebound of T cells 160 hours after the first CD20-TCB infusion was associated with response to treatment. Responding patients showed long-term T-cell activation after the first infusion of CD20-TCB at doses from 0.6mg and above. T-cell activation was demonstrated by 2-4-fold elevation of T-cell activation markers such as Ki67, HLA-DR, PD-1, ICOS, OX40, and 4-1BB, which was sustained up to Cycle 5 (105 days). Analysis of paired pre- and on-treatment tumor biopsies (n=6) obtained before and 2-3 weeks after the first dose of CD20-TCB showed evidence of T-cell-mediated tumor cell killing. Analysis of archival and pre-treatment tumor biopsies (n=80) revealed that clinical responses were achieved irrespective of the amount of tumor T-cell infiltration at baseline. In contrast, preliminary baseline bulk tumor RNA sequencing data (n=46) showed upregulation of gene signatures associated with cell proliferation/Myc and T-cell subsets (effector vs exhausted-like) in non-responding patients. Conclusions: In this study, we demonstrated the mode of action of CD20-TCB, a novel bispecific antibody with promising clinical activity in R/R NHL. We also demonstrated that biomarker data on T-cell activation can support dose finding in conjunction with pharmacokinetics. Additional analysis is ongoing to evaluate response predictors and better characterize the population that will benefit most from T-cell mediated therapies. Disclosures Bröske: Roche: Employment, Equity Ownership. James:A4P Consulting Ltd: Consultancy. Belousov:Roche: Employment. Gomez:F. Hoffmann-La Roche Ltd: Employment. Canamero:F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Ooi:F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Grabole:F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Wilson:F. Hoffmann-La Roche Ltd: Employment. Korfi:F. Hoffmann-La Roche Ltd: Consultancy. Kratochwil:F. Hoffmann-La Roche Ltd: Employment. Morcos:Roche: Employment, Equity Ownership. Ferlini:Roche: Employment, Equity Ownership. Thomas:F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Dimier:F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Moore:F. Hoffmann-La Roche Ltd: Employment, Equity Ownership. Bacac:Roche: Employment, Equity Ownership, Patents & Royalties: Patents, including the one on CD20-TCB. Weisser:Pharma Research and Early Development Roche Innovation Center Munich: Employment, Equity Ownership, Patents & Royalties. Dickinson:Merck Sharpe and Dohme: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; Celgene: Consultancy, Honoraria, Research Funding, Speakers Bureau; Takeda: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; F. Hoffmann-La Roche Ltd: Consultancy, Honoraria, Research Funding, Speakers Bureau; Novartis: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau; GlaxoSmithKline: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding; Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees, Research Funding, Speakers Bureau. OffLabel Disclosure: CD20-TCB (also known as RG6026, RO7082859) is a full-length, fully humanized, immunoglobulin G1 (IgG1), T-cell-engaging bispecific antibody with two fragment antigen binding (Fab) regions that bind to CD20 (on the surface of B cells) and one that binds to CD3 (on the surface of T cells) (2:1 format). The 2:1 molecular format of CD20-TCB, which incorporates bivalent binding to CD20 on B cells and monovalent binding to CD3 on T cells, redirects endogenous non-specific T cells to engage and eliminate malignant B cells. CD20-TCB is an investigational agent.

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Clinical Dosing Regimen of Selinexor Maintains Normal Immune Homeostasis and T Cell Effector Function in Mice: Implications for Combination with Immunotherapy

Blood ◽

10.1182/blood.v128.22.2525.2525 ◽

2016 ◽

Vol 128 (22) ◽

pp. 2525-2525

Author(s):

Paul M Tyler ◽

Mariah M Servos ◽

Boris Klebanov ◽

Trinayan Kashyap ◽

Sharon Shacham ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

T Cell Activation ◽

Cd8 T Cells ◽

Cell Activation ◽

T Cell Development ◽

Immune Homeostasis ◽

Dosing Regimen ◽

Employment Equity ◽

Equity Ownership

Abstract Selinexor (KPT-330) is a first in class nuclear transport inhibitor of exportin-1(XPO1) currently in advanced clinical trials to treat patients with solid and hematological malignancies. To determine how selinexor might impact anti-tumor immunity, we analyzed immune homeostasis in mice treated with high selinexor doses (15 mg/kg, three times a week: M, W, F) and found disruptions in T cell development, a progressive loss of CD8 T cells and increases in inflammatory monocytes. Antibody production in response to immunization was mostly normal. Precursor populations in bone marrow and thymus were unaffected by high doses of selinexor, suggesting that normal immune homeostasis could recover. We found that high dose of selinexor given once per week preserved nearly normal immune functioning, whereas a lower dose given 3 times per week (7.5 mg/kg, M, W, F) was not able to restore immune homeostasis. Both naïve and effector CD8 T cells cultured in vitro showed impaired activation in the presence of selinexor. These experiments suggest that XPO1 function is required for T cell development and function. We then determined the minimum concentration of selinexor required to block T cell activation, and showed that T cell inhibitory effects of selinexor occur at levels above 100nM, corresponding to the first 24 hours post-oral dosing of 10 mg/kg. In a model of implantable melanoma, we used selinexor treatment at the clinically relevant dosing regimen of 10 mg/kg with a 5-day drug holiday (M, W selinexor treatment). After two weeks of treatment, tumors were harvested and tumor infiltrating leukocyte (TIL) populations were analyzed. This treatment led to intratumoral IFNg+, granzyme B+ cytotoxic CD8 T cells that were comparable to vehicle treated mice. Overall, selinexor treatment leads to transient inhibition of T cell activation but the clinically relevant once and twice weekly dosing schedules that incorporate sufficient drug holidays allow for normal CD8 T cell functioning and development of anti-tumor immunity. These results provide additional support to the recommended selinexor phase 2 dosing regimen, as was determined recently (Razak et al. 2016). Disclosures Klebanov: Karyopharm Therapeutics: Employment, Equity Ownership. Kashyap:Karyopharm Therapeutics: Employment, Equity Ownership. Shacham:Karyopharm Therapeutics: Employment, Equity Ownership, Membership on an entity's Board of Directors or advisory committees. Landesman:Karyopharm Therapeutics: Employment, Equity Ownership. Dougan:Karyopharm Therapeutics: Consultancy. Dougan:Karyopharm Therapeutics: Consultancy.

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Avadomide (CC-122) Alters T Cell Repertoire and Enhances Infiltration of Lymphocytes into Tumor Microenvironment in DLBCL Patients

Blood ◽

10.1182/blood-2018-99-114481 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 4211-4211

Author(s):

Patrick R. Hagner ◽

Fadi Towfic ◽

Frank Schmitz ◽

Xuehai Wang ◽

Andrew P. Weng ◽

...

Keyword(s):

Gene Expression ◽

T Cells ◽

Dendritic Cells ◽

T Cell ◽

Tumor Microenvironment ◽

T Cell Activation ◽

Cell Activation ◽

Cell Populations ◽

Employment Equity ◽

Equity Ownership

Abstract Background : Diffuse large B-cell lymphoma (DLBCL) is the most common subtype of non-Hodgkin lymphoma, constituting 30-40% of all new cases. Avadomide, a small molecule cereblon modulator currently being developed in DLBCL, binds to cereblon in the CRL4CRBN E3 ligase, leading to ubiquitination and subsequent proteasomal degradation of transcription factors Aiolos and Ikaros. This results in decreased proliferation and increased apoptosis of DLBCL cells, independent of cell-of-origin, and immunostimulatory effects in T and NK cells, as measured by increased cytokine production, cell surface activation markers, and enhanced antibody-dependent cellular cytotoxicity. A novel gene expression-based classifier, which detects DLBCL patients with T cell and macrophage infiltration within the tumor microenvironment, has been shown to enrich for responders to avadomide. Avadomide, as a single agent and in combination with rituximab, is currently being investigated in relapsed/refractory DLBCL (NCT01421524 and NCT02031419). Methods : Eighty-one DLBCL patients were enrolled in the expansion phase of the CC-122-ST-001 study (NCT01421524). Peripheral blood T cell subsets were enumerated at screening (baseline), cycle 1 day 15 (C1D15) and cycle 2 day 15 (C2D15) by flow cytometric immunophenotyping. Ex vivo production of IL-2 and IFNγ, as a measure of T cell activation, was determined using the α-CD3 TruCulture Assay. Changes from baseline were evaluated using the t-test with P<0.05 considered significant. T cell receptor (TCR) repertoire analysis through TCRB CDR3 region sequencing was done to derive metrics of population diversity and composition. RNAseq was performed on screening and on-treatment (C1D10/15) biopsies; gene expression deconvolution analyses were used to identify immune cell populations within the tumor microenvironment. Results : Avadomide treatment results in decreased peripheral CD4+ and CD8+ naïve (CD45RA+/CD45RO-) T cells and increased memory (CD45RA-/CD45RO+) and activated (HLA-DR+) T cells, without significantly affecting the absolute numbers of total CD3+, CD4+ or CD8+ populations (Table). High-dimensional single-cell mass cytometry of longitudinally collected peripheral blood samples confirmed the significant increase in CD8+ memory T cells and identified an increase in Treg populations and decreases in CD16+ monocytes and dendritic cells (adj. P<0.02). A single dose of avadomide on C1D1 significantly activated T cells, as indicated by a 300% increase in IL-2 (P=0.018) and 185% increase in IFNγ (P=0.003) secretion. Assessment of TCR B clonotypes revealed that avadomide increases the TCRB repertoire breadth, while reducing its clonality. To understand the influence of avadomide treatment on the tumor microenvironment, we performed RNA sequencing on tumor biopsies collected at screening and two weeks after initiating avadomide treatment (n=18 patients). Deconvolution analyses identified an increase in the expression of genes indicative of various T cell populations, dendritic cells and macrophages, while B cell associated gene expression decreased in on-treatment biopsies compared to screening biopsies. Gene set enrichment analysis (GSEA) revealed significantly increased expression of genes associated with "HALLMARK Interferon Alpha Response" (adj. P=0.04), indicative of an increase in Type I/II interferon production by cells such as T and NK cells. Buttressing the in vitro observations of avadomide-mediated inhibition of DLBCL cell proliferation, GSEA identified a decrease in "E2F targets" (adj. P=0.007) consistent with decreased proliferation of malignant B cells. Conclusion : Avadomide is a potent immunomodulating agent with multiple immune activating properties, including positive effects on T cell activation, as well as a broad expansion of T cell populations as defined by an increase in the richness of the T cell repertoire in blood. In addition, our data demonstrate decreased proliferation of malignant B cells in the tumor, with concomitant increased trafficking of immune cells, such as dendritic cells and macrophages, to the tumor microenvironment. These data further delineate the immune enhancing activity of avadomide in DLBCL patients beyond T-cell activation and provide rational combination strategies. Table. Table. Disclosures Hagner: Celgene Corporation: Employment, Equity Ownership. Towfic:Celgene Corporation: Employment, Equity Ownership. Schmitz:Celgene Corporation: Employment, Equity Ownership. Pourdehnad:Celgene Corporation: Employment, Equity Ownership. Gandhi:Celgene Corporation: Employment, Equity Ownership.

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Mechanism of Synergistic Effects on T Cell Activation By Avadomide (CC-122) and Nivolumab

Blood ◽

10.1182/blood-2018-99-114469 ◽

2018 ◽

Vol 132 (Supplement 1) ◽

pp. 4133-4133

Author(s):

Yumi Nakayama ◽

Matthew E. Stokes ◽

Michelle Waldman ◽

Patrick R. Hagner ◽

Anita K. Gandhi

Keyword(s):

T Cells ◽

T Cell ◽

T Cell Activation ◽

Cell Activation ◽

Synergistic Effects ◽

Single Agent ◽

Differentially Expressed ◽

Cytotoxic T Cell ◽

Employment Equity ◽

Equity Ownership

Abstract Background: Avadomide (CC-122) is a cereblon modulator that promotes ubiquitination and degradation of the hematopoietic transcription factors Ikaros and Aiolos, leading to immunomodulation, such as T cell activation and increased interleukin-2 (IL-2) production in primary peripheral blood mononuclear cells (PBMCs). The immune checkpoint inhibitor nivolumab (nivo), an anti-PD-1 antibody, induces immune activation and can enhance immune response against various solid tumors. Previously, we have shown that the combination of avadomide and nivo synergistically enhance IL-2 production, T cell proliferation, and immune-mediated cytotoxicity, relative to single agent activity. To understand molecular mechanisms underlying these synergistic effects, we compared the effects of avadomide, nivo, or the combination on gene expression in primary human T cells using whole transcriptome RNA sequencing and differential pathway analysis. Methods: PBMCs were isolated from healthy donors (N=6), treated with DMSO/IgG, avadomide 50 nM, nivo 10 µg/mL, or avadomide and nivo for 1 hour, then stimulated with 0.5 ng/mL staphylococcus enterotoxin B for 48 hours. Culture supernatants were collected for cytokine analysis; T cells were isolated by magnetic cell separation for RNA extraction. RNA was sequenced by Illumina HiSeq v4; data was filtered to transcripts ≥10 counts across all samples and processed by DESeq2. Significantly differentially expressed genes (FDR-adj. P values <0.05) were computed for each treatment group relative to DMSO/IgG controls. Pathway analysis was performed with the GSEA Molecular Signatures Database (MSigDB) using the Hallmark and C2 curated gene sets, which comprise a diverse set of biological pathways, including KEGG and Reactome, to provide unbiased enrichment analysis. T cell-related pathways from the MSigDB C5 (Gene Ontology) collection were used to investigate specific effects on immune function. Synergy was defined by the fractional product method. Results: Avadomide, nivo, and the combination enhanced IL-2 production in SEB-stimulated PBMCs by 282%, 47%, and 586% respectively, compared with DMSO/IgG controls, confirming the synergistic effects on cytokine production. The top pathways upregulated in each treatment group included the following T cell related pathways: for avadomide - T cell receptor (TCR) signaling, JAK/STAT, cytokine/receptor interaction; for nivo - CD8 TCR pathway and HIF1A targets; and for the combination - TCR signaling, JAK/STAT, and HDAC3 targets which are required for T cell maturation and cytokine production. Combination treatment uniquely upregulated pathways including the Biocarta cytotoxic T cell pathway and calcium signaling in CD4+ T cells. Among the 7732 genes modified by any treatment, 1949 were uniquely differentially expressed by the combination. A targeted enrichment analysis using only T cell-related pathways from the C5 collection revealed that these uniquely differentially expressed genes represent processes such as T cell differentiation, proliferation, and activation. Conclusions: At the gene expression level, many T cell-related pathways were upregulated by one or more single agent and/or the combination. However, the presence of uniquely differentially regulated genes suggests that combination treatment induced broader effects in pathways involved in T cell differentiation, proliferation, and activation than either avadomide or nivo alone. Interestingly, the cytotoxic T cell pathway was uniquely upregulated by the combination, consistent with our previous finding of a significant increase in cytotoxicity with avadomide/nivo in combination. Calcium signaling in CD4+ T cell genes were also uniquely upregulated, suggesting that avadomide/nivo combination effects may involve nuclear factor of activated T cells (NFAT)-dependent T cell immune regulation. These data provide molecular support for the in vitro phenotypic activity of avadomide and checkpoint blockade on enhancing T cell activity. Avadomide is now under investigation in combination with checkpoint blockade in solid tumors (NCT02859324) and with CAR T therapy in lymphoma (NCT03310619). Disclosures Nakayama: Celgene Corporation: Employment, Equity Ownership. Stokes:Celgene Corporation: Employment, Equity Ownership. Waldman:Celgene Corporation: Employment, Equity Ownership. Hagner:Celgene Corporation: Employment, Equity Ownership. Gandhi:Celgene Corporation: Employment, Equity Ownership.

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Inducible MyD88/CD40 Allows AP1903-Dependent Costimulation to Control Proliferation and Survival of Chimeric Antigen Receptor-Modified T Cells

Blood ◽

10.1182/blood.v124.21.1121.1121 ◽

2014 ◽

Vol 124 (21) ◽

pp. 1121-1121 ◽

Cited By ~ 1

Author(s):

Aaron Foster ◽

Aruna Mahendravada ◽

Peter Chang ◽

Nicholas Shinners ◽

Kevin Slawin ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Cell Lines ◽

T Cell Activation ◽

Cell Activation ◽

First Generation ◽

Employment Equity ◽

Co Activation ◽

Equity Ownership

Abstract Introduction: Adoptive transfer of T cells genetically engineered to express chimeric antigen receptors (CARs) has begun to show impressive clinical results. The efficacy of T cell therapy is dependent not only on tumor recognition, but also on the survival and expansion of T cells following infusion. T cells modified with CAR constructs encoding costimulatory domains such as CD28 or 4-1BB have the capacity to rapidly proliferate in vivo, but severe toxicities have been observed due to unchecked T cell activation. Thus, strategies to regulate T cell activation in vivowould allow physicians to prevent toxicities and maximize anti-tumor efficacy. Here, we describe a novel T cell costimulation switch, inducible MyD88/CD40 (iMC), that can be activated by a small molecule chemical inducer of dimerization, AP1903, to enhance survival and drive T cell proliferation. Methods: T cells were activated with anti-CD3/28 antibodies and subsequently transduced with a biscistronic retrovirus encoding myristolated tandem AP1903 binding domains (FKBPv36), cloned in-frame with MyD88 and CD40 cytoplasmic signaling molecules, and truncated CD19 to identify transduced T cells (SFG-iMC.2A.ΔCD19). Control vectors without signaling elements, or with only MyD88 or cytoplasmic CD40 were also used to generate gene-modified T cell lines. iMC activation was measured by treating T cells with and without AP1903 and measuring cytokine production by ELISA, and assessing cell surface activation markers by flow cytometry. Co-activation of T cells through CD3ζ in combination with iMC was accomplished using anti-CD3 antibodies, or by co-transducing T cells with first generation CAR constructs recognizing prostate stem cell antigen or CD19 (PSCA.ζ or CD19.ζ, respectively), and coculturing T cells with PSCA+ (Capan-1) or CD19+ tumor cell lines (Raji, Daudi and Nalm-1) with and without AP1903. Efficacy of iMC-modified CAR T cells were assessed using NOD scid gamma (NSG) immune deficient mice engrafted with tumor cell lines followed by intravenous injection of T cells. The iMC costimulatory molecule was subsequently activated in vivo by intraperitoneal injection of AP1903 (5 mg/kg). Tumor burden was assessed and T cell expansion in vivowas measured by bioluminescent imaging using an IVIS instrument. Results: T cells transduced with iMC produce cytokines (e.g. IFN-γ, TNF-α, IL-6) in response to AP1903. iMC activation permits T cell survival in the absence of growth cytokines, such as IL-2, but by itself is not sufficient to induce IL-2 production or autonomous growth. Interestingly, AP1903-induction of MyD88 or cytoplasmic CD40 alone showed minimal T cell activation, suggesting potential synergy of the two signaling molecules. However, co-activation of the T cell receptor (TCR) with soluble anti-CD3 and iMC with AP1903 upregulated CD25 expression, induced IL-2 production and promoted T cell expansion. Importantly, endogenous TCR signaling could be substituted by a PSCA-specific CAR linked to the CD3 ζ endodomain (PSCA.ζ CAR), where co-activation of iMC by AP1903, and CAR by tumor cells expressing PSCA (Capan-1) induced high levels of IL-2 secretion, CD25 upregulation and rapid T cell proliferation. Similar results were achieved using T cells transduced with iMC-enabled CD19 CAR (SFG-iMC.2A.CD19.ζ) when cocultured with CD19+lymphoma cell lines. Treatment of tumor bearing immunodeficient mice with T cells modified with iMC and PSCA.ζ CAR showed enhanced antitumor efficacy when mice were administered with AP1903 dimerizer. Bioluminescence imaging also demonstrated marked proliferation and persistence of iMC-transduced T cells in response to AP1903 administration. Following AP1903 withdrawal, T cell levels declined, consistent with the requirement for costimulation in combination with CAR activation. Summary: Inducible MyD88/CD40 represents a novel activation switch that can be used to provide a controllable costimulatory signal to T cells transduced with a first generation CAR. The separation of the cytolytic signal 1 (CD3 ζ) domain from signal 2 costimulation (iMC) provides a unique mechanism by which T cells can be expanded only in response to both AP1903 and tumor antigen, or reduced in number by withdrawal of AP1903-induced iMC costimulation. Disclosures Foster: Bellicum Pharmaceuticals: Employment, Patents & Royalties. Mahendravada:Bellicum Pharmaceuticals: Employment. Chang:Bellicum Pharmaceuticals: Employment. Shinners:Bellicum Pharmaceuticals: Employment. Slawin:Bellicum Pharmaceuticals: Employment, Equity Ownership, Patents & Royalties. Spencer:Bellicum Pharmaceuticals: Employment, Equity Ownership, Patents & Royalties.

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Tuning T Cell Affinity Improves Efficacy and Safety of Anti-CD38 × Anti-CD3 Bispecific Antibodies in Monkeys - a Potential Therapy for Multiple Myeloma

Blood ◽

10.1182/blood.v126.23.1798.1798 ◽

2015 ◽

Vol 126 (23) ◽

pp. 1798-1798 ◽

Cited By ~ 14

Author(s):

Gregory L. Moore ◽

Sung-Hyung Lee ◽

Suzanne Schubbert ◽

Yvonne Miranda ◽

Rumana Rashid ◽

...

Keyword(s):

Multiple Myeloma ◽

T Cells ◽

T Cell ◽

T Cell Activation ◽

Cell Activation ◽

Bispecific Antibodies ◽

Employment Equity ◽

High Affinity ◽

Cell Immunotherapy ◽

Equity Ownership

Abstract CD38 is highly expressed on plasma cells and is an attractive target for multiple myeloma (MM) therapies. Several anti-CD38 antibodies including daratumumab and SAR650984 show promising results in clinical development, though such antibodies are not able to stimulate T cell-mediated killing of myeloma cells. To exploit a T cell immunotherapy mechanism while retaining the favorable drug properties of therapeutic antibodies, we designed bispecific antibodies that recruit T cells to CD38+ MM cells. Such bispecifics act via redirected T cell-cytotoxicity (RTCC) to stimulate T cell-mediated target cell killing regardless of T cell receptor antigen specificity. These anti-CD38 × anti-CD3 antibodies possess a full Fc domain and spontaneously form stable heterodimers that are readily manufactured. Their Fc domain lacks binding to Fcγ receptors to minimize nonselective T cell activation, yet retains binding to FcRn to maintain long serum half-life. We have previously reported that XmAb13551, a humanized and affinity-optimized anti-CD38 × anti-CD3 antibody, stimulates killing of the CD38+ MM cell line RPMI8226 by human T cells and suppresses human Ig levels in SCID mice engrafted with human PBMCs, showing much greater efficacy than daratumumab in these models (Blood 2014 124:4727). We also investigated efficacy of XmAb13551 in monkeys given a single dose of 2, 5, and 20 μg/kg. Within 1 hr after dosing, CD25 and CD69 activation markers were upregulated on T cells and within 8 hr, circulating CD38+ cells were depleted by > 95% at the 20 μg/kg dose. However, depletion of peripheral CD38+ cells was not sustained, suggesting that a large antigen sink was limiting drug exposure. Although higher dosing might overcome an antigen sink, higher doses of XmAb13551 (0.2 mg/kg or higher) resulted in a T cell-mediated cytokine release syndrome (CRS) in monkeys. We reasoned that an anti-CD38 × anti-CD3 antibody with reduced CD3 affinity would stimulate sufficient RTCC to deplete MM cells, yet would attenuate the acute T cell activation (and associated CRS) induced by high-affinity coengagement of T cells with CD38+ target cells. Using XmAb13551 as a starting point, we engineered a series of bispecifics retaining the same high-affinity (0.2 nM) binding to CD38, but with reduced affinity to CD3. We selected two antibodies - XmAb15426 and XmAb14702 - that have significantly reduced CD3 affinity. As expected, these molecules showed reduced potency in RTCC assays using T cells to kill RPMI8226 cells, with potency correlating with CD3 affinity (XmAb13551 > XmAb15426 >> XmAb14702). We next tested XmAb15426 and XmAb14702 at single doses of 0.5 mg/kg and 3 mg/kg, respectively, in cynomolgus monkeys. Both antibodies were well-tolerated at these higher doses, consistent with the moderate levels of IL6 observed in serum from the treated monkeys. Moreover, XmAb15426, with intermediate CD3 affinity, more effectively depletes CD38+ cells at 0.5 mg/kg compared to the original high-affinity XmAb13551 dosed at 2, 5 or 20 µg/kg. Depletion by XmAb15426 was more sustained compared to the highest dose of XmAb13551 in the previous study (7 vs. 2 days, respectively). Notably, although target cell depletion was greater for XmAb15426, T cell activation (CD69, CD25 and PD1 induction) was much lower in monkeys treated with XmAb15426 even dosed 25-fold higher than the 20 µg/kg XmAb13551 group. XmAb14702, with very low CD3 affinity, had little effect on CD38+ cells and T cell activation. Our results demonstrate that modulating T cell activation by attenuating CD3 affinity is a promising method to improve the therapeutic window of T cell-engaging bispecific antibodies. This strategy has potential to expand the set of antigens amenable to targeted T cell immunotherapy by improving tolerability and enabling higher dosing to overcome antigen sink clearance with targets such as CD38. We have shown that by reducing affinity for CD3, XmAb15426 effectively depletes CD38+ cells while minimizing the CRS effects seen with comparable doses of its high-affinity counterpart XmAb13551. Our preclinical data for XmAb15426 provide a rationale for clinical testing of this bispecific antibody in patients with multiple myeloma and other CD38+ malignancies. Disclosures Moore: Xencor, Inc.: Employment, Equity Ownership. Lee:Xencor, Inc.: Employment, Equity Ownership. Schubbert:Xencor, Inc.: Employment, Equity Ownership. Miranda:Xencor, Inc.: Employment, Equity Ownership. Rashid:Xencor, Inc.: Employment, Equity Ownership. Pong:Xencor, Inc.: Employment, Equity Ownership. Phung:Xencor, Inc.: Employment, Equity Ownership. Chan:Xencor, Inc.: Employment, Equity Ownership. Chen:Xencor, Inc.: Employment, Equity Ownership. Endo:Xencor, Inc.: Employment, Equity Ownership. Ardila:Xencor, Inc.: Employment, Equity Ownership. Bernett:Xencor, Inc.: Employment, Equity Ownership. Chu:Xencor, Inc.: Employment, Equity Ownership. Leung:Xencor, Inc.: Employment, Equity Ownership. Muchhal:Xencor, Inc.: Employment, Equity Ownership. Bonzon:Xencor, Inc.: Employment, Equity Ownership. Szymkowski:Xencor, Inc.: Employment, Equity Ownership. Desjarlais:Xencor, Inc.: Employment, Equity Ownership.

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Itolizumab As a Potential Therapeutic for the Prevention and Treatment of Graft Vs Host Disease

Blood ◽

10.1182/blood-2019-122787 ◽

2019 ◽

Vol 134 (Supplement_1) ◽

pp. 5603-5603 ◽

Cited By ~ 1

Author(s):

Cherie Tracy Ng ◽

Jeanette Ampudia ◽

Robert J. Soiffer ◽

Jerome Ritz ◽

Stephen Connelly

Keyword(s):

Weight Loss ◽

T Cells ◽

T Cell ◽

Peripheral Blood ◽

Research Funding ◽

Chronic Gvhd ◽

Vehicle Control ◽

Control Group ◽

Employment Equity ◽

Equity Ownership

Background: CD6 is a co-stimulatory receptor, predominantly expressed on T cells, that binds to activated leukocyte cell adhesion molecule (ALCAM), a ligand expressed on antigen presentation cells and various epithelial and endothelial tissues. The CD6-ALCAM pathway plays an integral role in modulating T cell activation, proliferation, differentiation and trafficking and is central to inflammation. While effector T cell (Teff) are CD6hi and upregulate expression upon activation, regulatory T cells (Treg) remain CD6lo/-, making this an attractive target to modulate Teff activity while preserving Treg activity. Early studies by Soiffer and colleagues demonstrated using T12, an anti-CD6 monoclonal antibody (mAb) that ex-vivo depletion of CD6+ donor cells prior to transplantation decreased the incidence of both acute and chronic GVHD, highlighting the importance of CD6+ cells in GVHD pathogenesis and validating it as a therapeutic target. However, it remains to be shown whether modulating the CD6-ALCAM pathway in vivo can attenuate GVHD. We investigated the use of itolizumab, a humanized anti-CD6 mAb that has demonstrated clinical efficacy in other autoimmune diseases, as both a preventive and therapeutic treatment for GVHD, using a humanized xenograft mouse model. Methods: Humanized xenograft mice were generated by intravenous transfer of 2x10^7 human PBMCs into 6-8 weeks old NOD/SCID IL2rγ-null (NSG). To investigate the ability of itolizumab to prevent GVHD, mice were dosed with either 60μg or 300μg of itolizumab, 150μg of abatacept (CTLA4-Ig), or vehicle, starting one day prior to PBMC transplantation. To investigate the therapeutic effect of itolizumab, mice were dosed with either 150μg of itolizumab or vehicle, starting at Day 5 post-PBMC transfer, when transplanted T cells are already activated. All treatments were administered IP every other day. Weight and disease scores were monitored throughout the study. At Days 18 and 35, peripheral blood was evaluated by flow cytometry to examine T cell prevalence, and tissues were collected for histological examination of pathology and T cell infiltration. Results: When administered as prevention (Day -1), treatment with either 60μg or 300μg of itolizumab significantly decreased mortality compared to the vehicle control (100% vs. 10%); this decrease was similar to the positive control group treated with abatacept (Figure 1). At 60μg, itolizumab-treated mice demonstrated significant reductions in the prevalence of human T cells in peripheral blood vs. vehicle-treated mice at Day 18 (<0.2% vs. 74.5%; p < 0.001). The reduction in peripheral T cells was accompanied by reductions in tissue-infiltrating T cells in lung (85-fold) and gut (9.5-fold), as well as reductions in disease scores and weight loss. When administered therapeutically, treatment with itolizumab was associated with a survival rate of 50% compared to 10% in the control group (Figure 2). Similarly, peripheral T cell prevalence (34.3% vs. 65.1%; p < 0.001), weight loss, and disease scores were inhibited by itolizumab compared to vehicle control mice. Conclusions: These data suggest that systemic treatment with itolizumab can modulate pathogenic Teff cell activity, establishing this antibody as a potential therapeutic for patents with GvHD. A phase I/II study using itolizumab as first line treatment in combination with steroids for patients with aGVHD is currently ongoing (NCT03763318). Disclosures Ng: Equillium: Employment, Equity Ownership. Ampudia:Equillium: Employment. Soiffer:Mana therapeutic: Consultancy; Kiadis: Other: supervisory board; Gilead, Mana therapeutic, Cugene, Jazz: Consultancy; Juno, kiadis: Membership on an entity's Board of Directors or advisory committees, Other: DSMB; Cugene: Consultancy; Jazz: Consultancy. Ritz:Equillium: Research Funding; Merck: Research Funding; Avrobio: Consultancy; TScan Therapeutics: Consultancy; Talaris Therapeutics: Consultancy; Draper Labs: Consultancy; LifeVault Bio: Consultancy; Celgene: Consultancy; Aleta Biotherapeutics: Consultancy; Kite Pharma: Research Funding. Connelly:Equillium: Employment, Equity Ownership.

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Characterisation of Human CD83 Expression on Immune Cells and Their Targeting with CD83 Antibodies to Prevent Graft Versus Host Disease in Allogeneic Haematopoietic Cell Transplantation

Blood ◽

10.1182/blood.v126.23.3081.3081 ◽

2015 ◽

Vol 126 (23) ◽

pp. 3081-3081

Author(s):

Derek NJ Hart ◽

Xinsheng Ju ◽

Zehra Elgundi ◽

Nirupama Verma ◽

Pablo Silveira ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

T Cell Activation ◽

Immune Cells ◽

Cell Activation ◽

Splice Variants ◽

Scid Mice ◽

Human Pbmc ◽

Graft Versus Host ◽

Equity Ownership

Abstract Introduction: CD83 is an important marker of activated dendritic cells (DC) but it is also expressed on other immune cells. Polyclonal anti-CD83 antibody depletes activated DC and prevents human peripheral blood mononuclear cell (PBMC) induced xenogeneic graft versus host disease (GVHD) in immunosuppressed SCID mice (J Exp Med 2009;206;387). We therefore generated a potential therapeutic human anti-CD83 mAb (3C12C), which had similar efficacy and T cell sparing effects in the same model (Leukemia 2015; in press). To investigate the specific immunosuppressive effect of 3C12C further, we undertook a comprehensive analysis of CD83 expression and its glycosylation pattern on various immune cell populations and tested the effect of 3C12C on T cell function using preclinical models, including a human CD83 (hCD83) knock in (KI) mouse. Methods: A panel of mouse and recombinant mAbs to hCD83 were used to analyse its expression by flow cytometry on resting and activated healthy donor PBMC. The expression of potential CD83 splice variants was examined by PCR. T cell expression was examined by flow cytometry and confocal microscopy after PHA, CD3/CD28 beads and allogeneic mixed leukocyte reaction (alloMLR) culture. Control human IgG1 (trastuzumab) and 3C12C mAbs were tested (0.125mg d-1) in a xenogeneic model of GVHD utilizing human PBMC transplanted into total body irradiation and anti-NK conditioned SCID mice. The genetically engineered hCD83 KI mouse was shown to be immune-competent and used to test the effect of 3C12C on LPS activated DC and T cells. Results: There were distinct CD83 splice variants (full length CD83, splicing variant CD83a, CD83b and CD83c) in different immune cells. CD83 glycosylation status also differed with high glycosylation required for surface expression on activated DC, whereas its expression on activated B cells and monocytes was resistant to de-glycosylation. Increases in CD83 expression on T cells occurred early with different kinetics, underlining the distinct signal pathway involved. The 3C12C mAb reduced T cell proliferation in the alloMLR but did not affect cytomegalovirus (CMV) or influenza (Flu) specific CD8+T cell numbers. Treatment with 3C12C prevented GVHD in human PBMC transplanted SCID mice, which otherwise developed histological GVHD between d8-13. Human DC were activated by d2 and expressed the CMRF-44 activation marker plus CD83, CD80 and CD86. Treatment with 3C12C mAb eliminated CD83+ CMRF44+ DC early post-transplant and reduced T cell activation. Further studies, established CMV and Flu specific T cells were retained and responded to antigen by IFNg production. Furthermore, Treg numbers were preserved. The 3C12C mAb depleted LPS activated DC in hCD83 KI mice in experiments performed prior to commencing transplant studies. Conclusion: These findings suggest that the potential therapeutic human anti-CD83 mAb induced significant immune suppression, by depletion of activated DC and consequential modulation of T cell activation. The reduction in allo/xeno activated T cells may result in part from a direct effect of anti-CD83 on early T cell responses. This apparently selective immunosuppressive effect preserves anti-viral T cell immunity and Treg pathways, suggesting that 3C12C merits further investigation as a novel agent for GVHD prophylaxis. Disclosures Hart: DendroCyte BioTech Pty Ltd: Equity Ownership. Clark:DendroCyte BioTech Pty Ltd: Equity Ownership.

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Impact of Lenalidomide Maintenance Therapy on Immune Polarization and Activation in Multiple Myeloma

Blood ◽

10.1182/blood.v126.23.2966.2966 ◽

2015 ◽

Vol 126 (23) ◽

pp. 2966-2966 ◽

Cited By ~ 1

Author(s):

Manisha Bhutani ◽

David Foureau ◽

Tammy Cogdill ◽

Kyle Madden ◽

Qing Zhang ◽

...

Keyword(s):

Multiple Myeloma ◽

T Cells ◽

T Cell ◽

Maintenance Therapy ◽

T Cell Activation ◽

Research Funding ◽

Cell Activation ◽

Lymphoid Cells ◽

Relative Distribution ◽

The Impact

Abstract BACKGROUND: Lenalidomide is an immunomodulatory drug (IMiD) with co-stimulatory effects on immune effector cells in vitro and is an approved treatment for multiple myeloma (MM), although its mode of action in patients is not well defined. We studied the impact of lenalidomide maintenance therapy, following autologous stem cell transplant (ASCT), on NK and NK-T polarization (i.e. activating or inhibitory molecules) and, T cell activation (early vs. late activation) in patients with multiple myeloma. PATIENTS AND METHODS: In this ongoing prospective study with a targeted enrollment of 28 newly diagnosed multiple myeloma patients, blood samples are being collected at 2 to 3 months post ASCT, before starting lenalidomide maintenance therapy (baseline), and serially after 1, 3 and 6 months of treatment (T+1mo, T+3mo, T+6mo). Using a 9 color flow cytometry panel, peripheral blood samples were analyzed for expression of CD3 and CD56 to define NK (CD56+ CD3-), NKT (CD56+ CD3+), and T cell (CD56- CD3+) subsets. Killer 'inhibitory' Ig-like receptors, (KiR2DS4, KiR3DL1) natural killer group 2 proteins (NKG2a, NKG2D) and natural killer p46 protein (NKp46) expression were quantified to assess polarization of NK, and NK-T cells. Programmed death receptor 1 (PD-1) and T-cell Ig and mucin receptor 3 (Tim3) expression was quantified to assess T cell activation state. Flow cytometry data were acquired on a BD FACSAria II, and analyzed using FlowJo version X software. RESULTS: Samples from 11 patients have been collected and analyzed so far (11 baseline, 6 T+1mo, 4 T+3mo). At baseline lymphoid cells represent 12-46% of white blood cells (WBC), this heterogeneity being mainly driven by a wide range of T cell relative distribution among patients (30-74 % lymphoid cells). Phenotypically, NK cells at baseline mainly express natural cytotoxicity receptors (NKp46 and NKG2D), whereas NK-T cell also express NKG2D but approximately 1/3 also express PD-1 indicating they may be functionally defective. T cells at baseline express early T cell activation markers NKG2D and approximately 1/3 also stained positive for late T cell activation marker PD-1. Lymphoid cells relative distribution among WBC tends to normalize at T+1mo of treatment (15 to 35 % of WBC) before expanding at T+3mo (35 to 43 % of WBC). Phenotypically, across the 27 immune variables analyzed, each multiple myeloma patient displayed high level of immune homeostasis after 1 or 3 months of lenalidomide treatment. Noticeably, Nkp46 expression by NK cell and PD-1 expression by NK-T cells decreased in 4/6 patients and, NKG2D expression by T cell decreased in all but one patient during lenalidomide therapy. CONCLUSION: To our knowledge, this is the first study examining the influence of lenalidomide maintenance on the comprehensive immune repertoire in the post-ASCT setting in MM patients. The wide heterogeneity of NK, NK-T and T cell distribution observed at baseline among lymphoid cells indicates the potential effect of post-ASCT immune reconstitution and immunomodulatory the impact of lenalidomide. The capacity of lenalidomide to mediate effects on several immune cells raises the question as to which, if any, of these changes correlate with clinical responses. In our study, serially collected data from each patient, when completed would determine the impact of lenalidomide immunomodulatory effect of therapeutic efficacy and PFS duration in relation to immune reconstitution stage. Disclosures Cogdill: Millennium: Speakers Bureau; Onyx: Speakers Bureau; Celgene: Speakers Bureau; Novartis: Speakers Bureau. Ghosh:Celgene: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau; Pharmacyclics: Membership on an entity's Board of Directors or advisory committees, Speakers Bureau. Usmani:Sanofi: Honoraria, Research Funding; Millennium: Honoraria, Speakers Bureau; Onyx: Honoraria, Research Funding, Speakers Bureau; Pharmacyclics: Research Funding; Celgene: Honoraria, Speakers Bureau; Janssen Oncology: Honoraria, Research Funding; Array BioPharma: Honoraria, Research Funding.

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New Insights into the Mechanism of Action (MoA) of First-in-Class IgG-Based Bcma T-Cell Bispecific Antibody (TCB) for the Treatment of Multiple Myeloma (MM)

Blood ◽

10.1182/blood.v128.22.2096.2096 ◽

2016 ◽

Vol 128 (22) ◽

pp. 2096-2096 ◽

Cited By ~ 7

Author(s):

Laura Moreno ◽

Aintzane Zabaleta ◽

Diego Alignani ◽

Marta Lasa ◽

Patricia Maiso ◽

...

Keyword(s):

T Cells ◽

T Cell ◽

Nk Cells ◽

T Cell Activation ◽

Cd8 T Cells ◽

Research Funding ◽

Cell Activation ◽

Rational Combination ◽

Dose Dependent ◽

Tumor Cell Lysis

Abstract Novel agents have improved outcomes in MM, but prognosis after patients relapse remains poor and new drugs with novel MoA are needed. The breakthrough of immuno-oncology has rendered new therapeutic options, and most recently we reported on EM801, a novel BCMA-TCB that showed remarkably efficacy when used as single agent in primary bone marrow (BM) samples from MM patients (Seckinger, Blood 2015;126: abstr 117). Because of its novelty, further knowledge about the MoA of BCMA-TCB is of utmost importance to improve its efficacy by designing rational treatment combinations. In order to optimize the in vitro efficacy of the BCMA-TCB, we started by investigating in primary BM samples from 6 MM patients whether longer treatment periods with BCMA-TCB2 (a BCMA-TCB candidate sharing similar "2+1" structure of EM801 but displaying higher affinity to BCMA) would increase MM cell death. Upon treating samples with BCMA-TCB2 for 48h vs 96h, we noted a 2-fold increment in MM tumor cell lysis at 1nM and 10nM concentrations (Panel A). In parallel, the phenotypic profiles of CD4 and CD8 T cells showed that BCMA-TCB2 induced robust activation (ie. dose-dependent increment in CD69, CD25, HLADR after exposure to 100pM, 1nM and 10nM of BCMA-TCB2), but also led to the natural emergence of the checkpoint inhibitor PD-1 in the surface of activated CD4 and CD8 T cells (Panel B). We then investigated if there was a correlation between the percentage of PD-1 positive CD4 and CD8 T cells and the efficacy of BCMA-TCB2; interestingly, those patients with lower frequencies of PD-1 positive CD4 and CD8 T cells prior to treatment showed the highest rates of MM tumor cell lysis after 48h and 96h of BCMA-TCB2 at 10nM of (r=0.6, P=0.04; Panel C). By contrast, upon measuring the concentration of soluble BCMA and APRIL in the supernatants of primary BM samples from 16 MM patients treated with BCMA-TCB, we found no significant differences between responding (n=11) and non-responding (n=5) patients. Similar results were observed upon comparing the density of BCMA in the surface of MM tumor cells from responding vs non-responding patients (1256 vs 1522 SABC units; P=87). Since the efficacy of BCMA-TCB2 was found to be intrinsically related to the phenotype and activation status of T cells, we then investigated whether we could further harness immune cells by combining BCMA-TCB2 with three drugs representing different types of immunotherapy: lenalidomide (IMIDs), anti-PD1 (checkpoint inhibitors) and daratumumab (mAb). H929 MM cells were co-cultured with human leukocytes (n=5) and challenged to suboptimal concentrations of BCMA-TCB2 (10pM) alone, or in combination with standard doses of lenalidomide (1µM), anti-PD1 (10µg/ml) and daratumumab (10µg/ml) (Panel D). Interestingly, we observed that combining BCMA-TCB2 with lenalidomide or daratumumab significantly increased their anti-MM efficacy by 4-fold and 2.5-fold, respectively. Because lenalidomide and daratumumab share in common that they rely, at least in part, on activated NK cells to eradicate MM cells, we hypothesized whether such robust T cell activation induced by BCMA-TCB2 was leading to co-stimulation of NK cells. First, we demonstrated by analyzing the transcriptomes of T cells prior and after treatment exposure (n=3), that BCMA-TCB2 modulated the transcriptomes of CD4 and CD8 T cells (159 and 141 deregulated genes, respectively), consistent with enhanced activation and T-cell mediated inflammatory response (eg. TNFRS18, STAT1, CCL4). Furthermore, we observed a dose-dependent and significant increment of the CD69 (2-fold), CD25 (2.5-fold) and HLADR (4-fold) activation markers in the surface of NK cells from primary BM samples of 11 MM patients treated with BCMA-TCB2 (Panel E), suggesting a functional crosstalk between activated T cells and NK cells. In conclusion, we showed that the promising pre-clinical activity of the first-in-class IgG-based BCMA-TCB can be further enhanced by longer treatment periods followed by robust T cell activation. The observation that the efficacy of BCMA-TCB is intrinsically related to the activation status of T cells suggests its rational combination with IMIDs as demonstrated here. Most interestingly, potential crosstalk between activated T and NK cells could lead to enhanced function of the later immune subset, and provide a rational combination between BCMA-TCB and anti-CD38 antibodies to eradicate MM cells through highly activated T and NK cells. Figure Figure. Disclosures Strein: EngMab: Employment. Vu:EngMab: Employment. Paiva:Celgene: Honoraria, Research Funding; Janssen: Honoraria; Takeda: Honoraria, Research Funding; Sanofi: Consultancy, Research Funding; EngMab: Research Funding; Amgen: Honoraria; Binding Site: Research Funding.

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