Immunoreceptor Tyrosine-based Activation Motif Research Articles

A highly sensitive approach for the analysis of tyrosine phosphoproteome in primary T cells

Tyrosine phosphorylation, a common post-translational modification process for proteins, is involved in a variety of biological processes. However, the abundance of tyrosine-phosphorylated proteins is very low, making their identification by mass spectrometry (MS) is difficult; thus, milligrams of the starting material are often required for their enrichment. For example, tyrosine phosphorylation plays an important role in T cell signal transduction. However, the number of primary T cells derived from biological tissue samples is very small, and these cells are difficult to culture and expand; thus, the study of T cell signal transduction is usually carried out on immortalized cell lines, which can be greatly expanded. However, the data from immortalized cell lines cannot fully mimic the signal transduction processes observed in the real physiological state, and they usually lead to conclusions that are quite different from those of primary T cells. Therefore, a highly sensitive proteomic method was developed for studying tyrosine phosphorylation modification signals in primary T cells. To address the issue of the limited T cells numbers, a comprehensive protocol was first optimized for the isolation, activation, and expansion of primary T cells from mouse spleen. CD3+ primary T cells were successfully sorted; more than 91% of the T cells collected were well activated on day 2, and the number of T cells expanded to over 7-fold on day 4. Next, to address the low abundance of tyrosine-phosphorylated proteins, we used SH2-superbinder affinity enrichment and immobilized Ti4+affinity chromatography (Ti4+-IMAC) to enrich the tyrosine-phosphorylated polypeptides of primary T cells that were co-stimulated with anti-CD3 and anti-CD28. These polypeptides were resolved using nanoscale liquid chromatography-tandem mass spectrometry (nanoLC-MS/MS). Finally, 282 tyrosine phosphorylation sites were successfully identified in 1 mg of protein, including many tyrosine phosphorylation sites on the immunoreceptor tyrosine-based activation motif (ITAM) in the intracellular region of the T cell receptor membrane protein CD3, as well as the phosphotyrosine sites of ZAP70, LAT, VAV1, and other proteins related to signal transduction under costimulatory conditions. In summary, to solve the technical problems of the limited number of primary cells, low abundance of tyrosine-phosphorylated proteins, and difficulty of detection by MS, we developed a comprehensive proteomic method for the in-depth analysis of tyrosine phosphorylation modification signals in primary T cells. This protocol may be applied to map signal transduction networks that are closely related to physiological states.

Phospho-mimetic CD3ε variants prevent TCR and CAR signaling.

Antigen binding to the T cell antigen receptor (TCR) leads to the phosphorylation of the immunoreceptor tyrosine-based activation motifs (ITAMs) of the CD3 complex, and thereby to T cell activation. The CD3ε subunit plays a unique role in TCR activation by recruiting the kinase LCK and the adaptor protein NCK prior to ITAM phosphorylation. Here, we aimed to investigate how phosphorylation of the individual CD3ε ITAM tyrosines impacts the CD3ε signalosome. We mimicked irreversible tyrosine phosphorylation by substituting glutamic acid for the tyrosine residues in the CD3ε ITAM. Integrating CD3ε phospho-mimetic variants into the complete TCR-CD3 complex resulted in reduced TCR signal transduction, which was partially compensated by the involvement of the other TCR-CD3 ITAMs. By using novel CD3ε phospho-mimetic Chimeric Antigen Receptor (CAR) variants, we avoided any compensatory effects of other ITAMs in the TCR-CD3 complex. We demonstrated that irreversible CD3ε phosphorylation prevented signal transduction upon CAR engagement. Mechanistically, we demonstrated that glutamic acid substitution at the N-terminal tyrosine residue of the CD3ε ITAM (Y39E) significantly reduces NCK binding to the TCR. In contrast, mutation at the C-terminal tyrosine of the CD3ε ITAM (Y50E) abolished LCK recruitment to the TCR, while increasing NCK binding. Double mutation at the C- and N-terminal tyrosines (Y39/50E) allowed ZAP70 to bind, but reduced the interaction with LCK and NCK. The data demonstrate that the dynamic phosphorylation of the CD3ε ITAM tyrosines is essential for CD3ε to orchestrate optimal TCR and CARsignaling and highlights the key role of CD3ε signalosome to tune signal transduction.

Targeting Siglec-Sialylated MUC1 Immune Axis in Cancer.

Siglecs play a key role in mediating cell-cell interactions via the recognition of different sialylated glycoconjugates, including tumor-associated MUC1, which can lead to the activation or inhibition of the immune response. The activation occurs through the signaling of Siglecs with the cytoplasmic immunoreceptor tyrosine-based activation motif (ITAM)-containing proteins, while the inhibition signal is a result of the interaction of intracellular immunoreceptor tyrosine-based inhibition motif (ITIM)-bearing receptors. The interaction of tumor-associated MUC1 sialylated glycans with Siglecs via ITIM motifs decreases antitumor immunity. Consequently, these interactions are expected to play a key role in tumor evasion. Efforts to modulate the response of immune cells by blocking the immune-suppressive effects of inhibitory Siglecs, driving immune-activating Siglecs, and/or altering the synthesis and expression of the sialic acid glycocalyx are new therapeutic strategies deserving further investigation. We will highlight the role of Siglec's family receptors in immune evasion through interactions with glycan ligands in their natural context, presented on the protein such as MUC1, factors affecting their fine binding specificities, such as the role of multivalency either at the ligand or receptor side, their spatial organization, and finally the current and future therapeutic interventions targeting the Siglec-sialylated MUC1 immune axis in cancer.

Abstract 1319: In vivo programming of natural killer cells and T cells using mRNA delivered cytotoxic chimeric antigen receptors

Abstract Introduction: Current generation of adoptive cell therapy relies on ex vivo engineering of immune cells with tumor-targeting chimeric antigen receptors. In addition to manufacturing challenges, ex vivo engineered cells such as CAR-NK and CAR-T show limited tumor infiltration and persistency within tumor microenvironment. A method leveraging mRNA-based delivery for in-vivo engineering of these cells could address these issues but has not been established. Conventional mRNA/LNP when infused systemically result in significant accumulation in liver tissue and the CAR has no immune cell specificity in their expression or function. Method: Many immune receptors are heterodimeric complexes composed of a ligand binding subunit (e.g. CD16 and TCR) and a signaling adaptor containing Immunoreceptor Tyrosine-based Activation Motif (ITAM) (e.g. FcRγ and CD3ζ). Notably, the cell surface expression of the ligand binding subunit often depends on the expression of the ITAM adaptor. Based on this we fused HER2-targeting scFv to multiple activating receptors whose expression is restricted to NK cells and T cells, and evaluated their expression and anti-tumor function. Results: We developed a series of Natural Cytotoxic Receptor (NCR)-based in vivo CAR constructs by fusing HER2-targeting scFv to the native extracellular and transmembrane sequences of the receptor NKp30, NKp44 and NKp46, These CARs engage signaling adaptor FcRγ or DAP12 expressed in NK cells, and exhibit potent tumoricidal activity against HER2+ ovarian cancer cells as well as mediate tumor-induced cytokine and chemokine response. Using Huh7 liver cell as a model for off-target expression in hepatocytes, we found that NKp44 and NKp46-based CAR requires their cognate signaling adaptors for stable cell surface expression. We also showed that similar strategy can be used to design receptors for selective expression on the surface of T cells utilizing CD3ε chain fused with tumor targeting scFv. Conclusion: These results demonstrated the feasibility of engineering primary NK cells with CARs based on the NCR family of receptors NKp44 and NKp46, whose expression requires the immune-restricted signaling adaptors. These CAR-NK receptors do not contain intracellular signaling motifs but can engage and activate their signaling natural adaptors to initiate tumor killing and cytokine response. An mRNA/LNP based delivery of NKp44-based CAR for cancer treatment is currently under clinical development. Citation Format: Neha Diwanji, Daniel Getts, Yuxiao Wang. In vivo programming of natural killer cells and T cells using mRNA delivered cytotoxic chimeric antigen receptors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1319.

Abstract 1321: In vivo immune cell programming using mRNA-LNP chimeric antigen receptors

Abstract Introduction: The tumor microenvironment (TME) is a dynamic and multifaceted system that comprises largely myeloid lineage immune cells including monocytes, neutrophils, macrophages, and dendritic cells. Reprogramming the myeloid compartment within the context of cancer therapy presents an attractive strategy to overcome current limitations in solid tumor treatment. We have developed a novel approach that harnesses the natural ability of Myeloid cells to take up mRNA loaded lipid nanoparticles, to reprogram these cells with chimeric antigen receptors (CAR’s) that arm these cells to recognize and kill tumor cells. Methods: Current LNPs technology is sufficient to deliver significant mRNA cargo to numerous cell types, including B cells, T cells and myeloid cells. Leveraging this phenomenon we have developed a new class of chimeric antigen receptors (CARs), using protein biology that imparts targeted immune cell expression and functionality, specifically in Myeloid cells. These CARs harness Immunoreceptor Tyrosine-based Activation Motif (ITAM) signaling adaptors expressed exclusively in immune cells, achieving immune cell-type specific CAR-directed tumor lysis and cytokine responses. With a FcaR I (CD89) based CAR design, we have developed a CAR that is dependent on the common Fc receptor gamma chain, primarily restricted to myeloid cells, for stable expression and function. Results: We have demonstrated specific expression of CD89-based CAR in myeloid cells in mouse and monkey following systemic mRNA/LNP delivery, and in human myeloid cells following in vitro treatment with mRNA/LNPs. Systemic mRNA/LNP delivery of CD89-based CAR has demonstrated robust anti-tumor efficacy against multiple tumor antigens in various xenograft mouse models of human breast cancer, hepatocellular carcinoma, and ovarian cancer. Furthermore, in syngeneic mouse tumor models, robust anti-tumor immune responses, characterized by tumoral infiltration of activated CD8+ T cells, diminished tumor-associated Tregs, systemic enhancement of dendritic cells and anti-tumor IgG production, were observed for treated animals. Conclusions: Taken together, we present CAR designs that achieve expression and function in targeted immune cell populations, capable of eliciting anti-tumor efficacy against multiple target antigens by leveraging innate and adaptive immune responses, and demonstrating a class of novel CAR designs to overcome limitations faced by current in vivo mRNA/LNP delivery strategy. A phase I clinical trial is currently on-going to assess the safety and preliminary efficacy of CD89-based CAR against TROP2+ epithelial malignancies. Citation Format: Shannon Argueta, Franciele K. Melber, Michael Gorgievski, Neha Divangi, Edward Cochran, Thach Chu, Yuxiao Wang, Jian Ding, Daniel Getts. In vivo immune cell programming using mRNA-LNP chimeric antigen receptors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 1321.

Characterization of covalent inhibitors that disrupt the interaction between the tandem SH2 domains of SYK and FCER1G phospho-ITAM.

RNA sequencing and genetic data support spleen tyrosine kinase (SYK) and high affinity immunoglobulin epsilon receptor subunit gamma (FCER1G) as putative targets to be modulated for Alzheimer's disease (AD) therapy. FCER1G is a component of Fc receptor complexes that contain an immunoreceptor tyrosine-based activation motif (ITAM). SYK interacts with the Fc receptor by binding to doubly phosphorylated ITAM (p-ITAM) via its two tandem SH2 domains (SYK-tSH2). Interaction of the FCER1G p-ITAM with SYK-tSH2 enables SYK activation via phosphorylation. Since SYK activation is reported to exacerbate AD pathology, we hypothesized that disruption of this interaction would be beneficial for AD patients. Herein, we developed biochemical and biophysical assays to enable the discovery of small molecules that perturb the interaction between the FCER1G p-ITAM and SYK-tSH2. We identified two distinct chemotypes using a high-throughput screen (HTS) and orthogonally assessed their binding. Both chemotypes covalently modify SYK-tSH2 and inhibit its interaction with FCER1G p-ITAM, however, these compounds lack selectivity and this limits their utility as chemical tools.

Controling the cytoskeleton during CEACAM3-mediated phagocytosis

Phagocytosis, an innate defense mechanism of multicellular animals, is initiated by specialized surface receptors. A phagocytic receptor expressed by human polymorphonuclear granulocytes, the major professional phagocytes in our body, is one of the fastest evolving human proteins implying a special role in human biology. This receptor, CEACAM3, is a member of the CarcinoEmbryonic Antigen-related Cell Adhesion Molecule (CEACAM) family and dedicated to the immediate recognition and rapid internalization of human-restricted pathogens. In this focused contribution, we will review the special adaptations of this protein, which co-evolves with different species of mucosa-colonizing bacteria. While the extracellular Immunoglobulin-variable (IgV)-like domain recognizes various bacterial adhesins, an Immunoreceptor Tyrosine-based Activation Motif (ITAM)-like sequence in the cytoplasmic tail of CEACAM3 constitutes the central signaling hub to trigger actin rearrangements needed for efficient phagocytosis. A major emphasis of this review will be placed on recent findings, which have revealed the multi-level control of this powerful phagocytic device. As tyrosine phosphorylation and small GTPase activity are central for CEACAM3-mediated phagocytosis, the counterregulation of CEACAM3 activity involves the receptor-type protein tyrosine phosphatase J (PTPRJ) as well as the Rac-GTP scavenging protein Cyri-B. Interference with such negative regulatory circuits has revealed that CEACAM3-mediated phagocytosis can be strongly enhanced. In principle, the knowledge gained by studying CEACAM3 can be applied to other phagocytic systems and opens the door to treatments, which boost the phagocytic capacity of professional phagocytes.

Potential therapeutic applications of targeting signal-transducing adaptor protein-2 in autoimmune diseases

Adaptor proteins are involved in various immune responses via the modulation of many signaling pathways. Signal-transducing adaptor protein-2 (STAP-2) is an adaptor protein that contains typical domains such as the pleckstrin homology (PH) domain, Src homology domain, and a proline-rich region from the N-terminal region. In T cells, STAP-2 positively regulates T cell receptor (TCR)-mediated signaling by associating with CD3ζ immunoreceptor tyrosine-based activation motifs (ITAMs) and lymphocyte-specific protein tyrosine kinase (LCK). Therefore, a peptide that inhibits the interaction between STAP-2 and CD3ζ ITAMs is likely to suppress TCR-mediated T cell activation, as well as T cell-mediated diseases. As expected, the peptide successfully inhibited the STAP-2/CD3ζ ITAM interaction and suppressed TCR-mediated signaling, cell proliferation, and interleukin (IL)-2 production in human/murine T cells. Furthermore, this inhibitor suppressed the pathogenesis of experimental autoimmune encephalomyelitis (EAE), which is widely recognized as a mouse model of multiple sclerosis, via the downregulation of T cell activation and infiltration of T helper (Th) 1/Th17 cells. These results suggest a new strategy for the treatment of multiple sclerosis and other immune diseases.

Counteracting immunotyrosine-based signaling motifs augment zebrafish leukocyte immune-type receptor-mediated phagocytic activity

Leukocyte immune-type receptors (LITRs) represent a polymorphic and polygenic family of immunoregulatory proteins originally discovered in channel catfish (Ictalurus punctatus; IpLITRs). Belonging to the immunoglobulin superfamily (IgSF), IpLITRs are generally classified as stimulatory or inhibitory types based on their utilization of various intracellular tyrosine-based signaling motifs. While research has shown that IpLITRs can activate as well as abrogate different immune cell effector responses including phagocytosis, recent identification of LITRs within the zebrafish genome (Danio rerio; DrLITRs) revealed the existence of fish LITR-types uniquely containing counteracting stimulatory and inhibitory cytoplasmic tail (CYT) region motifs (i.e., an immunoreceptor tyrosine-based activation motif; ITAM, and immunoreceptor tyrosine-based inhibitory motif; ITIM) within the same receptor. This arrangement is unusual as these motifs typically exist on separate stimulatory (i.e., ITAM-containing) or inhibitory (i.e., ITIM-containing) immunoregulatory receptors that then co-engage to fine-tune cellular signaling and effector responses. Using a flow cytometric-based phagocytosis assay, we show here that engagement of DrLITR 1.2-expressing cells with antibody coated 4.5 μm beads causes a robust ITAM-dependent phagocytic response and reveal that its tandem ITIM motif surprisingly enhances the DrLITR 1.2-induced phagocytic activity while simultaneously decreasing the receptors ability to bind the beads. Confocal microscopy studies also revealed that the ITIM-associated inhibitory signaling molecule SHP-2 is localized to the phagocytic synapse during the phagocytic response. Overall, these results provide the first functional characterization of teleost immune receptors containing a tandem ITAM and ITIM and allow for the proposal of an intracytoplasmic tail signaling model for ITIM-mediated enhancement of ITAM-dependent cellular activation.

An inducible Cd79b mutation confers ibrutinib sensitivity in mouse models of Myd88-driven diffuse large B-cell lymphoma

AbstractDiffuse large B-cell lymphoma (DLBCL) is the most common aggressive lymphoma and constitutes a highly heterogenous disease. Recent comprehensive genomic profiling revealed the identity of numerous molecularly defined DLBCL subtypes, including a cluster which is characterized by recurrent aberrations in MYD88, CD79B, and BCL2, as well as various lesions promoting a block in plasma cell differentiation, including PRDM1, TBL1XR1, and SPIB. Here, we generated a series of autochthonous mouse models to mimic this DLBCL cluster and specifically focused on the impact of Cd79b mutations in this setting. We show that canonical Cd79b immunoreceptor tyrosine-based activation motif (ITAM) mutations do not accelerate Myd88- and BCL2-driven lymphomagenesis. Cd79b-mutant murine DLBCL were enriched for IgM surface expression, reminiscent of their human counterparts. Moreover, Cd79b-mutant lymphomas displayed a robust formation of cytoplasmic signaling complexes involving MYD88, CD79B, MALT1, and BTK. These complexes were disrupted upon pharmacological BTK inhibition. The BTK inhibitor–mediated disruption of these signaling complexes translated into a selective ibrutinib sensitivity of lymphomas harboring combined Cd79b and Myd88 mutations. Altogether, this in-depth cross-species comparison provides a framework for the development of molecularly targeted therapeutic intervention strategies in DLBCL.

CCR1-Targeting CAR T Cells for Acute Myeloid Leukemia

BACKGROUND Chimeric antigen receptor (CAR) T cell therapy is highly effective in patients with B cell malignancies and multiple myeloma, but initial clinical trials with CARs targeting acute myeloid leukemia (AML) have shown less successful results. Challenges inherent to using CAR T cells for AML include lack of a leukemia-specific target antigen due to heterogeneous antigen expression and potential on-target/off-tumor toxicity due to co-expression of target antigens on normal myeloid cells. C-C chemokine receptor 1 (CCR1, also known as CD191), a G protein-coupled receptor that binds to members of the C-C chemokine family, is a promising AML-associated antigen that is reported to be expressed on over 75% of AML samples and minimally expressed on hematopoietic stem/progenitor cells and T cells. The present study aimed to explore the potential of CCR1 as a novel CAR target antigen using a syngeneic mouse model that allows investigation of both efficacy and toxicity of the CAR T cells. METHODS AND RESULTS We developed a CAR based on the single chain variable fragment (scFv) KM5907 targeting both mouse and human CCR1. We constructed a second-generation CCR1-CAR containing a CD28 hinge, a CD28 transmembrane domain, a CD3 zeta signaling domain, and a CD28 co-stimulatory domain. We mutated the immunoreceptor tyrosine-based activation motifs (ITAMs) of the CD3 zeta chain to retain only a single active membrane-proximal (1XX) ITAM, based on a prior study showing that the 1XX ITAM format enhanced CAR T cell activity by reducing T cell exhaustion. Primary murine T cells were retrovirally transduced and CCR1-CAR expression was assessed by flow cytometry. CCR1-CAR T cells promoted effective elimination of BM185 leukemia cells overexpressing murine CCR1 in vitro. Similarly, primary human T cells transduced with the CCR1-CAR exhibited potent cytotoxicity against C1498 leukemia cells overexpressing human CCR1 in vitro. To evaluate anti-leukemia activity of the CCR1-CAR T cells in vivo, BALB/c mice were sublethally irradiated and engrafted with 1x10 5 BM185 leukemia cells modified to overexpress murine CCR1. Two days later, mice were treated with 2x10 6 CCR1-CAR T cells and monitored for weight changes and survival. Growth of BM185 leukemia cells (expressing firefly luciferase) and expansion of CAR T cells (expressing gaussia luciferase) were assessed via two-color bioluminescence imaging (BLI). On day 6, mice were bled retro-orbitally and serum was analyzed for cytokine levels. The CCR1-CAR T cells demonstrated potent anti-leukemia activity and T cell expansion in vivo, promoting improved overall survival compared with control mice that received only tumor cells (Figure 1). CCR1-CAR T cell activity was accompanied by mild, self-limited toxicity, characterized by transient weight loss (Figure 2), but not significant elevation of serum levels of cytokines associated with cytokine release syndrome (CRS) such as IL-6 and TNF-α. BLI of the CCR1-CAR T cells revealed enhanced trafficking into the bone marrow and spleen followed by proliferation in irradiated mice even in the absence of tumor, suggesting that CCR1-CAR T cells are stimulated by CCR1 antigen expressed on non-leukemic host cells in addition to leukemia cells. CONCLUSIONS In summary, CCR1-CAR T cells represent a promising therapeutic strategy for AML that to our knowledge has not yet been evaluated in preclinical or clinical studies. We generated CCR1-CAR T cells that demonstrated potent anti-leukemia activity in vitro and in vivo in a syngeneic mouse model. Clinical signs of self-limited toxicity were not associated with elevated levels of inflammatory cytokines and might be caused by an on-target/off-tumor effect, which warrants further investigations to better characterize the safety profile of CCR1-CAR T cells. The CCR1-CAR T cells also displayed potent cytotoxicity in vitro via human CCR1, which will facilitate clinical translation of the findings. A CCR1-CAR may also offer benefit in other hematologic malignancies with reported CCR1 expression such as multiple myeloma or Hodgkin's lymphoma.

The Novel Profiling Relative Inhibition Simultaneously in Mixtures (PRISM) Platform Identifies Synergistic Activity of Lanraplenib and Ruxolitinib in Hematological Malignancies

Background: Investigation of drug combinations across different contexts can provide useful insights on the anti-cancer mechanism and can ultimately lead to new treatments. However, conventional drug combination screening methods are limited by throughput. Efforts to systematically identify the most effective active combinations and the optimal molecular contexts in a high throughput screening (HTS) format could greatly accelerate the development of combination treatments. Spleen Tyrosine Kinase, SYK, is a non-receptor tyrosine kinase known to regulate intracellular signaling, including FLT3, AKT/mTOR and STAT5 pathways, via its immunoreceptor tyrosine-based activation motif (ITAM). Deregulated SYK signaling has been reported to play a central role in pathogenesis of allergic and autoimmune diseases as well as hematological malignancies. Lanraplenib (LANRA) is a next-generation SYK inhibitor currently being evaluated in combination with gilteritinib, a FLT3 inhibitor, in patients with relapsed or refractory (R/R) FLT3-mutated acute myeloid leukemia (AML) (NCT05028751). Given its critical role in intracellular signaling and interaction with receptor tyrosine kinases(RTKs), we hypothesized that LANRA could synergize with ruxolitinib, a JAK inhibitor. To address this hypothesis, we performed a high throughput drug combination screen using the Broad Institute's Profiling Relative Inhibition Simultaneously in Mixtures (PRISM) platform, which enables rapid screening of thousands of compounds in a 930-cell line panel across 45 different lineages. Methods: In this study, we performed a combination screen using the PRISM platform with ruxolitinib as the test compound, with a 10 μM top dose (7 dose concentrations with 3-fold dilutions), in combination with LANRA at two anchor doses, 2 μM and 10 μM. PRISM is a pooled, multiplexed cell viability assay that provides 7-point dose response curves, IC 50, AUC values, and relative abundance of unique cell line barcodes. To understand the drug synergy landscape across different lineages, we developed a bioinformatics pipeline which uses PRISM viability data to calculate synergy scores across all the cell lines and drug combinations. Secondary validation studies of the combinations used CTG viability measurements. Phospho-SYK expression was evaluated in archival formalin-fixed paraffin-embedded (FFPE) bone marrow biopsies from patients with myeloid proliferative neoplasm (MPN) by immunohistochemistry (IHC). RNA-seq was performed to evaluate differential changes in gene expression in response to LANRA. Gene set enrichment analysis (GSEA) was performed to evaluate perturbation in leukemogenic signaling pathways. Results: In the PRISM cell line panel, ruxolitinib in combination with LANRA demonstrated synergistic activity in hematological malignancy cell lines. Among AML cell lines in the panel, OCIAML5, OCIM1, HL60, HEL, EOL1, MONOMAC6, NB4, U937, PL21, and TF1 showed the highest synergy scores. The most sensitive cell lines to the combination showed up-regulation of JAK-STAT and inflammatory signaling pathways in a gene set enrichment analysis (GSEA) prior to treatment. Consistent with this, phosphorylated SYK was associated with inflammatory megakaryocytes and fibrosis in primary samples from patients with MPN. LANRA down-regulated JAK-STAT signaling in a reporter cell line and repressed gene expression associated with dysregulated inflammatory pathways in AML cells. Additionally, the combination of LANRA and ruxolitinib showed synergistic antiproliferative activity across a broad range of concentrations in FLT3-ITD primary AML cells and a panel of hematological malignancy cell lines, confirming the PRISM results. Conclusion: These studies demonstrate the utility of PRISM as a platform to rapidly identify rational combination agents. Importantly, LANRA is effective in combination with ruxolitinib in AML and other hematological malignancy preclinical models. This finding is consistent with the observation that SYK can regulate STAT signaling and cooperate with other RTKs like FLT3. Given the central role of SYK in regulation of oncogenic and inflammatory signaling, SYK inhibition with LANRA in combination with ruxolitinib may be a promising strategy for patients with myeloid malignancies.

Ablation of Cullin-5 in Primary Human T Cells Improves Tumor Killing and Persistence in BCMA-Targeting CAR-T Cells in a Multiple Myeloma Model

While adoptive T cell therapies have led to remarkable clinical responses in certain subsets of B cell leukemia and lymphoma, many challenges remain that are limiting the efficacy in other hematological malignancies. Compromised T cell function and exhaustion due to chronic antigen exposure can impair the persistence of chimeric antigen receptor (CAR)-T and T-cell-receptor (TCR)-T cells. Gene editing strategies have the potential to circumvent some of these challenges and enhance T cell function. To identify key genes that are involved in regulating T cell dysfunction, we performed a genome-wide CRISPR loss-of-function screen in primary human T cells in conditions that mimic chronic antigen exposure. Primary T cells from two donors were transduced with lentivirus containing a NY-ESO-1 TCR as well as a genome-wide sgRNA library and subsequently CRISPR edited using Cas9-RNP electroporation. These antigen specific TCR-T cells were then co-cultured with the NY-ESO-1+ melanoma cell line A375 at an effector-to-target (E:T) ratio of 1:1 for 48 hours and challenged under the pressure of chronic tumor stimulation for 9 rounds in total. The resulting next-generation sequencing data was then analyzed utilizing the MAGeCK pipeline to identify top scoring hits for validation regarding their role in T cell fitness and persistence. Among the hits with the highest positive fold changes, we found seven genes which are part of the Cullin-RING ligase 5 multi-protein complex (Fig. 1). These hits were then validated in a CAR-T cell context. We first edited primary human T cells by knocking out CUL5 as well as the endogenous TCR. The template for the B Cell Maturation Antigen (BCMA)-specific CAR bb2121 was then delivered to the TRAC locus via CRISPR/Cas9-RNP and adeno-associated virus (AAV). Here, we tested a panel with four CAR modifications, including two different co-stimulatory domains (CD28ζ, 4-1BB), a CAR with mutated immunoreceptor tyrosine-based activation motifs (ITAM) (1XX CAR), and a CAR containing an alternative BCMA-targeting single-chain variable fragment. This panel of CUL5 ablated CAR-T cells were then repeatedly co-cultured with BCMA-expressing tumor cells. After 6 rounds of tumor exposures, CUL5 ablated T cells showed a striking tumor killing advantage compared to control edited cells in a functional tumor killing assay (Fig. 2). Notably, we also observed vastly increased production of the cytotoxic cytokines INF-γand TNF-α in CUL5 ablated cells. Furthermore, the distinct tumor killing advantage of CUL5 KO cells in vitro was reproduced in the context of a CD19-specific CAR, which will be relevant in other clinical settings. Finally, we evaluated the striking tumor killing capacity of CUL5 ablated BCMA-specific CAR-T cells in vivo. For this, NOD.Cg- PrkdcscidIl2rgtm1Wjl/SzJ mice engrafted with luciferase-expressing BCMA+ multiple myeloma cell line OPM2 were treated with this panel of CUL5 ablated and control CAR-T cells and tumor burden was measured via Bioluminescent Imaging (BLI) over time. Mice treated with CUL5 KO BCMA-specific CAR-T cells showed lower median radiance measured by BLI, except for the 1XX CAR condition where both cohorts completely cleared the disease. In addition to the complete tumor clearance in both the control and CUL5 edited cohorts, we observed that the BLI levels in the 1XX CAR treated animals remained stable even after the mice were subjected to five tumor rechallenges. After 90 days, the mice were sacrificed and CAR+ human T cells were isolated from the bone marrow and spleens and phenotypically assessed. Analysis of these samples revealed a significantly higher frequency of CAR+ cells in the mouse bone marrow in the CUL5 KO group compared to control, while there were equivalent numbers in the spleens, suggesting an antigen-specific expansion advantage for the CUL5 KO CAR-T cells. We then co-cultured the isolated BCMA CAR-T cells from the spleens of these mice with OMP2 tumor cells in different E:T ratios and assessed tumor killing. We found a significant advantage in tumor killing of CUL5 ablated T cells compared to control cells in this ex vivo setting, suggesting an improved functional persistence. In summary, our findings identify the CUL5 complex as a novel potential therapeutic target to improve T cell persistence and counteract T cell exhaustion in order to improve the efficacy of adaptive cell immunotherapies for the treatment of BCMA+ hematological malignancies.

Role of Cell Therapy Product Characteristics in Patient Response to TAK-940 (CD19(T2)28z1xx Chimeric Antigen Receptor (CAR) T): Biomarker Analyses from a Phase I Study in Adult Patients with Relapsed or Refractory B-Cell Malignancies

TAK-940 (CD19(T2)28z1XX Chimeric Antigen Receptor (CAR) T) is an autologous CD19 CAR T cell therapy utilizing an optimized 1XX signaling domain substituting for the natural CD3ζ immunoreceptor tyrosine-based activation motifs. This 1XX design extends the functional persistence of CAR T cells with increased potency in mice (Feucht J et al. Nat Med 2019). TAK-940 is being evaluated in a Ph1 trial in patients with Relapsed or Refractory B-cell malignancies (NCT04464200) with demonstrated early signals of clinical efficacy (Park J et al. ASH 2022). The present study aims to provide a better understanding of the clinical performance of CD19(T2)28z1XX CAR T cells by in depth characterization of the cellular products and patient samples from this Ph1 trial. A total of 28 subjects were enrolled and treated in the dose escalation and expansion cohorts of the Ph1 trial. Responses were observed across all dose levels (25x10 6 to 200x10 6 CAR T cells), achieving ORR 82%, CR 71%. Immunophenotyping by flow cytometry was conducted on patient apheresis material, un-transduced cells, transduced cellular drug product and peripheral blood samples from infused subjects. Circulating cytokine profiling was performed on patient serum samples collected pre and post treatment with TAK-940. In the transduced cellular drug products, CAR+ and CAR- CD8+ central memory and transitional memory T cells were more abundant than naïve, stem cell memory or terminal effector populations. This elevation in central and transitional memory T cells seen in the drug product was not observed in the patient apheresis material, indicating that this effect is likely driven by the production process. CD57 and TIM3 expression in both CD4+ and CD8+ CAR+ T cells in the drug product showed a positive association with clinical response, while CTLA4 or LAG3 expression independently was negatively associated with response. The drug product also contained low numbers of dysregulated/exhausted T cells, with no observable difference between responders and non-responders. Interestingly, in the starting apheresis material, increased expression of TIM3 as well as decreased expression of either LAG3 or KLRG1 in CD8 T cells, independently associated with responses. Current analysis is based on associations with complete response. Additional analyses to be reported will include associations with ORR and durability of responses. These findings suggest potential utility of these T cell markers in predicting patient response and warrant evaluation in a larger population. Although CD57 expression has been associated with a senescent phenotype, we hypothesize that the observed increase in CD57 expression in CD4+ and CD8+ CAR+ T cells in the product may indicate higher cytotoxic potential of those cells. Increase in CD57+ CAR+ T cell subsets has been previously associated with durable CRs in large B cell lymphoma patients treated with axi-cel (Good Z et al. Nat Med 2022). Additional analyses to further characterize the CD57+ cell populations and establish their role in clinical responses to CAR T cell therapy with the 1XX CAR design are in progress. The increased expression of CD57 and the activation marker TIM3, and decreased expression of inhibitory receptors CTLA4 and LAG3 in the drug product from responders, together with the robust clinical responses observed with doses as low as 25x10 6 CAR T cells, suggest that the product consists of highly potent T cells, in accordance with the preclinical results obtained with the 1XX CAR. Low levels of circulating cytokines were observed following treatment with TAK-940, including IFNg, IL-6, IL-10, indicating a safe and tolerable CAR T product consistent with the observed clinical safety profile of TAK-940. Correlative analysis of T cell immunophenotypes observed in the product to clinical parameters including durability of responses, metabolic tumor volume/tumor burden, and induction of cytokines and chemokines is ongoing and will be reported. This will further contribute to our understanding of CD19 CAR T cells endowed with a 1XX signaling domain and potentially support the identification of product and/or apheresis biomarkers that may predict patient response.

Signaling Role of Viral Protein Motif and Its Application in CAR T Cell Therapy

Adoptive cell therapy using Chimeric Antigen Receptor (CAR) T cells, such as Tisagenlecleucel and Axicabtagene Ciloleucel, has revolutionized cancer immunotherapy and become a game-changer in cancer care. However, several challenges, including durable remission and limited expansion after infusion, persist. Recent work from the Riddell lab (PMID: 34429382) demonstrated that T Cell Receptors (TCRs) are more sensitive than CARs due to the presence of T cell signaling proteins like CD3-, CD3ε, and CD3-, which facilitate the recruitment of Lck to phosphorylate immunoreceptor tyrosine-based activation motifs (ITAMs). Although CARs were designed to mimic TCR signaling, they still lack the full sensitivity. In this study, we hypothesized that enhancing tyrosine phosphorylation of the immunoreceptor tyrosine-based activation motifs (ITAMs) presented on CD3 in CAR T cells amplifies the CAR-mediated signaling as well as improves sensitivity of CAR co-stimulatory signaling. To achieve this, we developed a novel co-stimulation system where anti-CD19 CAR T cells co-expressed Tip37, a 37-amino acid segment of the Herpesvirus saimiri (HVS) tyrosine-protein kinase-interacting protein (Tip). This specific segment interacts exclusively with the major T cell kinase, Lck, effectively regulating its kinase activation. The critical region for this interaction lies within 37 amino acids (146-182) in the central part of Tip, which contains two motifs: the SH3 binding motif (SH3B; 174-182) and the C-terminal Src-related kinase homology motif (CSKH; 146-155). The 37 amino acid peptide fragments alone form a stable complex with Lck. Lck is crucial in the initial stages of T cell activation, not only when triggered by the native TCR stimulation but also in response to CAR-antigen stimulation. Following antigen-induced T cell activation, Lck initiates the phosphorylation of tyrosines in the ITAMs present in CD3ζ domains. This leads to the recruitment of ZAP70 kinases to the ITAMs of CD3ζ, facilitating the formation of signaling protein complexes. The results of our in vitro experiments using the immortalized T cell line, Jurkat cells, demonstrate that the inclusion of the Tip37 component in the CAR leads to the formation of the Lck-CAR complex. This, in turn, significantly enhances the phosphorylation of ITAMs in CARs and triggers downstream signaling. Importantly, the CAR T cells with the Tip37 co-stimulatory domain do not secrete cytokines when in an unstimulated state. This suggests that the heightened Lck phosphorylation does not lead to the auto-activation of T cells. As a result, CAR T cells engineered with Tip37 can be considered safe and hold promise for future applications. We engineered CAR19 T cells co-expressing Tip (Tip-CART19 cells) with a co-stimulatory domain of 4-1BB and CD3 (Tip-CART19 cells). As a control, we generated CART19 cells lacking the TIP domain (WT CART19 cells). We confirmed that Tip expression induced enhanced CD3 phosphorylation in CART19 T cells. Additionally, we observed that a significantly augmented outgrowth of CD8+ cells engineered with the TIP-containing CAR compared with canonical CAR T cells. Further, TIP-CAR T cells displayed increased expression of CD38 and Ki67. Interestingly, we also noted an expansion of CCR7+CD45RA- central memory subsets in CD4+ CART19 cells and CCR7-CD45RA- effector memory subsets in CD8+ CART19 cells. Finally, as evidenced by apparent changes in phenotype, Tip-CART19 cells exhibited improved cytotoxic ability and significant outgrowth of CART19 cells with in vitro repeated CAR stimulation using CD19-expressing tumor cells, as previously described in our study (Fraietta et al., Nature 2018). This study highlights that amplification of the constitutive Lck recruitment and amplified CD3 phosphorylation in CART19 cells via the introduction of Tip37 domain results in enhanced anti-leukemia cytotoxic ability and preservation of proliferative function in CART19 cells. Our discovery introduces a novel approach for amplifying CAR signaling to improve CAR T cell therapy.

A Phase I Study of CD19-Targeted 19(T2)28z1xx CAR T Cells in Adult Patients with Relapsed or Refractory Diffuse Large B-Cell Lymphoma

Background: Autologous CD19 CAR T cell therapies have demonstrated favorable clinical responses in relapsed or refractory (R/R) diffuse large B-cell lymphomas (DLBCL), but only a subset of patients (pts) experience durable remissions. We hypothesized that the redundancy of CD28 and CD3ζ signaling in a CAR design incorporating all 3 CD3ζ immunoreceptor tyrosine-based activation motifs (ITAMs) might negatively affect T cell differentiation and promote exhaustion. Therefore, we created a new CD19 CAR construct with calibrated CAR activation potential by mutating 2 of the 3 ITAMs, termed 1XX, and hypothesized that a 1XX CAR would afford durable responses at lower dose and fewer toxicities compared to CARs comprising 3 ITAMs. We previously presented the data from the dose-escalation portion of the phase I clinical trial of 19(T2)28z-1XX CAR T cells in DLBCL (Park J et al. ASH 2022). We have now completed accrual and report the updated results from both dose escalation and expansion portion of the study with a longer follow-up (NCT04464200). Methods: This is a single-center, phase I, dose-escalation and expansion trial of 19(T2)28z1XX CAR T cells in adult pts with R/R DLBCL conducted at Memorial Sloan Kettering Cancer Center. Pts received fludarabine and cyclophosphamide lymphodepleting chemotherapy followed by a single infusion of CAR T cells. There were 4 dose levels in the dose escalation cohort: dose level (DL) 1 (25x10 6), DL2 (50x10 6), DL3 (100x10 6) and DL4 (200x10 6 CAR T cells). The primary objective of the trial was to evaluate safety and tolerability and determine the recommended phase 2 dose. Key secondary objectives include assessment of overall response and complete response rates. Results: 28 pts have been enrolled and treated; 16 pts on the dose escalation and 12 pts on the dose expansion phase of the study. Median age was 62 (range, 48-86). 20 pts (71%) had primary refractory disease, 3 pts (11%) had prior autologous HSCT, and 2 pts (7%) had prior autologous CD19 CAR T therapy. In the dose-escalation phase (n=16), 15 pts experienced grade 1-2 CRS (94%) and no pt experienced ≥grade 3 CRS. Two pts (13%) experienced ICANS: 1 pt with grade 1 and 1 pt with grade 3 (Table 1). Eight pts received tocilizumab and 5 pts received corticosteroid. Complete response (CR) was observed in 11 of 16 pts (69%) and partial remission (PR) in 1 pt (6%) with overall response rate (ORR) of 75%. Responses were seen across all dose levels (Table 1). The lowest dose (DL1: 25x10 6) was selected for dose-expansion based on exposure-response analysis and 12 additional pts were treated at that dose level. In a pooled analysis of 16 pts who received DL1 dose (4 in dose escalation and 12 in dose expansion), 12 pts and 1 pt experienced grade 1-2 (75%) and grade 3 CRS (6%), respectively. Only 1 pt experienced ICANS (6%) at grade 3 (same pt who had grade 3 CRS), which was reversible and transient (Table 1). 11 pts received tocilizumab and 9 pts received corticosteroids. Twelve pts achieved CR (75%) and 2 pts (12%) PR with the best ORR of 87% (Table 1). A lower metabolic tumor volume (MTV) at screening but not at post-bridging was associated with a higher likelihood of achieving CR (p=0.039). With a median follow-up of 345 days (range, 33-1024), 4 pts experienced relapse (1 CR and 3 PR pts) and 16 pts have ongoing CR > 6 months (Figure 1). While CAR T cell persistence analysis is ongoing, 5 pts have CAR T cells detected beyond one year in ongoing CR including a patient treated at DL1 with detectable CAR T cells at 2 years. Conclusions: Treatment with 19(T2)28z1XX CAR T cells was shown to be safe with durable remissions with low rates of severe CRS (4%) and ICANS (7%). The overall CR rate of 71% is encouraging and appears durable with the majority of CR patients in ongoing remission > 6 months at a median follow-up of 345 days and with persisting CAR T cells. With more patients treated at DL1 with a longer follow-up, the study demonstrates a high efficacy of 19(T2)28z1XX CAR T cells at a dose significantly lower (25x10 6) than those of approved CD19 CAR T cells (100-300x10 6) and support that the 1XX single ITAM signaling domain may lead to enhanced efficacy of CD19 CARs and allow infusion of a lower T cell dose with favorable toxicity profiles.

Dual Split-Signaling TIM3+CLEC12a Targeting CAR T-Cells with Optimized Signaling As a Safe Potential Therapy for Acute Myeloid Leukemia

Background: The success of chimeric antigen receptor (CAR) T-cell therapies targeting B cell maturation antigen (BCMA) in multiple myeloma and CD19 in B-cell malignancies has demonstrated the immense potential of this immunotherapeutic strategy. However, the translation of CAR T-cell therapy to acute myeloid leukemia (AML) patients has encountered challenges due to the absence of surface antigens specifically or preferentially expressed on AML cells. To overcome this hurdle, we explored the feasibility and safety of simultaneously targeting the AML-associated antigens CLEC12a and TIM3 using an AND-gate strategy in which the essential stimulatory and co-stimulatory T-cell activation signals are segregated into separate CARs. To improve the safety of our strategy we also attenuated signaling through the stimulatory anti-CLEC12a CAR via affinity-optimization or through targeted mutations in its immunoreceptor tyrosine-based activation motif (ITAM) regions. Methods: To identify the most optimal dual-split CAR T-cell configuration, we designed several chimeric antigen receptor constructs in which we targeted CLEC12a with stimulatory CARs (sCARs) with high (C hi) or low (C low) affinities. In addition, the high affinity C hi stimulatory CAR was mutated in the second and third ITAM regions (denoted as C hixx) to attenuate the CD3ζ stimulatory signal. TIM3 was targeted by a costimulatory CAR (cCAR) containing both CD28 and 41BB signaling domains. The dual-split CARs were generated using two separate retroviral constructs. After the assessment of the CAR expression and specific surface markers associated with memory phenotype and exhaustion, dual-split CAR T-cells were functionally tested using an isogenic cell line model for specific lysis against dual CLEC12a/TIM3 positive or single CLEC12a or TIM3 positive isogenic target cells as well as for dual antigen-specific cytokine secretion. The dual-split CAR T-cells were also tested for their efficiency to specifically eliminate leukemic stem/progenitor cells by the colony formatting unit (CFU) assay. Moreover, anti-AML activity and persistence of the dual-split CAR T-cells was assessed using an AML PDX mouse model in which human primary AML cells expressing TIM3 and CLEC12a were injected. Results: Using the isogenic cell line model, we revealed that the dual-split CAR T-cells with the combination of the high affinity CLEC12a sCAR and TIM3 cCAR (C hi+T) show antigen-specific cytokine secretion and cytotoxicity, and that this specificity was enhanced when the CLEC12a sCAR was attenuated through ITAM mutations (C hixx+T). In CFU assays, all tested CLEC12a/TIM3 dual-split CAR T-cell combinations exhibited potent inhibition (up to 95%) of leukemia blast viability and leukemia stem/progenitor self-renewal. In vivo, although AML did not engraft in all mice, the best-performing dual-split C hixx+T1 CAR T-cells displayed potent anti-leukemic activity, as they prevented engraftment in two additional mice compared to control groups (n=6 each group). Furthermore, in contrast to control groups dual-split CAR T-cells exhibited prolonged persistence in the blood up to 20 weeks after injection. Conclusion: We successfully generated highly specific dual-targeting CAR T-cells by splitting the T-cell activation signals into two simultaneously expressed CARs, and using a novel approach of attenuating the sCAR through mutations in ITAM regions. Overall, we show that dual-split CAR T cells targeting CLEC12a and TIM3, particularly the combination C hixx+T CAR T-cells, have specific and promising anti-AML activity. Our findings underscore the potential of innovative dual-split CAR T-cell therapies as a novel and effective immunotherapeutic approach for combating AML.

KB-Lanra 1001: A Phase 1b/2 Study of Safety, PK, PD, and Preliminary Efficacy of the Selective SYK Inhibitor Lanraplenib in Combination with the FLT3 Inhibitor Gilteritinib in FLT3-Mutated R/R AML

Background and Significance: FMS-like tyrosine kinase (FLT3)-mutation (FLT3 mut) in patients with newly diagnosed and relapsed/refractory (R/R) acute myeloid leukemia (AML) is associated with shorter overall survival (OS) and relapse-free survival. Gilteritinib is an approved therapy for R/R FLT3 mut AML, but reduction in FLT3 mut burden and sustained efficacy are rarely achieved, thus necessitating investigation of rational therapeutic combinations to improve outcomes. Spleen Tyrosine Kinase (SYK) is a non-receptor tyrosine kinase known to regulate intracellular signaling in response to extracellular stimuli via its immunoreceptor tyrosine-based activation motif (ITAM). SYK serves as a relay to an oncogenic transcriptional regulatory network (TRN) linked to HOXA9 and MEIS1-facilitated suppression of myeloid progenitor maturation and proliferation. SYK cooperates with internal tandem duplication (ITD)-mutated FLT3 to drive leukemogenesis. Lanraplenib (LANRA) is an oral, potent, selective, next-generation SYK inhibitor with a 24-hour half-life, and once-daily (QD) dosing. In preclinical studies, the combination of LANRA and the FLT3 inhibitor gilteritinib demonstrated strong antileukemic effects ex vivo, resulting in deeper responses, and extended overall survival in FLT3 ITD-driven AML patient-derived xenograft mouse models. LANRA in combination with gilteritinib is currently being evaluated in patients with R/R FLT3 mut AML in the KB-LANRA 1001 trial (NCT05028751). Study Design and Methods: KB-LANRA 1001 is a global, multicenter, open-label phase 1b/2 trial designed to determine the safety and maximally tolerated and/or recommended phase 2 dose (MTD/RP2D) of LANRA in combination with standard dose gilteritinib (120 mg QD) in patients with R/R FLT3 mut AML. Secondary endpoints include evaluating pharmacokinetics (PK), pharmacodynamics (PD), and response evaluation (complete response (CR), CR with partial hematologic recovery (CRh), duration of response (DoR), event-free survival (EFS) and OS of the combination. Key exploratory endpoints include reduction of FLT3 mutvariant allele frequency among patients who achieve CR/CRh, correlation with selected baseline biomarkers that may predict efficacy outcomes, and assessment of LANRA PD properties (including target engagement). Eligibility requirements include documented FLT3 mut (ITD, tyrosine kinase domain [TKD] or both), age ≥18, and receipt of at least 1 prior therapy. Oral LANRA + gilteritinib will be administered daily until progression/relapse, intolerance, or failure to achieve at least a partial response (PR) after 6 cycles. The phase 1b component will follow a 3+3 dose escalation design. A dose-escalation committee (DEC) will decide LANRA dose escalation based on prospectively defined definitions of dose-limiting toxicity and safety metrics. Enrollment of additional patients to dose cohort(s) previously cleared for safety and tolerability by the DEC will be allowed under specific conditions. The phase 2 component will further evaluate safety, PK, PD, and anti-leukemic activity of the combination at the LANRA RP2D

A key role for platelet GPVI in neutrophil recruitment, migration, and NETosis in the early stages of acute lung injury

AbstractAcute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are associated with high morbidity and mortality. Excessive neutrophil infiltration into the pulmonary airspace is the main cause for the acute inflammation and lung injury. Platelets have been implicated in the pathogenesis of ALI/ARDS, but the underlying mechanisms are not fully understood. Here, we show that the immunoreceptor tyrosine-based activation motif–coupled immunoglobulin-like platelet receptor, glycoprotein VI (GPVI), plays a key role in the early phase of pulmonary thrombo-inflammation in a model of lipopolysaccharide (LPS)-induced ALI in mice. In wild-type (WT) control mice, intranasal LPS application triggered severe pulmonary and blood neutrophilia, hypothermia, and increased blood lactate levels. In contrast, GPVI-deficient mice as well as anti-GPVI–treated WT mice were markedly protected from pulmonary and systemic compromises and showed no increased pulmonary bleeding. High-resolution multicolor microscopy of lung sections and intravital confocal microcopy of the ventilated lung revealed that anti-GPVI treatment resulted in less stable platelet interactions with neutrophils and overall reduced platelet–neutrophil complex (PNC) formation. Anti-GPVI treatment also reduced neutrophil crawling and adhesion on endothelial cells, resulting in reduced neutrophil transmigration and alveolar infiltrates. Remarkably, neutrophil activation was also diminished in anti-GPVI–treated animals, associated with strongly reduced formation of PNC clusters and neutrophil extracellular traps (NETs) compared with that in control mice. These results establish GPVI as a key mediator of neutrophil recruitment, PNC formation, and NET formation (ie, NETosis) in experimental ALI. Thus, GPVI inhibition might be a promising strategy to reduce the acute pulmonary inflammation that causes ALI/ARDS.

A Phase I Study of CD19‐targeted 19(T2)28z1xx CAR T Cells in Adult Patients with Relapsed or Refractory Diffuse Large B‐cell Lymphoma

Background: The redundancy of CD28 and CD3 signaling in a CAR design incorporating all 3 immunoreceptor tyrosine-based activation motifs (ITAMs) might negatively affect T cell differentiation and promote exhaustion. Therefore, we created a novel CD19 CAR construct with calibrated CAR signaling potential by mutating 2 of the 3 ITAMs, termed 1XX. In mouse models, 19-28z1XX CAR successfully induced tumor eradication at low CAR T cell doses with improved survival compared to conventional 19-28z CAR and with enhanced persistence of functional CAR T cells. We report on adult pts with DLBCL treated with 19(T2)28z-1XX CAR T cells (NCT04464200). Methods: This is a single center, phase I, dose-escalation and expansion trial of 19(T2)28z1XX CAR T cells in adult pts with R/R DLBCL. Pts received lymphodepleting chemotherapy followed by escalating doses of CAR T cells: 25–200 × 106. The primary objective was to evaluate safety and tolerability and determine the recommended phase 2 dose. Secondary objectives include overall response rate and duration of response. Results: Sixteen pts were treated on the dose escalation phase of the study. Median age was 62 (range, 50–80), and median number of prior treatments was 2 (range, 1–5). 4, 6, 3 and 3 pts were treated at DL1, DL2, DL3 and DL4 CAR T cells, respectively. 15 pts (94%) experienced cytokine release syndrome (CRS): grade 1 (n = 9), grade 2 (n = 6). No pts experienced ≥ grade 3 CRS. Two pts (13%) experienced neurotoxicity (NTX): 1 pt with grade 1 and 1 pt with grade 3. NTX was transient and reversible in both cases.Ten of 16 pts (63%) achieved a complete response (CR) and 2 pts (13%) achieved a partial response (PR), with overall response rate (ORR) of 75%. One pt who achieved initial PR spontaneously converted to CR without further treatment after month 6, resulting in best CR rate of 69%. Responses were seen across all dose levels. With a median follow-up of 155 days (range, 33–667), no pt in CR has experienced relapse including 7 pts with >6 months of follow-up (Figure 1). Peak CAR T cell expansion occurred at a median of 14 days after CAR T cell infusion (range, 7–83.3 days). CAR T cell detection beyond 350 days has been noted. DL 1 (25 × 10e6 cells) was chosen as the recommended dose for the expansion phase. Updated responses in the dose escalation cohort and the full expansion cohort, as well as PK data, will be presented. Conclusions: Treatment with 19(T2)28z1XX CAR T cells was safe. No severe CRS was observed and only 1 pt experienced transient grade 3 NTX. The overall CR rate was 69% and durable with no relapse observed with a median follow-up of 155 days. CRs were observed at DL1, which was chosen for the expansion phase. These findings corroborate our preclinical data and suggest that the 1XX signaling domain may lead to enhanced efficacy of CD19 CAR and allow infusion of a lower T cell dose with favorable toxicity profile. Keyword: Cellular therapies Conflicts of interests pertinent to the abstract. M. L. Palomba Consultant or advisory role: Synthekine, Cellectar, Kite, Bristol Meyer Squibb I. Riviere Consultant or advisory role: Fate Therapeutics, Akron Biotechnology Stock ownership: Mnemo Therapeutics, J. Li Employment or leadership position: Takeda L. Sellner Employment or leadership position: Takeda M. Sadelain Consultant or advisory role: Atara Research funding: Takeda, Mnemo Therapeutics S. Chen Employment or leadership position: Takeda Y. Zhao Employment or leadership position: Takeda J. H. Park Consultant or advisory role: Novartis, Kite, Kura, Astra-Zeneca, Servier, Curocell, Intella, Autolus, Allogene, Affymmune, Amgen Research funding: Genentech