Ultra-Deep Sequencing Reveals the Mutational Landscape of Classical Hodgkin Lymphoma

The malignant Hodgkin and Reed Sternberg (HRS) cells of classical Hodgkin lymphoma (cHL) are scarce in affected lymph nodes, creating a challenge to detect driver somatic mutations. As an alternative to cell purification techniques, we hypothesized that ultra-deep exome sequencing would allow genomic study of HRS cells, thereby streamlining analysis and avoiding technical pitfalls. To test this, 31 cHL tumor/normal pairs were exome sequenced to approximately 1,000× median depth of coverage. An orthogonal error-corrected sequencing approach verified >95% of the discovered mutations. We identified mutations in genes novel to cHL including: CDH5 and PCDH7, novel stop gain mutations in IL4R, and a novel pattern of recurrent mutations in pathways regulating Hippo signaling. As a further application of our exome sequencing, we attempted to identify expressed somatic single-nucleotide variants (SNV) in single-nuclei RNA sequencing (snRNA-seq) data generated from a patient in our cohort. Our snRNA analysis identified a clear cluster of cells containing a somatic SNV identified in our deep exome data. This cluster has differentially expressed genes that are consistent with genes known to be dysregulated in HRS cells (e.g., PIM1 and PIM3). The cluster also contains cells with an expanded B-cell clonotype further supporting a malignant phenotype. This study provides proof-of-principle that ultra-deep exome sequencing can be utilized to identify recurrent mutations in HRS cells and demonstrates the feasibility of snRNA-seq in the context of cHL. These studies provide the foundation for the further analysis of genomic variants in large cohorts of patients with cHL.

SIGNIFICANCE

Our data demonstrate the utility of ultra-deep exome sequencing in uncovering somatic variants in Hodgkin lymphoma, creating new opportunities to define the genes that are recurrently mutated in this disease. We also show for the first time the successful application of snRNA-seq in Hodgkin lymphoma and describe the expression profile of a putative cluster of HRS cells in a single patient.

Learning to Fly

In this narrative medicine essay, an infectious diseases fellow understands while grieving her father that care cannot always be measured in cure but rather in listening and loving.

T-BET and EOMES sustain mature human NK cell identity and antitumor function

Since the T-box transcription factors (TFs) T-BET and EOMES are necessary for initiation of NK cell development, their ongoing requirement for mature NK cell homeostasis, function, and molecular programming remains unclear. To address this, T-BET and EOMES were deleted in unexpanded primary human NK cells using CRISPR/Cas9. Deleting these TFs compromised in vivo antitumor response of human NK cells. Mechanistically, T-BET and EOMES were required for normal NK cell proliferation and persistence in vivo. NK cells lacking T-BET and EOMES also exhibited defective responses to cytokine stimulation. Single-cell RNA-Seq revealed a specific T-box transcriptional program in human NK cells, which was rapidly lost following T-BET and EOMES deletion. Further, T-BET- and EOMES-deleted CD56bright NK cells acquired an innate lymphoid cell precursor-like (ILCP-like) profile with increased expression of the ILC-3-associated TFs RORC and AHR, revealing a role for T-box TFs in maintaining mature NK cell phenotypes and an unexpected role of suppressing alternative ILC lineages. Our study reveals the critical importance of sustained EOMES and T-BET expression to orchestrate mature NK cell function and identity.

A novel fusion protein scaffold 18/12/TxM activates the IL-12, IL-15, and IL-18 receptors to induce human memory-like natural killer cells

Natural killer (NK) cells are cytotoxic innate lymphoid cells that are emerging as a cellular immunotherapy for various malignancies. NK cells are particularly dependent on interleukin (IL)-15 for their survival, proliferation, and cytotoxic function. NK cells differentiate into memory-like cells with enhanced effector function after a brief activation with IL-12, IL-15, and IL-18. N-803 is an IL-15 superagonist composed of an IL-15 mutant (IL-15N72D) bound to the sushi domain of IL-15Rα fused to the Fc region of IgG1, which results in physiological trans-presentation of IL-15. Here, we describe the creation of a novel triple-cytokine fusion molecule, 18/12/TxM, using the N-803 scaffold fused to IL-18 via the IL-15N72D domain and linked to a heteromeric single-chain IL-12 p70 by the sushi domain of the IL-15Rα. This molecule displays trispecific cytokine activity through its binding and signaling through the individual cytokine receptors. Compared with activation with the individual cytokines, 18/12/TxM induces similar short-term activation and memory-like differentiation of NK cells on both the transcriptional and protein level and identical in vitro and in vivo anti-tumor activity. Thus, N-803 can be modified as a functional scaffold for the creation of cytokine immunotherapies with multiple receptor specificities to activate NK cells for adoptive cellular therapy.

A Fusion Protein Complex that Combines IL-12, IL-15, and IL-18 Signaling to Induce Memory-Like NK Cells for Cancer Immunotherapy

Natural killer (NK) cells are a promising cellular therapy for cancer, with challenges in the field including persistence, functional activity, and tumor recognition. Briefly, priming blood NK cells with recombinant human (rh)IL-12, rhIL-15, and rhIL-18 (12/15/18) results in memory-like NK cell differentiation and enhanced responses against cancer. However, the lack of available, scalable Good Manufacturing Process (GMP)-grade reagents required to advance this approach beyond early-phase clinical trials is limiting. To address this challenge, we developed a novel platform centered upon an inert tissue factor scaffold for production of heteromeric fusion protein complexes (HFPC). The first use of this platform combined IL-12, IL-15, and IL-18 receptor engagement (HCW9201), and the second adds CD16 engagement (HCW9207). This unique HFPC expression platform was scalable with equivalent protein quality characteristics in small- and GMP-scale production. HCW9201 and HCW9207 stimulated activation and proliferation signals in NK cells, but HCW9207 had decreased IL-18 receptor signaling. RNA sequencing and multidimensional mass cytometry revealed parallels between HCW9201 and 12/15/18. HCW9201 stimulation improved NK cell metabolic fitness and resulted in the DNA methylation remodeling characteristic of memory-like differentiation. HCW9201 and 12/15/18 primed similar increases in short-term and memory-like NK cell cytotoxicity and IFNγ production against leukemia targets, as well as equivalent control of leukemia in NSG mice. Thus, HFPCs represent a protein engineering approach that solves many problems associated with multisignal receptor engagement on immune cells, and HCW9201-primed NK cells can be advanced as an ideal approach for clinical GMP-grade memory-like NK cell production for cancer therapy.

Reliance on Cox10 and oxidative metabolism for antigen-specific NK cell expansion

Natural killer (NK) cell effector functions are dependent on metabolic regulation of cellular function; however, less is known about in vivo metabolic pathways required for NK cell antiviral function. Mice with an inducible NK-specific deletion of Cox10, which encodes a component of electron transport chain complex IV, were generated to investigate the role of oxidative phosphorylation in NK cells during murine cytomegalovirus (MCMV) infection. Ncr1-Cox10Δ/Δ mice had normal numbers of NK cells but impaired expansion of antigen-specific Ly49H+ NK cells and impaired NK cell memory formation. Proliferation in vitro and homeostatic expansion were intact, indicating a specific metabolic requirement for antigen-driven proliferation. Cox10-deficient NK cells upregulated glycolysis, associated with increased AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) activation, although this was insufficient to protect the host. These data demonstrate that oxidative metabolism is required for NK cell antiviral responses in vivo.

T-box transcription factors Eomes and T-bet regulate primary human NK cell IFNγ response and in vivo persistence

T-box transcription factors (TF) Eomes and T-bet are vital for NK cell development. However, their role in mature NK cell homeostasis and function remains unclear. Recently we reported that Eomes regulates mouse NK cell cytotoxicity and stage-specific survival using an NK-specific, tamoxifen-inducible Eomes KO model. However, the role of Eomes and T-bet have not been investigated in primary human NK (hNK) cell biology using genetic loss-of-function approaches. We hypothesized that these TFs play a critical role in maintaining NK cell functional molecular programs.

Here we used CRISPR-Cas9 to genetically delete Eomes and T-bet expression in primary hNK cells. In vitro stimulation assays revealed that IFNγ response is impaired in CD56bright NK cells only when Eomes is deleted (p<0.01) but not T-bet. This impairment is even more striking when both TFs are deleted, resulting in both CD56bright and CD56dim NK cells having reduced IFNγ (p<0.01 and p<0.05, respectively).

Using NSG xenografts, we found that Eomes/T-bet double CRISPR-edited (DKO) hNK cells have impaired persistence/expansion in vivo. After 3 weeks, we recovered in the spleen on average 3E5 control compared to only 6E4 DKO hNK cells. A similar ~80% decrease was also observed in the blood. To determine the mechanism of this, we assessed proliferation and apoptosis of control compared to DKO cells. Ki-67 and dye dilution revealed impaired proliferation of DKO cells in vivo, and we also observed increased apoptosis measured by Annexin V/7-AAD staining (p<0.05).

Our data suggest that Eomes and T-bet are critical for the function and homeostasis of mature hNK cells. Understanding their function in mature NK cells will provide insights to improve NK cell therapy for diseases such as cancer.

Phase I Trial of N-803, an IL15 Receptor Agonist, with Rituximab in Patients with Indolent Non-Hodgkin Lymphoma

PURPOSE

N-803 is an IL15 receptor superagonist complex, designed to optimize in vivo persistence and trans-presentation, thereby activating and expanding natural killer (NK) cells and CD8⁺ T cells. Monoclonal antibodies (mAbs) direct Fc receptor-bearing immune cells, including NK cells, to recognize and eliminate cancer targets. The ability of IL15R agonists to enhance tumor-targeting mAbs in patients has not been reported previously.

PATIENTS AND METHODS

Relapsed/refractory patients with indolent non-Hodgkin lymphoma were treated with rituximab and intravenous or subcutaneous N-803 on an open-label, dose-escalation phase I study using a 3+3 design (NCT02384954). Primary endpoint was maximum tolerated dose. Immune correlates were performed using multidimensional analysis via mass cytometry and cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq) which simultaneously measures protein and single-cell RNA expression.

RESULTS

This immunotherapy combination was safe and well tolerated and resulted in durable clinical responses including in rituximab-refractory patients. Subcutaneous N-803 plus rituximab induced sustained proliferation, expansion, and activation of peripheral blood NK cells and CD8 T cells, with increased NK cell and T cells present 8 weeks following last N-803 treatment. CITE-seq revealed a therapy-altered NK cell molecular program, including enhancement of AP-1 transcription factor. Furthermore, the monocyte transcriptional program was remodeled with enhanced MHC expression and antigen-presentation genes.

CONCLUSIONS

N-803 combines with mAbs to enhance tumor targeting in patients, and warrants further investigation in combination with immunotherapies.

Flow cytometry-based ex vivo murine NK cell cytotoxicity assay

Direct killing of diseased cells is a hallmark function of NK cells. This protocol describes a flow-based assay to measure in vivo activated murine NK cells’ ability to kill target cells ex vivo. Existing published protocols for assaying ex vivo NK cell killing utilized the radioactive chromium release assay or were designed for human NK cells. This protocol details specifically an ex vivo cytotoxicity assay using primary murine NK cells enriched from splenocytes that were activated in vivo with poly(I:C).

For complete details on the use and execution of this protocol, please refer to Wagner et al. (2020).

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This protocol describes a flow-based assay to assess mouse NK cell killing ex vivo

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Protocol details the procedure for enriching NK cells from mouse splenocytes

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In vivo poly(I:C) activated NK cells are used as effectors to kill labeled targets

Multidimensional Analyses of Donor Memory-Like NK Cells Reveal New Associations with Response after Adoptive Immunotherapy for Leukemia

Natural killer (NK) cells are an emerging cancer cellular therapy and potent mediators of antitumor immunity. Cytokine-induced memory-like (ML) NK cellular therapy is safe and induces remissions in patients with acute myeloid leukemia (AML). However, the dynamic changes in phenotype that occur after NK-cell transfer that affect patient outcomes remain unclear. Here, we report comprehensive multidimensional correlates from ML NK cell-treated patients with AML using mass cytometry. These data identify a unique in vivo differentiated ML NK-cell phenotype distinct from conventional NK cells. Moreover, the inhibitory receptor NKG2A is a dominant, transcriptionally induced checkpoint important for ML, but not conventional NK-cell responses to cancer. The frequency of CD8α⁺ donor NK cells is negatively associated with AML patient outcomes after ML NK therapy. Thus, elucidating the multidimensional dynamics of donor ML NK cells in vivo revealed critical factors important for clinical response, and new avenues to enhance NK-cell therapeutics. SIGNIFICANCE: Mass cytometry reveals an in vivo memory-like NK-cell phenotype, where NKG2A is a dominant checkpoint, and CD8α is associated with treatment failure after ML NK-cell therapy. These findings identify multiple avenues for optimizing ML NK-cell immunotherapy for cancer and define mechanisms important for ML NK-cell function.This article is highlighted in the In This Issue feature, p. 1775.

The IL-15 receptor agonist N-803 combined with the anti-CD20 monoclonal antibody rituximab expands NK and CD8 T cells and alters single cell immune transcriptomes in a phase 1 clinical trial in lymphoma

IL-15 is a cytokine that is crucial for the development, survival, and activation of NK cells, and pre-clinical studies demonstrated that IL-15 augments antibody-dependent cellular cytotoxicity. We hypothesized that IL-15 would augment anti-CD20 mAb (rituximab)-directed responses in patients with indolent non-Hodgkin’s lymphoma. To address this, we performed a first-in-human combination clinical trial of the IL-15 super agonist N-803 with rituximab, and investigated the impact of this novel immune combination on NK, CD8 T cells, and monocytes. The combination was safe and demonstrated clinical activity, including in patients refractory to rituximab. To understand the in vivo impact on the patients’ immune systems, we performed mass cytometry and cellular indexing of transcriptomes and epitopes by sequencing (CITE-seq), which measures single-cell RNA-seq and cell surface proteins simultaneously. N-803 induced expansion of NK (12.5-fold) and CD8 T cells (2-fold) in serial blood samples and upregulated CD38, chemokines, and MHC class II family member expression while maintaining CD16 expression on NK. On CD56dim NK, N-803 increased activating receptors, decreased CD57, and modulated transcription factor expression (AP-1, Eomes, CEBPB/D). CD56bright NK cells were primed, with increases in granzyme A, B, and K. Therapy also markedly altered the monocyte compartment, significantly upregulating type 1 interferon and interferon gamma pathways in CD14+ monocytes, and decreased the percent of CD16+ monocytes, suggestive of potential trafficking to the tumor. Collectively, our data demonstrates that N-803 plus rituximab induces complex immune activation, and supports N-803 combination with other mAbs and immunotherapies.

Potently Cytotoxic Natural Killer Cells Initially Emerge from Erythro-Myeloid Progenitors during Mammalian Development

Natural killer (NK) cells are a critical component of the innate immune system. However, their ontogenic origin has remained unclear. Here, we report that NK cell potential first arises from Hoxaneg/low Kit+CD41+CD16/32+ hematopoietic-stem-cell (HSC)-independent erythro-myeloid progenitors (EMPs) present in the murine yolk sac. EMP-derived NK cells and primary fetal NK cells, unlike their adult counterparts, exhibit robust degranulation in response to stimulation. Parallel studies using human pluripotent stem cells (hPSCs) revealed that HOXAneg/low CD34+ progenitors give rise to NK cells that, similar to murine EMP-derived NK cells, harbor a potent cytotoxic degranulation bias. In contrast, hPSC-derived HOXA+ CD34+ progenitors, as well as human cord blood CD34+ cells, give rise to NK cells that exhibit an attenuated degranulation response but robustly produce inflammatory cytokines. Collectively, our studies identify an extra-embryonic origin of potently cytotoxic NK cells, suggesting that ontogenic origin is a relevant factor in designing hPSC-derived adoptive immunotherapies.

Monetary reinforcement for self-monitoring of blood glucose among young people with type 1 diabetes: evaluating effects on psychosocial functioning

AIMS

To explore the auxiliary psychosocial effects of a monetary reinforcement intervention targeting self-monitoring of blood glucose among young people with Type 1 diabetes.

METHODS

Sixty young people with Type 1 diabetes, HbA_1c concentrations between 58 and 119 mmol/mol (7.5-13.0%), and average self-monitoring of blood glucose <4 times per day were randomized to either enhanced usual care or a 24-week intervention of monetary rewards for self-monitoring of blood glucose and associated behaviours (e.g. uploading glucose meters). Data were collected from the young people and their parents at baseline, during the intervention (6, 12 and 24 weeks) and after the intervention (36 weeks).

RESULTS

Linear mixed models were used to evaluate the intervention effects on psychosocial outcomes, adjusting for corresponding baseline levels and potential moderation by baseline level. The intervention reduced diabetes distress at week 6 among young people who had average and high baseline distress. It also reduced diabetes distress at weeks 12 and 24 among those with low baseline distress. The intervention also reduced young person-reported diabetes-related family conflict and diabetes-related interference among those with high baseline scores in these areas; however, the intervention worsened young person-reported diabetes interference among those with low baseline interference. Effects were medium-sized and time-limited.

CONCLUSIONS

Findings indicate predominantly positive impacts of monetary reinforcement interventions on psychosocial outcomes, although effects varied by outcome and time point. Whereas early improvements in diabetes distress were observed for all who received the intervention, improvements in other areas varied according to the level of psychosocial challenge at baseline. Incorporating psychosocial interventions may bolster and maintain effects over time.

Blood natural killer cell deficiency reveals an immunotherapy strategy for atopic dermatitis

Atopic dermatitis (AD) is a widespread, chronic skin disease associated with aberrant allergic inflammation. Current treatments involve either broad or targeted immunosuppression strategies. However, enhancing the immune system to control disease remains untested. We demonstrate that patients with AD harbor a blood natural killer (NK) cell deficiency that both has diagnostic value and improves with therapy. Multidimensional protein and RNA profiling revealed subset-level changes associated with enhanced NK cell death. Murine NK cell deficiency was associated with enhanced type 2 inflammation in the skin, suggesting that NK cells play a critical immunoregulatory role in this context. On the basis of these findings, we used an NK cell-boosting interleukin-15 (IL-15) superagonist and observed marked improvement in AD-like disease in mice. These findings reveal a previously unrecognized application of IL-15 superagonism, currently in development for cancer immunotherapy, as an immunotherapeutic strategy for AD.

MicroRNA-142 Is Critical for the Homeostasis and Function of Type 1 Innate Lymphoid Cells

Natural killer (NK) cells are cytotoxic type 1 innate lymphoid cells (ILCs) that defend against viruses and mediate anti-tumor responses, yet mechanisms controlling their development and function remain incompletely understood. We hypothesized that the abundantly expressed microRNA-142 (miR-142) is a critical regulator of type 1 ILC biology. Interleukin-15 (IL-15) signaling induced miR-142 expression, whereas global and ILC-specific miR-142-deficient mice exhibited a cell-intrinsic loss of NK cells. Death of NK cells resulted from diminished IL-15 receptor signaling within miR-142-deficient mice, likely via reduced suppressor of cytokine signaling-1 (Socs1) regulation by miR-142-5p. ILCs persisting in Mir142^-/- mice demonstrated increased expression of the miR-142-3p target αV integrin, which supported their survival. Global miR-142-deficient mice exhibited an expansion of ILC1-like cells concurrent with increased transforming growth factor-β (TGF-β) signaling. Further, miR-142-deficient mice had reduced NK-cell-dependent function and increased susceptibility to murine cytomegalovirus (MCMV) infection. Thus, miR-142 critically integrates environmental cues for proper type 1 ILC homeostasis and defense against viral infection.

Abstract 1546: The CD30/CD16A bispecific innate immune cell engager AFM13 elicits heterogeneous single-cell NK cell responses and effectively triggers memory-like (ML) NK cells

Natural killer (NK) cells are crucial effector cells of the innate immune system capable of rapidly recognizing and eliminating infected, stressed and malignant cells. NK cells discriminate tumor targets from healthy cells via integration of activating and inhibitory receptor signals. One barrier to the broad application of NK cells across many cancer types is inconsistent cancer cell recognition, which may be overcome by immune cell engagers. AFM13 is a tetravalent bispecific antibody based on the ROCK platform characterized by bivalent binding to CD30 and CD16A with clinical efficacy in CD30+ malignancies. However, our understanding of NK cell functional responses triggered via AFM13 remain incomplete. Moreover, adoptively transferred memory-like (ML) NK cells have demonstrated enhanced anti-tumor activity (Romee R et al, Sci Transl Med, 2016) that may be receptive to AFM13-based targeting to enhance target cell recognition. To address these questions, we analyzed single-cell conventional (cNK) and ML (IL-12/15/18-induced) NK cell functional responses to NK-resistant CD30+ lymphoma cells +/- AFM13. Primary cNK cells co-incubated with AFM13-treated Hut-78 cells demonstrated increased IFN-γ, TNF, and degranulation, compared to Hut-78 cells or Raji (CD30-) targets + AFM13 as a negative control (p&lt;0.05). To define the single-cell specificity of NK cell responses to AFM13, similar assays were performed using mass cytometry analysis of 39 lineage, maturation, activating and inhibitory receptors, and function-relevant NK cell markers. tSNE-based multidimensional analyses revealed marked distinctions between Hut-78 and AFM13-Hut-78 stimulated cNK cells, due in part to IFN-γ, MIP-1α, CD107a, and CD16. To define the impact of specific NK receptors, SPADE was used to define highly activated IFN-γ+ NK cell sub-populations. In a KIR3DL1+ donor, activation was primarily within the KIR3DL1+ subset, consistent with the lack of its inhibitory ligand (HLA-Bw4). In KIR3DL1 negative donors, responding NK cells were enriched in mature KIR2DL2/L3+CD57+ NK cells that lacked NKG2A. Additional experiments revealed that both control and ML NK cells exhibited increased IFN-γ, degranulation, and cytotoxicity with AFM13 (P&lt;0.01), and AFM13-stimulated ML NK cells exhibited the highest IFN-γ response and killing. Collectively, these data indicate that target cell recognition of NK cells can be significantly enhanced by AFM13, yet influenced by inhibitory receptor expression, maturation state, and memory-like differentiation. Thus, these data suggest that the status and repertoire of NK cells in a patient may offer diagnostic potential for therapeutic response, and the combination of ML NK cells with AFM13 appears to be a promising therapeutic approach.

Citation Format: Nancy Marin, Michelle Becker-Hapak, Joachim Koch, Melissa M. Berrien-Elliott, Mark Foster, Carly Neal, Ethan McClain, Sweta Desai, Julia A. Wagner, Timothy Schappe, Lynne Marsala, Pamela Wong, Martin Treder, Todd A. Fehniger. The CD30/CD16A bispecific innate immune cell engager AFM13 elicits heterogeneous single-cell NK cell responses and effectively triggers memory-like (ML) NK cells [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 1546.

Abstract 5704: Mass cytometry identifies the expansion, persistence, and immune checkpoints of adoptively transferred memory-like NK cells in patients with leukemia

NK cells are an emerging cell therapy for cancer, however, the optimal approaches to maximize NK cell anti-tumor attack are unclear. NK cells exhibit memory-like (ML) properties following combined cytokine (IL-12/15/18) pre-activation, evidenced by enhanced responses to cancer cells upon re-stimulation weeks later. A first-in-human clinical trial for acute myeloid leukemia (AML) (Romee R et al., Sci Transl Med, 2016) revealed that 7 of 11 (54%) evaluable patients responded to ML NK cell therapy. To inform key aspects of response, we used mass cytometry to track ML NK cell diversity, checkpoints, and effector functions in AML patients treated with ML NK cells. Multidimensional analyses (viSNE) of patient samples collected 7 days after NK transfer accurately identified in vivo-differentiated ML NK cells that were distinct from conventional NK (cNK) cells: CD56hiCD11bloCD62L+ NKG2AhiNKp30hi Ki-67+ (cNK: 3%±0.5% vs. ML: 87%±5%, mean±SEM within ML gate, P&lt;0.05, N=10). In a second clinical trial of MHC-haploidentical hematopoietic transplantation (HCT), augmented with same-donor IL-12/15/18 activated NK cells (NCT02782546), mass cytometry identified marked ML NK cell expansion in vivo in this immune-compatible environment. In the first two patients treated, ML NK cells expanded (&gt;1000-fold expansion in vivo, peak &gt;2000 cells/uL blood), persisted &gt;= 60 days, and were distinct from immature CD56brightKIR-CD16- NK cells developing from the graft. These ML NK cells exhibited potent anti-leukemic functional responses at day +28. Utilizing the phase 1 study cohort, Citrus analysis identified increased NKG2A expression as significantly correlated with treatment failure [median NKG2A = 89±25 (treatment failure); 8±3 (clinical response); p=0.007, FDR&lt;0.1]. NKG2A is an inhibitory receptor that binds to non-classical MHC HLA-E expressed on AML. We hypothesized that NKG2A/HLA-E interactions in vivo represent a key checkpoint on ML NK cell responses. Consistent with this idea, HLA-Ehi AML blasts resulted in reduced ML NK cells responses (P&lt;0.05) in vitro. ML NK cells also triggered with HLA-E+ K562-AML in the presence of control or anti-NKG2A blocking antibodies. Increased functional responses including IFN-γ (p=0.02) and TNF (p=0.05) production by NKG2A-blocked ML NK cells were detected, compared to isotype-treated ML NK cells. Similar results were observed with HLA-E+ primary AML blasts as targets, showing that ML NK cells treated with NKG2A blockade produced significantly more IFN-γ (p=0.001). Thus, mass cytometry identified that in vivo-differentiated ML NK cells are distinct from cNK cells, and exhibit marked expansion and persistence in an immune-compatible environment. NKG2A was identified as a key ML NK cell checkpoint in vivo, and blockade of NKG2A signals may enhance the clinical efficacy of ML NK cell therapy for AML patients.

Citation Format: Melissa M. Berrien-Elliott, Julia A. Wagner, Rizwan Romee, Michelle Becker-Hapak, Timothy Schappe, Carly Neal, Ethan McClain, John DiPersio, Peter Westervelt, Amanda F. Cashen, Todd A. Fehniger. Mass cytometry identifies the expansion, persistence, and immune checkpoints of adoptively transferred memory-like NK cells in patients with leukemia [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5704.

Cytokine-induced memory-like natural killer cells exhibit enhanced responses against myeloid leukemia

Natural killer (NK) cells are an emerging cellular immunotherapy for patients with acute myeloid leukemia (AML); however, the best approach to maximize NK cell antileukemia potential is unclear. Cytokine-induced memory-like NK cells differentiate after a brief preactivation with interleukin-12 (IL-12), IL-15, and IL-18 and exhibit enhanced responses to cytokine or activating receptor restimulation for weeks to months after preactivation. We hypothesized that memory-like NK cells exhibit enhanced antileukemia functionality. We demonstrated that human memory-like NK cells have enhanced interferon-γ production and cytotoxicity against leukemia cell lines or primary human AML blasts in vitro. Using mass cytometry, we found that memory-like NK cell functional responses were triggered against primary AML blasts, regardless of killer cell immunoglobulin-like receptor (KIR) to KIR-ligand interactions. In addition, multidimensional analyses identified distinct phenotypes of control and memory-like NK cells from the same individuals. Human memory-like NK cells xenografted into mice substantially reduced AML burden in vivo and improved overall survival. In the context of a first-in-human phase 1 clinical trial, adoptively transferred memory-like NK cells proliferated and expanded in AML patients and demonstrated robust responses against leukemia targets. Clinical responses were observed in five of nine evaluable patients, including four complete remissions. Thus, harnessing cytokine-induced memory-like NK cell responses represents a promising translational immunotherapy approach for patients with AML.

CD56bright NK cells exhibit potent antitumor responses following IL-15 priming

NK cells, lymphocytes of the innate immune system, are important for defense against infectious pathogens and cancer. Classically, the CD56dim NK cell subset is thought to mediate antitumor responses, whereas the CD56bright subset is involved in immunomodulation. Here, we challenge this paradigm by demonstrating that brief priming with IL-15 markedly enhanced the antitumor response of CD56bright NK cells. Priming improved multiple CD56bright cell functions: degranulation, cytotoxicity, and cytokine production. Primed CD56bright cells from leukemia patients demonstrated enhanced responses to autologous blasts in vitro, and primed CD56bright cells controlled leukemia cells in vivo in a murine xenograft model. Primed CD56bright cells from multiple myeloma (MM) patients displayed superior responses to autologous myeloma targets, and furthermore, CD56bright NK cells from MM patients primed with the IL-15 receptor agonist ALT-803 in vivo displayed enhanced ex vivo functional responses to MM targets. Effector mechanisms contributing to IL-15-based priming included improved cytotoxic protein expression, target cell conjugation, and LFA-1-, CD2-, and NKG2D-dependent activation of NK cells. Finally, IL-15 robustly stimulated the PI3K/Akt/mTOR and MEK/ERK pathways in CD56bright compared with CD56dim NK cells, and blockade of these pathways attenuated antitumor responses. These findings identify CD56bright NK cells as potent antitumor effectors that warrant further investigation as a cancer immunotherapy.

Cytokine-Induced Memory-Like Differentiation Enhances Unlicensed Natural Killer Cell Antileukemia and FcγRIIIa-Triggered Responses

Cytokine-induced memory-like natural killer (NK) cells differentiate after short-term preactivation with IL-12, IL-15, and IL-18 and display enhanced effector function in response to cytokines or tumor targets for weeks after the initial preactivation. Conventional NK cell function depends on a licensing signal, classically delivered by an inhibitory receptor engaging its cognate MHC class I ligand. How licensing status integrates with cytokine-induced memory-like NK cell responses is unknown. We investigated this interaction using killer cell immunoglobulin-like receptor- and HLA-genotyped primary human NK cells. Memory-like differentiation resulted in enhanced IFN-γ production triggered by leukemia targets or FcγRIIIa ligation within licensed NK cells, which exhibited the highest functionality of the NK cell subsets interrogated. IFN-γ production by unlicensed memory-like NK cells was also enhanced to a level comparable with that of licensed control NK cells. Mechanistically, differences in responses to FcγRIIIa-based triggering were not explained by alterations in key signaling intermediates, indicating that the underlying biology of memory-like NK cells is distinct from that of adaptive NK cells in human cytomegalovirus-positive individuals. Additionally, memory-like NK cells responded robustly to cytokine receptor restimulation with no impact of licensing status. These results demonstrate that both licensed and unlicensed memory-like NK cell populations have enhanced functionality, which may be translated to improve leukemia immunotherapy.

Human Adaptive Natural Killer Cells: Beyond NKG2C

Paradigm-shifting studies have identified NKG2C(+) adaptive natural killer (NK) cells in individuals infected with cytomegalovirus. Recently in Cell Reports, Liu et al. demonstrate that NKG2C(-/-) HCMV(+) individuals also generate adaptive NK cells, and reveal CD2 as a major co-stimulatory receptor for these NK cells specialized to respond via FcγRIIIa/CD16.

Mechanisms governing human memory-like natural killer cell function

Natural killer (NK) cells are innate lymphoid cells critical for host defense against viral infection and malignant transformation. NK cells exhibit innate immunologic memory in response to specific haptens, viruses, or combined cytokine pre-activation. Human cytokine-induced memory-like NK cells, generated by overnight pre-activation with IL-12, IL-15, and IL-18, respond more robustly to numerous stimuli (including leukemia target cells) for weeks to months following the initial activation. The mechanisms responsible for the enhanced effector function of human memory-like NK cells are poorly understood. We hypothesized that memory-like NK cell differentiation alters the balance of signal integration downstream of activating and inhibitory receptors. NK cells achieve functional competence through self-MHC class I interactions (licensing) during maturation; if this does not occur, NK cells remain anergic. We tested this hypothesis using normal donors with licensed and unlicensed NK cell populations. We observed that cytokine pre-activation increases IFN-γ production by both licensed and unlicensed NK cells in response to tumor targets, activating receptor (FcγRIIIa) ligation, or cytokine stimulation. In fact, in response to cytokine stimulation, memory-like NK cells produce significantly more IFN-γ than controls with no impact of licensing. We observed no difference in the expression level of several signaling adaptor molecules or in phospho-signaling downstream of FcγRIIIa ligation in memory-like vs. control NK cells. We are currently investigating epigenetic modification of the IFN-γ gene locus in memory-like NK cells as a potential mechanism for their enhanced function; updated results will be presented.

Transcriptional and post-transcriptional regulation of NK cell development and function

Natural killer (NK) cells are specialized innate lymphoid cells that survey against viral infections and malignancy. Numerous advances have improved our understanding of the molecular mechanisms that control NK cell development and function over the past decade. These include both studies on the regulatory effects of transcription factors and translational repression via microRNAs. In this review, we summarize our current knowledge of DNA-binding transcription factors that regulate gene expression and thereby orchestrate NK cell development and activation, with an emphasis on recent discoveries. Additionally, we highlight our understanding of how RNA-binding microRNAs fine tune the NK cell molecular program. We also underscore the large number of open questions in the field that are now being addressed using new technological approaches and genetically engineered model organisms. Ultimately, a deeper understanding of the basic molecular biology of NK cells will facilitate new strategies to manipulate NK cells for the treatment of human disease.

Memory NK Cells Take Out the (Mitochondrial) Garbage

The molecular mechanisms important to generate innate natural killer cell "memory" are poorly understood. In this issue of Immunity, O'Sullivan et al. (2015) demonstrate that mitophagy plays a critical role in natural killer cell memory formation following viral infection.

Measuring Biomarker Progress

A biomarker has been defined as "a characteristic that is objectively measured and evaluated as an indicator of normal biologic processes, pathogenic process, or pharmacologic responses to a therapeutic intervention." This comprehensive definition of biomarkers arose from the April 1999 US Food and Drug Administration (FDA)/National Institutes of Health consensus conference on "Biomarkers and Surrogate Endpoints: Advancing Clinical Research and Applications," and emphasized that biomarkers are medical measurements, including physiological measurements, blood tests, molecular analyses of biopsies, genetic or metabolic data, and measurements from images. Research on biomarkers-organized and propelled by this definition-has skyrocketed, with over 200,000 PubMed citations in the last five years.

Perceptions about professionally and non-professionally trained hypoglycemia detection dogs

AIMS

Patients with diabetes increasingly have questions about diabetes alert dogs. This study evaluated perceptions about dogs trained professionally or otherwise to detect glucose levels.

METHODS

A link to a survey about glucose detecting dogs was announced on diabetes websites.

RESULTS

135 persons responded, with 63 answering about their child with diabetes. Most respondents obtained their dog from a professional trainer (n = 54) or trained it themselves (n = 51). Owners of self- and professionally-trained dogs were very positive about dogs' abilities to alert them to low and high glucose levels, while owners of dogs that learned entirely on their own (n = 15) reported lower frequencies of alerts and more missed hypoglycemic episodes, p<.01. Regardless of how dogs learned, perceptions about managing diabetes were improved during periods of dog ownership relative to times without, p<.001. Self-reported rates of diabetes-related hospitalizations, assistance from others for treating hypoglycemia, and accidents or near accidents while driving reduced during periods of dog ownership compared to periods without dogs, ps<.01.

CONCLUSIONS

These data suggest potential effectiveness of and high satisfaction with glucose-detecting dogs. Clinicians can use these results to address pros and cons of dog ownership with patients who inquire about them.

Implications of the Institute of Medicine Report: Evaluation of Biomarkers and Surrogate Endpoints in Chronic Disease

The Institute of Medicine (IOM) released a groundbreaking 2010 report, Evaluation of Biomarkers and Surrogate Endpoints in Chronic Disease. Key recommendations included a harmonized scientific process and a general framework for biomarker evaluation with three interrelated steps: (1) Analytical validation -- is the biomarker measurement accurate? (2) Qualification -- is the biomarker associated with the clinical endpoint of concern? (3) Utilization -- what is the specific context of the proposed use?

Human Cytokine-Induced Memory-Like Natural Killer Cells

Natural killer (NK) cells are innate lymphoid cells that are important for host defense against infection and mediate antitumor responses. Recent reports from several laboratories have identified that NK cells can remember a prior activation event and consequently respond more robustly when restimulated, a property termed innate NK cell memory. NK cell memory has now been identified following hapten exposure, viral infection, and combined cytokine preactivation with IL-12, IL-15, and IL-18. Many questions in the field remain regarding the cellular and molecular mechanisms regulating memory NK cells and their responses, as well as their formation and function in mice and humans. Here we review our current understanding of cytokine-induced memory-like (CIML) NK cells that are generated by combined preactivation with IL-12, IL-15, and IL-18. These cells exhibit enhanced NK cell effector functions weeks after the initial cytokine preactivation. Further, we highlight the preclinical rationale and ongoing therapeutic application of CIML NK cells for adoptive immunotherapy in patients with hematologic malignancies.

First-to-patent does not predict first- or best-in-class: analysis of approved small molecule vs. biologic drugs

The biopharmaceutical enterprise continues to analyze, refine, and identify key strategic factors predicting success of innovative therapeutic advances to address important unmet medical needs. A key comparison has focused on the relative benefits of the novel mechanism of a first-in-class drug vs. the superior properties that differentiate improved follow-on drugs (best-in-class). A corollary question to first-in-class vs. best-in-class is the impact of patent timing. Surprisingly, first-to-patent does not predict first- or best-in-class.

Individual and Combined Effects of Peroxisome Proliferator-Activated Receptor α and γ Agonists, Fenofibrate and Rosiglitazone, on Biomarkers of Lipid and Glucose Metabolism in Healthy Nondiabetic Volunteers

This open-label, randomized, placebo-controlled, incomplete-block, 3-period crossover pilot study investigated the effects of peroxisome proliferator-activated receptor alpha- and gamma-agonists on biomarkers of lipid and glucose metabolism in 12 nondiabetic subjects. Plasma samples were collected before and after each 14-day treatment with placebo, fenofibrate (201 mg/d), rosiglitazone (4 mg twice daily), and combined fenofibrate (201 mg/d) plus rosiglitazone (4 mg twice daily). Except for triglycerides (P < .042) and free fatty acids (P < .074), no significant interaction was demonstrated between fenofibrate and rosiglitazone; thus, the effect due to each drug alone was evaluated (presence/absence of drug). Fenofibrate significantly (P < .050) increased lipoprotein lipase activity (35%) and decreased apolipoproteins B (13%) and C-III (20%). Rosiglitazone significantly (P < .050) decreased fasting glucose (7.3%) and increased apolipoprotein C-III (19%) and adiponectin (137%). Fenofibrate and rosiglitazone also produced effects on triglycerides and free fatty acids, but it was not possible to determine if these effects were synergistic in nature.

UGT2B17 genetic polymorphisms dramatically affect the pharmacokinetics of MK-7246 in healthy subjects in a first-in-human study

MK-7246, an antagonist of the chemoattractant receptor on T helper type 2 (Th2) cells, is being developed for the treatment of respiratory diseases. In a first-in-human study, we investigated whether genetic polymorphisms contributed to the marked intersubject variability in the pharmacokinetics of MK-7246 and its glucuronide metabolite M3. Results from in vitro enzyme kinetic studies suggested that UGT2B17 is probably the major enzyme responsible for MK-7246 metabolism in both the liver and the intestine. As compared with those with the UGT2B17*1/*1 wild-type genotype, UGT2B17*2/*2 carriers, who possess no UGT2B17 protein, had 25- and 82-fold greater mean dose-normalized values of area under the plasma concentration–time curve (AUC) and peak concentration of MK-7246, respectively, and a 24-fold lower M3-to-MK-7246 AUC ratio. The apparent half-life of MK-7246 was not as variable between these two genotypes. Therefore, the highly variable pharmacokinetics of MK-7246 is attributable primarily to the impact of UGT2B17 genetic polymorphisms and extensive first-pass metabolism of MK-7246.

[Necrotizing fasciitis caused by Acinetobacter baumannii : A case report]

A 42-year-old man developed necrotizing fasciitis on the right leg. A multidrug-resistant Acinetobacter baumannii was cultivated from the deep wound. Following therapy with imipenem and tobramycin as well as extensive debridement, the lesions improved slowly. A. baumannii is today an important cause of nosocomial infections, especially in intensive care units.

Rifampin's acute inhibitory and chronic inductive drug interactions: experimental and model-based approaches to drug-drug interaction trial design

We studied the time course for the reversal of rifampin's effect on the pharmacokinetics of oral midazolam (a cytochrome P450 (CYP) 3A4 substrate) and digoxin (a P-glycoprotein (P-gp) substrate). Rifampin increased midazolam metabolism, greatly reducing the area under the concentration-time curve (AUC(0-∞)). The midazolam AUC(0-∞) returned to baseline with a half-life of ~8 days. Rifampin's effect on the AUC(0-3 h) of digoxin was biphasic: the AUC(0-3 h) increased with concomitant dosing of the two drugs but decreased when digoxin was administered after rifampin. Digoxin was found to be a weak substrate of organic anion-transporting polypeptide (OATP) 1B3 in transfected cells. Although the drug was transported into isolated hepatocytes, it is not likely that this transport was through OATP1B3 because the transport was not inhibited by rifampin. However, rifampin did inhibit the P-gp-mediated transport of digoxin with a half-maximal inhibitory concentration (IC(50)) below anticipated gut lumen concentrations, suggesting that rifampin inhibits digoxin efflux from the enterocyte to the intestinal lumen. Pharmacokinetic modeling suggested that the effects on digoxin are consistent with a combination of inhibitory and inductive effects on gut P-gp. These results suggest modifications to drug-drug interaction (DDI) trial designs.

Lifetime depression and diabetes self-management in women with Type 2 diabetes: a case-control study

AIMS

Little is known about the association between lifetime history of major depressive disorder (L-MDD) and diabetes self-management, particularly when depression is remitted. We examined the association between L-MDD and diabetes self-management in women with Type 2 diabetes who were not depressed at the time of assessment.

METHODS

L-MDD was assessed with structured psychiatric interview. Participants completed paper-and-pencil measures of demographics, diabetes-related distress, self-care behaviours, healthcare utilization and diabetes self-efficacy.

RESULTS

One-hundred and fifty-three women participated; 41% had L-MDD. Compared with their never-depressed counterparts, women with L-MDD had more diabetes distress, reported lower overall rates of self-monitoring of blood glucose (SMBG) and greater tendency to skip SMBG, had lower diet adherence and were less likely to have seen a primary care provider in the past year. Diabetes self-efficacy mediated the relationship between L-MDD and self-management.

CONCLUSIONS

Interventions to promote self-management for patients with L-MDD may be warranted.

Drug development perspective on pharmacokinetic studies of new drugs in patients with renal impairment

Severe renal impairment can, through diverse mechanisms, alter the pharmacokinetics (PK) of drugs that are renally eliminated and even of some drugs that are nonrenally eliminated. Consequently, dose adjustment for new molecular entities in patients with renal insufficiency is a critical issue in drug development. Clinical pharmacology studies undertaken in patients with renal impairment are generally quite small. We therefore recommend that all pertinent pharmacokinetic data relating to subjects with different degrees of renal impairment and from different clinical trials, including population pharmacokinetic evaluation, form the basis for dosage recommendations in renal impairment. The Modification of Diet in Renal Disease (MDRD) equation has gained popularity for renal insufficiency classification, but traditional equations such as the Cockcroft-Gault (C-G) formula should enjoy continued use so as to avoid confusion, particularly for drugs for which dosing guidelines have previously been developed.

Utility of adiponectin as a biomarker predictive of glycemic efficacy is demonstrated by collaborative pooling of data from clinical trials conducted by multiple sponsors

This study, conducted under the Metabolic Disorders Steering Committee of the Biomarkers Consortium (a public-private partnership managed by the Foundation for the National Institutes of Health (FNIH)), analyzed blinded data on 2,688 type 2 diabetes (T2D) patients from randomized clinical trials conducted by four pharmaceutical companies. An increase in the levels of adiponectin was observed after peroxisome proliferator-activated receptor (PPAR)-agonist treatment (P < 0.0001), but not after treatment with non-PPAR drugs. This increase correlated with decreases in levels of glucose, hemoglobin A(1c) (Hb(A1c)), hematocrit, and triglycerides, and increases in levels of blood urea nitrogen, creatinine, and high-density lipoprotein cholesterol (HDL-C). Early (6-8 weeks) increases in levels of adiponectin after treatment with PPAR agonists showed a negative correlation (r = -0.21, P < 0.0001) with subsequent changes in levels of Hb(A1c). Changes in adiponectin level did not appear to be associated with baseline level of Hb(A1c). Logistic regression demonstrated that an increase in the level of adiponectin predicts a decrease in the level of Hb(A1c). These analyses confirm previously demonstrated relationships between adiponectin levels and metabolic parameters and support the robust predictive utility of adiponectin across the spectrum of glucose tolerance. Cross-company precompetitive collaboration is a feasible and powerful approach to biomarker qualification.

The value, qualification, and regulatory use of surrogate end points in drug development

The acceptance and use of either surrogate end points (SEPs) or efficient clinical end points are associated with greater and more rapid availability of new medicines as compared with disease situations for which clinical end points are inefficient or no surrogates exist. This review of the history of the development, qualification, and acceptance of key SEPs shows that both successes and failures had three key characteristics: (i) apparent biologic plausibility, (ii) prognostic value for the outcome of the disease, and (iii) an association between changes in the SEP and changes in outcome with therapeutic intervention--the three factors recommended for SEPs in the International Conference on Harmonisation's "Statistical Principles for Clinical Trials." We recommend that only prognostic value be an absolute prerequisite for surrogacy, because therapeutic interventions may not exist a priori, and biological plausibility can be subjective. Ideally, all three of these factors would be traded off against one another in a consistent and transparent risk-management process.

Effect of the cathepsin K inhibitor odanacatib on bone resorption biomarkers in healthy postmenopausal women: two double-blind, randomized, placebo-controlled phase I studies

Inhibition of cathepsin K (CatK) is a potential new treatment for osteoporosis. In two double-blind, randomized, placebo-controlled phase I studies, postmenopausal female subjects received odanacatib (ODN), an orally active, potent, and selective CatK inhibitor, once weekly for 3 weeks or once daily for 21 days. Bone turnover biomarkers, safety monitoring, and plasma ODN concentrations were assessed. These studies showed ODN to be well tolerated. Pharmacokinetic (PK) analysis revealed a long half-life (t(1/2); 66-93 h) consistent with once-weekly dosing. Pronounced reductions in C-terminal telopeptide of type I collagen (approximately 62%) and N-terminal telopeptide of type I collagen normalized to creatinine (NTx/Cr) (approximately 62%) at trough (C(168 h)) were seen following weekly administration. Robust reductions in CTx (up to 81%) and NTx/Cr (up to 81%) were seen following daily administration. ODN exhibits robust and sustained suppression of bone resorption biomarkers (CTx and NTx/Cr) at weekly doses > or = 25 mg and daily doses > or = 2.5 mg.

Pharmacokinetics of raltegravir in individuals with UGT1A1 polymorphisms

Raltegravir is a human immunodeficiency virus-1 (HIV-1) integrase strand transfer inhibitor metabolized by glucuronidation via UDP-glucuronosyltransferase 1A1 (UGT1A1). In this study, 30 subjects with a UGT1A1*28/*28 genotype (associated with decreased activity of UGT1A1) and 27 UGT1A1*1/*1 control subjects (matched by race, age, gender, and body mass index) received a single 400-mg dose of raltegravir after fasting. No serious adverse experiences were reported, and there were no discontinuations due to adverse experiences. The geometric mean ratio (GMR) (UGT1A1*28/*28 to UGT1A1*1/*1) and 90% confidence interval (CI) were 1.41 (0.96, 2.09) for raltegravir area under the concentration-time curve (AUC(0-infinity)), 1.40 (0.86, 2.28) for maximum plasma concentration (C(max)), and 1.91 (1.43, 2.55) for concentration at the 12-h time point (C(12 h)). No clinically important differences in time to maximum concentration (T(max)) or half-life were observed. Plasma concentrations of raltegravir are modestly higher in individuals with the UGT1A1*28/*28 genotype than in those with the UGT1A1*1/*1 genotype. This increase is not clinically significant, and therefore no dose adjustment of raltegravir is required for individuals with the UGT1A1*28/*28 genotype.

Pharmacokinetics, Pharmacodynamics, and Safety of a Prostaglandin D2 Receptor Antagonist

Laropiprant is a selective antagonist of the prostaglandin D(2) (PGD(2)) receptor subtype 1 (DP1). Three double-blind, randomized, placebo-controlled studies evaluated the safety, tolerability, pharmacokinetics, and pharmacodynamics of single and multiple oral doses of laropiprant in healthy male volunteers. Single doses up to 900 mg and multiple doses up to 450 mg were generally well tolerated. Laropiprant exhibited dose-proportional pharmacokinetics. Oral absorption is rapid (T(max)=0.8-2.0 h) and the terminal half-life is approximately 12-18 h. The pharmacokinetics of laropiprant was not affected by food. Single doses of 6 mg and higher were effective in suppressing PGD(2)-induced cyclic AMP accumulation in platelets, demonstrating laropiprant target engagement with DP1. Laropiprant has detectable off-target antagonist effects at the thromboxane A(2) receptor but no clinically significant effect on collagen-induced platelet aggregation or bleeding times with multiple doses up to 200 mg.