KIR3DL3-HHLA2 is a human immunosuppressive pathway and a therapeutic target.

The B7 family ligand HERV-H LTR-associating protein 2 (HHLA2) is an attractive target for cancer immunotherapy because of its coinhibitory function, overexpression in human cancers, and association with poor prognoses. However, the knowledge of the HHLA2 pathway is incomplete. HHLA2 has an established positive receptor transmembrane and immunoglobulin (Ig) domain containing 2 (TMIGD2) but a poorly characterized negative receptor human killer cell Ig-like receptor, three Ig domains, and long cytoplasmic tail (KIR3DL3). Here, KIR3DL3 and TMIGD2 simultaneously bound to different sites of HHLA2. KIR3DL3 was mainly expressed on CD56dim NK and terminally differentiated effector memory CD8+ T (CD8+ TEMRA) cells. KIR3DL3+ CD8+ TEMRA acquired an NK-like phenotype and function. HHLA2 engagement recruited KIR3DL3 to the immunological synapse and coinhibited CD8+ T and NK cell function and killing, inducing immune-evasive HHLA2+ tumors. KIR3DL3 recruited SHP-1 and SHP-2 to attenuate Vav1, ERK1/2, AKT, and NF-κB signaling. HHLA2+ tumors from human kidney, lung, gallbladder, and stomach were infiltrated by KIR3DL3+ immune cells. KIR3DL3 blockade inhibited tumor growth in multiple humanized mouse models. Thus, our findings elucidated the molecular and cellular basis for the inhibitory function of KIR3DL3, demonstrating that the KIR3DL3-HHLA2 pathway is a potential immunotherapeutic target for cancer.

A phase 1b study of dual PD-1 and CTLA-4 or KIR blockade in patients with relapsed/refractory lymphoid malignancies.

Simultaneously targeting other pathways could increase the activity of PD-1 blockade in lymphoid malignancies not sensitive to single-agent blockade. We explored the safety and efficacy of combined PD-1 and CTLA-4 or KIR blockade in patients with relapsed/refractory (R/R) lymphoid malignancies. This phase 1b trial enrolled adult patients with R/R classical Hodgkin lymphoma (cHL), non-Hodgkin lymphoma (NHL), or multiple myeloma (MM). Patients received nivolumab plus ipilimumab (nivo/ipi) or lirilumab (nivo/liri) until complete response (CR), progression, or unacceptable toxicity. The primary endpoint was safety and tolerability, while secondary endpoints included overall (ORR) and CR rates (CRR), progression-free and overall survival. Sixty-five patients were treated with nivo/ipi, and 72 with nivo/liri. Twenty-nine percent of patients experienced grade 3-4 treatment-related adverse events with nivo/ipi, and 15% with nivo/liri. In cHL, ORR was 74% for nivo/ipi and 76% for nivo/liri, CRRs were 23% and 24%, respectively. In B-NHL and T-NHL, ORR range was 9-22% and CRR was 0-6%. No patient with MM had an objective response. While both combinations were active in cHL, the toxicity of nivo/ipi was higher than expected from nivolumab alone. These data suggest no meaningful improvement in the efficacy of the combinations over single-agent nivolumab in the diseases studied.

Treatment of cancer with an anti-KIR antibody: a patent evaluation of US9879082 and US2018208652.

Introduction: KIR is an inhibitory receptor expressed by natural killer cells that suppress the immune response against tumor cells. There is a great need to discover and develop new therapies focused on inhibiting the action of KIR and consequently improving the immune response in the various types of cancer. Authors of US9879082 and US2018208652 patents propose a method to eradicate cancer that utilizes anti-KIR antibody.Areas covered: US9879082 and US2018208652 patents describe an anti-KIR antibody, a pharmaceutical composition that contains it, and their application for cancer treatment, particularly, multiple myeloma and acute myeloid leukemia. Anti-KIR antibody is used to a dosage of 0.0003-3 mg antibody/kg patient weight, and is suspended in an isotonic solution consisting of sodium phosphate, sucrose, NaCl, and polysorbate 80.Expert opinion: The results of the clinical trials only support trials regarding the pharmacokinetic, pharmacodynamic, safety, and tolerability. In addition, these results demonstrate that treatment with the anti-KIR antibody can induce an antitumor response in cancer patients.

Immunogenomic correlates of response to cetuximab monotherapy in head and neck squamous cell carcinoma.

BACKGROUND: Mechanisms of resistance to immune-modulating cancer treatments are poorly understood. Using a novel cohort of patients with head and neck squamous cell carcinoma (HNSCC), we investigated mechanisms of immune escape from epidermal growth factor receptor-specific monoclonal antibody (mAb) therapy. METHODS: HNSCC tumors (n = 20) from a prospective trial of neoadjuvant cetuximab monotherapy underwent whole-exome sequencing. Expression of killer-cell immunoglobulin-like receptor (KIR) and human leukocyte antigen-C (HLA-C) and the effect of KIR blockade were assessed in HNSCC cell lines. RESULTS: Nonresponders to cetuximab had an increased rate of mutations in HLA-C compared to responders and HNSCC tumors (n = 528) in The Cancer Genome Atlas (P < 0.00001). In vitro, cetuximab-activated natural killer (NK) cells induced upregulation of HLA-C on HNSCC cells (P < 0.01) via interferon gamma. Treatment of NK cells with the anti-KIR mAb lirilumab increased killing of HNSCC cells (P < 0.001). CONCLUSIONS: Alterations in HLA-C may provide a mechanism of immune evasion through disruption of NK activation.

Role of natural killer cells for immunotherapy in chronic myeloid leukemia (Review).

The majority of natural killer (NK) cells serve an important role in eliminating malignant cells. The cytotoxic effects of NK cells were first identified against leukemia cells, and it is now hypothesized that they may have a critical role in leukemia therapy. The cellular functions of NK cells are mediated by their cell surface receptors, which recognize ligands on cancer cells. The role of NK cells is specifically regulated by the activating or inhibitory killer cell immunoglobulin­like receptors (KIRs) on their surface, which bind to the human leukocyte antigen (HLA) class I ligands present on the target cells. The association between KIR and HLA is derived from the diversity of KIR/HLA gene profiles present in different individuals, and this determines the cytotoxic effect of NK cells on cancer cells. Chronic myeloid leukemia (CML) is a hematological leukemia characterized by the hyper­proliferation of myeloid cells, with the majority of patients with CML presenting with abnormal immune cells. Tyrosine kinase inhibitors are the present standard therapy for CML, but are associated with numerous adverse side effects. Various studies have proposed CML therapy by immunotherapeutic approaches targeting the immune cells. This review summarizes the contents of NK cells and the association between KIR/HLA and leukemia, especially CML. This is followed by a discussion on the development of NK cell immunotherapy in hematological malignancies and research into strategies to enhance NK cell function for CML treatment.

A Pilot Trial of Lirilumab With or Without Azacitidine for Patients With Myelodysplastic Syndrome.

BACKGROUND: Enhancement of natural killer cell activity by blocking interactions between killer immunoglobulin (Ig)-like receptors (KIRs) and human leukocyte antigen-C (HLA-C) molecules can improve outcomes in myeloid malignancies. Lirilumab is a human IgG4 monoclonal antibody that blocks KIR/HLA-C interaction. We designed a study to evaluate the safety and efficacy of lirilumab as a single agent and in combination with azacitidine in patients with myelodysplastic syndrome (MDS). PATIENTS AND METHODS: Adult patients with MDS who had not received previous hypomethylating agents were included. Lower-risk MDS patients received single-agent lirilumab (3 mg/kg); higher-risk patients received azacitidine (75 mg/m2/day for 7 days) in combination with lirilumab (3 mg/kg, on day 7), in a 28-day cycle. Responses were evaluated according to 2006 International Working Group criteria. RESULTS: A total of 10 patients including 8 with higher and 2 with lower-risk enrolled. The median age was 70 (range, 50-84) years and 4 (40%) had complex cytogenetics. Baseline molecular mutations included TP53 (n = 5), TET2 (n = 3), and NRAS (n = 2). Patients received a median of 4 (range, 2-13) and 9 (range, 5-14) cycles of treatment with azacitidine with lirilumab and single-agent lirilumab, respectively. Two patients achieved complete remission (CR), 5 marrow CR, and 3 had stable disease. The median event-free survival for the entire cohort was 8 months (95% confidence interval, 4 months to not reached), and the median overall survival has not yet been reached. Five patients experienced 8 episodes of Grade ≥3 adverse events attributable to study drug, with the most frequent being infection or neutropenic fever (75%). CONCLUSION: Lirilumab either as a single agent as well as used in combination with azacitidine has clinical activity in patients with MDS. Further studies are needed to confirm our findings.

The combination of anti-KIR monoclonal antibodies with anti-PD-1/PD-L1 monoclonal antibodies could be a critical breakthrough in overcoming tumor immune escape in NSCLC.

BACKGROUND: The anti-programmed death-1 (PD-1)/programmed death ligand-1 (PD-L1) monoclonal antibody has a good effect in the treatment of non-small cell lung cancer (NSCLC), but not all PD-1/PD-L1 positive patients can get benefit from it. Compensatory expression of other immune checkpoints may be correlated with the poor efficacy of anti-PD-1/PD-L1 monoclonal antibodies. The inhibitory human leukocyte antigen (HLA)/killer cell Ig-like receptor (KIR) can effectively block the killing effect of natural killer (NK) cells on tumors. Our previous studies have confirmed that high expression of KIR was correlated with poor prognosis of NSCLC. Inhibitory KIR expression was positively correlated with the expression of PD-1. METHODS: The expressions of KIR 2D (L1, L3, L4, S4) (BC032422/ADQ31987/NP_002246/NP_036446, Abcam) and PD-1 (NAT 105, Cell marque) proteins was assessed by immunohistochemistry. RESULTS: The expression of inhibitory KIR in tumor cells or tumor infiltrating lymphocytes (TILs) is associated with PD-1 expression. Among PD-1 positive patients, 76.3% were KIR 2D (L1, L3, L4, S4) positive on tumor cells, and 74.6% were KIR 2D (L1, L3, L4, S4) positive on TILs. We compared the expression of inhibitory KIR before and after treatment with nivolumab in 11 patients with NSCLC. We found that five (45.5%) patients had positive expression of inhibitory KIR in tumor tissue after being treated with anti-PD-1 monoclonal antibodies, two of whom exhibited a significant increase in expression of inhibitory KIR, and three showed no change. CONCLUSIONS: PD-1 expression was correlated with KIR 2D (L1, L3, L4, S4) on tumor cells or TILs. The resistance to anti-PD-1 monoclonal antibody treatment might be related to KIR. The inhibitory HLA/KIR could combine with the PD-1/PD-L1 signaling pathway negatively regulating NSCLC tumor immunity.

Intrinsic Functional Potential of NK-Cell Subsets Constrains Retargeting Driven by Chimeric Antigen Receptors.

Natural killer (NK) cells hold potential as a source of allogeneic cytotoxic effector cells for chimeric antigen receptor (CAR)-mediated therapies. Here, we explored the feasibility of transfecting CAR-encoding mRNA into primary NK cells and investigated how the intrinsic potential of discrete NK-cell subsets affects retargeting efficiency. After screening five second- and third-generation anti-CD19 CAR constructs with different signaling domains and spacer regions, a third-generation CAR with the CH2-domain removed was selected based on its expression and functional profiles. Kinetics experiments revealed that CAR expression was optimal after 3 days of IL15 stimulation prior to transfection, consistently achieving over 80% expression. CAR-engineered NK cells acquired increased degranulation toward CD19+ targets, and maintained their intrinsic degranulation response toward CD19- K562 cells. The response of redirected NK-cell subsets against CD19+ targets was dependent on their intrinsic thresholds for activation determined through both differentiation and education by killer cell immunoglobulin-like receptors (KIR) and/or CD94/NKG2A binding to self HLA class I and HLA-E, respectively. Redirected primary NK cells were insensitive to inhibition through NKG2A/HLA-E interactions but remained sensitive to inhibition through KIR depending on the amount of HLA class I expressed on target cells. Adaptive NK cells, expressing NKG2C, CD57, and self-HLA-specific KIR(s), displayed superior ability to kill CD19+, HLA low, or mismatched tumor cells. These findings support the feasibility of primary allogeneic NK cells for CAR engineering and highlight a need to consider NK-cell diversity when optimizing efficacy of cancer immunotherapies based on CAR-expressing NK cells. Cancer Immunol Res; 6(4); 467-80. ©2018 AACR.

[New frontiers in the fight against cancer]. / Nouvelles frontières de la lutte contre le cancer☆.

After many years of research, recent advances shed a new light on the role of the immune system in cancer. New therapeutic antibodies, such as anti-PD-1/L1, that block the interactions of inhibitory receptors (immune checkpoint inhibitors, ICI) with their ligands, have revolutionized the management of cancer patients. Nevertheless, they only affect a small part of the patient population. The main current challenge for immuno-oncology is to overcome these resistances by targeting new control points and new immune cells, combining these new immunotherapies with one another and with other standard treatments. Monalizumab is a novel antibody that simultaneously stimulates the anti-tumor action of NK and T cells by blocking one of their inhibitory receptors: NKG2A. NKG2A is present on the surface of both cell types and its ligand, HLA-E, and is very frequently overexpressed by human tumors, opening a wide therapeutic window to monalizumab.

Second- and third-generation drugs for immuno-oncology treatment-The more the better?

Recent success in cancer immunotherapy (anti-CTLA-4, anti-PD1/PD-L1) has confirmed the hypothesis that the immune system can control many cancers across various histologies, in some cases producing durable responses in a way not seen with many small-molecule drugs. However, only less than 25% of all patients do respond to immuno-oncology drugs and several resistance mechanisms have been identified (e.g. T-cell exhaustion, overexpression of caspase-8 and ß-catenin, PD-1/PD-L1 gene amplification, MHC-I/II mutations). To improve response rates and to overcome resistance, novel second- and third-generation immuno-oncology drugs are currently evaluated in ongoing phase I/II trials (either alone or in combination) including novel inhibitory compounds (e.g. TIM-3, VISTA, LAG-3, IDO, KIR) and newly developed co-stimulatory antibodies (e.g. CD40, GITR, OX40, CD137, ICOS). It is important to note that co-stimulatory agents strikingly differ in their proposed mechanism of action compared with monoclonal antibodies that accomplish immune activation by blocking negative checkpoint molecules such as CTLA-4 or PD-1/PD-1 or others. Indeed, the prospect of combining agonistic with antagonistic agents is enticing and represents a real immunologic opportunity to 'step on the gas' while 'cutting the brakes', although this strategy as a novel cancer therapy has not been universally endorsed so far. Concerns include the prospect of triggering cytokine-release syndromes, autoimmune reactions and hyper immune stimulation leading to activation-induced cell death or tolerance, however, toxicity has not been a major issue in the clinical trials reported so far. Although initial phase I/II clinical trials of agonistic and novel antagonistic drugs have shown highly promising results in the absence of disabling toxicity, both in single-agent studies and in combination with chemotherapy or other immune system targeting drugs; however, numerous questions remain about dose, schedule, route of administration and formulation as well as identifying the appropriate patient populations. In our view, with such a wealth of potential mechanisms of action and with the ability to fine-tune monoclonal antibody structure and function to suit particular requirements, the second and third wave of immuno-oncology drugs are likely to provide rapid advances with new combinations of novel immunotherapy (especially co-stimulatory antibodies). Here, we will review the mechanisms of action and the clinical data of these new antibodies and discuss the major issues facing this rapidly evolving field.

Checkpoint Inhibition of KIR2D with the Monoclonal Antibody IPH2101 Induces Contraction and Hyporesponsiveness of NK Cells in Patients with Myeloma.

PURPOSE: Immune checkpoint inhibitors have recently revolutionized cancer immunotherapy. On the basis of data showing KIR-ligand mismatched natural killer (NK) cells reduce the risk of leukemia and multiple myeloma relapse following allogeneic hematopoietic stem cell transplantation, investigators have developed a checkpoint inhibition antibody that blocks KIR on NK cells. Although in vitro studies suggest the KIR2D-specific antibody IPH2101 induces KIR-ligand mismatched tumor killing by NK cells, our single-arm phase II clinical trial in patients with smoldering multiple myeloma was prematurely terminated due to lack of clinical efficacy. This study aimed at unveiling the underlying mechanisms behind the lack of clinical efficacy. EXPERIMENTAL DESIGN: Treatment-naïve patients received an intravenous infusion of 1 mg/kg IPH2101 every other month for up to a year. Peripheral blood was collected at baseline and 24 hours after first infusion, followed by weekly samples for the first month and monthly samples thereafter. NK cell phenotype and function was analyzed using high-resolution flow cytometry. RESULTS: Unexpectedly, infusion of IPH2101 resulted in rapid reduction in both NK cell responsiveness and KIR2D expression on the NK cell surface. In vitro assays revealed KIR2D molecules are removed from the surface of IPH2101-treated NK cells by trogocytosis, with reductions in NK cell function directly correlating with loss of free KIR2D surface molecules. Although IPH2101 marginally augmented the antimyeloma cytotoxicity of remaining KIR2Ddull patient NK cells, the overall response was diminished by significant contraction and reduced function of KIR2D-expressing NK cells. CONCLUSIONS: These data raise concerns that the unexpected biological events reported in this study could compromise antibody-based strategies designed at augmenting NK cell tumor killing via checkpoint inhibition. Clin Cancer Res; 22(21); 5211-22. ©2016 AACRSee related commentary by Felices and Miller, p. 5161.

Influenza Virus Targets Class I MHC-Educated NK Cells for Immunoevasion.

The immune response to influenza virus infection comprises both innate and adaptive defenses. NK cells play an early role in the destruction of tumors and virally-infected cells. NK cells express a variety of inhibitory receptors, including those of the Ly49 family, which are functional homologs of human killer-cell immunoglobulin-like receptors (KIR). Like human KIR, Ly49 receptors inhibit NK cell-mediated lysis by binding to major histocompatibility complex class I (MHC-I) molecules that are expressed on normal cells. During NK cell maturation, the interaction of NK cell inhibitory Ly49 receptors with their MHC-I ligands results in two types of NK cells: licensed ("functional"), or unlicensed ("hypofunctional"). Despite being completely dysfunctional with regard to rejecting MHC-I-deficient cells, unlicensed NK cells represent up to half of the mature NK cell pool in rodents and humans, suggesting an alternative role for these cells in host defense. Here, we demonstrate that after influenza infection, MHC-I expression on lung epithelial cells is upregulated, and mice bearing unlicensed NK cells (Ly49-deficient NKCKD and MHC-I-deficient B2m-/- mice) survive the infection better than WT mice. Importantly, transgenic expression of an inhibitory self-MHC-I-specific Ly49 receptor in NKCKD mice restores WT influenza susceptibility, confirming a direct role for Ly49. Conversely, F(ab')2-mediated blockade of self-MHC-I-specific Ly49 inhibitory receptors protects WT mice from influenza virus infection. Mechanistically, perforin-deficient NKCKD mice succumb to influenza infection rapidly, indicating that direct cytotoxicity is necessary for unlicensed NK cell-mediated protection. Our findings demonstrate that Ly49:MHC-I interactions play a critical role in influenza virus pathogenesis. We suggest a similar role may be conserved in human KIR, and their blockade may be protective in humans.

Controlling natural killer cell responses: integration of signals for activation and inhibition.

Understanding how signals are integrated to control natural killer (NK) cell responsiveness in the absence of antigen-specific receptors has been a challenge, but recent work has revealed some underlying principles that govern NK cell responses. NK cells use an array of innate receptors to sense their environment and respond to alterations caused by infections, cellular stress, and transformation. No single activation receptor dominates; instead, synergistic signals from combinations of receptors are integrated to activate natural cytotoxicity and cytokine production. Inhibitory receptors for major histocompatibility complex class I (MHC-I) have a critical role in controlling NK cell responses and, paradoxically, in maintaining NK cells in a state of responsiveness to subsequent activation events, a process referred to as licensing. MHC-I-specific inhibitory receptors both block activation signals and trigger signals to phosphorylate and inactivate the small adaptor Crk. These different facets of inhibitory signaling are incorporated into a revocable license model for the reversible tuning of NK cell responsiveness.

A phase 1 trial of the anti-KIR antibody IPH2101 in patients with relapsed/refractory multiple myeloma.

Natural killer (NK) cells elicit cytotoxicity against multiple myeloma (MM); however, MM cells express HLA class I molecules as ligands to NK cell inhibitory killer immunoglobulin-like receptors (KIRs) as a means of immunoevasion. KIR-ligand mismatch may improve outcomes in allogeneic transplantation for MM. Extrapolating on this concept, we conducted a phase 1 trial of IPH2101, an anti-KIR antibody, in patients with relapsed/refractory MM. IPH2101 was administered intravenously every 28 days in 7 dose-escalated cohorts (0.0003-3 mg/kg) for up to 4 cycles. Pharmacokinetic, pharmacodynamic, and correlative immunologic studies were completed. A total of 32 patients were enrolled. The biologic endpoint of full KIR2D occupancy across the dosing cycle was achieved without dose-limiting toxicity or maximally tolerated dose. One severe adverse event was noted. Pharmacokinetic and pharmacodynamic findings approximated preclinical predictions, and IPH2101 enhanced ex vivo patient-derived NK cell cytotoxicity against MM. No objective responses were seen. No evidence of autoimmunity was observed. These findings suggest that IPH2101 is safe and tolerable at doses that achieve full inhibitory KIR saturation, and this approach warrants further development in MM. This trial was registered at www.clinicaltrials.gov as #NCT00552396.

A phase 1 trial of the anti-inhibitory KIR mAb IPH2101 for AML in complete remission.

IPH2101 is an anti-killer inhibitory receptor (anti-KIR) mAb that can block KIR-mediated inhibition of natural killer (NK) cells to enhance cytotoxicity against acute myeloid leukemia blasts. We have conducted a phase 1 study of IPH2101 in elderly patients with acute myeloid leukemia in first complete remission. Patients received escalating doses (0.0003-3 mg/kg) of IPH2101 following a 3 + 3 design. Safety, toxicity (primary end points), pharmacokinetics, outcome, and immunologic correlates were evaluated. Twenty-three patients (median age, 71 years), were enrolled. Adverse events were mild and transient, consisting mainly of infusion syndrome and erythema. The maximum tolerated dose was not reached, although full KIR saturation (> 90%) was sustained for more than 2 weeks at 1 and 3 mg/kg. There was a clear correlation between mAb exposure and KIR occupancy. Neither hematologic toxicity nor significant changes in the numbers and distribution of lymphocyte subsets, NK cell receptor expression, or in vitro cytotoxicity were seen. At the highest dose levels (0.3, 1, and 3 mg/kg), transient increases in TNF-α and MIP-1ß serum concentrations and NK cell CD69 expression were observed. Overall and relapse-free survival in the present study compared favorably to reports in comparable patient populations. We conclude that IPH2101 administration is safe and can block KIR for prolonged periods of time with limited side effects. Registered with the European Union Drug Regulating Authorities Clinical Trials (EUDRACT) as 2005-005298-31.

Targeted immunotherapy for acute myeloid leukemia.

Allogeneic hematopoietic stem cell transplantation (HSCT) demonstrated convincingly the potential of allogeneic T cells in causing sustained remissions in high-risk hematologic malignancies. However toxicity of allogeneic HSCT limits its application to a broader group of patients. An improved understanding of NK biology along with mechanisms of natural killer (NK) cell and T-cell-mediated alloreactivity against leukemia has led to several clinical immunotherapeutic strategies that preserve graft versus leukemia (GVL) while minimizing the toxicity of HSCT. Here we review strategies being explored both in HSCT and non-HSCT settings that include an emphasis on two key aspects: (a) Maximizing cytotoxicity of alloreactive cells, ie, NK cells and T cells, and (b) Targeted manipulation of critical pathways in T and NK cells contributing to sustained anti-leukemia effects.

IPH2101, a novel anti-inhibitory KIR antibody, and lenalidomide combine to enhance the natural killer cell versus multiple myeloma effect.

Multiple myeloma (MM) patients who receive killer cell Ig-like receptor (KIR) ligand-mismatched, T cell-depleted, allogeneic transplantation may have a reduced risk of relapse compared with patients who receive KIR ligand-matched grafts, suggesting the importance of this signaling axis in the natural killer (NK) cell-versus-MM effect. Expanding on this concept, IPH2101 (1-7F9), an anti-inhibitory KIR mAb, enhances NK-cell function against autologous MM cells by blocking the engagement of inhibitory KIR with cognate ligands, promoting immune complex formation and NK-cell cytotoxicity specifically against MM cell targets but not normal cells. IPH2101 prevents negative regulatory signals by inhibitory KIR, whereas lenalidomide augments NK-cell function and also appears to up-regulate ligands for activating NK-cell receptors on MM cells. Lenalidomide and a murine anti-inhibitory NK-cell receptor Ab mediate in vivo rejection of a lenalidomide-resistant tumor. These mechanistic, preclinical data support the use of a combination of IPH2101 and lenalidomide in a phase 2 trial for MM.

Peptide antagonism as a mechanism for NK cell activation.

Inhibition of natural killer (NK) cells is mediated by MHC class I receptors including the killer cell Ig-like receptor (KIR). We demonstrate that HLA-C binding peptides can function as altered peptide ligands for KIR and antagonize the inhibition mediated by KIR2DL2/KIR2DL3. Antagonistic peptides promote clustering of KIR at the interface of effector and target cells, but do not result in inhibition of NK cells. Our data show that, as for T cells, small changes in the peptide content of MHC class I can regulate NK cell activity.

Protease-activated receptor 2 and bradykinin-mediated vasodilation in the cerebral arteries of stroke-prone rats.

Protease-activated receptor 2 (PAR(2)) expression is up-regulated during vascular injury associated with edema. PAR(2) and bradykinin subtype 2 receptor (B(2)) expression and function were assessed in relation to hypertensive encephalopathy (HE) and cerebral hemorrhage (CH) in middle cerebral arteries (MCA) of Kyoto Wistar stroke-prone spontaneously hypertensive rats (SHRsp). Before stroke, bradykinin and PAR(2) activation by 2-furoyl-leucine-isoleucine-glycine-arginine-leucine-ornithine-amide (2Fly) produced endothelium-dependent vasodilation that was inhibited by K(+) depolarization, carbenoxolone, and the blockade of intermediate (IK(Ca)) plus small (SK(Ca)) and (in the case of bradykinin) smooth muscle (SM) large conductance (BK(Ca)) calcium-activated K(+) channels. Responses were not altered by N omega-nitro-L-arginine methyl ester, indomethacin, 17-octadecynoic acid or Ba(2+)+ouabain. We concluded that vasodilation to 2Fly or bradykinin was not mediated by NO, cyclooxygenases, arachidonic acid-metabolizing cytochrome P450s or SM K(ir) channels+Na(+)/K(+) ATPase activation. Vasodilation likely involved the spread of endothelial hyperpolarization (generated by IK(Ca)+SK(Ca)) through myoendothelial junctions and in some cases SM BK(Ca) activation. SHRsp with HE or CH had MCA that could not constrict to pressure and did not vasodilate to bradykinin. Their responses to 2Fly remained unaltered. The patterns and densities of PAR(2) and B(2) immunoreactivity in frozen MCA sections were not altered with stroke. MCA function remained normal in SHRsp subjected to dietary manipulations that prevented stroke without altering hypertension. Despite the presence of vascular injury, edema, inflammation and the loss of endothelium-dependent bradykinin vasodilation we found no evidence that PAR(2) expression or vascular function was altered in MCA after stroke.