Low frequency of Vγ9Vδ2 T-cells predicts poor survival in newly diagnosed acute myeloid leukemia

In several tumor subtypes, increased infiltration of Vγ9Vδ2 T-cells has been shown to have the highest prognostic value compared to other immune subsets. In acute myeloid leukemia (AML), similar findings have been based solely on the inference of transcriptomic data and have not been assessed with respect to confounding factors. This study aimed at determining, by immunophenotypic analysis (flow or mass cytometry) of peripheral blood from AML patients at diagnosis, the prognostic impact of Vγ9Vδ2 T-cell frequency. This was adjusted for potential confounders (age at diagnosis, disease status, European LeukemiaNet classification, leukocytosis, and allogeneic hematopoietic stem cell transplantation as a time-dependent covariate). The cohort was composed of 198 newly diagnosed AML patients. By univariate analysis, patients with lower Vγ9Vδ2 T-cells at diagnosis had significantly lower 5-year overall and relapse-free survivals. These results were confirmed in multivariate analysis (Hazard Ratio [HR]=1.55[1.04-2.30], p=0.030 and HR=1.64[1.06, 2.53], p=0.025). Immunophenotypic alterations observed in patients with lower Vγ9Vδ2 T-cells included a loss of some cytotoxic Vγ9Vδ2 T-cell subsets and a decreased expression of BTN3A on the surface of blasts. Samples expanded regardless of their Vγ9Vδ2 T-cell levels and displayed similar effector functions in vitro. This study confirms the prognostic value of elevated Vγ9Vδ2 T-cells among lymphocytes, in newly diagnosed AML patients. These results provide a strong rationale to consider consolidation protocols aiming at enhancing Vγ9Vδ2 T-cell responses.

Prognostic Immune Effector Signature in Adult Acute Lymphoblastic Leukemia Patients Is Dominated by γδ T Cells

The success of immunotherapy has highlighted the critical role of the immune microenvironment in acute lymphoblastic leukemia (ALL); however, the immune landscape in ALL remains incompletely understood and most studies have focused on conventional T cells or NK cells. This study investigated the prognostic impact of circulating γδ T-cell alterations using high-dimensional analysis in a cohort of newly diagnosed adult ALL patients (10 B-ALL; 9 Philadelphia+ ALL; 9 T-ALL). Our analysis revealed common alterations in CD8+ T cells and γδ T cells of relapsed patients, including accumulation of early stage differentiation and increased expression of BTLA and CD73. We demonstrated that the circulating γδ T-cell signature was the most discriminating between relapsed and disease-free groups. In addition, Vδ2 T-cell alterations strongly discriminated patients by relapse status. Taken together, these data highlight the role of ɣδ T cells in adult ALL patients, among whom Vδ2 T cells may be a pivotal contributor to T-cell immunity in ALL. Our findings provide a strong rationale for further monitoring and potentiating Vδ2 T cells in ALL, including in the autologous setting.

Immune biology of NSCLC revealed by single-cell technologies: implications for the development of biomarkers in patients treated with immunotherapy

First-line immunotherapy in non-small-cell lung cancer largely improved patients' survival. PD-L1 testing is required before immune checkpoint inhibitor initiation. However, this biomarker fails to accurately predict patients' response. On the other hand, immunotherapy exposes patients to immune-related toxicity, the mechanisms of which are still unclear. Hence, there is an unmet need to develop clinically approved predictive biomarkers to better select patients who will benefit the most from immune checkpoint inhibitors and improve risk management. Single-cell technologies provide unprecedented insight into the tumor and its microenvironment, leading to the discovery of immune cells involved in immune checkpoint inhibitor response or toxicity. In this review, we will underscore the potential of the single-cell approach to identify candidate biomarkers improving non-small-cell lung cancer patients' care.

High-throughput mass cytometry staining for deep phenotyping of human natural killer cells

This protocol details the step-by-step procedure for in-depth immune phenotyping of peripheral blood natural killer (NK) cells from clinical samples by mass cytometry. The protocol consists of three main steps: PBMC incubation with a mix of metal-conjugated antibodies for extracellular phenotyping followed by fixation, permeabilization and incubation with a mix of metal-conjugated antibodies for staining of intracellular proteins, and sample acquisition on a mass cytometer. High-dimensional analysis enables the visualization of NK cell subsets and their phenotypical characteristics. For complete details on the use and execution of this protocol, please refer to Chretien et al. (2021).

Celiac Disease After Administration of Immune Checkpoint Inhibitors: A Case Report

Immune checkpoint inhibitors (ICI) reinvigorate the immune system to recognize and destroy tumor cells. Because of this biological mechanism, patients might develop autoimmune toxicities, notably in the digestive tract (most frequently, hepatitis or colitis). A 70-year-old man with relapsed mesothelioma was treated with nivolumab in 3rd line. He was hospitalized for watery and foul-smelling diarrhea. He underwent gastrointestinal endoscopy, showing duodenitis and villous atrophy and measurement of serum IgA antibodies to tissue transglutaminase (tTG-IgA+), leading to the diagnosis of ICI-induced celiac disease. He was treated with steroids, proton pump inhibitors, and a gluten-free diet. If ICI-induced celiac disease is rare in the literature, increasing reports suggest that celiac disease might represent an underestimated ICI toxicity. This case highlights the necessity of complementary investigation (including tTG-IgA and endoscopic biopsies) in patients with atypical digestive symptoms during immunotherapy.

Soluble BTN2A1 Is a Potential Prognosis Biomarker in Pre-Treated Advanced Renal Cell Carcinoma

The development of immune checkpoint inhibitors (ICI) has dramatically changed the landscape of therapies for metastatic renal cell carcinoma. However, many patients do not benefit from such therapy and prognostic or predictive validated biomarker validated for ICI are still needed to better select and treat patient. Plasmatic soluble immune checkpoints have been described as potential immune biomarkers in hematological malignancies and solids tumors, then, we would like to explore the prognostic value of different soluble immune checkpoints in patients with mRCC treated with nivolumab after TKI. We prospectively collected plasma samples before nivolumab infusion from 38 patients previously treated for mRCC with TKI at Paoli-Calmettes Institute, from the NIVOREN GETUG-AFU 26 study (NCT03013335). Enzyme-linked immunosorbent assays (ELISA) were performed for soluble forms of PD-1, PD-L1, global BTN3, BTLA, BTN3A1 and BTN2A1. Among the different soluble checkpoints analyzed, only high baseline plasmatic level of BTN2A1 was significantly associated with shorter PFS: median PFS was 3.95 months for sBTN2A1high vs 14.30 months for sBTN2A1low (sBTN2A1 cut-off: 6.7ng/mL; HR = 2.26, 95%CI [0.68 - 4.60], p = 0.0307). There was no statistical difference in OS between sBTN2A1high and sBTN2A1^low. Our results suggest that the baseline level of plasmatic BTN2A1 could be an independent prognosis factor of PFS after nivolumab for pre-treated patient with mRCC. However, these results need to be validated in a larger prospective cohort and the biological role of BTN subfamily and γδ T cell immunity in mRCC must be elucidated.

Quantification of Immune Variables from Liquid Biopsy in Breast Cancer Patients Links Vδ2+ γδ T Cell Alterations with Lymph Node Invasion

The rationale for therapeutic targeting of Vδ2+ γδ T cells in breast cancer is strongly supported by in vitro and murine preclinical investigations, characterizing them as potent breast tumor cell killers and source of Th1-related cytokines, backing cytotoxic αβ T cells. Nonetheless, insights regarding Vδ2+ γδ T cell phenotypic alterations in human breast cancers are still lacking. This paucity of information is partly due to the challenging scarcity of these cells in surgical specimens. αβ T cell phenotypic alterations occurring in the tumor bed are detectable in the periphery and correlate with adverse clinical outcomes. Thus, we sought to determine through an exploratory study whether Vδ2+ γδ T cells phenotypic changes can be detected within breast cancer patients' peripheral blood, along with association with tumor progression. By using mass cytometry, we quantified 130 immune variables from untreated breast cancer patients' peripheral blood. Supervised analyses and dimensionality reduction algorithms evidenced circulating Vδ2+ γδ T cell phenotypic alterations already established at diagnosis. Foremost, terminally differentiated Vδ2+ γδ T cells displaying phenotypes of exhausted senescent T cells associated with lymph node involvement. Thereby, our results support Vδ2+ γδ T cells implication in breast cancer pathogenesis and progression, besides shedding light on liquid biopsies to monitor surrogate markers of tumor-infiltrating Vδ2+ γδ T cell antitumor activity.

Correction: NKp30 expression is a prognostic immune biomarker for stratification of patients with intermediate-risk acute myeloid leukemia

[This corrects the article DOI: 10.18632/oncotarget.17747.].

Dynamic of systemic immunity and its impact on tumor recurrence after radiofrequency ablation of hepatocellular carcinoma

Background: Percutaneous radiofrequency ablation (RFA) is one of the main treatments of small hepatocellular carcinoma (HCC). However, it remains unclear whether this local treatment can induce systemic immune variations. Methods: We conducted a prospective study in a tertiary center including consecutive cirrhotic patients with unifocal HCC<5 cm treated by a first RFA between 2010 and 2014. Peripheral blood mononuclear cells were isolated on the day before (D0), day after (D1) and month after RFA (M1). Frequencies and phenotypes of myeloid cells, T cells, and NK cells were compared between timepoints. Overall recurrence and associated variables were estimated using Kaplan-Meier, log-rank and Cox proportional-hazards models. Results: 80 patients were included (69% male, median age: 67 years old). Main aetiologies of HCC were alcohol (51%), hepatitis C virus (45%), non-alcoholic steatohepatitis (36%) and hepatitis B virus (9%). Median overall survival was 55 months (M); median progression-free survival was 29.5M. Among innate immune populations, we observed variations between D0, D1 and M1 in NKp30+ NK cells (p < .0001) and in plasmacytoid dendritic cells (pDC, p < .01). Concerning adaptive immunity, we observed variations in CD8 Central Memory (p < .05) and CD28+ CD8 Central Memory (p < .01). An early dynamic (D0/D1) of activated NKp30+ NK cells was associated with a decreased overall recurrence (log-rank, p = .016, median delay 25.1 vs 40.6 months). In contrast, a late dynamic (D1/M1) of immature NK cells (CD56bright) and altered myeloid DC (PDL1+) was associated with an increased overall recurrence (log-rank, p = .011 and p = .0044, respectively). In multivariate analysis, variation of immature NK cells predicts tumor recurrence independently of classical clinical prognostic features (HR = 2.41, 95% CI: 1.15-5.057), p = .019). Conclusions: Percutaneous RFA of small HCC leads to systemic modifications of innate and adaptive immunity closely linked with overall tumor recurrence.

Prognostic significance of circulating PD-1, PD-L1, pan-BTN3As, BTN3A1 and BTLA in patients with pancreatic adenocarcinoma

PDAC is one of the most heterogeneous cancers with low chemotherapeutic sensitivity due to a dense stroma, a weak vasculature and significant biological aggressivity. In cancer, suppressive immune checkpoints are often hyper-activated to ensure an effective evasion of tumor cells from immune surveillance. These immune checkpoints include in part, the B7/butyrophilin-like receptors such as butyrophilin sub-family 3A/CD277 receptors (BTN3A), the B and T lymphocyte attenuator (BTLA) belonging to the B7-like receptors and the programmed death protein (PD-1) with its ligand PD-L1. We evaluated the plasma level of these markers in 32 PDAC patients (learning cohort) by ad hoc developed ELISA’s and showed that there are highly correlated. We used ROC curves and univariate analysis to characterize their prognostic relevance in these patients and showed that their plasma level can serve as survival predictor. Plasma level thresholds that correlate with less than six months survival were established for sPD-1 (>8.6 ng/ml), sPD-L1 (>0.36 ng/ml), sBTLA (>1.91 ng/ml), sBTN3A1 (>6.98 ng/ml) and pan-sBTN3A (>6.92 ng/ml). These thresholds were applied in independent validation cohort composed by 27 new samples and could efficiently discriminate short versus long PDAC survivors. Our study reveals that monitoring the concentration of soluble forms of inhibitory immune checkpoints in plasma can help predict survival in PDAC patients and therefore improve their treatments.

NKp30 expression is a prognostic immune biomarker for stratification of patients with intermediate-risk acute myeloid leukemia

Cytogenetics and European Leukemia Net (ELN) genetic classification predict patients at increased risk of relapse in acute myeloid leukemia (AML) except in the intermediate risk group for which further prognostic determinants are required. We have previously shown that Natural Killer (NK) cell defects in AML are predictors of poor overall survival (OS). This study aimins at validating NKp30, a receptor that mediates NK activation, as a prognostic biomarker for AML patients with intermediate prognosis.

NKp30 expression was prospectively assessed at diagnosis on NK cells from peripheral blood by flow cytometry (N = 201 patients). Clinical outcome was evaluated with regard to NKp30 status.

In patients with intermediate cytogenetic (N = 162), NKp30^high phenotype at diagnosis was predictive of better OS (HR = 0.26; 95%CI = [0.14-0.50]; P < 0.0001) and relapse-free survival (RFS) (HR = 0.21; 95%CI = [0.08-0.52]; P = 0.0007). In patients with intermediate ELN (N = 116), NKp30^high phenotype at diagnosis was predictive of better OS (HR = 0.33; 95%CI = [0.16–0.67]; P = 0.0019) and RFS (HR = 0.24; 95%CI = [0.08-0.67]; P = 0.0058). In multivariate analysis, high NKp30 expression independently predicted improved OS (HR = 0.56, P = 0.046) and RFS (HR = 0.37, P = 0.048). Consistently, cumulative incidence of relapse (CIR) was lower in patients with high NKp30 expression (HR = 0.37, P = 0.026).

In conclusion, we propose NKp30 status as a simple and early prognostic biomarker that identifies intermediate-risk patients with poor prognosis who otherwise may not be identified with existing risk stratification systems.

JAM-C Identifies Src Family Kinase-Activated Leukemia-Initiating Cells and Predicts Poor Prognosis in Acute Myeloid Leukemia

Acute myeloid leukemia (AML) originates from hematopoietic stem and progenitor cells that acquire somatic mutations, leading to disease and clonogenic evolution. AML is characterized by accumulation of immature myeloid cells in the bone marrow and phenotypic cellular heterogeneity reflective of normal hematopoietic differentiation. Here, we show that JAM-C expression defines a subset of leukemic cells endowed with leukemia-initiating cell activity (LIC). Stratification of de novo AML patients at diagnosis based on JAM-C-expressing cells frequencies in the blood served as an independent prognostic marker for disease outcome. Using publicly available leukemic stem cell (LSC) gene expression profiles and gene expression data generated from JAM-C-expressing leukemic cells, we defined a single cell core gene expression signature correlated to JAM-C expression that reveals LSC heterogeneity. Finally, we demonstrated that JAM-C controls Src family kinase (SFK) activation in LSC and that LIC with exacerbated SFK activation was uniquely found within the JAM-C-expressing LSC compartment. Cancer Res; 77(23); 6627-40. ©2017 AACR.

Natural Killer Defective Maturation Is Associated with Adverse Clinical Outcome in Patients with Acute Myeloid Leukemia

Accumulating evidence highlights natural killer (NK) cell parameters as potential prognostic factors in cancer patients, which provides a strong rationale for developing therapeutic strategies aiming at restoring NK cell. However, reaching this point warrants better characterization of tumor-induced NK cell alterations. Our group recently reported heterogeneous NK maturation in acute myeloid leukemia (AML) patients. However, the clinical significance of such observations remained to be assessed on a larger cohort of patients. NK maturation based on expression of CD56, CD57, and KIR was assessed by flow cytometry in newly diagnosed AML patients (N = 87 patients from GOELAMS-LAM-IR-2006 multicenter trial). Clinical outcome was evaluated with regard to NK maturation profiles. Unsupervised integrated analysis of NK maturation markers confirmed the existence of three distinct groups of patients [hypomaturation (24.1%), intermediate maturation (66.7%), and hypermaturation (9.2%)]. In univariate analysis, significant differences in overall survival (OS) (P = 0.0006) and relapse-free survival (RFS) (P < 0.0001) were observed among these different groups. Patients with hypomaturation profile had reduced OS, with 3-year OS rates of 12.5 vs 57.1 and 57.4% for patients with intermediate and hypermaturation, respectively. Consistently, patients with hypomaturation profile had reduced RFS, with 3-year RFS rates of 0 vs 52.6 and 73.3% for patients with intermediate and hypermaturation, respectively. In multivariate Cox regression models, NK hypomaturation remained significantly associated with reduced OS and RFS, independent of other factors [hazard ratio (HR) = 4.15, P = 0.004 and HR = 8.23, P = 0.003, respectively]. NK maturation defects were further explored by mass cytometry and revealed that NK hypomaturation profile is associated with a reduced frequency of memory-like NK cells. In conclusion, besides classical alterations of NK triggering and inhibitory receptors expression in AML, we confirm that the homeostasis of NK maturation can be modified in the context of AML, notably with a deep maturation blockade in almost 10% patients.

NKp46 expression on NK cells as a prognostic and predictive biomarker for response to allo-SCT in patients with AML

NKp46 is a major determinant of natural killer (NK) cell function and it is implicated in tumor immune surveillance in acute myeloid leukemia (AML). The purpose of this study was to investigate the prognostic significance of NKp46 expression in an independent cohort of patients with AML, and to investigate the impact of NKp46 on clinical outcome after allogeneic stem cell transplantation (allo-SCT).

NKp46 expression was assessed at diagnosis on NK cells by flow cytometry (N = 180 patients). Clinical outcome was evaluated with regard to NKp46 expression. Patients with NKp46^high phenotype at diagnosis had better progression-free survival (PFS) and overall survival (OS) than patients with NKp46^low phenotype (74.3% vs. 46.6%, p = 0.014; 82.6% vs. 57.1%, p = 0.010, respectively). In multivariate analysis, high NKp46 was an independent factor for improved OS (HR = 0.409, p = 0.010) and PFS (HR = 0.335, p = 0.011). Subgroup analysis revealed that allo-SCT had a favorable impact on PFS in patients with NKp46^high phenotype (p = 0.025). By contrast, allo-SCT did not impact PFS in patients with low NKp46 expression (p = 0.303).

In conclusion, we validate the prognostic value of NKp46 expression at diagnosis in AML. However, the prognostic value of NKp46 expression is limited to patients treated with allo-SCT, thus suggesting that NKp46 status may be predictive for allo-SCT responsiveness.

Increased NK Cell Maturation in Patients with Acute Myeloid Leukemia

Understanding immune alterations in cancer patients is a major challenge and requires precise phenotypic study of immune subsets. Improvement of knowledge regarding the biology of natural killer (NK) cells and technical advances leads to the generation of high dimensional dataset. High dimensional flow cytometry requires tools adapted to complex dataset analyses. This study presents an example of NK cell maturation analysis in Healthy Volunteers (HV) and patients with Acute Myeloid Leukemia (AML) with an automated procedure using the FLOCK algorithm. This procedure enabled to automatically identify NK cell subsets according to maturation profiles, with 2D mapping of a four-dimensional dataset. Differences were highlighted in AML patients compared to HV, with an overall increase of NK maturation. Among patients, a strong heterogeneity in NK cell maturation defined three distinct profiles. Overall, automatic gating with FLOCK algorithm is a recent procedure, which enables fast and reliable identification of cell populations from high-dimensional cytometry data. Such tools are necessary for immune subset characterization and standardization of data analyses. This tool is adapted to new immune cell subsets discovery, and may lead to a better knowledge of NK cell defects in cancer patients. Overall, 2D mapping of NK maturation profiles enabled fast and reliable identification of NK cell subsets.

Human plasmacytoid dendritic cells regulate IFN-α production through activation-induced splicing of IL-18Rα

IFN-α production by pDCs regulates host protection against viruses and is implicated in autoimmune pathology. Human pDCs express high levels of IL-18R, but little is known of its role in pDC function. We report that IL-18R signaling negatively regulates IFN-α production through activation-induced splicing of IL-18Rα in human pDCs. Our data reveal two distinct isoforms of IL-18Rα in human pDCs: the known, full-length receptor (IL-18Rα1) and a novel, truncated variant (IL-18Rα2), which functions as a molecular decoy that competitively inhibits the canonical IL-18Rα1/IL-18Rβ signaling pathway. Whereas NK cells and pDCs both express IL-18Rα1, pDCs express significantly higher levels of IL-18Rα2, resulting in differential responses of these populations to IL-18. Flu exposure increases IL-18Rα1 expression in pDCs, and the blocking of IL-18R enhances pDC production of IFN-α and IP-10; thus, pDCs use activation-induced splicing to regulate IFN-α production in response to flu. These data demonstrate that IL-18R modulates IFN-α release by human pDCs and suggest that IL-18R signaling may represent a promising therapeutic target.

Cancer-Induced Alterations of NK-Mediated Target Recognition: Current and Investigational Pharmacological Strategies Aiming at Restoring NK-Mediated Anti-Tumor Activity

Despite evidence of cancer immune-surveillance, which plays a key role in tumor rejection, cancer cells can escape immune recognition through different mechanisms. Thus, evasion to Natural killer (NK) cell-mediated anti-tumor activity is commonly described and is mediated by various mechanisms, mainly cancer cell-induced down-regulation of NK-activating receptors (NCRs, NKG2D, DNAM-1, and CD16) as well as up-regulation of inhibitory receptors (killer-cell immunoglobulin-like receptors, KIRs, NKG2A). Alterations of NK cells lead to an impaired recognition of tumor cells as well as a decreased ability to interact with immune cells. Alternatively, cancer cells downregulate expression of ligands for NK cell-activating receptors and up-regulate expression of the ligands for inhibitory receptors. A better knowledge of the extent and the mechanisms of these defects will allow developing pharmacological strategies to restore NK cell ability to recognize and lyse tumor cells. Combining conventional chemotherapy and immune modulation is a promising approach likely to improve clinical outcome in diverse neoplastic malignancies. Here, we overview experimental approaches as well as strategies already available in the clinics that restore NK cell functionality. Yet successful cancer therapies based on the manipulation of NK cell already have shown efficacy in the context of hematologic malignancies. Additionally, the ability of cytotoxic agents to increase susceptibility of tumors to NK cell lysis has been studied and may require improvement to maximize this effect. More recently, new strategies were developed to specifically restore NK cell phenotype or to stimulate NK cell functions. Overall, pharmacological immune modulation trends to be integrated in therapeutic strategies and should improve anti-tumor effects of conventional cancer therapy.

Optimization of routine KRAS mutation PCR-based testing procedure for rational individualized first-line-targeted therapy selection in metastatic colorectal cancer

KRAS mutation detection represents a crucial issue in metastatic colorectal cancer (mCRC). The optimization of KRAS mutation detection delay enabling rational prescription of first-line treatment in mCRC including anti-EGFR-targeted therapy requires robust and rapid molecular biology techniques. Routine analysis of mutations in codons 12 and 13 on 674 paraffin-embedded tissue specimens of mCRC has been performed for KRAS mutations detection using three molecular biology techniques, that is, high-resolution melting (HRM), polymerase chain reaction restriction fragment length polymorphism (PCR-RFLP), and allelic discrimination PCR (TaqMan PCR). Discordant cases were assessed with COBAS 4800 KRAS CE-IVD assay. Among the 674 tumor specimens, 1.5% (10/674) had excessive DNA degradation and could not be analyzed. KRAS mutations were detected in 38.0% (256/674) of the analysable specimens (82.4% in codon 12 and 17.6% in codon 13). Among 613 specimens in whom all three techniques were used, 12 (2.0%) cases of discordance between the three techniques were observed. 83.3% (10/12) of the discordances were due to PCR-RFLP as confirmed by COBAS 4800 retrospective analysis. The three techniques were statistically comparable (κ > 0.9; P < 0.001). From these results, optimization of the routine procedure consisted of proceeding to systematic KRAS detection using HRM and TaqMan and PCR-RFLP in case of discordance and allowed significant decrease in delays. The results showed an excellent correlation between the three techniques. Using HRM and TaqMan warrants high-quality and rapid-routine KRAS mutation detection in paraffin-embedded tumor specimens. The new procedure allowed a significant decrease in delays for reporting results, enabling rational prescription of first-line-targeted therapy in mCRC.

Cellular response to cetuximab in PTEN-silenced head and neck squamous cell carcinoma cell line

The implication of loss of PTEN expression in resistance to targeted therapy has already been described in many tumor types. The absence of response to anti-EGFR agents in PTEN-deficient tumors relies on persistent activation of signaling pathways downstream of pEGFR. To investigate the role of PTEN loss of expression in head and neck squamous cell carcinoma (HNSCC) response to cetuximab, we used siRNA in Cal 27 cells and then evaluated key signaling protein activation (pAKT and pERK 1/2) as well as cell viability and proliferation. PTEN silencing in Cal 27 cells led to a constitutive activation of signaling pathways evidenced by a strong increase in pAKT and pERK 1/2 expression. Moreover, PTEN-silenced cells did not show any significant changes either in cell viability or proliferation, only slight modifications on cell cycle. Additionally and unpredictably, our results indicated that PTEN silencing, led to a drastic reduction in pEGFR expression whereas total EGFR level did not significantly vary. Strikingly, despite this overactivation of signaling pathways ruling cell survival and proliferation in siPTEN cells, cetuximab fully exerted pAKT and pERK 1/2 inhibition of expression, similarly to its effect in untransfected Cal 27 cells. In conclusion, our study established that in Cal 27 cells, cetuximab keeps full ability to inhibit EGFR-dependent mechanisms, as shown by a decreased pAKT and pERK 1/2 level of expression, despite a strong PTEN silencing-induced overactivation. In Cal 27 cells, loss of PTEN expression does not lead to a loss of cetuximab efficacy in inhibiting EGFR-downstream signaling pathways, contrarily to data shown in previous works conducted in other tumor types.