Deep learning for dual detection of microsatellite instability and POLE mutations in colorectal cancer histopathology.

In the spectrum of colorectal tumors, microsatellite-stable (MSS) tumors with DNA polymerase ε (POLE) mutations exhibit a hypermutated profile, holding the potential to respond to immunotherapy similarly to their microsatellite-instable (MSI) counterparts. Yet, due to their rarity and the associated testing costs, systematic screening for these mutations is not commonly pursued. Notably, the histopathological phenotype resulting from POLE mutations is theorized to resemble that of MSI. This resemblance not only could facilitate their detection by a transformer-based Deep Learning (DL) system trained on MSI pathology slides, but also indicates the possibility for MSS patients with POLE mutations to access enhanced treatment options, which might otherwise be overlooked. To harness this potential, we trained a Deep Learning classifier on a large dataset with the ground truth for microsatellite status and subsequently validated its capabilities for MSI and POLE detection across three external cohorts. Our model accurately identified MSI status in both the internal and external resection cohorts using pathology images alone. Notably, with a classification threshold of 0.5, over 75% of POLE driver mutant patients in the external resection cohorts were flagged as "positive" by a DL system trained on MSI status. In a clinical setting, deploying this DL model as a preliminary screening tool could facilitate the efficient identification of clinically relevant MSI and POLE mutations in colorectal tumors, in one go.

Differential diagnosis of small hepatocellular nodules in cirrhosis: surrogate histological criteria of TERT promoter mutations.

AIMS: The differential diagnosis of small hepatocellular nodules in cirrhosis between dysplastic nodules and hepatocellular carcinoma (HCC) remains challenging on biopsy. As TERT promoter (pTERT) mutations may indicate the nodules already engaged in the malignant process, the aim of this study was to identify histological criteria associated with pTERT mutations by detecting these mutations by ddPCR in small formalin-fixed paraffin-embedded (FFPE) hepatocellular nodules arising in cirrhosis. METHODS AND RESULTS: We built a bicentric cohort data set of 339 hepatocellular nodules < 2 cm from cirrhotic samples, divided into a test cohort of 299 resected samples and a validation cohort of 40 biopsies. Pathological review, based on the evaluation of 14 histological criteria, classified all nodules. pTERT mutations were identified by ddPCR in FFPE samples. Among the 339 nodules, ddPCR revealed pTERT mutations in 105 cases (31%), including 90 and 15 cases in the test and validation cohorts, respectively. On multivariate analysis, three histological criteria were associated with pTERT mutations in the test cohort: increased cell density (P = 0.003), stromal invasion (P = 0.036) and plate-thickening anomalies (P < 0.001). With the combination of at least two of these major criteria, the AUC for predicting pTERT mutations was 0.84 in the test cohort (sensitivity: 86%, specificity: 83%) and 0.81 in the validation cohort (sensitivity: 87%, specificity: 76%). CONCLUSIONS: We identified three histological criteria as surrogate markers of pTERT mutations that may be used in routine biopsy to more clearly classify small hepatocellular nodules arising in cirrhosis.

Deep learning-based phenotyping reclassifies combined hepatocellular-cholangiocarcinoma.

Primary liver cancer arises either from hepatocytic or biliary lineage cells, giving rise to hepatocellular carcinoma (HCC) or intrahepatic cholangiocarcinoma (ICCA). Combined hepatocellular- cholangiocarcinomas (cHCC-CCA) exhibit equivocal or mixed features of both, causing diagnostic uncertainty and difficulty in determining proper management. Here, we perform a comprehensive deep learning-based phenotyping of multiple cohorts of patients. We show that deep learning can reproduce the diagnosis of HCC vs. CCA with a high performance. We analyze a series of 405 cHCC-CCA patients and demonstrate that the model can reclassify the tumors as HCC or ICCA, and that the predictions are consistent with clinical outcomes, genetic alterations and in situ spatial gene expression profiling. This type of approach could improve treatment decisions and ultimately clinical outcome for patients with rare and biphenotypic cancers such as cHCC-CCA.

Intentional R1 resection of liver metastases: A new treatment paradigm for patients with advanced colorectal cancer based on a propensity score-Matched case-control analysis.

BACKGROUND: Clinical outcomes of colorectal cancer (CRC) patients after an incomplete microscopic (R1) resection of liver metastases may not differ from those following a microscopically margin negative (R0) resection, when the latest is not feasible because of anatomic issues. We aimed at comparing the clinical outcomes of CRC patients with an intentional R1 or with a R0 resection of liver metastases. METHODS: All patients with advanced in CRC and liver metastases consecutively treated by liver resection between February 2005 and January 2019 at in the department of Digestive and Hepatobiliary Surgery of Henri Mondor University Hospital (Créteil, France) were included in this retrospective case-control study. Overall survival (OS) and event-free survival (EFS) were compared between patients who underwent an intentional (pre-operative decision) R1 resection (iR1) to those who had a R0 resection of liver metastases. To account for confounding, comparison between the 2 groups was performed after adjustment using propensity score analysis. RESULTS: Twenty-six CRC patients treated by iR1 resection of liver metastases were compared to 98 patients treated by R0 resection. Median OS reached 39 months [95% confidence interval (CI): 25-67] and 63 months [95% CI: 52-76] in the iR1 and R0 groups, respectively. After adjustment by inverse probability of treatment weighting, patients' OS and EFS did not differ significantly between the iR1 and R0 groups (hazard ratio (HR): 1.19 [0.54-2.62] and 1.67 [0.93-3.03]), respectively. CONCLUSION: iR1 resection of liver metastases in advanced CRC patients is an acceptable therapeutic strategy, when R0 resection is not feasible.

[Myeloid neoplasms associated with rearrangement of PDGFRB: A rare and tricky disease]. / La néoplasie myéloïde associée à un réarrangement de PDGFRB : une pathologie rare de diagnostic difficile.

In the latest World Health Organization classification (WHO), eosinophilic disorders represent a group of rare pathologic conditions with highly heterogeneous pathophysiology. In this report, we describe a case of myeloid neoplasm associated with eosinophilia and rearrangement of PDGFRB gene in a 67-year-old-male patient hospitalized with cerebellous ataxia. Initial investigations showed a bicytopenia with hypereosinophilia varying from 1.1 to 1.6×109/L. Bone marrow aspiration was rich and showed a heterogeneous distribution of myeloid cells with clusters of promyelocytes and proerythroblasts associated with numerous eosinophils and spindle-shaped mast cells but without excess of blasts, dysplasia nor maturation skewing. These aspects suggested an atypical myeloproliferative neoplasm. Bone marrow biopsy was performed showing also a very high cellularity with area of myeloid and erythroid precursors associated with numerous spindle-shaped mast cells. Diagnoses of unclassified myeloid neoplasm and/or systemic mastocytosis were then proposed. Further chromosome analysis showed a t(5;8) translocation with PDGFRB rearrangement revealed in fluorescent in situ hybridization. Patient was treated with imatinib and intravenous immunoglobulin therapy allowing a significant improvement in neurological symptoms and biological results. Patient condition is currently stable after six lines of treatment. This rare hematopoietic neoplasm displays unusual histological and cytological features and can mimic other myeloproliferative neoplasm. Specific cytogenetics analysis should be considered for such cases with hypereosinophilia to select patients that may benefit from targeted therapy.

Evaluation of two new highly multiplexed PCR assays as an alternative to next-generation sequencing for IDH1/2 mutation detection.

IDH1 and IDH2 somatic mutations have been identified in solid tumors and blood malignancies. The development of inhibitors of mutant IDH1 and IDH2 in the past few years has prompted the development of a fast and sensitive assay to detect IDH1R132 , IDH2R140 and IDH2R172 mutations to identify patients eligible for these targeted therapies. This study aimed to compare two new multiplexed PCR assays - an automated quantitative PCR (qPCR) on the PGX platform and a droplet digital PCR (ddPCR) with next-generation sequencing (NGS) for IDH1/2 mutation detection. These assays were evaluated on 102 DNA extracted from patient peripheral blood, bone marrow and formalin-fixed paraffin-embedded tissue samples with mutation allelic frequency ranging from 0.6% to 45.6%. The ddPCR assay had better analytical performances than the PGX assay with 100% specificity, 100% sensitivity and a detection limit down to 0.5% on IDH1R132 , IDH2R140 and IDH2R172 codons, and a high correlation with NGS results. Therefore, the new highly multiplexed ddPCR is a fast and cost-effective assay that meets most clinical needs to identify and follow cancer patients in the era of anti-IDH1/2-targeted therapies.

NA1-115-7, from Zygogynum pancheri, is a new selective MCL-1 inhibitor inducing the apoptosis of hematological cancer cells but non-toxic to normal blood cells or cardiomyocytes.

The overexpression of antiapoptotic members (BCL-2, BCL-xL, MCL-1, etc.) of the BCL-2 family contributes to tumor development and resistance to chemotherapy or radiotherapy. Synthetic inhibitors targeting these proteins have been developed, and some hematological malignancies are now widely treated with a BCL-2 inhibitor (venetoclax). However, acquired resistance to venetoclax or chemotherapy drugs due to an upregulation of MCL-1 has been observed, rendering MCL-1 an attractive new target for treatment. Six MCL-1 inhibitors (S64315, AZD-5991, AMG-176, AMG-397, ABBV-467 and PRT1419) have been evaluated in clinical trials since 2016, but some were affected by safety issues and none are currently used clinically. There is, therefore, still a need for alternative molecules. We previously described two drimane derivatives as the first covalent BH3 mimetics targeting MCL-1. Here, we described the characterization and biological efficacy of one of these compounds (NA1-115-7), isolated from Zygogynum pancheri, a plant belonging to the Winteraceae family. NA1-115-7 specifically induced the apoptosis of MCL-1-dependent tumor cells, with two hours of treatment sufficient to trigger cell death. The treatment of lymphoma cells with NA1-115-7 stabilized MCL-1, disrupted its interactions with BAK, and rapidly induced apoptosis through a BAK- and BAX-mediated process. Importantly, a similar treatment with NA1-115-7 was not toxic to erythrocytes, peripheral blood mononuclear cells, platelets, or cardiomyocytes. These results highlight the potential of natural products for use as specific BH3 mimetics non-toxic to normal cells, and they suggest that NA1-115-7 may be a promising tool for use in cancer treatment.

Nestin as a diagnostic and prognostic marker for combined hepatocellular-cholangiocarcinoma.

BACKGROUND & AIMS: Combined hepatocellular-cholangiocarcinoma (cHCC-CCA) is a rare primary liver cancer (PLC) associated with a poor prognosis. Given the challenges in its identification and its clinical implications, biomarkers are critically needed. We aimed to investigate the diagnostic and prognostic value of the immunohistochemical expression of Nestin, a progenitor cell marker, in a large multicentric series of PLCs. METHODS: We collected 461 cHCC-CCA samples from 32 different clinical centers. Control cases included 368 hepatocellular carcinomas (HCCs) and 221 intrahepatic cholangiocarcinomas (iCCAs). Nestin immunohistochemistry was performed on whole tumor sections. Diagnostic and prognostic performances of Nestin expression were determined using receiver-operating characteristic curves and Cox regression modeling. RESULTS: Nestin was able to distinguish cHCC-CCA from HCC with AUCs of 0.85 and 0.86 on surgical and biopsy samples, respectively. Performance was lower for the distinction of cHCC-CCA from iCCA (AUCs of 0.59 and 0.60). Nestin, however, showed a high prognostic value, allowing identification of the subset of cHCC-CCA ("Nestin High", >30% neoplastic cells with positive staining) associated with the worst clinical outcome (shorter disease-free and overall survival) after surgical resection and liver transplantation, as well as when assessment was performed on biopsies. CONCLUSION: We show in different clinical settings that Nestin has diagnostic value and that it is a useful biomarker to identify the subset of cHCC-CCA associated with the worst clinical outcome. Nestin immunohistochemistry may be used to refine risk stratification and improve treatment allocation for patients with this highly aggressive malignancy. LAY SUMMARY: There are different types of primary liver cancers (i.e. cancers that originate in the liver). Accurately identifying a specific subtype of primary liver cancer (and determining its associated prognosis) is important as it can have a major impact on treatment allocation. Herein, we show that a protein called Nestin could be used to refine risk stratification and improve treatment allocation for patients with combined hepatocellular carcinoma, a rare but highly aggressive subtype of primary liver cancer.

High prevalence of unusual KRAS, NRAS, and BRAF mutations in POLE-hypermutated colorectal cancers.

Exonucleasic domain POLE (edPOLE) mutations, which are responsible for a hypermutated tumor phenotype, occur in 1-2% of colorectal cancer (CRC) cases. These alterations represent an emerging biomarker for response to immune checkpoint blockade. This study aimed to assess the molecular characteristics of edPOLE-mutated tumors to facilitate patient screening. Based on opensource data analysis, we compared the prevalence of edPOLE mutations in a control group of unselected CRC patients (n = 222) vs a group enriched for unusual BRAF/RAS mutations (n = 198). Tumor mutational burden (TMB) and immune infiltrate of tumors harboring edPOLE mutations were then analyzed. In total, 420 CRC patients were analyzed: 11 edPOLE-mutated tumors were identified, most frequently in microsatellite (MMR)-proficient young (< 70 years) male patients, with left-sided tumors harboring noncodon 12 KRAS mutation. The prevalence of edPOLE-mutated tumors in the control vs the experimental screening group was, respectively, 0.45% (n = 1) vs 5.0% (n = 10). Among the 11 edPOLE-mutated cases, two had a low TMB, three were hypermutated, and six were ultramutated. EdPOLE-mutated cases had a high CD8+ tumor-infiltrating lymphocyte (TIL) infiltration. These clinicopathological and molecular criteria may help to identify edPOLE mutations associated with a high TMB in CRC, and improve the selection of patients who could benefit from immunotherapy.

Immune Profiling of Combined Hepatocellular- Cholangiocarcinoma Reveals Distinct Subtypes and Activation of Gene Signatures Predictive of Response to Immunotherapy.

PURPOSE: Combined hepatocellular-cholangiocarcinoma (cHCC-CCA) is a rare malignancy associated with an overall poor prognosis. We aimed to investigate the immune profile of cHCC-CCA and determine its impact on disease outcome. EXPERIMENTAL DESIGN: We performed a multicenter study of 96 patients with cHCC-CCA. Gene expression profile was analyzed using nCounter PanCancer IO 360 Panel. Densities of main immune cells subsets were quantified from digital slides of IHC stainings. Genetic alterations were investigated using targeted next-generation sequencing. RESULTS: Two main immune subtypes of cHCC-CCA were identified by clustering analysis: an "immune-high" (IH) subtype (57% of the cases) and an "immune-low" (IL) subtype (43% of the cases). Tumors classified as IH showed overexpression of genes related to immune cells recruitment, adaptive and innate immunity, antigen presentation, cytotoxicity, immune suppression, and inflammation (P < 0.0001). IH cHCC-CCAs also displayed activation of gene signatures recently shown to be associated with response to immunotherapy in patients with HCC. Quantification of immunostainings confirmed that IH tumors were also characterized by higher densities of immune cells. Immune subtypes were not associated with any genetic alterations. Finally, multivariate analysis showed that the IH subtype was an independent predictor of improved overall survival. CONCLUSIONS: We have identified a subgroup of cHCC-CCA that displays features of an ongoing intratumor immune response, along with an activation of gene signatures predictive of response to immunotherapy in HCC. This tumor subclass is associated with an improved clinical outcome. These findings suggest that a subset of patients with cHCC-CCA may benefit from immunomodulating therapeutic approaches.

What management for epidermal growth factor receptor-mutated non-small-cell lung cancer, with squamous cell transformation and T790M-acquired resistance mechanisms? A Case report and review of literature.

Histological transformation into squamous cell carcinoma (SCC) is a rare mechanism of resistance to epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors. Its pathophysiology remains unclear and its management is particularly challenging. We report on tumor progression with SCC histological transformation associated with the T790M mutation in a patient with stage IV bronchial adenocarcinoma with an L858R mutation of the EGFR gene and treated with gefitinib. We will discuss the importance of liquid and tumor biopsy in the diagnostic management of resistance mechanisms as well as therapeutic management options.

Idylla MSI test as a new tool for microsatellite instability detection in sebaceous tumours and keratoacanthomas.

AIM: Sebaceous tumours and keratoacanthomas can be associated with mismatch repair (MMR) deficiency and thus microsatellite instability (MSI). In such tumours, MSI phenotype could be an argument to search for an underlying Muir-Torre syndrome (MTS). MTS has been recognised as a variant of Lynch syndrome, characterised by a deficiency of the MMR proteins. In Lynch syndrome, the sensitivity and specificity of the techniques used to detect MSI is well described, which is not the case for skin tumours. In our hands, immunohistochemistry is a sensitive and specific method to detect MMR deficiency in those tumours. Contrasting with tumours of Lynch spectrum, sensitivity and specificity of molecular methods has not been extensively studied. This study aimed at evaluating two molecular methods to detect MSI phenotype in MTS associated tumours: a commonly used pentaplex PCR using Bethesda markers and the fully automated method using the Idylla MSI assay. METHODS: A comparison between PCR, and Idylla was performed on 39 DNA extracted from cutaneous tumours. Immunohistochemistry was used as the gold standard to calculate sensitivity and specificity of both molecular techniques. RESULTS: Concordant results were found in 32 cases (82%) with pentaplex PCR and in 36 cases (92%) with Idylla. The sensitivity of pentaplex PCR to detect MSI phenotype was 76% whereas Idylla sensitivity was 90%. CONCLUSION: Idylla is more performant than PCR, for the detection of MSI in MTS-associated tumours and is a reliable additional technique to help detecting MTS in these tumours.

Detection of microsatellite instability in a panel of solid tumours with the Idylla MSI Test using extracted DNA.

AIM: During the last few years, determination of microstatellite instability (MSI) status has become a routine part of clinical practice, essentially to detect Lynch syndrome. Recently, MSI testing has increased with the development of immunotherapy and has expanded to a large panel of solid tumours. The aim of our work was to evaluate a fully automated system developed by Biocartis, the Idylla MSI Test, which performs an MSI analysis within 150 min. METHODS: A comparison between pentaplex PCR, immunohistochemistry and Idylla MSI Test was performed in 53 colorectal carcinoma samples, 7 small intestine adenocarcinomas, 15 duodenal and pancreatic adenocarcinomas, 16 gastric tumours, 15 endometrial adenocarcinomas, 5 ovarian carcinomas and 4 cases of urinary tract tumours using extracted DNA. Limit-of-detection (LOD) experiment was also done using a commercial DNA known to harbour MSI phenotype. RESULTS: The overall sensitivity was 94% and the overall specificity was 100%. Two invalid and three false-negative results were observed. Our experiments showed that the amount of DNA loaded into the cartridge was decisive and should be superior to 25 ng. LOD comprised between 4% and 8%. CONCLUSION: Overall, we have demonstrated that the Idylla MSI Test is a rapid and valid option to detect MSI phenotype which can be used in a large panel of solid tumours.

The BCL-2 family protein inhibitor ABT-737 as an additional tool for the treatment of EBV-associated post-transplant lymphoproliferative disorders.

Post-transplant lymphoproliferative disorders (PTLD) and Burkitt's lymphoma (BL) are B-cell malignancies strongly associated with Epstein-Barr virus (EBV) infection. In these lymphoproliferative disorders, EBV infection induces an increase in the expression of the anti-apoptotic protein BCL-2. Given its chemoprotective effect, BCL-2 constitutes an attractive target for new therapeutic strategies for EBV-positive B-cell malignancies. Here, we show that ABT-737, a small inhibitor of BCL-2, BCL-X(L), and BCL-w, strongly induced apoptosis in vitro in EBV-positive lymphoblastoid cell lines (which is a model for PTLD), whereas BL was less sensitive. ABT-737 reduced tumor growth and increased the overall survival of mice in a xenograft model of PTLD but had no effect on BL xenograft mice. ABT-737 combined with a low dose of cyclophosphamide, a major component of the conventional CHOP chemotherapy regimen for BL patients, reduced tumor growth during treatment but failed to improve the overall survival of BL xenograft mice. By contrast, the combination of ABT-737 and rituximab, one of the main options for the treatment of PTLD, was highly efficient and induced approximately 70% remission in PTLD xenograft mice. These results suggest that the use of agents targeting BCL-2, either alone or in combination with other conventional drugs, represents a novel promising approach for post-transplant EBV-positive B lymphoproliferative disorders.

Evaluation of the Idylla system to detect the EGFRT790M mutation using extracted DNA.

INTRODUCTION: During the last few years, detection of epidermal growth-factor-receptor (EGFR)-activating mutations has become a routine part of clinical practice because of their importance in choosing the optimal treatment strategy for non-small-cell lung cancers (NSCLCs). The emergence of third-generation EGFR-tyrosine-kinase inhibitors required the implementation of sensitive methods to detect the subclonal EGFRT790M mutation. Clinical implications make it essential to rapidly search for the T790M mutation, which is a real challenge for laboratories. The aim of this study was to compare performances of next-generation sequencing (NGS), one of the most frequently used molecular biology methods, and Idylla EGFR-Mutation Assay (henceforth Idylla), a fully automated real-time polymerase chain reaction (PCR) that is increasingly used in pathology laboratories, to detect the EGFRT790M mutation using DNA. METHODS: This retrospective study used 47 DNA samples extracted from NSCLC biopsies that previous NGS identified as: 29 harboring EGFR and T790M resistance mutations, 11 EGFR-activating mutation without T790 M and 7 wild-type EGFR. EGFRT790M limit-of-detection (LOD) experiments used a commercial DNA known to harbor that mutation. RESULTS: Idylla detected primary EGFR-activating mutations and the T790 M mutation in 97.5 % and 65.5 % of the cases, respectively. The results of this retrospective analysis and LOD experiments showed that the Idylla should only be used to detect EGFR mutations in samples with > 25 ng of DNA and > 10 % tumor cells. CONCLUSIONS: Idylla was able to rapidly detect EGFR-activating mutations but detecting subclone mutations, like T790M, with < 25 ng of good-quality DNA or < 10 % tumor cells (variant allele frequency below the assay's validated LOD) was not always reliable.

Dual inhibitors of the pro-survival proteins Bcl-2 and Mcl-1 derived from natural compound meiogynin A.

Thirty analogues of natural meiogynin A, a pan-Bcl-2 inhibitor, were prepared in order to elaborate cytotoxic compounds on specific cancer cells overexpressing one or more proteins of the Bcl-2 family. The interaction of all the new analogues with Bcl-xL, Mcl-1 and Bcl-2 proteins was first evaluated by fluorescence polarization assay (FPA) and showed that modulation of the lateral chain has a dramatic impact as subtle changes significantly modify the activity on the target proteins. The acetoxymethyl prodrugs of the two most active compounds were then elaborated to determine their cytotoxicity on B cell lines. A strong cytotoxic effect on BL2, RS4;11 and H929 cells was observed with a triazole prodrug that induces apoptosis.

Constitutive autophagy contributes to resistance to TP53-mediated apoptosis in Epstein-Barr virus-positive latency III B-cell lymphoproliferations.

The Epstein-Barr virus (EBV) is associated with various lymphoproliferative disorders and lymphomas. We have previously demonstrated that treating wild-type TP53-expressing B cell lines with the TP53 pathway activator nutlin-3 induced apoptosis in EBV-negative and EBV-positive latency I cells whereas EBV-positive latency III cells remained much more apoptosis-resistant. Here, we report a constitutively high level of autophagy in these resistant cells which express high levels of the proautophagic protein BECN1/Beclin 1 based, at least in part, on the activation of the NFKB signaling pathway by the viral protein LMP1. Following treatment with nutlin-3, several autophagy-stimulating genes were upregulated both in EBV-negative and EBV-positive latency III cells. However the process of autophagy was only triggered in the latter and was associated with an upregulation of SESN1/sestrin 1 and inhibition of MTOR more rapid than in EBV-negative cells. A treatment with chloroquine, an inhibitor of autophagy, potentiated the apoptotic effect of nutlin-3, particularly in those EBV-positive cells which were resistant to apoptosis induced by nutlin-3 alone, thereby showing that autophagy participates in this resistant phenotype. Finally, using immunohistochemical staining, clinical samples from various B cell lymphoproliferations with the EBV-positive latency II or III phenotype were found to harbor a constitutively active autophagy.

Granzyme B-activated p53 interacts with Bcl-2 to promote cytotoxic lymphocyte-mediated apoptosis.

Granzyme B (GzmB) plays a major role in CTLs and NK cell-mediated elimination of virus-infected cells and tumors. Human GzmB preferentially induces target cell apoptosis by cleaving the proapoptotic Bcl-2 family member Bid, which, together with Bax, induces mitochondrial outer membrane permeabilization. We previously showed that GzmB also induces a rapid accumulation of the tumor-suppressor protein p53 within target cells, which seems to be involved in GzmB-induced apoptosis. In this article, we show that GzmB-activated p53 accumulates on target cell mitochondria and interacts with Bcl-2. This interaction prevents Bcl-2 inhibitory effect on both Bax and GzmB-truncated Bid, and promotes GzmB-induced mitochondrial outer membrane permeabilization. Consequently, blocking p53-Bcl-2 interaction decreases GzmB-induced Bax activation, cytochrome c release from mitochondria, and subsequent effector caspases activation leading to a decreased sensitivity of target cells to both GzmB and CTL/NK-mediated cell death. Together, our results define p53 as a new important player in the GzmB apoptotic signaling pathway and in CTL/NK-induced apoptosis.