Anshuman Panda

Immune activation and response to pembrolizumab in POLE-mutant endometrial cancer

Antibodies that target the immune checkpoint receptor programmed cell death protein 1 (PD-1) have resulted in prolonged and beneficial responses toward a variety of human cancers. However, anti-PD-1 therapy in some patients provides no benefit and/or results in adverse side effects. The factors that determine whether patients will be drug sensitive or resistant are not fully understood; therefore, genomic assessment of exceptional responders can provide important insight into patient response. Here, we identified a patient with endometrial cancer who had an exceptional response to the anti-PD-1 antibody pembrolizumab. Clinical grade targeted genomic profiling of a pretreatment tumor sample from this individual identified a mutation in DNA polymerase epsilon (POLE) that associated with an ultramutator phenotype. Analysis of The Cancer Genome Atlas (TCGA) revealed that the presence of POLE mutation associates with high mutational burden and elevated expression of several immune checkpoint genes. Together, these data suggest that cancers harboring POLE mutations are good candidates for immune checkpoint inhibitor therapy.

Immune Activation and Benefit From Avelumab in EBV-Positive Gastric Cancer

Response to immune checkpoint therapy can be associated with a high mutation burden, but other mechanisms are also likely to be important. We identified a patient with metastatic gastric cancer with meaningful clinical benefit from treatment with the anti-programmed death-ligand 1 (PD-L1) antibody avelumab. This tumor showed no evidence of high mutation burden or mismatch repair defect but was strongly positive for presence of Epstein-Barr virus (EBV) encoded RNA. Analysis of The Cancer Genome Atlas gastric cancer data (25 EBV+, 80 microsatellite-instable [MSI], 310 microsatellite-stable [MSS]) showed that EBV-positive tumors were MSS. Two-sided Wilcoxon rank-sum tests showed that: 1) EBV-positive tumors had low mutation burden (median = 2.07 vs 3.13 in log10 scale, P < 10-12) but stronger evidence of immune infiltration (median ImmuneScore 2212 vs 1295, P < 10-4; log2 fold-change of CD8A = 1.85, P < 10-6) compared with MSI tumors, and 2) EBV-positive tumors had higher expression of immune checkpoint pathway (PD-1, CTLA-4 pathway) genes in RNA-seq data (log2 fold-changes: PD-1 = 1.85, PD-L1 = 1.93, PD-L2 = 1.50, CTLA-4 = 1.31, CD80 = 0.89, CD86 = 1.31, P < 10-4 each), and higher lymphocytic infiltration by histology (median tumor-infiltrating lymphocyte score = 3 vs 2, P < .001) compared with MSS tumors. These data suggest that EBV-positive low-mutation burden gastric cancers are a subset of MSS gastric cancers that may respond to immune checkpoint therapy.

Widespread alternative exon usage in clinically distinct subtypes of Invasive Ductal Carcinoma

Cancer cells can have different patterns of exon usage of individual genes when compared to normal tissue, suggesting that alternative splicing may play a role in shaping the tumor phenotype. The discovery and identification of gene variants has increased dramatically with the introduction of RNA-sequencing technology, which enables whole transcriptome analysis of known, as well as novel isoforms. Here we report alternative splicing and transcriptional events among subtypes of invasive ductal carcinoma in The Cancer Genome Atlas (TCGA) Breast Invasive Carcinoma (BRCA) cohort. Alternative exon usage was widespread, and although common events were shared among three subtypes, ER+ HER2−, ER− HER2−, and HER2+, many events on the exon level were subtype specific. Additional RNA-seq analysis was carried out in an independent cohort of 43 ER+ HER2− and ER− HER2− primary breast tumors, confirming many of the exon events identified in the TCGA cohort. Alternative splicing and transcriptional events detected in five genes, MYO6, EPB41L1, TPD52, IQCG, and ACOX2 were validated by qRT-PCR in a third cohort of 40 ER+ HER2− and ER− HER2− patients, showing that these events were truly subtype specific.

Identifying a Clinically Applicable Mutational Burden Threshold as a Potential Biomarker of Response to Immune Checkpoint Therapy in Solid Tumors

Purpose An association between mutational burden and response to immune checkpoint therapy has been documented in several cancer types. The potential for such a mutational burden threshold to predict response to immune checkpoint therapy was evaluated in several clinical datasets, where mutational burden was measured either by whole-exome sequencing (WXS) or using commercially available sequencing panels. Methods WXS and RNA-seq data of 33 solid cancer types from TCGA were analyzed to determine whether a robust immune checkpoint activating mutation (iCAM) burden threshold associated with evidence of immune checkpoint activation exists in these cancers that may serve as a biomarker for response to immune checkpoint blockade therapy. Results We find that a robust iCAM threshold, associated with signatures of immune checkpoint activation, exists in 8 of 33 solid cancers: melanoma, lung adenocarcinoma, colon adenocarcinoma, endometrial cancer, stomach adenocarcinoma, cervical cancer, ER+HER2- breast cancer, and bladder-urothelial cancer. Tumors with mutational burden higher than the threshold (iCAM+) also had clear histologic evidence of lymphocytic infiltration. In published datasets of melanoma, lung adenocarcinoma and colon cancer, patients with iCAM+ tumors had significantly better response to immune checkpoint therapy compared to those with iCAM- tumors. ROC analysis using TCGA predictions as gold standard showed that iCAM+ tumors are accurately identifiable using clinical sequencing assays, such as FoundationOne or StrandAdvantage. Using the FoundationOne derived threshold, analysis of 113 melanoma tumors, showed that iCAM+ patients have significantly better response to immune checkpoint therapy. iCAM+ and iCAM- tumors have distinct mutation patterns and different immune microenvironments. Conclusion In 8 solid cancers, a mutational burden threshold exists that may predict response to immune checkpoint blockade. This threshold is identifiable using available clinical sequencing assays.

The Modular Adaptive Ribosome

The ribosome is an ancient machine, performing the same function across organisms. Although functionally unitary, recent experiments suggest specialized roles for some ribosomal proteins. Our central thesis is that ribosomal proteins function in a modular fashion to decode genetic information in a context dependent manner. We show through large data analyses that although many ribosomal proteins are essential with consistent effect on growth in different conditions in yeast and similar expression across cell and tissue types in mice and humans, some ribosomal proteins are used in an environment specific manner. The latter set of variable ribosomal proteins further function in a coordinated manner forming modules, which are adapted to different environmental cues in different organisms. We show that these environment specific modules of ribosomal proteins in yeast have differential genetic interactions with other pathways and their 5’UTRs show differential signatures of selection in yeast strains, presumably to facilitate adaptation. Similarly, we show that in higher metazoans such as mice and humans, different modules of ribosomal proteins are expressed in different cell types and tissues. A clear example is nervous tissue that uses a ribosomal protein module distinct from the rest of the tissues in both mice and humans. Our results suggest a novel stratification of ribosomal proteins that could have played a role in adaptation, presumably to optimize translation for adaptation to diverse ecological niches and tissue microenvironments.

Endogenous retroviral signatures predict immunotherapy response in clear cell renal cell carcinoma

Human endogenous retroviruses (hERVs) are remnants of exogenous retroviruses that have integrated into the genome throughout evolution. We developed a computational workflow, hervQuant, which identified more than 3,000 transcriptionally active hERVs within The Cancer Genome Atlas (TCGA) pan-cancer RNA-Seq database. hERV expression was associated with clinical prognosis in several tumor types, most significantly clear cell renal cell carcinoma (ccRCC). We explored two mechanisms by which hERV expression may influence the tumor immune microenvironment in ccRCC: (i) RIG-I–like signaling and (ii) retroviral antigen activation of adaptive immunity. We demonstrated the ability of hERV signatures associated with these immune mechanisms to predict patient survival in ccRCC, independent of clinical staging and molecular subtyping. We identified potential tumor-specific hERV epitopes with evidence of translational activity through the use of a ccRCC ribosome profiling (Ribo-Seq) dataset, validated their ability to bind HLA in vitro, and identified the presence of MHC tetramer–positive T cells against predicted epitopes. hERV sequences identified through this screening approach were significantly more highly expressed in ccRCC tumors responsive to treatment with programmed death receptor 1 (PD-1) inhibition. hervQuant provides insights into the role of hERVs within the tumor immune microenvironment, as well as evidence that hERV expression could serve as a biomarker for patient prognosis and response to immunotherapy.

Abstract PR05: Exceptional Response to PD-1 antibody treatment in a POLE-mutant endometrial cancer

Genomic assessment of exceptional responders is a promising approach to identify predictors of response to antibody therapy directed against the immune checkpoint programmed death 1 (PD-1) receptor, which has been shown to yield prolonged and deep responses in multiple types of human cancer. We identified a patient with endometrial cancer who experienced an exceptional response to pembrolizumab, an antibody to programmed death 1 (PD-1) receptor. The primary endometrial cancer specimen and the biopsy from the recurrent supraclavicular lymph node (LN) metastasis obtained prior to treatment were analyzed by hybrid-capture based genomic profiling at a commercial CLIA-certified laboratory, Foundation Medicine, targeting all exons of 315 cancer-related genes. In the patient9s pre-treatment endometrial cancer specimens we identified a mutation in DNA polymerase epsilon gene (POLE), which is associated with disruption of the exonuclease activity required for proofreading function and results in a high mutation burden or “ultramutator” phenotype. This tumor did harbor a large number of mutations: 32 likely pathogenic sequence variants and 116 variants of unknown significance (VUS). We next reviewed genomic alterations in 252 deidentified endometrioid endometrial cancers that underwent genomic profiling with the FoundationOne assay and determined that 23 (9.1%) had sequence variants in POLE. The cancers with POLE sequence variants had a mean of 21.2 +/-4.1 mutations identified as likely pathogenic and 82.2 +/-25 variants identified as VUS, compared with a mean of 7.5+/-0.5 likely pathogenic variants and 12.8 +/- 2.6 VUS in POLE wt cases (mean +/- S.E.; p Citation Format: Janice M. Mehnert, Anshuman Panda, Hua Zhong, Kim M. Hirshfield, Sherri Damare, Katherine Stiles, Levi Sokol, Mark N. Stein, Lorna Rodriguez-Rodriguez, Howard L. Kaufman, Siraj Ali, Jeffery Ross, Dean C. Pavlick, Gyan Bhanot, Eileen P. White, Robert S. DiPaola, Ann Lovell, Jonathan Cheng, Shridar Ganesan. Exceptional Response to PD-1 antibody treatment in a POLE-mutant endometrial cancer. [abstract]. In: Proceedings of the AACR-NCI-EORTC International Conference: Molecular Targets and Cancer Therapeutics; 2015 Nov 5-9; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2015;14(12 Suppl 2):Abstract nr PR05.

Endogenous retrovirus expression is associated with response to immune checkpoint blockade in clear cell renal cell carcinoma

Although a subset of clear cell renal cell carcinoma (ccRCC) patients respond to immune checkpoint blockade (ICB), predictors of response remain uncertain. We investigated whether abnormal expression of endogenous retroviruses (ERVs) in tumors is associated with local immune checkpoint activation (ICA) and response to ICB. Twenty potentially immunogenic ERVs (πERVs) were identified in ccRCC in The Cancer Genome Atlas data set, and tumors were stratified into 3 groups based on their expression levels. πERV-high ccRCC tumors showed increased immune infiltration, checkpoint pathway upregulation, and higher CD8+ T cell fraction in infiltrating leukocytes compared with πERV-low ccRCC tumors. Similar results were observed in ER+/HER2- breast, colon, and head and neck squamous cell cancers. ERV expression correlated with expression of genes associated with histone methylation and chromatin regulation, and πERV-high ccRCC was enriched in BAP1 mutant tumors. ERV3-2 expression correlated with ICA in 11 solid cancers, including the 4 named above. In a small retrospective cohort of 24 metastatic ccRCC patients treated with single-agent PD-1/PD-L1 blockade, ERV3-2 expression in tumors was significantly higher in responders compared with nonresponders. Thus, abnormal expression of πERVs is associated with ICA in several solid cancers, including ccRCC, and ERV3-2 expression is associated with response to ICB in ccRCC.

Abstract 1424: Predicting response to immune checkpoint therapy using an mutation burden threshold

Treatment with antibodies to PD-1 or CTLA-4 leads to prolonged response in some cancer patients. Patients whose tumors have a high mutational burden have a better response to anti-CTLA-4 treatment with ipilimumab in melanoma5, and to anti-PD-1 treatment with pembrolizumab in non-small cell lung6 and colorectal cancer7. These results suggest that a sufficiently high non-synonymous somatic mutation burden in the tumor may lead to protein alterations that serve as neo-antigens to stimulate CD8 T-cell immune response. This immune response may be blocked by the tumor by engaging the immune checkpoint pathway, making such tumors especially vulnerable to immune checkpoint disruption. However, the specific criteria to identify patients likely to respond to immune checkpoint therapy have remained elusive so far. Using somatic mutation and RNA-Seq data from TCGA, we propose that there exists a mutational threshold, which we call the “Activated Immune Mutational” (AIM) Threshold, which can identify patients likely to respond to immune checkpoint therapy. Compared to AIM- patients (potential non-responders), AIM+ patients (potential responders) have tumors that meet four criteria: (1) a high non-synonymous mutation burden; (2) a high level of immune infiltration in the tumor; (3) a high CD8 T cell fraction in the leukocyte component of the immune infiltrate plus high expression of the T cell marker CD8A; and (4) a high expression of immune checkpoint genes PD-1, PD-L1, PD-L2, CTLA-4. We find that in melanoma, endometrial, colon, cervical and breast cancer, a clear AIM threshold satisfying all four criteria exists. The distribution of mutations in AIM- versus AIM+ tumors for these cancers is very different. In the former, there are high frequency somatic mutations in only a few genes, while in the latter, high frequency somatic mutations are found in many genes distributed over the whole genome. Pathological analysis of high-resolution images from 150 TCGA tumors (30 from each of the five tumor types) validated the presence of significantly higher lymphocytic infiltration in the AIM+ tumors compared to AIM- tumors. We show that AIM+ tumors can be identified using sequencing assays which are currently in clinical use. Finally, survival analysis in melanoma patients from TCGA treated with immunotherapy will be presented. Citation Format: Anshuman Panda, Anil Betigeri, Kalyanasundaram Subramanian, Kim Hirshfield, Lorna Rodriguez, Shridar Ganesan, Gyan Bhanot. Predicting response to immune checkpoint therapy using an mutation burden threshold. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 1424.