Digital sorting and copy number profiling of purified, PD-L1 positive, Reed Sternberg cells in classical Hodgkin lymphoma

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Background: Classical Hodgkin Lymphoma (cHL) is one of the disease in which the check-point inhibitors have been demonstrated to be more successful. Lately, it has been reported that in malignant Reed-Sternberg Cells (RSCs), PD-1 ligands (PD-Ls) are overexpressed and that chr.9 amplification correlates with advanced stages of the disease, when the standard therapy have already failed. Unfortunately, the detection of the genetic alterations in RSCs is challenging, as one of the hallmark of cHL is the presence of a small number of malignant cells sparse in an abundant and heterogeneous immune infiltrate. Here we present a method for the isolation and the genetic characterization of purified RSCs, which overcomes the limitations posed by the low-cellularity of cHL biopsies, and could be helpful for earlier detection of genetic alterations and adoption of immunotherapy. Methods: FFPE tissue sections from cHL patients were dissociated down to single-cell suspension and stained using anti-CD30 and anti-PD-L1 antibodies. Beyond the positivity to CD30 and PD-L1, RSCs were selected according to morphological criteria such as cell size and the presence of polylobate nuclei compared to surrounding lymphocytes. Target cells were isolated using the DEPArray™ cell sorter, as single cells or in small pools of cells. Recovered cells were whole genome amplified ( Ampli1™ WGA), and genome-wide copy-number aberrations (CNAs) profiles were obtained using Ampli1™ LowPass kit on IonTorrent platform. Results: After the dissociation, RSCs maintained cell morphology and therefore, we were able to discriminate them from the heterogeneous immune infiltrate. RSCs appeared as large multinucleated cells with a big central nucleolus surrounded by a clear halo; cell diameter and ploidy were computed from the images. Pools of lymphocytes and pools of CD30+/ PD-L1+ RSCs were isolated. Sequencing results confirmed the expected flat profile for lymphocytes, while RSCs showed an aberrant profile with multiple losses and gains. Conclusions: The analysis of purified RSCs, could offer a valuable tool to uncover genetic alterations hidden by cHL immune infiltrate, for earlier adoption of more effective treatment regimens.

Isolation and genetic analysis of pure cells from forensic biological mixtures: The precision of a digital approach

Latest genotyping technologies allow to achieve a reliable genetic profile for the offender identification even from extremely minute biological evidence. The ultimate challenge occurs when genetic profiles need to be retrieved from a mixture, which is composed of biological material from two or more individuals. In this case, DNA profiling will often result in a complex genetic profile, which is then subject matter for statistical analysis. In principle, when more individuals contribute to a mixture with different biological fluids, their single genetic profiles can be obtained by separating the distinct cell types (e.g. epithelial cells, blood cells, sperm), prior to genotyping. Different approaches have been investigated for this purpose, such as fluorescent-activated cell sorting (FACS) or laser capture microdissection (LCM), but currently none of these methods can guarantee the complete separation of different type of cells present in a mixture. In other fields of application, such as oncology, DEPArray™ technology, an image-based, microfluidic digital sorter, has been widely proven to enable the separation of pure cells, with single-cell precision. This study investigates the applicability of DEPArray™ technology to forensic samples analysis, focusing on the resolution of the forensic mixture problem. For the first time, we report here the development of an application-specific DEPArray™ workflow enabling the detection and recovery of pure homogeneous cell pools from simulated blood/saliva and semen/saliva mixtures, providing full genetic match with genetic profiles of corresponding donors. In addition, we assess the performance of standard forensic methods for DNA quantitation and genotyping on low-count, DEPArray™-isolated cells, showing that pure, almost complete profiles can be obtained from as few as ten haploid cells. Finally, we explore the applicability in real casework samples, demonstrating that the described approach provides complete separation of cells with outstanding precision. In all examined cases, DEPArray™ technology proves to be a groundbreaking technology for the resolution of forensic biological mixtures, through the precise isolation of pure cells for an incontrovertible attribution of the obtained genetic profiles.

Digital Sorting of Pure Cell Populations Enables Unambiguous Genetic Analysis of Heterogeneous Formalin-Fixed Paraffin-Embedded Tumors by Next Generation Sequencing

Precision medicine in oncology requires an accurate characterization of a tumor molecular profile for patient stratification. Though targeted deep sequencing is an effective tool to detect the presence of somatic sequence variants, a significant number of patient specimens do not meet the requirements needed for routine clinical application. Analysis is hindered by contamination of normal cells and inherent tumor heterogeneity, compounded with challenges of dealing with minute amounts of tissue and DNA damages common in formalin-fixed paraffin-embedded (FFPE) specimens. Here we present an innovative workflow using DEPArray™ system, a microchip-based digital sorter to achieve 100%-pure, homogenous subpopulations of cells from FFPE samples. Cells are distinguished by fluorescently labeled antibodies and DNA content. The ability to address tumor heterogeneity enables unambiguous determination of true-positive sequence variants, loss-of-heterozygosity as well as copy number variants. The proposed strategy overcomes the inherent trade-offs made between sensitivity and specificity in detecting genetic variants from a mixed population, thus rescuing for analysis even the smaller clinical samples with low tumor cellularity.

Abstract 1552: Image-based microchip sorting of pure, immuno-phenotypically defined subpopulations of tumor cells from tiny formalin-fixed paraffin embedded (FFPE) samples reveals their distinct genetic features

Background: We provide a solution of pressing needs in preparation of FFPE samples for genomic analysis: small sample size, unwanted admixture of normal cells, analysis of tumor rare-cell subpopulations present at low percentages in the tumor fraction.

Methods: We disaggregated into cell suspensions archival FFPE samples from 12 ovarian, pancreatic and lung cancer patients, staining for Vimentin, Keratin and DNA. We sorted by DEPArray™ precise numbers (mean = 107, median 58, range = 5-600) of pure homogenous cells from the major population of tumor cells, the contaminant diploid stromal cells, and other minority tumor cell types indicative of epithelial-to-mesenchymal transition (EMT). Using IonTorrent AmpliSeq CHPv2, we generated sequencing libraries, after lysis of the pure cells recovered by DEPArray™ (n = 54), or unsorted samples (either QIAmp DNA columns or disaggregated cells). Libraries were sequenced with IonTorrent PGM (mean depth>2,000x), and analyzed using IonTorrent software.

Results: On several loci, we detected somatic mutations with 100% variant frequency, only observable as heterozygous in the unsorted samples and as wild-type in stromal cells of same patient, confirming 100% purity of sorted cells. Moreover, in the EMT-phenotype subpopulations we identified clear somatic mutations, different from tumor cells majority and undetectable in unsorted samples. Frequently, for loci harboring germ-line heterozygous SNPs with variant frequency around 50% for pure stromal cells, we readily detected loss-of-heterozygosis in tumor cells subpopulations as binary (0%/100%) variants. Quantitative traits such as copy number gains and losses were also reproducibly identified in tumor cell replicates as deviations from the 50% variant frequency of germline SNPs of pure stromal cells. Furthermore, we observed an excellent coverage uniformity (mean = 96%) for recoveries (n = 27) in the range of 81-600 cells, even higher than the uniformity obtained with (n = 2) QIAmp-purified DNA (92%). Mean uniformity gradually decreased to 89% for cell recoveries (n = 13) in the range 21-80, and further decreased to 70% for lower cell numbers (n = 14).

Highlights: Sorting tumor rare-cell subpopulations reveals their genetic characteristics, undetectable in unsorted samples. Analyzing homogenous cell subpopulations boosts signal-to-noise ratio working around inherent sensitivity/specifitiy trade-offs of rare-variant calls. The proposed workflow further enables reliable detection of quantitative traits such as CNVs. Sorting pure stromal cells yields internal controls for archival samples.

Citation Format: Chiara Bolognesi, Anna Doffini, Genny Buson, Rossana Lanzellotto, Giulio Signorini, Valeria Sero, Alex Calanca, Francesca Fontana, Rita Romano, Stefano Gianni, Giulia Bregola, Gianni Medoro, Raimo Tanzi, Giuseppe Giorgini, Hans Morreau, Massimo Barberis, Willem E. Corver, Nicolo Manaresi. Image-based microchip sorting of pure, immuno-phenotypically defined subpopulations of tumor cells from tiny formalin-fixed paraffin embedded (FFPE) samples reveals their distinct genetic features. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1552. doi:10.1158/1538-7445.AM2015-1552

Development of a tetraplex PCR assay for CYP2D6 genotyping in degraded DNA samples

CYP2D6 polymorphism analysis is gaining increasing interest in forensic pharmacogenetics. Nevertheless, DNA recovered from forensic samples could be of poor quality and not suitable for long polymerase chain reaction required to type CYP2D6 gene prior to SNaPshot minisequencing analysis performed to define alleles with different enzymatic activity. We developed and validated following the guidelines of the Scientific Working Group on DNA Analysis Methods a tetraplex PCR yielding four amplicons of 597, 803, 1142, and 1659 bp encompassing the entire CYP2D6 gene to analyze eleven SNP positions by SNaPshot minisequencing. Concordance, sensitivity, and specificity were assessed. The method, applied to thirty-two forensic samples failed to amplify with long PCR, allowed the amplification of CYP2D6 gene in 62.5% of degraded samples. The new tetraplex PCR appears a suitable method for CYP2D6 analysis in forensic pharmacogenetics.