Stephen J. Goldfless

Efficient CRISPR-Cas9-mediated genome editing in Plasmodium falciparum.

Malaria is a major cause of global morbidity and mortality, and new strategies for treating and preventing this disease are needed. Here we show that the Streptococcus pyogenes Cas9 DNA endonuclease and single guide RNAs (sgRNAs) produced using T7 RNA polymerase (T7 RNAP) efficiently edit the Plasmodium falciparum genome. Targeting the genes encoding native knob-associated histidine-rich protein (kahrp) and erythrocyte binding antigen 175 (eba-175), we achieved high (≥50–100%) gene disruption frequencies within the usual time frame for generating transgenic parasites.

Combined confocal Raman and quantitative phase microscopy system for biomedical diagnosis

We have developed a novel multimodal microscopy system that incorporates confocal Raman, confocal reflectance, and quantitative phase microscopy (QPM) into a single imaging entity. Confocal Raman microscopy provides detailed chemical information from the sample, while confocal reflectance and quantitative phase microscopy show detailed morphology. Combining these intrinsic contrast imaging modalities makes it possible to obtain quantitative morphological and chemical information without exogenous staining. For validation and characterization, we have used this multi-modal system to investigate healthy and diseased blood samples. We first show that the thickness of a healthy red blood cell (RBC) shows good correlation with its hemoglobin distribution. Further, in malaria infected RBCs, we successfully image the distribution of hemozoin (malaria pigment) inside the cell. Our observations lead us to propose morphological screening by QPM and subsequent chemical imaging by Raman for investigating blood disorders. This new approach allows monitoring cell development and cell-drug interactions with minimal perturbation of the biological system of interest.

Direct and specific chemical control of eukaryotic translation with a synthetic RNA–protein interaction

Sequence-specific RNA–protein interactions, though commonly used in biological systems to regulate translation, are challenging to selectively modulate. Here, we demonstrate the use of a chemically-inducible RNA–protein interaction to regulate eukaryotic translation. By genetically encoding Tet Repressor protein (TetR)-binding RNA elements into the 5′-untranslated region (5′-UTR) of an mRNA, translation of a downstream coding sequence is directly controlled by TetR and tetracycline analogs. In endogenous and synthetic 5′-UTR contexts, this system efficiently regulates the expression of multiple target genes, and is sufficiently stringent to distinguish functional from non-functional RNA–TetR interactions. Using a reverse TetR variant, we illustrate the potential for expanding the regulatory properties of the system through protein engineering strategies.

Versatile control of Plasmodium falciparum gene expression with an inducible protein–RNA interaction

The available tools for conditional gene expression in Plasmodium falciparum are limited. Here, to enable reliable control of target gene expression, we build a system to efficiently modulate translation. We overcame several problems associated with other approaches for regulating gene expression in P. falciparum. Specifically, our system functions predictably across several native and engineered promoter contexts, and affords control over reporter and native parasite proteins irrespective of their subcellular compartmentalization. Induction and repression of gene expression are rapid, homogeneous, and stable over prolonged periods. To demonstrate practical application of our system, we used it to reveal direct links between antimalarial drugs and their native parasite molecular target. This is an important out come given the rapid spread of resistance, and intensified efforts to efficiently discover and optimize new antimalarial drugs. Overall, the studies presented highlight the utility of our system for broadly controlling gene expression and performing functional genetics in P. falciparum.

Tumor-infiltrating immune repertoires captured by single-cell barcoding in emulsion

Tumor-infiltrating lymphocytes (TILs) are critical to anti-cancer immune responses, but their diverse phenotypes and functions remain poorly understood and challenging to study. We therefore developed a single-cell barcoding technology for deep characterization of TILs without the need for cell-sorting or culture. Our emulsion-based method captures full-length, natively paired B-cell and T-cell receptor (BCR and TCR) sequences from lymphocytes among millions of input cells. We validated the method with 3 million B-cells from healthy human blood and 350,000 B-cells from an HIV elite controller, before processing 400,000 cells from an unsorted dissociated ovarian adenocarcinoma and recovering paired BCRs and TCRs from over 11,000 TILs. We then extended the barcoding method to detect DNA-labeled antibodies, allowing ultra-high throughput, simultaneous protein detection and RNA sequencing from single cells.

An integrated strategy for efficient vector construction and multi-gene expression in Plasmodium falciparum

BackgroundThe construction of plasmid vectors for transgene expression in the malaria parasite, Plasmodium falciparum, presents major technical hurdles. Traditional molecular cloning by restriction and ligation often yields deletions and re-arrangements when assembling low-complexity (A + T)-rich parasite DNA. Furthermore, the use of large 5′- and 3′- untranslated regions of DNA sequence (UTRs) to drive transgene transcription limits the number of expression cassettes that can be incorporated into plasmid vectors.MethodsTo address these challenges, two high fidelity cloning strategies, namely yeast homologous recombination and the Gibson assembly method, were evaluated for constructing P. falciparum vectors. Additionally, some general rules for reliably using the viral 2A-like peptide to express multiple proteins from a single expression cassette while preserving their proper trafficking to various subcellular compartments were assessed.ResultsYeast homologous recombination and Gibson assembly were found to be effective strategies for successfully constructing P. falciparum plasmid vectors. Using these cloning methods, a validated family of expression vectors that provide a flexible starting point for user-specific applications was created. These vectors are also compatible with traditional cloning by restriction and ligation, and contain useful combinations of commonly used features for enhancing plasmid segregation and site-specific integration in P. falciparum. Additionally, application of a 2A-like peptide for the synthesis of multiple proteins from a single expression cassette, and some rules for combinatorially directing proteins to discrete subcellular compartments were established.ConclusionsA set of freely available, sequence-verified and functionally validated parts that offer greater flexibility for constructing P. falciparum vectors having expanded expression capacity is provided.

Single-cell sequencing reveals αβ chain pairing shapes the T cell repertoire

A diverse T cell repertoire is a critical component of the adaptive immune system, providing protection against invading pathogens and neoplastic changes, relying on the recognition of foreign antigens and neoantigen peptides by T cell receptors (TCRs). However, the statistical properties and function of the T cell pool in an individual, under normal physiological conditions, are poorly understood. In this study, we report a comprehensive, quantitative characterization of the T cell repertoire from over 1.9 million cells, yielding over 200,000 high quality paired αβ sequences in 5 healthy human subjects. The dataset was obtained by leveraging recent biotechnology developments in deep RNA sequencing of lymphocytes via single-cell barcoding in emulsion. We report non-random associations and non-monogamous pairing between the α and β chains, lowering the theoretical diversity of the T cell repertoire, and increasing the frequency of public clones shared among individuals. T cell clone size distributions closely followed a power law, with markedly longer tails for CD8+ cytotoxic T cells than CD4+ helper T cells. Furthermore, clonality estimates based on paired chains from single T cells were lower than that from single chain data. Taken together, these results highlight the importance of sequencing αβ pairs to accurately quantify lymphocyte receptor diversity.

Abstract 643: Identification of novel pancreatic cancer-specific antibodies and their target antigens through a next generation immune sequencing platform

One of the major challenges in developing new therapies for pancreatic cancer is the lack of known specific and sensitive targets to the cancer cells. In this study, we present a powerful way to identify novel specific targets to pancreatic cancer by leveraging the antibody responses of tumor infiltrating lymphocytes (TILs) using a novel next-generation immune sequencing approach. We first deeply characterize the antibody repertoire produced by TILs, followed by antibody expression, screening and functional characterization to identify their biological targets. We aim to manipulate the antibody cancer targeting specificity into potential therapeutics by utilizing antibody-drug conjugation (ADC) technology. We obtained tumor resections and matched normal adjacent tissue from patients diagnosed with pancreatic ductal adenocarcinoma or acinar cell carcinoma, and characterized each sample9s TIL immune repertoire using AbVitro9s proprietary Next-Generation Immune Sequencing platform. Interestingly, results indicated the presence of millions of B and T cells in both tumor and normal tissues. Strikingly, tumor tissues across all patients were characterized by an abundance of expanded B-cell lineages expressing IgG, whereas normal adjacent tissue and healthy control samples contained almost exclusively IgA expressing cells. Antibody candidates were selected from the sequencing data and heavy and light chains were synthesized and expressed in a mammalian cell-based expression system. The antibodies were then screened for cell surface binding, tissue specificity and cell killing potential against pancreatic cancer cell lines and FFPE human cancer tissues. Selected antibodies from these screens were then chosen as candidates for antigen identification. Our study uncovered multiple antibodies that specifically bind to pancreatic cancer tissues but not to healthy tissues. Interestingly, some of the antibodies also showed strong binding to other types of cancer such as lung squamous cell carcinoma. Initial target identification efforts for these antibodies yielded a short list of antigens which are known to be expressed at high levels in the pancreas or pancreatic cancer cell lines. We are currently performing studies to further understand the antigen specificity and sensitivity of these antibodies and evaluate their cell killing potential as ADCs, as well as investigating the diagnostic value of the novel antigen targets. In summary, our study demonstrates the potential of next-generation sequencing in TIL analysis for the discovery of novel cancer-specific targets of potential therapeutic value. Citation Format: David A. Fabrizio, Sonia Timberlake, Brian Belmont, Stephen J. Goldfless, Adrian W. Briggs, Teresa J. Broering, Francois Vigneault. Identification of novel pancreatic cancer-specific antibodies and their target antigens through a next generation immune sequencing platform. [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 643. doi:10.1158/1538-7445.AM2015-643

T-cell receptor αβ chain pairing is associated with CD4+ and CD8+ lineage specification

While a highly diverse T-cell receptor (TCR) repertoire is the hallmark of a healthy adaptive immune system, relatively little is understood about how the CD4+ and CD8+ TCR repertoires differ from one another. We here utilize high-throughput single T-cell sequencing to obtain approximately 100,000 TCR αβ chain pairs from human subjects, stratified into CD4+ and CD8+ lineages. We reveal that substantial information about T-cell lineage is encoded by Vαβ gene pairs and, to a lesser extent, by several other TCR features such as CDR3 length and charge. We further find that the strength of association between the β chain and T-cell lineage is surprisingly weak, similar in strength to that of the α chain. Using machine learning classifiers to predict T-cell lineage from TCR features, we demon-strate that αβ chain pairs are significantly more informative than individual chains alone. These findings provide unprecedented insight into the CD4+ and CD8+ TCR repertoires and highlight the importance of αβ chain pairing in TCR function and specificity.