Evaluation of combination treatment with DS-1205c, an AXL kinase inhibitor, and osimertinib in metastatic or unresectable EGFR-mutant non-small cell lung cancer: results from a multicenter, open-label phase 1 study.

The objective of this study was to evaluate the safety and tolerability of DS-1205c, an oral AXL-receptor inhibitor, in combination with osimertinib in metastatic or unresectable EFGR-mutant non-small cell lung cancer (NSCLC) patients who developed disease progression during EGFR tyrosine kinase inhibitor (TKI) treatment. An open-label, non-randomized phase 1 study was conducted in Taiwan, in which 13 patients received DS-1205c monotherapy at a dosage of 200, 400, 800, or 1200 mg twice daily for 7 days, followed by combination treatment with DS-1205c (same doses) plus osimertinib 80 mg once daily in 21-day cycles. Treatment continued until disease progression or other discontinuation criteria were met. At least one treatment-emergent adverse event (TEAE) was reported in all 13 patients treated with DS-1205c plus osimertinib; with ≥ 1 grade 3 TEAE in 6 patients (one of whom also had a grade 4 increased lipase level), and 6 patients having ≥ 1 serious TEAE. Eight patients experienced ≥ 1 treatment-related AE (TRAE). The most common (2 cases each) were anemia, diarrhea, fatigue, increased AST, increased ALT, increased blood creatinine phosphokinase, and increased lipase. All TRAEs were non-serious, with the exception of an overdose of osimertinib in 1 patient. No deaths were reported. Two-thirds of patients achieved stable disease (one-third for > 100 days), but none achieved a complete or partial response. No association between AXL positivity in tumor tissue and clinical efficacy was observed. DS-1205c was well-tolerated with no new safety signals in patients with advanced EGFR-mutant NSCLC when administered in combination with the EFGR TKI osimertinib. ClinicalTrials.gov ; NCT03255083.

Phase 1 study of DS-1205c combined with gefitinib for EGFR mutation-positive non-small cell lung cancer.

BACKGROUND: Tyrosine kinase inhibitors (TKIs) are effective for the treatment of non-small cell lung cancer (NSCLC) patients with activating mutations of the epidermal growth factor receptor (EGFR), but responses are not durable as tumors develop resistance. DS-1205c is a novel, specific, orally bioavailable, small-molecule AXL receptor TKI. In preclinical studies, DS-1205c restored TKI antitumor activity in a TKI acquired-resistance EGFR-mutant NSCLC tumor xenograft model. METHODS: This first-in-human, multicenter, open-label Phase 1 study (registered at ClinicalTrials.gov: NCT03599518) primarily evaluated the safety and tolerability of combination therapy with DS-1205c and gefitinib in Japanese patients with metastatic or unresectable EGFR-mutant NSCLC and tumor progression during treatment with EGFR-TKIs. Patients (n = 20) received DS-1205c monotherapy (200-1200 mg twice daily [BID]) in a 7-day safety monitoring period before combination DS-1205c/gefitinib (250 mg once daily) in 21-day cycles. RESULTS: The observed common treatment-emergent adverse events (TEAEs) were increased aspartate aminotransferase (35%), increased alanine aminotransferase (30%), rash maculo-papular (30%), and diarrhea (25%). No serious TEAEs were reported. Plasma concentrations and pharmacokinetic parameters of DS-1205a (free form of DS-1205c) were unaffected by concomitant administration of gefitinib. No patient achieved a complete or partial response and 5 patients (25%) had stable disease. CONCLUSION: DS-1205c was generally safe and well tolerated at all dose levels, but the safety profile of ≤800 mg BID was more favorable than 1200 mg BID. The recommended dose for dose-expansion cohorts of DS-1205c in combination therapy with gefitinib was 800 mg BID.

Endotoxin contamination in commercially available Cas9 proteins potentially induces T-cell mediated responses.

Immune responses to Cas proteins have been demonstrated recently and these may prove to be an impediment to their clinical use in gene editing. To make meaningful assessments of Cas9 immunogenicity during drug development and licensure it is imperative the reagents are free of impurities that could affect in vitro assessments of immunogenicity. Here we address the issue of endotoxin levels in laboratory grade Cas9 proteins used to measure T-cell memory responses. Many of these reagents have not been developed for immunogenicity assays, are or microbial origin and carry varying levels of endotoxin. The use of these reagents, off the shelf, without measuring endotoxin levels is likely to introduce incorrect estimates of the prevalence of memory T-cell responses in research studies. We demonstrate wide variation in endotoxin levels in Cas9 proteins from seven suppliers. Different lots from the same supplier also contained varying levels of endotoxin. ELISPOT assays showed similar large variations in the interferon-γ signals. Finally, when we carried out endotoxin depletion in four Cas9 proteins with strong signals in the ELISPOT assay, we found dampening of the interferon-γ signals.

A structural homology approach to identify potential cross-reactive antibody responses following SARS-CoV-2 infection.

The emergence of the novel SARS-CoV-2 virus is the most important public-health issue of our time. Understanding the diverse clinical presentations of the ensuing disease, COVID-19, remains a critical unmet need. Here we present a comprehensive listing of the diverse clinical indications associated with COVID-19. We explore the theory that anti-SARS-CoV-2 antibodies could cross-react with endogenous human proteins driving some of the pathologies associated with COVID-19. We describe a novel computational approach to estimate structural homology between SARS-CoV-2 proteins and human proteins. Antibodies are more likely to interrogate 3D-structural epitopes than continuous linear epitopes. This computational workflow identified 346 human proteins containing a domain with high structural homology to a SARS-CoV-2 Wuhan strain protein. Of these, 102 proteins exhibit functions that could contribute to COVID-19 clinical pathologies. We present a testable hypothesis to delineate unexplained clinical observations vis-à-vis COVID-19 and a tool to evaluate the safety-risk profile of potential COVID-19 therapies.

Identifying drivers of breast cancer metastasis in progressively invasive subpopulations of zebrafish-xenografted MDA-MB-231.

Cancer metastasis is the primary cause of the high mortality rate among human cancers. Efforts to identify therapeutic agents targeting cancer metastasis frequently fail to demonstrate efficacy in clinical trials despite strong preclinical evidence. Until recently, most preclinical studies used mouse models to evaluate anti-metastatic agents. Mouse models are time-consuming and expensive. In addition, an important drawback is that mouse models inadequately model the early stages of metastasis which plausibly leads to the poor correlation with clinical outcomes.Here, we report an in vivo model based on xenografted zebrafish embryos where we select for progressively invasive subpopulations of MDA-MB-231 breast cancer cells. A subpopulation analogous to circulating tumor cells found in human cancers was selected by injection of MDA-MB-231 cells into the yolk sacs of 2 days post-fertilized zebrafish embryos and selecting cells that migrated to the tail. The selected subpopulation derived from MDA-MB-231 cells were increasingly invasive in zebrafish. Isolation of these subpopulations and propagation in vitro revealed morphological changes consistent with activation of an epithelial-mesenchymal transition program. Differential gene analysis and knockdown of genes identified gene-candidates (DDIT4, MT1X, CTSD, and SERPINE1) as potential targets for anti-metastasis therapeutics. Furthermore, RNA-splicing analysis reinforced the importance of BIRC5 splice variants in breast cancer metastasis. This is the first report using zebrafish to isolate and expand progressively invasive populations of human cancer cells. The model has potential applications in understanding the metastatic process, identification and/or development of therapeutics that specifically target metastatic cells and formulating personalized treatment strategies for individual cancer patients.

Structural, functional, and immunogenicity implications of F9 gene recoding.

Hemophilia B is a blood clotting disorder caused by deficient activity of coagulation factor IX (FIX). Multiple recombinant FIX proteins are currently approved to treat hemophilia B, and several gene therapy products are currently being developed. Codon optimization is a frequently used technique in the pharmaceutical industry to improve recombinant protein expression by recoding a coding sequence using multiple synonymous codon substitutions. The underlying assumption of this gene recoding is that synonymous substitutions do not alter protein characteristics because the primary sequence of the protein remains unchanged. However, a critical body of evidence shows that synonymous variants can affect cotranslational folding and protein function. Gene recoding could potentially alter the structure, function, and in vivo immunogenicity of recoded therapeutic proteins. Here, we evaluated multiple recoded variants of F9 designed to further explore the effects of codon usage bias on protein properties. The detailed evaluation of these constructs showed altered conformations, and assessment of translation kinetics by ribosome profiling revealed differences in local translation kinetics. Assessment of wild-type and recoded constructs using a major histocompatibility complex (MHC)-associated peptide proteomics assay showed distinct presentation of FIX-derived peptides bound to MHC class II molecules, suggesting that despite identical amino acid sequence, recoded proteins could exhibit different immunogenicity risks. Posttranslational modification analysis indicated that overexpression from gene recoding results in suboptimal posttranslational processing. Overall, our results highlight potential functional and immunogenicity concerns associated with gene-recoded F9 products. These findings have general applicability and implications for other gene-recoded recombinant proteins.

Mathematical model of a personalized neoantigen cancer vaccine and the human immune system.

Cancer vaccines are an important component of the cancer immunotherapy toolkit enhancing immune response to malignant cells by activating CD4+ and CD8+ T cells. Multiple successful clinical applications of cancer vaccines have shown good safety and efficacy. Despite the notable progress, significant challenges remain in obtaining consistent immune responses across heterogeneous patient populations, as well as various cancers. We present a mechanistic mathematical model describing key interactions of a personalized neoantigen cancer vaccine with an individual patient's immune system. Specifically, the model considers the vaccine concentration of tumor-specific antigen peptides and adjuvant, the patient's major histocompatibility complexes I and II copy numbers, tumor size, T cells, and antigen presenting cells. We parametrized the model using patient-specific data from a clinical study in which individualized cancer vaccines were used to treat six melanoma patients. Model simulations predicted both immune responses, represented by T cell counts, to the vaccine as well as clinical outcome (determined as change of tumor size). This model, although complex, can be used to describe, simulate, and predict the behavior of the human immune system to a personalized cancer vaccine.

Cas9-derived peptides presented by MHC Class II that elicit proliferation of CD4+ T-cells.

CRISPR-Cas9 mediated genome editing offers unprecedented opportunities for treating human diseases. There are several reports that demonstrate pre-existing immune responses to Cas9 which may have implications for clinical development of CRISPR-Cas9 mediated gene therapy. Here we use 209 overlapping peptides that span the entire sequence of Staphylococcus aureus Cas9 (SaCas9) and human peripheral blood mononuclear cells (PBMCs) from a cohort of donors with a distribution of Major Histocompatibility Complex (MHC) alleles comparable to that in the North American (NA) population to identify the immunodominant regions of the SaCas9 protein. We also use an MHC Associated Peptide Proteomics (MAPPs) assay to identify SaCas9 peptides presented by MHC Class II (MHC-II) proteins on dendritic cells. Using these two data sets we identify 22 SaCas9 peptides that are both presented by MHC-II proteins and stimulate CD4+ T-cells.

HLA Variants and Inhibitor Development in Hemophilia A: A Retrospective Case-Controlled Study Using the ATHNdataset.

In hemophilia A (HA) patients, F8 gene-defects as genetic risk-factors for developing inhibitors to Factor VIII have been extensively studied. Here we provide estimates of inhibitor-risk associated with the patient's Human Leukocyte Antigen (HLA). We used next generation sequencing for high-resolution HLA Class II typing of 997 HA patients. Using inhibitor prevalence reports from the My Life Our Future (MLOF) research repository, we calculated Odds Ratios (OR) for inhibitor development in a multivariate model considering HLA-DRB1/3/4/5, HLA-DPB1, HLA-DQB1, race, F8 pathogenic variant type, and age. Participants with 1 HLA variant (DPB1*02:02) had developed inhibitors at a higher rate while participants with 2 HLA variants (DRB1*04:07; DRB1*11:04) had developed inhibitors at a lower rate. Additionally, patients with missense variants had developed inhibitors at a lower rate and participants with large structural changes (>50 bp) had developed inhibitors at a higher rate (both compared to Intron 22 inversion). Using a cohort of participants with a distribution of HLA-DRB1 alleles comparable to that in the North American population we show that the HLA repertoire of a HA patient can be a risk-factor for inhibitor development.

Modified aptamers as reagents to characterize recombinant human erythropoietin products.

Reliable and reproducible monitoring of the conformational state of therapeutic protein products remains an unmet technological need. This need is amplified by the increasing number of biosimilars entering the drug development pipeline as many branded biologics are reaching the end of their market exclusivity period. Availability of methods to better characterize protein conformation may improve detection of counterfit and unlicensed therapeutic proteins. In this study, we report the use of a set of modified DNA aptamers with enhanced chemical diversity to probe the conformational state of 12 recombinant human erythropoietin (rHuEPO) therapeutic protein products; one FDA-licensed rHuEPO originator biological product, three rHuEPO products that are approved for marketing in the US or EU as biosimilars, and eight rHuEPO products that are not approved for marketing in the US or EU. We show that several of these modified aptamers are able to distinguish rHuEPO reference products or approved biosimilars from non-licensed rHuEPO products on the basis of differences in binding kinetics and equilibrium affinity constants. These reagents exhibit sensitivity to the conformational integrity of various forms of rHuEPO and as such represent powerful, simple-to-use analytical tools to monitor the conformational integrity of therapeutic-proteins during manufacture and to screen for and identify both substandard and counterfeit products.

Efficient Propagation of Circulating Tumor Cells: A First Step for Probing Tumor Metastasis.

Circulating tumor cells (CTCs) represent a unique population of cells that can be used to investigate the mechanistic underpinnings of metastasis. Unfortunately, current technologies designed for the isolation and capture of CTCs are inefficient. Existing literature for in vitro CTC cultures report low (6-20%) success rates. Here, we describe a new method for the isolation and culture of CTCs. Once optimized, we employed the method on 12 individual metastatic breast cancer patients and successfully established CTC cultures from all 12 samples. We demonstrate that cells propagated were of breast and epithelial origin. RNA-sequencing and pathway analysis demonstrated that CTC cultures were distinct from cells obtained from healthy donors. Finally, we observed that CTC cultures that were associated with CD45+ leukocytes demonstrated higher viability. The presence of CD45+ leukocytes significantly enhanced culture survival and suggests a re-evaluation of the methods for CTC isolation and propagation. Routine access to CTCs is a valuable resource for identifying genetic and molecular markers of metastasis, personalizing the treatment of metastatic cancer patients and developing new therapeutics to selectively target metastatic cells.

Further Evidence That MicroRNAs Can Play a Role in Hemophilia A Disease Manifestation: F8 Gene Downregulation by miR-19b-3p and miR-186-5p.

Hemophilia A (HA) is a F8 gene mutational disorder resulting in deficiency or dysfunctional FVIII protein. However, surprisingly, in few cases, HA is manifested even without mutations in F8. To understand this anomaly, we recently sequenced microRNAs (miRNAs) of two patients with mild and moderate HA with no F8 gene mutations and selected two highly expressing miRNAs, miR-374b-5p and miR-30c-5p, from the pool to explain the FVIII deficiency that could be mediated by miRNA-based F8/FVIII suppression. In this report, an established orthogonal in vivo RNA-affinity purification approach was utilized to directly identify a group of F8-interacting miRNAs and we tested them for F8/FVIII suppression. From this pool, two miRNAs, miR-19b-3p and miR-186-5p, were found to be upregulated in a severe HA patient with a mutation in the F8 coding sequence and two HA patients without mutations in the F8 coding sequence were selected to demonstrate their role in F8 gene expression regulation in mammalian cells. Overall, these results provide further evidence for the hypothesis that by targeting the 3'UTR of F8, miRNAs can modulate FVIII protein levels. This mechanism could either be the primary cause of HA in patients who lack F8 mutations or control the severity of the disease in patients with F8 mutations.

Clinical manifestation of hemophilia A in the absence of mutations in the F8 gene that encodes FVIII: role of microRNAs.

BACKGROUND: Hemophilia A (HA) is associated with mutations in the F8 gene that expresses factor VIII (FVIII). Unexpectedly, HA also manifests in a small subset of individuals with no mutations (exonic or intronic) in their F8 gene. MicroRNAs (miRNAs) cause translational interference, affecting protein quality and stoichiometry. Here, by analyzing miRNAs of two patients from this subset, we evaluated miRNA-based FVIII suppression as a testable hypothesis to explain FVIII deficiency in patients with HA with no F8 gene mutations. STUDY DESIGN AND METHODS: To test the hypothesis, miRNA sequencing from two patients with mild and moderate HA with no mutations in their F8 gene, followed by experimental verification, was used to identify a group of upregulated miRNAs in patients with HA compared to normal controls; with binding sites in the 3' untranslated region (UTR) of F8 messenger RNA (mRNA), a prerequisite for miRNA-based gene regulation. From this pool, miR-374b-5p and miR-30c-5p, known to be expressed in human liver, where FVIII is expressed, were subjected to extensive characterization. RESULTS: In two cell lines that constitutively express FVIII, we demonstrated that overexpression of miR-374b or miR-30c decreased FVIII expression, while an miR-30c inhibitor partially restored FVIII expression. CONCLUSION: These data support a role for microRNAs in fine-tuning F8 gene regulation. Based on our findings, our current model suggests that in HA cases where the F8 gene is normal and is predicted to express normal levels of FVIII, F8 mRNA 3' UTR targeting miRNAs may be responsible for a FVIII-deficiency phenotype clinically manifesting as HA.

Effects of codon optimization on coagulation factor IX translation and structure: Implications for protein and gene therapies.

Synonymous codons occur with different frequencies in different organisms, a phenomenon termed codon usage bias. Codon optimization, a common term for a variety of approaches used widely by the biopharmaceutical industry, involves synonymous substitutions to increase protein expression. It had long been presumed that synonymous variants, which, by definition, do not alter the primary amino acid sequence, have no effect on protein structure and function. However, a critical mass of reports suggests that synonymous codon variations may impact protein conformation. To investigate the impact of synonymous codons usage on protein expression and function, we designed an optimized coagulation factor IX (FIX) variant and used multiple methods to compare its properties to the wild-type FIX upon expression in HEK293T cells. We found that the two variants differ in their conformation, even when controlling for the difference in expression levels. Using ribosome profiling, we identified robust changes in the translational kinetics of the two variants and were able to identify a region in the gene that may have a role in altering the conformation of the protein. Our data have direct implications for codon optimization strategies, for production of recombinant proteins and gene therapies.

Mitigation of T-cell dependent immunogenicity by reengineering factor VIIa analogue.

Vatreptacog alfa (VA), a recombinant activated human factor VII (rFVIIa) variant with 3 amino acid substitutions, was developed to provide increased procoagulant activity in hemophilia patients with inhibitors to factor VIII or factor IX. In phase 3 clinical trials, changes introduced during the bioengineering of VA resulted in the development of undesired anti-drug antibodies in some patients, leading to the termination of a potentially promising therapeutic protein product. Here, we use preclinical biomarkers associated with clinical immunogenicity to validate our deimmunization strategy applied to this bioengineered rFVIIa analog. The reengineered rFVIIa analog variants retained increased intrinsic thrombin generation activity but did not elicit T-cell responses in peripheral blood mononuclear cells isolated from 50 HLA typed subjects representing the human population. Our algorithm, rational immunogenicity determination, offers a broadly applicable deimmunizing strategy for bioengineered proteins.

TCPro: an In Silico Risk Assessment Tool for Biotherapeutic Protein Immunogenicity.

Most immune responses to biotherapeutic proteins involve the development of anti-drug antibodies (ADAs). New drugs must undergo immunogenicity assessments to identify potential risks at early stages in the drug development process. This immune response is T cell-dependent. Ex vivo assays that monitor T cell proliferation often are used to assess immunogenicity risk. Such assays can be expensive and time-consuming to carry out. Furthermore, T cell proliferation requires presentation of the immunogenic epitope by major histocompatibility complex class II (MHCII) proteins on antigen-presenting cells. The MHC proteins are the most diverse in the human genome. Thus, obtaining cells from subjects that reflect the distribution of the different MHCII proteins in the human population can be challenging. The allelic frequencies of MHCII proteins differ among subpopulations, and understanding the potential immunogenicity risks would thus require generation of datasets for specific subpopulations involving complex subject recruitment. We developed TCPro, a computational tool that predicts the temporal dynamics of T cell counts in common ex vivo assays for drug immunogenicity. Using TCPro, we can test virtual pools of subjects based on MHCII frequencies and estimate immunogenicity risks for different populations. It also provides rapid and inexpensive initial screens for new biotherapeutics and can be used to determine the potential immunogenicity risk of new sequences introduced while bioengineering proteins. We validated TCPro using an experimental immunogenicity dataset, making predictions on the population-based immunogenicity risk of 15 protein-based biotherapeutics. Immunogenicity rankings generated using TCPro are consistent with the reported clinical experience with these therapeutics.

Peptides identified on monocyte-derived dendritic cells: a marker for clinical immunogenicity to FVIII products.

The immunogenicity of protein therapeutics is an important safety and efficacy concern during drug development and regulation. Strategies to identify individuals and subpopulations at risk for an undesirable immune response represent an important unmet need. The major histocompatibility complex (MHC)-associated peptide proteomics (MAPPs) assay directly identifies the presence of peptides derived from a specific protein therapeutic on a donor's MHC class II (MHC-II) proteins. We applied this technique to address several questions related to the use of factor VIII (FVIII) replacement therapy in the treatment of hemophilia A (HA). Although >12 FVIII therapeutics are marketed, most fall into 3 categories: (i) human plasma-derived FVIII (pdFVIII), (ii) full-length (FL)-recombinant FVIII (rFVIII; FL-rFVIII), and (iii) B-domain-deleted rFVIII. Here, we investigated whether there are differences between the FVIII peptides found on the MHC-II proteins of the same individual when incubated with these 3 classes. Based on several observational studies and a prospective, randomized, clinical trial showing that the originally approved rFVIII products may be more immunogenic than the pdFVIII products containing von Willebrand factor (VWF) in molar excess, it has been hypothesized that the pdFVIII molecules yield/present fewer peptides (ie, potential T-cell epitopes). We have experimentally tested this hypothesis and found that dendritic cells from HA patients and healthy donors present fewer FVIII peptides when administered pdFVIII vs FL-rFVIII, despite both containing the same molar VWF excess. Our results support the hypothesis that synthesis of pdFVIII under physiological conditions could result in reduced heterogeneity and/or subtle differences in structure/conformation which, in turn, may result in reduced FVIII proteolytic processing relative to FL-rFVIII.

Translational and transcriptional responses in human primary hepatocytes under hypoxia.

The liver is the primary source of a large number of plasma proteins and plays a critical role in multiple biological processes. Inadequate oxygen supply characterizing various clinical settings such as liver transplantation exposes the liver to hypoxic conditions. Studies assessing hypoxia-induced global translational changes in liver are lacking. Here, we employed a recently developed ribosome-profiling technique to assess global translational responses of human primary hepatocytes exposed to acute hypoxic stress (1% O2) for the short term. In parallel, transcriptome profiling was performed to assess mRNA expression changes. We found that translational responses appeared earlier and were predominant over transcriptional responses. A significant decrease in translational efficiency of several ribosome genes indicated translational inhibition of new ribosome protein synthesis in hypoxia. Pathway enrichment analysis highlighted altered translational regulation of MAPK signaling, drug metabolism, oxidative phosphorylation, and nonalcoholic fatty liver disease pathways. Gene Ontology enrichment analysis revealed terms related to translation, metabolism, angiogenesis, apoptosis, and response to stress. Transcriptional induction of genes encoding heat shock proteins was observed within 30 min of hypoxia. Induction of genes encoding stress response mediators, metabolism regulators, and proangiogenic proteins was observed at 240 min. Despite the liver being the primary source of coagulation proteins and the implicated role of hypoxia in thrombosis, limited differences were observed in genes encoding coagulation-associated proteins. Overall, our study demonstrates the predominance of translational regulation over transcription and highlights differentially regulated pathways or biological processes in short-term hypoxic stress responses of human primary hepatocytes. NEW & NOTEWORTHY The novelty of this study lies in applying parallel ribosome- and transcriptome-profiling analyses to human primary hepatocytes in hypoxia. To our knowledge, this is the first study to assess global translational responses using ribosome profiling in hypoxic hepatocytes. Our results demonstrate the predominance of translational responses over transcriptional responses in early hepatic hypoxic stress responses. Furthermore, our study reveals multiple pathways and specific genes showing altered regulation in hypoxic hepatocytes.

SampPick: Selection of a Cohort of Subjects Matching a Population HLA Distribution.

Immune responses to therapeutic proteins and peptides can adversely affect their safety and efficacy; consequently, immunogenicity risk-assessments are part of the development, licensure and clinical use of these products. In most cases the development of anti-drug antibodies is mediated by T cells which requires antigen presentation by Major Histocompatibility Complex Class II (MHCII) molecules (also called Human Leucocyte Antigen, HLA in humans). Immune responses to many protein therapeutics are thus HLA-restricted and it is important that the distribution of HLA variants used in the immunogenicity assessments provides adequate coverage of the target population. Due to biases inherent to the collection of samples in a blood bank or donor pool, simple random sampling will not achieve a truly representative sample of the population of interest. To help select a donor cohort we introduce SampPick, an implementation of simulated annealing which optimizes cohort selection to closely match the frequency distribution of a target population or subpopulation. With inputs of a target background frequency distribution for a population and a set of available, HLA-typed donors, the algorithm will iteratively create a cohort of donors of a user selected size that will closely match the target population rather than a random sample. In addition to optimizing the HLA types of donor cohorts, the software presented can be used to optimize donor cohorts for any other biallelic or monoallelic trait.

Prevalence of Pre-existing Antibodies to CRISPR-Associated Nuclease Cas9 in the USA Population.

The repurposing of the CRISPR/Cas microbial adaptive immune system for gene editing has resulted in an exponential rise in new technologies and promising approaches for treating numerous human diseases. While some of the approaches being currently developed involve ex vivo editing by CRISPR/Cas9, many more potential applications will require in vivo editing. The in vivo use of this technology comes with challenges, one of which is the immune response to Cas9, a protein of microbial origin. Thus, the prevalence of pre-existing antibodies to Cas9 could also be a relevant parameter. There are many avenues for how CRISPR/Cas9 technologies will be applied in vivo, including the mode of delivery. These may be expected to invoke different immunological pathways. Nonetheless, as with all protein therapeutics, it may be desirable to monitor for anti-Cas9 antibodies during clinical development. This will require the development of robust and reliable assays. Here, we describe ELISA-based assays that are capable of detecting antibodies to Cas9 from Staphylococcus aureus (SaCas9) and Streptococcs pyogenes (SpCas9) in human sera. Furthermore, using these assays to screen for pre-existing antibodies in 200 human serum samples, we found the prevalence of anti-SaCas9 and anti-SpCas9 antibodies to be 10% and 2.5%, respectively.