Development of a Replication-Deficient Bacteriophage Reporter Lacking an Essential Baseplate Wedge Subunit

Engineered bacteriophages (phages) can be effective diagnostic reporters for detecting a variety of bacterial pathogens. Although a promising biotechnology, the large-scale use of these reporters may result in the unintentional release of genetically modified viruses. In order to limit the potential environmental impact, the ability of these phages to propagate outside the laboratory was targeted. The phage SEA1 has been previously engineered to facilitate food safety as an accurate and sensitive reporter for Salmonella contamination. In this study, homologous recombination was used to replace the expression of an essential baseplate wedge subunit (gp141) in SEA1 with a luciferase, NanoLuc®. This reporter, referred to as SEA1Δgp141.NL, demonstrated a loss of plaque formation and a failure to increase in titer following infection of Salmonella. SEA1Δgp141.NL was thus incapable of producing infectious progeny in the absence of gp141. In contrast, production of high titer stocks was possible when gp141 was artificially supplied in trans during infection. As a reporter, SEA1Δgp141.NL facilitated rapid, sensitive, and robust detection of Salmonella despite an inability to replicate. These results suggest that replication-deficient reporter phages are an effective method to obtain improved containment without sacrificing significant performance or the ease of production associated with many phage-based diagnostic methods.

Evaluation of the pan-class I phosphoinositide 3-kinase (PI3K) inhibitor copanlisib in the Pediatric Preclinical Testing Consortium in vivo models of osteosarcoma

Copanlisib is a pan-class I phosphoinositide 3-kinase (PI3K) inhibitor, with activity against all four PI3K class I isoforms (PI3Kα, PI3Kβ, PI3Kγ, and PI3Kδ). Whole-genome and RNA sequencing data have revealed several PI3K aberrations in osteosarcoma tumor samples. The in vivo anticancer effects of copanlisib were assessed in a panel of six osteosarcoma models. Copanlisib induced prolonged event-free survival in five of six osteosarcoma models; however, all models demonstrated progressive disease suggesting minimal activity. While copanlisib did not result in tumor regression, more data are needed to fully explore the role of the PI3K pathway in the pathogenesis of osteosarcoma.

Bacteriophage-Based Detection of Staphylococcus aureus in Human Serum

Bacteriophages have been investigated for clinical utility, both as diagnostic tools and as therapeutic interventions. In order to be applied successfully, a detailed understanding of the influence of the human matrix on the interaction between bacteriophage and the host bacterium is required. In this study, a cocktail of luciferase bacteriophage reporters was assessed for functionality in a matrix containing human serum and spiked with Staphylococcus aureus. The inhibition of signal and loss of sensitivity was evident with minimal amounts of serum. This phenotype was independent of bacterial growth and bacteriophage viability. Serum-mediated loss of signal was common, albeit not universal, among S. aureus strains. Immunoglobulin G was identified as an inhibitory component and partial inhibition was observed with both the f(ab’)₂ and Fc region. A modified bacteriophage cocktail containing recombinant protein A was developed, which substantially improved signal without the need for additional sample purification. This study highlights the importance of assessing bacteriophage activity in relevant host matrices. Furthermore, it identifies an effective solution, recombinant protein A, for promoting bacteriophage-based detection of S. aureus in matrices containing human serum.

The ECOTOXicology Knowledgebase: A Curated Database of Ecologically Relevant Toxicity Tests to Support Environmental Research and Risk Assessment

The need for assembled existing and new toxicity data has accelerated as the amount of chemicals introduced into commerce continues to grow and regulatory mandates require safety assessments for a greater number of chemicals. To address this evolving need, the ECOTOXicology Knowledgebase (ECOTOX) was developed starting in the 1980s and is currently the world's largest compilation of curated ecotoxicity data, providing support for assessments of chemical safety and ecological research through systematic and transparent literature review procedures. The recently released version of ECOTOX (Ver 5, www.epa.gov/ecotox) provides single-chemical ecotoxicity data for over 12,000 chemicals and ecological species with over one million test results from over 50,000 references. Presented is an overview of ECOTOX, detailing the literature review and data curation processes within the context of current systematic review practices and discussing how recent updates improve the accessibility and reusability of data to support the assessment, management, and research of environmental chemicals. Relevant and acceptable toxicity results are identified from studies in the scientific literature, with pertinent methodological details and results extracted following well-established controlled vocabularies and newly extracted toxicity data added quarterly to the public website. Release of ECOTOX, Ver 5, included an entirely redesigned user interface with enhanced data queries and retrieval options, visualizations to aid in data exploration, customizable outputs for export and use in external applications, and interoperability with chemical and toxicity databases and tools. This is a reliable source of curated ecological toxicity data for chemical assessments and research and continues to evolve with accessible and transparent state-of-the-art practices in literature data curation and increased interoperability to other relevant resources. Environ Toxicol Chem 2022;41:1520-1539. © 2022 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Validation of PhageDx™Salmonella Assay in Raw Ground Turkey and Powdered Infant Formula: AOAC Performance Tested MethodSM 121904

Background

The PhageDx^™Salmonella Assay is based on the infection of Salmonella spp. by specific bacteriophages and expression of a luciferase reporter gene. Results are generated in as little as 9.5 h for raw ground turkey and 18.5 h for milk-based powdered infant formula (PIF).

Objective

An AOAC Performance Tested Methods^SM (PTM) study was conducted to validate the PhageDx Salmonella Assay for the detection of Salmonella in 25 g raw ground turkey and 100 g PIF test portions.

Method

The performance of the PhageDx Salmonella Assay was compared to that of the U.S. Department of Agriculture (USDA), Food Safety and Inspection Service (FSIS) Microbiology Laboratory Guidebook (MLG) 4.10 for raw ground turkey and the U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM) Chapter 5 for PIF. Inclusivity/exclusivity, product consistency and stability, and robustness testing were conducted.

Results

There was no significant difference between the 25 g raw ground turkey and 100 g PIF PhageDx Salmonella Assay and the USDA/FSIS MLG 4.10 and FDA/BAM Chapter 5, respectively. The reporter bacteriophages were specific for Salmonella and infected 108 strains in inclusivity testing. They did not infect 30 non-Salmonella bacteria in exclusivity testing. Robustness testing showed that the method performed well with specific deviations from the standard protocol. Consistency and stability testing demonstrated that the recombinant phage gave consistent results across three production lots and was stable when stored under appropriate conditions for at least eight months.

Conclusions

The data collected in the validation study demonstrate that the PhageDx Salmonella Assay meets the qualifications for PTM status.

Highlights

The PhageDx Salmonella Assay is a rapid, specific, sensitive assay capable of detecting a wide range of Salmonella spp. with a significantly shorter turn around time than the USDA/FSIS and FDA reference methods.

Validation of PhageDx™ Cronobacter Assay for the Identification of Cronobacter Spp. in Powdered Infant Formula: AOAC Performance Tested MethodSM 051803

Background

The PhageDx^™Cronobacter Assay is based on the infection of Cronobacter spp. by specific bacteriophages and expression of a luciferase reporter gene. Results are generated in as little as 18.5 h for powdered infant formula (PIF).

Objective

An AOAC Performance Tested Methods^SM (PTM) study was conducted to validate the PhageDx Cronobacter Assay for the detection of Cronobacter in 10, 100, and 300 g milk- and soy-based PIF test portions.

Method

The performance of the PhageDx method was compared to the ISO 22964:2006/2017 Microbiology of the Food Chain—Horizontal Method for the Detection of Cronobacter spp. and the U.S. Food and Drug Administration (FDA) Bacteriological Analytical Manual (BAM) Chapter 29 Cronobacter: 2012. Inclusivity/exclusivity, product consistency and stability, and robustness testing also were conducted.

Results

There was no significant difference between the 10, 100, or 300 g test portions for the milk and soy PIF matrixes between the PhageDx Cronobacter Assay, the ISO 22964:2006/2017, and the FDA BAM Chapter 29 Cronobacter: 2012 methods. The reporter bacteriophages were specific for Cronobacter and infected 75 strains in inclusivity testing. They did not infect 35 non-Cronobacter bacteria in exclusivity testing. Robustness testing showed that the method performed well with specific deviations from the standard protocol. Consistency and stability testing demonstrated that the recombinant phage gave consistent results across three production lots and was stable when stored under appropriate conditions for at least 3 months.

Conclusions

Work in the submitting and independent laboratories demonstrated that the PhageDx Cronobacter Assay meets the qualifications for PTM status.

Highlights

The PhageDx Cronobacter Assay is a rapid, simple, and specific test that has shown equivalence to both the FDA BAM and ISO reference methods for detecting Cronobacter spp. in PIF.

Validation of the PhageDx™ Listeria Assay for Detection of Listeria Spp. on Stainless Steel and Ceramic Environmental Surfaces AOAC Performance Tested MethodSM 102005

BACKGROUND

The PhageDx™ Listeria Assay is a simple, specific, and sensitive assay based on the infection of Listeria spp. by selected bacteriophages and the resultant expression of a luciferase reporter gene. Results are generated in as little as 24.5 h for stainless steel and ceramic environmental surfaces.

OBJECTIVE

An AOAC Performance Tested MethodsSM (PTM) study was conducted to validate the PhageDx Listeria Assay for the detection of Listeria on stainless steel and ceramic surfaces.

METHOD

The performance of the PhageDx method was compared to that of the U.S. Food and Drug Administration (FDA) Bacterial Analytical Manual (BAM) Ch. 10. Inclusivity/exclusivity, product consistency and stability, and robustness testing also were conducted.

RESULTS

Inclusivity testing demonstrated that the reporter bacteriophages were specific for Listeria ssp. and detected 58/61 Listeria strains tested, including all 34 L. monocytogenes strains. The reporter bacteriophage also was shown to not detect 46/47 non-Listeria bacteria in exclusivity testing. Robustness testing showed that the method performed well with specific deviations from the standard protocol. Consistency and stability testing demonstrated that the recombinant phage gave consistent results across three production lots and was stable when stored under appropriate conditions for at least 6 months. Matrix studies on stainless steel and ceramic surfaces showed that there was no significant difference between the PhageDx Listeria Assay and the FDA/BAM Chapter 10 reference method.

CONCLUSIONS AND HIGHLIGHTS

The validation study demonstrates that the PhageDx Listeria Assay is an effective method for the detection of Listeria spp. on stainless steel and ceramic environmental surfaces and meets the qualifications for AOAC PTM status.

PhageDx™ E. coli O157:H7 Assay in Ground Beef Level 3 Modification to Add 375 g Beef Trim and New Method Procedure for 25 g Ground Beef: AOAC Performance Tested MethodSM 081601

BACKGROUND

ThePhageDx™ E. coli O157:H7 Assay originally required a 5 h enrichment period and a 10 mL test sample for 25 g ground beef. The proposed method modifications seek to include beef trim (375 g) matrix and a new method procedure for 25 g ground beef comprised of 6-7 h enrichment and 1 mL test sample.

OBJECTIVE

To validate the method modifications for PhageDx E. coli O157:H7 Assay to include beef trim (375 g) matrix and modify enrichment time and test sample size for 25 g ground beef.

METHOD

For both matrixes, pre-warmed tryptic soya broth (TSB; 42 ± 1°C) was added in a 3:1 (media:sample size) ratio, blended, and enriched for 9-10 h (beef trim, 375 g) or 6 h (ground beef, 25 g) at 42 ± 1°C. One milliliter samples were transferred to a microfuge tube, centrifuged, and the supernatant removed. The pellet was resuspended in 0.2 mL of TSB and phage reagent was added. Samples were incubated for 2 h at 37 ± 1°C. After infection, the sample was centrifuged, and 150 µl of the supernatant was transferred to a 96-well plate. Then, lysis buffer and luciferase substrate were added and the sample read on a luminometer to determine the presence or absence of E. coli O157:H7.

RESULTS

No significant differences were found between the PhageDx E. coli O157:H7 Assay method modifications and the U.S. Department of Agriculture Food Safety and Inspection Service (FSIS) Microbiology Laboratory Guidebook (MLG) reference method.

CONCLUSIONS

The independent study demonstrated that the PhageDx E. coli O157:H7 Assay method modifications meet the qualifications for Performance Tested Method SM status.

HIGHLIGHTS

The PhageDx E. coli O157:H7 Assay is a rapid detection method capable of detecting E. coli O157:H7 in 25 g ground beef and 375 g beef trim samples in as little as 8.5 h and 11.5 h total turn around time, respectively.

Isolation and engineering of a Listeria grayi bacteriophage

The lack of bacteriophages capable of infecting the Listeria species, Listeria grayi, is academically intriguing and presents an obstacle to the development of bacteriophage-based technologies for Listeria. We describe the isolation and engineering of a novel L. grayi bacteriophage, LPJP1, isolated from farm silage. With a genome over 200,000 base pairs, LPJP1 is the first and only reported jumbo bacteriophage infecting the Listeria genus. Similar to other Gram-positive jumbo phages, LPJP1 appeared to contain modified base pairs, which complicated initial attempts to obtain genomic sequence using standard methods. Following successful sequencing with a modified approach, a recombinant of LPJP1 encoding the NanoLuc luciferase was engineered using homologous recombination. This luciferase reporter bacteriophage successfully detected 100 stationary phase colony forming units of both subspecies of L. grayi in four hours. A single log phase colony forming unit was also sufficient for positive detection in the same time period. The recombinant demonstrated complete specificity for this particular Listeria species and did not infect 150 non-L. grayi Listeria strains nor any other bacterial genus. LPJP1 is believed to be the first reported lytic bacteriophage of L. grayi as well as the only jumbo bacteriophage to be successfully engineered into a luciferase reporter.

Comparative Analysis of Felixounavirus Genomes Including Two New Members of the Genus That Infect Salmonella Infantis

Salmonella spp. is one of the most common foodborne pathogens worldwide; therefore, its control is highly relevant for the food industry. Phages of the Felixounavirus genus have the characteristic that one phage can infect a large number of different Salmonella serovars and, thus, are proposed as an alternative to antimicrobials in food production. Here, we describe two new members of the Felixounavirus genus named vB_Si_35FD and vB_Si_DR94, which can infect Salmonella Infantis. These new members were isolated and sequenced, and a subsequent comparative genomic analysis was conducted including 23 publicly available genomes of Felixounaviruses that infect Salmonella. The genomes of vB_Si_35FD and vB_Si_DR94 are 85,818 and 85,730 bp large and contain 129 and 125 coding sequences, respectively. The genomes did not show genes associated with virulence or antimicrobial resistance, which could be useful for candidates to use as biocontrol agents. Comparative genomics revealed that closely related Felixounavirus are found in distinct geographical locations and that this genus has a conserved genomic structure despite its worldwide distribution. Our study revealed a highly conserved structure of the phage genomes, and the two newly described phages could represent promising biocontrol candidates against Salmonella spp. from a genomic viewpoint.

Higher severe acute respiratory syndrome coronavirus 2 infection rate in pregnant patients

BACKGROUND

During the early months of the coronavirus disease 2019 pandemic, risks associated with severe acute respiratory syndrome coronavirus 2 in pregnancy were uncertain. Pregnant patients can serve as a model for the success of clinical and public health responses during public health emergencies as they are typically in frequent contact with the medical system. Population-based estimates of severe acute respiratory syndrome coronavirus 2 infections in pregnancy are unknown because of incomplete ascertainment of pregnancy status or inclusion of only single centers or hospitalized cases. Whether pregnant women were protected by the public health response or through their interactions with obstetrical providers in the early months of pandemic is not clearly understood.

OBJECTIVE

This study aimed to estimate the severe acute respiratory syndrome coronavirus 2 infection rate in pregnancy and to examine the disparities by race and ethnicity and English language proficiency in Washington State.

STUDY DESIGN

Pregnant patients with a polymerase chain reaction-confirmed severe acute respiratory syndrome coronavirus 2 infection diagnosed between March 1, 2020, and June 30, 2020 were identified within 35 hospitals and clinics, capturing 61% of annual deliveries in Washington State. Infection rates in pregnancy were estimated overall and by Washington State Accountable Community of Health region and cross-sectionally compared with severe acute respiratory syndrome coronavirus 2 infection rates in similarly aged adults in Washington State. Race and ethnicity and language used for medical care of pregnant patients were compared with recent data from Washington State.

RESULTS

A total of 240 pregnant patients with severe acute respiratory syndrome coronavirus 2 infections were identified during the study period with 70.7% from minority racial and ethnic groups. The principal findings in our study were as follows: (1) the severe acute respiratory syndrome coronavirus 2 infection rate was 13.9 per 1000 deliveries in pregnant patients (95% confidence interval, 8.3-23.2) compared with 7.3 per 1000 (95% confidence interval, 7.2-7.4) in adults aged 20 to 39 years in Washington State (rate ratio, 1.7; 95% confidence interval, 1.3-2.3); (2) the severe acute respiratory syndrome coronavirus 2 infection rate reduced to 11.3 per 1000 deliveries (95% confidence interval, 6.3-20.3) when excluding 45 cases of severe acute respiratory syndrome coronavirus disease 2 detected through asymptomatic screening (rate ratio, 1.3; 95% confidence interval, 0.96-1.9); (3) the proportion of pregnant patients in non-White racial and ethnic groups with severe acute respiratory syndrome coronavirus disease 2 infection was 2- to 4-fold higher than the race and ethnicity distribution of women in Washington State who delivered live births in 2018; and (4) the proportion of pregnant patients with severe acute respiratory syndrome coronavirus 2 infection receiving medical care in a non-English language was higher than estimates of pregnant patients receiving care with limited English proficiency in Washington State (30.4% vs 7.6%).

CONCLUSION

The severe acute respiratory syndrome coronavirus 2 infection rate in pregnant people was 70% higher than similarly aged adults in Washington State, which could not be completely explained by universal screening at delivery. Pregnant patients from nearly all racial and ethnic minority groups and patients receiving medical care in a non-English language were overrepresented. Pregnant women were not protected from severe acute respiratory syndrome coronavirus 2 infection in the early months of the pandemic. Moreover, the greatest burden of infections occurred in nearly all racial and ethnic minority groups. These data coupled with a broader recognition that pregnancy is a risk factor for severe illness and maternal mortality strongly suggested that pregnant people should be broadly prioritized for coronavirus disease 2019 vaccine allocation in the United States similar to some states.

Disease severity, pregnancy outcomes, and maternal deaths among pregnant patients with severe acute respiratory syndrome coronavirus 2 infection in Washington State

BACKGROUND

Evidence is accumulating that coronavirus disease 2019 increases the risk of hospitalization and mechanical ventilation in pregnant patients and for preterm delivery. However, the impact on maternal mortality and whether morbidity is differentially affected by disease severity at delivery and trimester of infection are unknown.

OBJECTIVE

This study aimed to describe disease severity and outcomes of severe acute respiratory syndrome coronavirus 2 infections in pregnancy across the Washington State, including pregnancy complications and outcomes, hospitalization, and case fatality.

STUDY DESIGN

Pregnant patients with a polymerase chain reaction-confirmed severe acute respiratory syndrome coronavirus 2 infection between March 1, 2020, and June 30, 2020, were identified in a multicenter retrospective cohort study from 35 sites in Washington State. Sites captured 61% of annual state deliveries. Case-fatality rates in pregnancy were compared with coronavirus disease 2019 fatality rates in similarly aged adults in Washington State using rate ratios and rate differences. Maternal and neonatal outcomes were compared by trimester of infection and disease severity at the time of delivery.

RESULTS

The principal study findings were as follows: (1) among 240 pregnant patients in Washington State with severe acute respiratory syndrome coronavirus 2 infections, 1 in 11 developed severe or critical disease, 1 in 10 were hospitalized for coronavirus disease 2019, and 1 in 80 died; (2) the coronavirus disease 2019-associated hospitalization rate was 3.5-fold higher than in similarly aged adults in Washington State (10.0% vs 2.8%; rate ratio, 3.5; 95% confidence interval, 2.3-5.3); (3) pregnant patients hospitalized for a respiratory concern were more likely to have a comorbidity or underlying conditions including asthma, hypertension, type 2 diabetes mellitus, autoimmune disease, and class III obesity; (4) 3 maternal deaths (1.3%) were attributed to coronavirus disease 2019 for a maternal mortality rate of 1250 of 100,000 pregnancies (95% confidence interval, 257-3653); (5) the coronavirus disease 2019 case fatality in pregnancy was a significant 13.6-fold (95% confidence interval, 2.7-43.6) higher in pregnant patients than in similarly aged individuals in Washington State with an absolute difference in mortality rate of 1.2% (95% confidence interval, -0.3 to 2.6); and (6) preterm birth was significantly higher among women with severe or critical coronavirus disease 2019 at delivery than for women who had recovered from coronavirus disease 2019 (45.4% severe or critical coronavirus disease 2019 vs 5.2% mild coronavirus disease 2019; P<.001).

CONCLUSION

Coronavirus disease 2019 hospitalization and case-fatality rates in pregnant patients were significantly higher than in similarly aged adults in Washington State. These data indicate that pregnant patients are at risk of severe or critical disease and mortality compared to nonpregnant adults, and also at risk for preterm birth.

ABBV-085, Antibody-Drug Conjugate Targeting LRRC15, Is Effective in Osteosarcoma: A Report by the Pediatric Preclinical Testing Consortium

Membrane protein leucine-rich repeat containing 15 (LRRC15) is known to be expressed in several solid tumors including osteosarcoma. ABBV-085, an antibody-drug conjugate against LRRC15, conjugated to monomethyl auristatin E (MMAE), was studied in osteosarcoma patient-derived xenografts (PDXs) by the Pediatric Preclinical Testing Consortium (PPTC). LRRC15 expression data were obtained from PPTC RNA-sequencing data for the PDX models. The TARGET database was mined for LRRC15 expression in human osteosarcoma. Protein expression was confirmed via IHC in three PDX models. Seven osteosarcoma PDX models (OS1, OS9, OS33, OS34, OS42, OS55, and OS60) with varying LRRC15 gene expression were studied. ABBV-085 was administered at 3 mg/kg (OS33), 6 mg/kg (all seven PDXs), and 12 mg/kg (OS60) weekly for 4 consecutive weeks via intraperitoneal injection. Control cohorts included vehicle and an isotype MMAE-linked antibody. Tumor volumes and responses were reported using PPTC statistical analysis. OS1, OS33, OS42, OS55, and OS60 had high LRRC15 expression while OS9 and OS34 had low LRRC15 expression. ABBV-085 inhibited tumor growth in six of seven PDX models as compared with vehicle control and significantly improved event-free survival in five of seven models as compared with isotype controls. Two models showed maintained complete responses while all others showed progressive disease. Response correlated with LRRC15 expression. ABBV-085's antitumor activity against osteosarcoma PDX suggests LRRC15 may be a rational target for pursuing clinical trials in patients with this disease.

Accurate and sensitive detection of Salmonella in foods by engineered bacteriophages

Salmonella is a major causative agent of foodborne illness and rapid identification of this pathogen is essential to prevent disease. Currently most assays require high bacterial burdens or prolonged enrichment to achieve acceptable performance. A reduction in testing time without loss of sensitivity is critical to allow food processors to safely decrease product holding time. To meet this need, a method was developed to detect Salmonella using luciferase reporter bacteriophages. Bacteriophages were engineered to express NanoLuc, a novel optimized luciferase originating from the deep-sea shrimp Oplophorus gracilirostris. NanoLuc-expressing bacteriophages had a limit of detection of 10-100 CFU per mL in culture without enrichment. Luciferase reporters demonstrated a broad host range covering all Salmonella species with one reporter detecting 99.3% of 269 inclusivity strains. Cross-reactivity was limited and only observed with other members of the Enterobacteriaceae family. In food matrix studies, a cocktail of engineered bacteriophages accurately detected 1 CFU in either 25 g of ground turkey with a 7 h enrichment or 100 g of powdered infant formula with a 16 h enrichment. Use of the NanoLuc reporter assay described herein resulted in a considerable reduction in enrichment time without a loss of sensitivity.

Dose-response effect of eribulin in preclinical models of osteosarcoma by the pediatric preclinical testing consortium

The pediatric preclinical testing program previously demonstrated activity of eribulin in osteosarcoma patient-derived xenograft (PDX) models. The phase 2 trial in patients with relapsed osteosarcoma failed to meet response endpoints. Eribulin was evaluated in the original and an expanded set of PDX models and tested at multiple dose levels and schedules to evaluate dose-response. Maximal response was observed at the highest dose, consistent with prior results. The alternative schedule generated similar responses. We demonstrate steep dose-response for eribulin in osteosarcoma PDX models, implying that any deviation from achievement of effective concentrations may have a significant impact on activity.

Abstract LB-217: Preclinical evaluation of trastuzumab deruxtecan (T-DXd; DS-8201a), a HER2 antibody-drug conjugate, in pediatric solid tumors by the Pediatric Preclinical Testing Consortium (PPTC)

Introduction: HER2 is expressed in a subset of pediatric solid tumors and is a target of interest for innovative immune therapies including CAR-T cells and antibody-drug conjugates (ADCs). We evaluated preclinical efficacy of T-DXd, a humanized monoclonal HER2 antibody conjugated to a topoisomerase 1 inhibitor payload, DXd, in solid tumor patient derived xenograft (PDX) models. Methods: 7 osteosarcoma (OS), 2 rhabdoid tumor (RT) and 3 Wilms tumor (WT) PDX models with varying HER2 expression were tested using 10 mice per group. ERBB2 mRNA expression was determined using RNA seq. T-DXd or vehicle control was administered IV to mice harboring flank tumors at a dose of 5mg/kg on Day 1. Standard PPTC statistical methods were employed for EFS for treatment (T) and control (C) groups, minimum relative tumor volume (minRTV) and objective response measure. Results: Among PPTC solid tumor models ERBB2 mRNA expression was observed across multiple histologies, with highest expression observed for WT (median = 22 FPKM), followed by RT, OS, and Ewing sarcoma. The relationship between HER2 expression by IHC and by RNAseq was inconsistent. Mice tolerated T-DXd with minimal toxicity. T-DXd significantly prolonged EFS in 5/7 OS, 2/2 RT and 3/3 WT PDX models (see table). Complete response (CR) or maintained CR were observed for 4 of 5 WT and RT models, while stable disease was the best response among OS models. Conclusions: T-DXd exhibits single agent anti-tumor activity in models of pediatric solid tumors. Single mouse testing experiments will be used to extend knowledge of the range of activity of T-DXd for pediatric solid tumors. Correlations between ERBB2 gene expression, HER2 expression by IHC, and genetic changes associated with camptothecin sensitivity are ongoing and will be presented. Clinical trials assessing efficacy of a HER2-directed ADC in pediatric patients with HER2-expressing tumors should be considered.

EFS T - C(days)EFS T/C Ratiop-value Gehan-WilcoxonminRTVmean±SDminRTVp-valueObjective Response MeasureOS-120.31.85p &lt; 0.0011.152±0.090p = 0.023PD1OS-230.12.76p &lt; 0.0010.815±0.183p &lt; 0.001PD2OS-94.11.14p = 0.1031.334±0.203p = 1.000PD1OS-1734.01.97p = 0.0091.172±0.179p = 0.017PD1OS-3111.91.84p &lt; 0.0011.676±0.395p = 0.015PD1OS-3361.34.87p &lt; 0.0010.486±0.220p &lt; 0.001SDOS-603.81.11p = 0.0161.084±0.103p = 0.007PD1BT29 (RT)&gt; 58.4&gt; 3.28p &lt; 0.0010.019±0.041p &lt; 0.001MCRRBD2 (RT)&gt; 97.3&gt; 13.57p &lt; 0.0010.021±0.066p &lt; 0.001CRKT-10 (WT)&gt; 85.1&gt; 7.57p &lt; 0.0010.000±0.000p &lt; 0.001MCRKT-11 (WT)18.32.62p &lt; 0.0010.954±0.486p &lt; 0.001PD2KT-13 (WT)&gt; 71.5&gt; 3.69p &lt; 0.0010.019±0.060p &lt; 0.001MCR

Citation Format: Pooja Hingorani, Wendong Zhang, Raushan Kurmasheva, Zhongting Zhang, Yifei Wang, Zhaohui Xu, Michael Roth, Jonathan Gill, Douglas Harrison, Stephen Erickson, Edward A. Kolb, Malcolm Smith, Peter Houghton, Richard Gorlick. Preclinical evaluation of trastuzumab deruxtecan (T-DXd; DS-8201a), a HER2 antibody-drug conjugate, in pediatric solid tumors by the Pediatric Preclinical Testing Consortium (PPTC) [abstract]. In: Proceedings of the Annual Meeting of the American Association for Cancer Research 2020; 2020 Apr 27-28 and Jun 22-24. Philadelphia (PA): AACR; Cancer Res 2020;80(16 Suppl):Abstract nr LB-217.

Initial in vivo testing of a multitarget kinase inhibitor, regorafenib, by the Pediatric Preclinical Testing Consortium

BACKGROUND

Regorafenib is a small molecule multikinase inhibitor that inhibits multiple kinases including BRAF, KIT, PDGFRB, RAF, RET, and VEGFR1-3.

PROCEDURES

The in vivo anticancer effects of regorafenib were assessed in a panel of six osteosarcoma models, three rhabdomyosarcoma models, and one Ewing sarcoma model.

RESULTS

Regorafenib induced modest inhibition of tumor growth in the models evaluated.

CONCLUSION

The overall pattern of response to regorafenib appears similar to that of the kinase inhibitor sorafenib, with pronounced slowing of tumor growth in some models, limited to the period of agent administration, being the primary treatment effect.

New and emerging treatments for inflammatory itch

OBJECTIVE

To summarize recent therapeutic developments for chronic pruritus with a focus on allergic and type 2 inflammatory pathways.

DATA SOURCES

Literature search of PubMed, industry websites, and review of the ClinicalTrials.gov database.

STUDY SELECTIONS

Peer-reviewed publications and public disclosures by industry relating to chronic pruritus pathophysiology and therapeutics.

RESULTS

Histamine and immunoglobulin E remain primary targets for the treatment of itch in the setting of chronic urticaria. More recently, blockade of type 2 immune cell-associated cytokines, including interleukin (IL) 4, IL-13, and IL-31, and the epithelial cell-derived cytokines, specifically IL-33 and thymic stromal lymphopoietin, has and is revolutionizing the treatment of chronic pruritic dermatoses, such as atopic dermatitis and prurigo nodularis. Other novel targets include histamine receptor 4, Janus kinases, κ-opioid receptor, neurokinin 1 receptor, and phosphodiesterase 4.

CONCLUSION

Advances in our understanding of the neuroimmunology of chronic pruritus have led to the identification of new therapeutic targets and the rapid development of cutting-edge clinical trials. Although incredible advances have already been made, chronic itch continues to be an area of great unmet need.

Abstract 5872: Pediatric Preclinical Testing Consortium (PPTC) of eribulin in osteosarcoma (OS) patient-derived xenograft (PDX) models

Introduction: Eribulin is a synthetic analogue of halichondrin B and inhibits cancer cell proliferation via blockade of microtubule function. It is FDA approved for patients with breast cancer with two prior chemotherapy regimens for the treatment of metastatic disease and for previously treated patients with inoperable or metastatic liposarcoma. In vivo testing of eribulin against osteosarcoma (OS) Pediatric Preclinical Testing Program (PPTP) PDX models, developed from primary tumors, demonstrated significant single-agent activity. However, a Children's Oncology Group (COG) phase 2 trial of eribulin in patients with relapsed OS did not demonstrate significant antitumor activity of single-agent eribulin. In the current study the efficacy of eribulin in PDX models generated from primary and relapsed tumors, as well as dose-response, were assessed.

Methods: Eribulin was evaluated in 6 PPTC models, 4 from primary OS specimens (OS46, OS51, OS55, OS56) and 2 from relapsed specimens (OS39R, OS60). Eribulin was administered via intraperitoneal (IP) injection at a dose of 1mg/kg on days 1 and 4, repeated every 21 days. Response to treatment was determined based on PPTP-established endpoints (1). In addition, 3 dose levels of eribulin were evaluated in 3 PPTP models developed from primary tumors (OS1, OS17, OS33) and 1 model developed from a relapsed tumor (OS60). In the dose-response studies, eribulin was administered IP at 1mg/kg, 0.5mg/kg and 0.25mg/kg on days 1 and 4, repeated every 21 days with follow-up through day 42.

Results: Eribulin at a dose level of 1mg/kg induced stable disease (SD) or partial response (PR) in 4/9 and 3/9 OS xenografts, respectively. SD/PR responses were observed in PDX models generated from primary tumors (5/7) as well as PDX models generated from relapsed tumors (2/2). Eribulin demonstrated maximal antitumor activity at the highest dose level, 1mg/kg (SD/PR in 3/4). At 0.5 mg/kg 1/4 models achieved SD/PR, and at 0.25mg/kg all 4 models showed progressive disease within the 6-week testing period. Minimum relative tumor volumes also showed a dose-response effect from 0.25 to 1.0 mg/kg.

Conclusions: Eribulin demonstrated antitumor activity against OS PDX models generated from primary and relapsed tumors at a dose level of 1mg/kg. Eribulin showed a clear dose-response effect in terms of its ability to induce SD/PR responses, highlighting the importance of dose selection. This dose-response effect suggests that an inability to achieve comparable serum drug concentrations in human clinical trials may explain the limited tumor responses observed in the COG phase 2 trial of eribulin. Pharmacokinetic studies from the COG phase 2 study are ongoing in an effort to understand the disparate tumor responses seen in the in vivo studies and the phase 2 clinical trial.

Reference: 1. Houghton PJ et al. Pediatr Blood Cancer 2007;49:928-40.

Supported by NCI Grants: CA199222, CA199221.

Citation Format: Wendong Zhang, E. Anders Kolb, Richard Gorlick, Michael Roth, Jonathan Gill, Sudie Rowshan, Stephen Erickson, Raushan Kurmasheva, Peter Houghton, Beverly Teicher, Malcolm A. Smith. Pediatric Preclinical Testing Consortium (PPTC) of eribulin in osteosarcoma (OS) patient-derived xenograft (PDX) models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr 5872.

Abstract P4-11-06: The role of patient perceptions in under reporting chemotherapy induced peripheral neuropathy (CIPN)

Background: Although paclitaxel remains one of the most efficacious and commonly used agents in the treatment of breast cancer, it can cause a number of side effects. Decisions to delay, decrease, or discontinue treatment are made based on the severity of chemotherapy induced peripheral neuropathy (CIPN), which is not objectively measured but relies on patient's accurately reporting symptoms to their clinical team. There is some concern that patients do not accurately or completely report CIPN symptoms during treatment. A previous study reported that 3 of 24 patients (12.5%) considered or could understand another patient's decision to under-report CIPN symptoms to avoid treatment disruption. The objective of this follow-up study was to determine whether under-reporting occurred and to understand patient perspectives on topics previously found relevant to a patient's decision to under-report CIPN.

Methods: Ten patients with early stage breast cancer who received adjuvant paclitaxel 80 mg/m2 for up to 12 weeks, who had no prior neuropathy or neurotoxic chemotherapy participated in a recorded, semi-structured, phone-based interview that followed an interview guide designed to cover topics relevant to patient under-reporting

Themes identified in patient perceptions of objectives found relevant to under reportingObjectiveResultPatient Understanding1. Patients had consistent descriptions of their expectations for CIPN prior to treatment. 2. Understanding of the long-term potential of CIPN varied among patients.Patient Education1. Patients used a variety of sources to find information about CIPN, with the most commonly used sources being medical staff and patient handouts.Patient Input1. Patients agree on the importance of reporting side effects, but not to what extent. 2. Patients felt included in the treatment decision-making process, but some felt the doctor ultimately made the decision. 3. Providers may plan an important role in the extent to which patients report their symptoms.Treatment Cycles1. Patients recognized that they may not complete all 12 cycles, but were determined to do so.Perception Changes1. Before treatment, patients are much more focused on efficacy and were not particularly concerned with side effects. 2. During treatment, patients reflected on their desire to complete treatment and the tolerability of the side effects they were experiencing. 3. After treatment, patients felt they should have asked more questions before starting treatment.

. The interviews were then transcribed and qualitatively analyzed using NVivo software to identify common themes.

Results: No patients in this study admitted to under-reporting neuropathy. Themes that emerged from the interviews are presented in Table 1.

Conclusion: Insight as to how patients perceive various aspects of paclitaxel treatment revealed that comfort level with providers, inclusion in the decision-making process, and encouragement to fully disclose all symptoms played an important role when patients considered whether to report adverse effects. Future research may focus on whether a lack of health literacy and/or health care related work experience predisposes to CIPN under-reporting.

Citation Format: Hertz DL, Krumbach E, Nobles B, Erickson S, Farris KB. The role of patient perceptions in under reporting chemotherapy induced peripheral neuropathy (CIPN) [abstract]. In: Proceedings of the 2017 San Antonio Breast Cancer Symposium; 2017 Dec 5-9; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2018;78(4 Suppl):Abstract nr P4-11-06.

Chained Bell Inequality Experiment with High-Efficiency Measurements

We report correlation measurements on two ^{9}Be^{+} ions that violate a chained Bell inequality obeyed by any local-realistic theory. The correlations can be modeled as derived from a mixture of a local-realistic probabilistic distribution and a distribution that violates the inequality. A statistical framework is formulated to quantify the local-realistic fraction allowable in the observed distribution without the fair-sampling or independent-and-identical-distributions assumptions. We exclude models of our experiment whose local-realistic fraction is above 0.327 at the 95% confidence level. This bound is significantly lower than 0.586, the minimum fraction derived from a perfect Clauser-Horne-Shimony-Holt inequality experiment. Furthermore, our data provide a device-independent certification of the deterministically created Bell states.

A Randomized, Controlled Trial of Rituximab in IgA Nephropathy with Proteinuria and Renal Dysfunction

IgA nephropathy frequently leads to progressive CKD. Although interest surrounds use of immunosuppressive agents added to standard therapy, several recent studies have questioned efficacy of these agents. Depleting antibody-producing B cells potentially offers a new therapy. In this open label, multicenter study conducted over 1-year follow-up, we randomized 34 adult patients with biopsy-proven IgA nephropathy and proteinuria >1 g/d, maintained on angiotensin-converting enzyme inhibitors or angiotensin receptor blockers with well controlled BP and eGFR<90 ml/min per 1.73 m², to receive standard therapy or rituximab with standard therapy. Primary outcome measures included change in proteinuria and change in eGFR. Median baseline serum creatinine level (range) was 1.4 (0.8-2.4) mg/dl, and proteinuria was 2.1 (0.6-5.3) g/d. Treatment with rituximab depleted B cells and was well tolerated. eGFR did not change in either group. Rituximab did not alter the level of proteinuria compared with that at baseline or in the control group; three patients in each group had ≥50% reduction in level of proteinuria. Serum levels of galactose-deficient IgA1 or antibodies against galactose-deficient IgA1 did not change. In this trial, rituximab therapy did not significantly improve renal function or proteinuria assessed over 1 year. Although rituximab effectively depleted B cells, it failed to reduce serum levels of galactose-deficient IgA1 and antigalactose-deficient IgA1 antibodies. Lack of efficacy of rituximab, at least at this stage and severity of IgA nephropathy, may reflect a failure of rituximab to reduce levels of specific antibodies assigned salient pathogenetic roles in IgA nephropathy.

Abstract 2825: Germline genetic variants in ANGPT1 & 2 and FGF2 are associated with pathologic complete response to bevacizumab in breast cancer patients

Purpose: Vascular endothelial growth factor (VEGF) is a central mediator of angiogenesis in cancer and may be targeted by the monoclonal antibody bevacizumab (B). We have conducted a prospective phase II study using neoadjuvant B and chemotherapy (CT) in breast cancer patients and showed improved pathologic complete response (pCR) with the combination compared to the expected pCR with CT alone (41% vs. 25%, p=0.029 one sided). We evaluated baseline serum levels of ten angiogenesis-related proteins (ANG1, ANG2, bFGF, IL-1a, MMP-9, PDGF-BB, PECAM-1, Tie-2, VEGF and VEGFR2) and found that baseline Tie-2 and bFGF serum levels were associated with pCR. The goal of the current study is to explore the association of germline single-nucleotide polymorphisms (SNPs) to pCR obtained with bevacizumab therapy.

Methods: Our original patient population consisted of 27 whites (EA) and 12 African Americans (AA) who received docetaxel/cyclophosphamide/bevacizumab and doxorubicin. Only 22 EA and 11 AA had buffy coat samples available for genotyping with the Illumina® HumanOmni2.5-8v1-1 BeadChip. We tested 555 SNPs with a minor allele frequency (MAF) of at least 5%, located in 10 angiogenesis-related genes.

Results: Univariate analysis revealed that 73% AA patients achieved pCR compared to 27% EA (p=0.012) and that 54% of the patients with ductal carcinomas achieved pCR compared to 11% with lobular or poorly differentiated tumors (p=0.021). We therefore included race and cancer type as covariates in a logistic regression model testing for association between pCR and each of the 555 SNPs. There were five SNPs in ANGPT1, five in ANGPT2, and four in FGF2 that were associated with pCR (p&lt;0.05). Because of the modest sample size, none of these SNPs reached levels of significance after adjusting for multiple comparisons.

Conclusion: ANGPT1, ANGPT2 and FGF2 are promising targets for future research. SNP analysis results support our hypothesis that the interaction of the host's angiogenic profile and the type of cancer explains differences in clinical response to VEGF inhibition. Specifically, our work showed that variants of the ANGPT1, ANGPT2, and FGF2 genes or their respective proteins might render certain tumors more susceptible to targeting of VEGF..

Citation Format: Issam Makhoul, Robert Griffin, Stephen Erickson, Ishwori Dhakal, Venay R. Raj, Dorothy A. Graves, Jeannette Y. Lee, Mohammed S. Orloff, Eric R. Siegel, Susan A. Kadlubar. Germline genetic variants in ANGPT1 & 2 and FGF2 are associated with pathologic complete response to bevacizumab in breast cancer patients. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 2825. doi:10.1158/1538-7445.AM2014-2825

Genetic epidemiology and nonsyndromic structural birth defects: from candidate genes to epigenetics

Birth defects are a leading cause of infant morbidity and mortality worldwide. The vast majority of birth defects are nonsyndromic, and although their etiologies remain mostly unknown, evidence supports the hypothesis that they result from the complex interaction of genetic, epigenetic, environmental, and lifestyle factors. Since our last review published in 2002 describing the basic tools of genetic epidemiology used to study nonsyndromic structural birth defects, many new approaches have become available and have been used with varying success. Through rapid advances in genomic technologies, investigators are now able to investigate large portions of the genome at a fraction of previous costs. With next-generation sequencing, research has progressed from assessing a small percentage of single-nucleotide polymorphisms to assessing the entire human protein-coding repertoire (exome)-an approach that is starting to uncover rare but informative mutations associated with nonsyndromic birth defects. Herein, we report on the current state of the genetic epidemiology of birth defects and comment on future challenges and opportunities. We consider issues of study design, and we discuss common variant approaches, including candidate gene studies and genome-wide association studies. We also discuss the complexities embedded in exploring interactions between genes and the environment. We complete our review by describing new and promising next-generation sequencing technologies and examining how the study of epigenetic mechanisms could become the key to unraveling the complex etiologies of nonsyndromic structural birth defects.

Experience with high frequency oscillation ventilation during the 2009 H1N1 influenza pandemic in Australia and New Zealand

During the 2009 H1N1 pandemic, large numbers of patients had severe respiratory failure. High frequency oscillation ventilation was used as a salvage technique for profound hypoxaemia. Our aim was to compare this experience with high frequency oscillation ventilation during the 2009 H1N1 pandemic with the same period in 2008 by performing a three-month period prevalence study in Australian and New Zealand intensive care units. The main study end-points were clinical demographics, care delivery and survival. Nine intensive care units contributed data. During 2009 there were 22 H1N1 patients (17 adults, five children) and 10 non-H1N1 patients (five adults, five children), while in 2008, 18 patients (two adults, 16 children) received high frequency oscillation ventilation. The principal non-H1N1 high frequency oscillation ventilation indication was bacterial or viral pneumonia (56%). For H1N1 patients, the median duration of high frequency oscillation ventilation was 3.7 days (interquartile range 1.8 to 5) with concomitant therapies including recruitment manoeuvres (22%), prone ventilation (41%), inhaled prostacyclins (18%) and inhaled nitric oxide (36%). Seven patients received extracorporeal membrane oxygenation, six having H1N1. Three patients had extracorporeal membrane oxygenation concurrently, two as salvage therapy following the commencement of high frequency oscillation ventilation. In 2008, no high frequency oscillation ventilation patient received extracorporeal membrane oxygenation. Overall hospital survival was 77% in H1N1 patients, while survival in patients having adjunctive extracorporeal membrane oxygenation was similar to those receiving high frequency oscillation ventilation alone (65% compared to 71%, P = 1.00). Survival rates were comparable to published extracorporeal membrane oxygenation outcomes. High frequency oscillation ventilation was used successfully as a rescue therapy for severe respiratory failure. High frequency oscillation ventilation was only available in a limited number of intensive care units during the H1N1 pandemic.

Drug approval processes in Australian Paediatric Hospitals

OBJECTIVE

To describe and evaluate the decision-making processes for drug approval in Australian paediatric hospitals.

DESIGN

Multicentre descriptive study involving face-to-face interviews of drug and therapeutics committee chairs and secretaries, review of committee documents and drug submissions for all Australian paediatric hospital drug and therapeutics committees over a 1-year period.

SETTING

All eight paediatric hospitals in Australia.

PARTICIPANTS

Eight committee chairs and seven secretaries or delegates.

MAIN OUTCOME MEASURES

Total drug expenditure, number of formulary submissions, individual-patient use approvals and approval rates for each hospital from 1 July 2006 to 30 June 2007, stratified by therapeutic class. Qualitative description of the approval processes.

RESULTS

Total drug expenditure varied from $A1.7 million (US$1.5 million) to $A11.1 million (US$9.8 million) per hospital. The number of formulary submissions also varied, from 7 to 21, but approval rate was high (76%-100%) and not significantly different among hospitals (p=0.17). Several committees approved identical submissions for five drugs. The number of individual-patient use applications varied considerably, ranging from 10 to 456 per hospital. Where estimable, individual-patient use approval was 76%-100% and variable (p=0.03). Quality of evidence relating to safety and efficacy of drugs being considered was regarded as the most important factors influencing decision making, with the cost less important. Most committees had poor infrastructural support for approval processes. No committee formally included a pharmaco-economic evaluation.

CONCLUSIONS

Most drug submissions in tertiary paediatric hospitals are approved; however, workload, drug expenditure and individual-patient use schemes vary considerably. Duplication of effort occurs, and few committees are resourced sufficiently given their terms of reference.

Rank-based inverse normal transformations are increasingly used, but are they merited?

Many complex traits studied in genetics have markedly non-normal distributions. This often implies that the assumption of normally distributed residuals has been violated. Recently, inverse normal transformations (INTs) have gained popularity among genetics researchers and are implemented as an option in several software packages. Despite this increasing use, we are unaware of extensive simulations or mathematical proofs showing that INTs have desirable statistical properties in the context of genetic studies. We show that INTs do not necessarily maintain proper Type 1 error control and can also reduce statistical power in some circumstances. Many alternatives to INTs exist. Therefore, we contend that there is a lack of justification for performing parametric statistical procedures on INTs with the exceptions of simple designs with moderate to large sample sizes, which makes permutation testing computationally infeasible and where maximum likelihood testing is used. Rigorous research evaluating the utility of INTs seems warranted.

Phenotypically concordant and discordant monozygotic twins display different DNA copy-number-variation profiles

The exploration of copy-number variation (CNV), notably of somatic cells, is an understudied aspect of genome biology. Any differences in the genetic makeup between twins derived from the same zygote represent an irrefutable example of somatic mosaicism. We studied 19 pairs of monozygotic twins with either concordant or discordant phenotype by using two platforms for genome-wide CNV analyses and showed that CNVs exist within pairs in both groups. These findings have an impact on our views of genotypic and phenotypic diversity in monozygotic twins and suggest that CNV analysis in phenotypically discordant monozygotic twins may provide a powerful tool for identifying disease-predisposition loci. Our results also imply that caution should be exercised when interpreting disease causality of de novo CNVs found in patients based on analysis of a single tissue in routine disease-related DNA diagnostics.

A likelihood-ratio test of twin zygosity using molecular genetic markers

The importance of using multiple polymorphic genetic markers to determine unambiguously whether a twin pair is monozygotic (MZ) or dizygotic (DZ) has long been recognized. Concordance among a set of markers is used as evidence of monozygosity, as it would be improbable for DZ twins to be concordant at a large number of polymorphic loci. Several sources give a formula for the probability of two DZ twins sharing the same genotype at a locus, assuming knowledge of allele frequencies but not of either twin's genotype; this probability can be used to determine whether a set of markers will reliably distinguish between MZ and DZ status in a randomly selected twin pair. If the shared genotype is known, however, the likelihood-ratio test (LRT) of the null hypothesis of dizygosity against the alternative hypothesis of monozygosity takes into account the observed genotype and, by the Neyman-Pearson lemma, is the most powerful test of its size. The LRT is equivalent to conditioning on the genotype of one of the twins, and computing the probability, assuming DZ status, of the other twin sharing that genotype. The resulting p values are frequently lower than those produced by the unconditional probability, especially if rare alleles are observed. The unconditional probability can be recapitulated from conditional probabilities by averaging across all of the conditioned sibling's possible genotypes. To illustrate properties of the LRT applied to multiple markers, the probability distribution of the LRT p value is computed from allele frequencies of twelve unlinked markers published in Elbaz et al. (2006) and compared with the p value computed from unconditional probabilities.