Mismatch repair gene mutations lead to lynch syndrome colorectal cancer in rhesus macaques

Modifications to rhesus macaque TCR constant regions improve TCR cell surface expression

T cell immunotherapy success is dependent on effective levels of antigen receptor expressed at the surface of engineered cells. Efforts to optimize surface expression in T cell receptor (TCR)-based therapeutic approaches include optimization of cellular engineering methods and coding sequences, and reducing the likelihood of exogenous TCR α and β chains mispairing with the endogenous TCR chains. Approaches to promote correct human TCR chain pairing include constant region mutations to create an additional disulfide bond between the two chains, full murinization of the constant region of the TCR α and β sequences, and a minimal set of murine mutations to the TCR α and β constant regions. Preclinical animal models are valuable tools to optimize engineering designs and methods, and to evaluate the potential for off-target tissue injury. To further develop rhesus macaque models for TCR based cellular immunotherapy, we tested methods for improving cell surface expression of rhesus macaque TCR in rhesus macaque primary cells by generating five alternative TCRαβ constant region constructs in the context of a SIV Gag-specific TCR: 1. human codon optimized rhesus macaque (RH); 2. RH TCR with an additional disulfide linkage; 3. rhesus macaque constant sequences with minimal murine amino acid substitutions; 4. murinized constant sequences; and 5. murinized constant sequences with a portion of the exposed FG loop in the β constant sequence replaced with rhesus macaque sequence to reduce potential immunogencity. Murinization or mutation of a minimal set of amino acids to the corresponding murine sequence of the constant region resulted in the greatest increase in rhesus macaque TCR surface expression relative to wild type. All novel TCR constructs retained the ability to induce production of cytokines in response to cognate peptide antigen specific stimulation. This work can inform the design of TCRs selected for use in rhesus macaque models of TCR-based cellular immunotherapy.

Nucleic acid-based drugs for patients with solid tumours

The treatment of patients with advanced-stage solid tumours typically involves a multimodality approach (including surgery, chemotherapy, radiotherapy, targeted therapy and/or immunotherapy), which is often ultimately ineffective. Nucleic acid-based drugs, either as monotherapies or in combination with standard-of-care therapies, are rapidly emerging as novel treatments capable of generating responses in otherwise refractory tumours. These therapies include those using viral vectors (also referred to as gene therapies), several of which have now been approved by regulatory agencies, and nanoparticles containing mRNAs and a range of other nucleotides. In this Review, we describe the development and clinical activity of viral and non-viral nucleic acid-based treatments, including their mechanisms of action, tolerability and available efficacy data from patients with solid tumours. We also describe the effects of the tumour microenvironment on drug delivery for both systemically administered and locally administered agents. Finally, we discuss important trends resulting from ongoing clinical trials and preclinical testing, and manufacturing and/or stability considerations that are expected to underpin the next generation of nucleic acid agents for patients with solid tumours.

Speeding up Glioblastoma Cancer Research: Highlighting the Zebrafish Xenograft Model

Glioblastoma multiforme (GBM) is a very aggressive and lethal primary brain cancer in adults. The multifaceted nature of GBM pathogenesis, rising from complex interactions between cells and the tumor microenvironment (TME), has posed great treatment challenges. Despite significant scientific efforts, the prognosis for GBM remains very poor, even after intensive treatment with surgery, radiation, and chemotherapy. Efficient GBM management still requires the invention of innovative treatment strategies. There is a strong necessity to complete cancer in vitro studies and in vivo studies to properly evaluate the mechanisms of tumor progression within the complex TME. In recent years, the animal models used to study GBM tumors have evolved, achieving highly invasive GBM models able to provide key information on the molecular mechanisms of GBM onset. At present, the most commonly used animal models in GBM research are represented by mammalian models, such as mouse and canine ones. However, the latter present several limitations, such as high cost and time-consuming management, making them inappropriate for large-scale anticancer drug evaluation. In recent years, the zebrafish (Danio rerio) model has emerged as a valuable tool for studying GBM. It has shown great promise in preclinical studies due to numerous advantages, such as its small size, its ability to generate a large cohort of genetically identical offspring, and its rapid development, permitting more time- and cost-effective management and high-throughput drug screening when compared to mammalian models. Moreover, due to its transparent nature in early developmental stages and genetic and anatomical similarities with humans, it allows for translatable brain cancer research and related genetic screening and drug discovery. For this reason, the aim of the present review is to highlight the potential of relevant transgenic and xenograft zebrafish models and to compare them to the traditionally used animal models in GBM research.

Epigenetic MLH1 silencing concurs with mismatch repair deficiency in sporadic, naturally occurring colorectal cancer in rhesus macaques

BACKGROUND

Naturally occurring colorectal cancers (CRC) in rhesus macaques share many features with their human counterparts and are useful models for cancer immunotherapy; but mechanistic data are lacking regarding the comparative molecular pathogenesis of these cancers.

METHODS

We conducted state-of-the-art imaging including CT and PET, clinical assessments, and pathological review of 24 rhesus macaques with naturally occurring CRC. Additionally, we molecularly characterized these tumors utilizing immunohistochemistry (IHC), microsatellite instability assays, DNAseq, transcriptomics, and developed a DNA methylation-specific qPCR assay for MLH1, CACNA1G, CDKN2A, CRABP1, and NEUROG1, human markers for CpG island methylator phenotype (CIMP). We furthermore employed Monte-Carlo simulations to in-silico model alterations in DNA topology in transcription-factor binding site-rich promoter regions upon experimentally demonstrated DNA methylation.

RESULTS

Similar cancer histology, progression patterns, and co-morbidities could be observed in rhesus as reported for human CRC patients. IHC identified loss of MLH1 and PMS2 in all cases, with functional microsatellite instability. DNA sequencing revealed the close genetic relatedness to human CRCs, including a similar mutational signature, chromosomal instability, and functionally-relevant mutations affecting KRAS (G12D), TP53 (R175H, R273*), APC, AMER1, ALK, and ARID1A. Interestingly, MLH1 mutations were rarely identified on a somatic or germline level. Transcriptomics not only corroborated the similarities of rhesus and human CRCs, but also demonstrated the significant downregulation of MLH1 but not MSH2, MSH6, or PMS2 in rhesus CRCs. Methylation-specific qPCR suggested CIMP-positivity in 9/16 rhesus CRCs, but all 16/16 exhibited significant MLH1 promoter hypermethylation. DNA hypermethylation was modelled to affect DNA topology, particularly propeller twist and roll profiles. Modelling the DNA topology of a transcription factor binding motif (TFAP2A) in the MLH1 promoter that overlapped with a methylation-specific probe, we observed significant differences in DNA topology upon experimentally shown DNA methylation. This suggests a role of transcription factor binding interference in epigenetic silencing of MLH1 in rhesus CRCs.

CONCLUSIONS

These data indicate that epigenetic silencing suppresses MLH1 transcription, induces the loss of MLH1 protein, abrogates mismatch repair, and drives genomic instability in naturally occurring CRC in rhesus macaques. We consider this spontaneous, uninduced CRC in immunocompetent, treatment-naïve rhesus macaques to be a uniquely informative model for human CRC.

Proceedings of the 2023 Division of Translational Toxicology Satellite Symposium

The 2023 annual Division of Translational Toxicology (DTT) Satellite Symposium, entitled "Pathology Potpourri," was held in Summerlin, Nevada, at the Society of Toxicologic Pathology's 41st annual meeting. The goal of this symposium was to present and discuss challenging diagnostic pathology and/or nomenclature issues. This article presents summaries of the speakers' talks along with select images that were used by the audience for voting and discussion. Various lesions and topics covered during the symposium included induced and spontaneous neoplastic and nonneoplastic lesions in the mouse liver, infectious and proliferative lesions in nonhuman primates, interesting presentations of mononuclear cell infiltrates in various animal models and a complex oral tumor in a rat.

Nonhuman primate genetic models for the study of rare diseases

Pre-clinical research and development relies heavily upon translationally valid models of disease. A major difficulty in understanding the biology of, and developing treatments for, rare disease is the lack of animal models. It is important that these models not only recapitulate the presentation of the disease in humans, but also that they share functionally equivalent underlying genetic causes. Nonhuman primates share physiological, anatomical, and behavioral similarities with humans resulting from close evolutionary relationships and high genetic homology. As the post-genomic era develops and next generation sequencing allows for the resequencing and screening of large populations of research animals, naturally occurring genetic variation in nonhuman primates with clinically relevant phenotypes is regularly emerging. Here we review nonhuman primate models of multiple rare genetic diseases with a focus on the similarities and differences in manifestation and etiologies across species. We discuss how these models are being developed and how they can offer new tools and opportunities for researchers interested in exploring novel therapeutics for these and other genetic diseases. Modeling human genetic diseases in translationally relevant nonhuman primates presents new prospects for development of therapeutics and a better understanding of rare diseases. The post-genomic era offers the opportunity for the discovery and further development of more models like those discussed here.

Whole genome sequencing of CCR5 CRISPR-Cas9-edited Mauritian cynomolgus macaque blastomeres reveals large-scale deletions and off-target edits

Introduction: Genome editing by CRISPR-Cas9 approaches offers promise for introducing or correcting disease-associated mutations for research and clinical applications. Nonhuman primates are physiologically closer to humans than other laboratory animal models, providing ideal candidates for introducing human disease-associated mutations to develop models of human disease. The incidence of large chromosomal anomalies in CRISPR-Cas9-edited human embryos and cells warrants comprehensive genotypic investigation of editing outcomes in primate embryos. Our objective was to evaluate on- and off-target editing outcomes in CCR5 CRISPR-Cas9-targeted Mauritian cynomolgus macaque embryos. Methods: DNA isolated from individual blastomeres of two embryos, along with paternal and maternal DNA, was subjected to whole genome sequencing (WGS) analysis. Results: Large deletions were identified in macaque blastomeres at the on-target site that were not previously detected using PCR-based methods. De novo mutations were also identified at predicted CRISPR-Cas9 off-target sites. Discussion: This is the first report of WGS analysis of CRISPR-Cas9-targeted nonhuman primate embryonic cells, in which a high editing efficiency was coupled with the incidence of editing errors in cells from two embryos. These data demonstrate that comprehensive sequencing-based methods are warranted for evaluating editing outcomes in primate embryos, as well as any resultant offspring to ensure that the observed phenotype is due to the targeted edit and not due to unidentified off-target mutations.

Spontaneous, naturally occurring cancers in non-human primates as a translational model for cancer immunotherapy

The complexity of cancer immunotherapy (CIT) demands reliable preclinical models to successfully translate study findings to the clinics. Non-human primates (NHPs; here referring to rhesus and cynomolgus macaques) share broad similarities with humans including physiology, genetic homology, and importantly also immune cell populations, immune regulatory mechanisms, and protein targets for CIT. Furthermore, NHP naturally develop cancers such as colorectal and breast cancer with an incidence, pathology, and age pattern comparable to humans. Thus, these tumor-bearing monkeys (TBMs) have the potential to bridge the experimental gap between early preclinical cancer models and patients with human cancer.This review presents our current knowledge of NHP immunology, the incidence and features of naturally-occurring cancers in NHP, and recent TBM trials investigating CIT to provide a scientific rationale for this unique model for human cancer.

Total-Body Irradiation Is Associated With Increased Incidence of Mesenchymal Neoplasia in a Radiation Late Effects Cohort of Rhesus Macaques (Macaca mulatta)

PURPOSE

Cancer is a severe delayed effect of acute radiation exposure. Total-body irradiation has been associated with an increased risk of solid cancer and leukemia in Japanese atomic bomb survivors, and secondary malignancies, such as sarcoma, are a serious consequence of cancer radiation therapy. The radiation late effects cohort (RLEC) of rhesus macaques (Macaca mulatta) is a unique resource of more than 200 animals for studying the long-term consequences of total-body irradiation in an animal model that closely resembles humans at the genetic and physiologic levels.

METHODS AND MATERIALS

Using clinical records, clinical imaging, histopathology, and immunohistochemistry, this retrospective study characterized the incidence of neoplasia in the RLEC.

RESULTS

Since 2007, 61 neoplasms in 44 of 239 irradiated animals were documented (18.4% of the irradiated population). Only 1 neoplasm was diagnosed among the 51 nonirradiated controls of the RLEC (2.0%). The most common malignancies in the RLEC were sarcomas (38.3% of diagnoses), which are rare neoplasms in nonirradiated macaques. The most common sarcomas included malignant nerve sheath tumors and malignant glomus tumors. Carcinomas were less common (19.7% of diagnoses), and consisted primarily of renal cell and hepatocellular carcinomas. Neoplasia occurred in most major body systems, with the skin and subcutis being the most common site (40%). RNA analysis showed similarities in transcriptional profiles between RLEC and human malignant nerve sheath tumors.

CONCLUSIONS

This study indicates that total-body irradiation is associated with an increased incidence of neoplasia years following irradiation, at more than double the incidence described in aging, nonirradiated animals, and promotes tumor histotypes that are rarely observed in nonirradiated, aging rhesus macaques.

Comparative molecular genomic analyses of a spontaneous rhesus macaque model of mismatch repair-deficient colorectal cancer

Colorectal cancer (CRC) remains the third most common cancer in the US with 15% of cases displaying Microsatellite Instability (MSI) secondary to Lynch Syndrome (LS) or somatic hypermethylation of the MLH1 promoter. A cohort of rhesus macaques from our institution developed spontaneous mismatch repair deficient (MMRd) CRC with a notable fraction harboring a pathogenic germline mutation in MLH1 (c.1029C Collapse

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MESH Headings

• Animals
• Colonic Neoplasms/genetics
• Colorectal Neoplasms/genetics
• Colorectal Neoplasms/pathology
• Colorectal Neoplasms, Hereditary Nonpolyposis/genetics
• Colorectal Neoplasms, Hereditary Nonpolyposis/pathology
• DNA Methylation/genetics
• DNA Mismatch Repair/genetics
• Genomics
• Humans
• Macaca mulatta/genetics
• Mice
• Microsatellite Instability
• MutL Protein Homolog 1/genetics

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Grants

• P30 CA016672 NCI NIH HHS
• R24 OD011173 NIH HHS
• Feinberg Family Foundation
• MDACC Institutional Research Grant Program
• Cattleman for Cancer Research
• National Institutes of Health
• National Cancer Institute

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Affiliation(s)

Nejla Ozirmak Lermi Department of Clinical Cancer Prevention, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America School of Health Professions, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America
Stanton B. Gray Michale E. Keeling Center for Comparative Medicine and Research, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America
Charles M. Bowen Department of Clinical Cancer Prevention, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America
Laura Reyes-Uribe Department of Clinical Cancer Prevention, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America
Beth K. Dray Charles River Laboratories, Ashland, Ohio, United States of America
Nan Deng Department of Clinical Cancer Prevention, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America
R. Alan Harris Human Genome Sequencing Center and Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
Muthuswamy Raveendran Human Genome Sequencing Center and Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
Fernando Benavides Department of Epigenetics and Molecular Carcinogenesis, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America
Carolyn L. Hodo Michale E. Keeling Center for Comparative Medicine and Research, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America
Melissa W. Taggart Department of Pathology, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America
Karen Colbert Maresso Department of Clinical Cancer Prevention, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America
Krishna M. Sinha Department of Clinical Cancer Prevention, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America
Jeffrey Rogers Human Genome Sequencing Center and Department of Molecular and Human Genetics, Baylor College of Medicine, Houston, Texas, United States of America
Eduardo Vilar Department of Clinical Cancer Prevention, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America Clinical Cancer Genetics Program, The University of Texas MD Anderson Cancer Center, Houston, Texas, United States of America

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Genomic resources for rhesus macaques (Macaca mulatta)

Rhesus macaques (Macaca mulatta) are among the most extensively studied of nonhuman primates. This species has been the subject of many investigations concerning basic primate biology and behavior, including studies of social organization, developmental psychology, physiology, endocrinology, and neurodevelopment. Rhesus macaques are also critically important as a nonhuman primate model of human health and disease, including use in studies of infectious diseases, metabolic diseases, aging, and drug or alcohol abuse. Current research addressing fundamental biological and/or applied biomedical questions benefits from various genetic and genomic analyses. As a result, the genome of rhesus macaques has been the subject of more study than most nonhuman primates. This paper briefly discusses a number of information resources that can provide interested researchers with access to genetic and genomic data describing the content of the rhesus macaque genome, available information regarding genetic variation within the species, results from studies of gene expression, and other aspects of genomic analysis. Specific online databases are discussed, including the US National Center for Biotechnology Information, the University of California Santa Cruz genome browser, Ensembl genome browser, the Macaque Genotype and Phenotype database (mGAP), Rhesusbase, and others.

Neuropeptide S receptor 1 is a nonhormonal treatment target in endometriosis

Endometriosis is a common chronic inflammatory condition causing pelvic pain and infertility in women, with limited treatment options and 50% heritability. We leveraged genetic analyses in two species with spontaneous endometriosis, humans and the rhesus macaque, to uncover treatment targets. We sequenced DNA from 32 human families contributing to a genetic linkage signal on chromosome 7p13-15 and observed significant overrepresentation of predicted deleterious low-frequency coding variants in NPSR1, the gene encoding neuropeptide S receptor 1, in cases (predominantly stage III/IV) versus controls (P = 7.8 × 10^-4). Significant linkage to the region orthologous to human 7p13-15 was replicated in a pedigree of 849 rhesus macaques (P = 0.0095). Targeted association analyses in 3194 surgically confirmed, unrelated cases and 7060 controls revealed that a common insertion/deletion variant, rs142885915, was significantly associated with stage III/IV endometriosis (P = 5.2 × 10^-5; odds ratio, 1.23; 95% CI, 1.09 to 1.39). Immunohistochemistry, qRT-PCR, and flow cytometry experiments demonstrated that NPSR1 was expressed in glandular epithelium from eutopic and ectopic endometrium, and on monocytes in peritoneal fluid. The NPSR1 inhibitor SHA 68R blocked NPSR1-mediated signaling, proinflammatory TNF-α release, and monocyte chemotaxis in vitro (P < 0.01), and led to a significant reduction of inflammatory cell infiltrate and abdominal pain (P < 0.05) in a mouse model of peritoneal inflammation as well as in a mouse model of endometriosis. We conclude that the NPSR1/NPS system is a genetically validated, nonhormonal target for the treatment of endometriosis with likely increased relevance to stage III/IV disease.

Sequence diversity analyses of an improved rhesus macaque genome enhance its biomedical utility

The rhesus macaque (Macaca mulatta) is the most widely studied nonhuman primate (NHP) in biomedical research. We present an updated reference genome assembly (Mmul_10, contig N50 = 46 Mbp) that increases the sequence contiguity 120-fold and annotate it using 6.5 million full-length transcripts, thus improving our understanding of gene content, isoform diversity, and repeat organization. With the improved assembly of segmental duplications, we discovered new lineage-specific genes and expanded gene families that are potentially informative in studies of evolution and disease susceptibility. Whole-genome sequencing (WGS) data from 853 rhesus macaques identified 85.7 million single-nucleotide variants (SNVs) and 10.5 million indel variants, including potentially damaging variants in genes associated with human autism and developmental delay, providing a framework for developing noninvasive NHP models of human disease.

Characteristics of cancer susceptibility genes mutations in 282 patients with gastric adenocarcinoma

Objective

To reveal the distribution signature of cancer susceptibility genes in patients with gastric adenocarcinoma, offering a diagnostic and prognostic surrogate for disease risk management and therapeutic decisions.

Methods

A total of 282 patients with gastric adenocarcinoma (182 males and 100 females) were enrolled in this study, with peripheral blood genomic DNA extracted. Mutations of 69 canonical cancer susceptibility genes or presumably tumor-related genes were analyzed by targeted capture-based high-throughput sequencing. Candidate mutations were particularly selected for discussion on tumor pathogenesis according to the American College of Medical Genetics and Genomics (ACMG) guidelines.

Results

In this study, 7.1% (20/282) of patients with gastric adenocarcinoma were found to harbor mutations of canonical or presumable cancer susceptibility genes. The detection rate in male patients (3.8%, 7/182) was significantly lower than that in female patients (13%, 13/100) (P=0.004). The most recurrent mutations were in A-T mutated (ATM) (1.1%, 3/282), followed by BRCA1, BRIP1 and RAD51D, all showed a detection rate of 0.7% (2/282). Mutations in three genes associated with hereditary gastric cancer syndromes were detected, namely, PMS2 and EPCAM associated with Lynch syndrome and CDH1 associated with hereditary diffuse gastric cancer. The detection frequencies were all 0.4% (1/282). Notwithstanding no significant difference observed, the age of patients with pathogenic mutations or likely pathogenic mutations is slightly younger than that of non-carriers (median age: 58.5 vs. 60.5 years old), while the age of patients with ATM mutations was the youngest overall (median age: 49.3 years old).

Conclusions

Our study shed more light on the distribution signature and pathogenesis of mutations in gastric cancer susceptibility genes, and found the detection rate of pathogenic and likely pathogenic mutations in male patients was significantly lower than that in female patients. Some known and unidentified mutations were found in gastric cancer, which allowed us to gain more insight into the hereditary gastric cancer syndromes from the molecular perspective.

Animal Models to Understand the Etiology and Pathophysiology of Polycystic Ovary Syndrome

More than 1 out of 10 women worldwide are diagnosed with polycystic ovary syndrome (PCOS), the leading cause of female reproductive and metabolic dysfunction. Despite its high prevalence, PCOS and its accompanying morbidities are likely underdiagnosed, averaging > 2 years and 3 physicians before women are diagnosed. Although it has been intensively researched, the underlying cause(s) of PCOS have yet to be defined. In order to understand PCOS pathophysiology, its developmental origins, and how to predict and prevent PCOS onset, there is an urgent need for safe and effective markers and treatments. In this review, we detail which animal models are more suitable for contributing to our understanding of the etiology and pathophysiology of PCOS. We summarize and highlight advantages and limitations of hormonal or genetic manipulation of animal models, as well as of naturally occurring PCOS-like females.

The primate model for understanding and restoring vision

Retinal degenerative diseases caused by photoreceptor cell death are major causes of irreversible vision loss. As only primates have a macula, the nonhuman primate (NHP) models have a crucial role not only in revealing biological mechanisms underlying high-acuity vision but also in the development of therapies. Successful translation of basic research findings into clinical trials and, moreover, approval of the first therapies for blinding inherited and age-related retinal dystrophies has been reported in recent years. This article explores the value of the NHP models in understanding human vision and reviews their contribution to the development of innovative therapeutic strategies to save and restore vision.

Naturally Occurring and Experimentally Induced Rhesus Macaque Models for Polycystic Ovary Syndrome: Translational Gateways to Clinical Application

Indian rhesus macaque nonhuman primate models for polycystic ovary syndrome (PCOS) implicate both female hyperandrogenism and developmental molecular origins as core components of PCOS etiopathogenesis. Establishing and exploiting macaque models for translational impact into the clinic, however, has required multi-year, integrated basic-clinical science collaborations. Paradigm shifting insight has accrued from such concerted investment, leading to novel mechanistic understanding of PCOS, including hyperandrogenic fetal and peripubertal origins, epigenetic programming, altered neural function, defective oocytes and embryos, adipogenic constraint enhancing progression to insulin resistance, pancreatic decompensation and type 2 diabetes, together with placental compromise, all contributing to transgenerational transmission of traits likely to manifest in adult PCOS phenotypes. Our recent demonstration of PCOS-related traits in naturally hyperandrogenic (High T) female macaques additionally creates opportunities to employ whole genome sequencing to enable exploration of gene variants within human PCOS candidate genes contributing to PCOS-related traits in macaque models. This review will therefore consider Indian macaque model contributions to various aspects of PCOS-related pathophysiology, as well as the benefits of using macaque models with compellingly close homologies to the human genome, phenotype, development and aging.

A nonhuman primate model of inherited retinal disease

Inherited retinal degenerations are a common cause of untreatable blindness worldwide, with retinitis pigmentosa and cone dystrophy affecting approximately 1 in 3500 and 1 in 10,000 individuals, respectively. A major limitation to the development of effective therapies is the lack of availability of animal models that fully replicate the human condition. Particularly for cone disorders, rodent, canine, and feline models with no true macula have substantive limitations. By contrast, the cone-rich macula of a nonhuman primate (NHP) closely mirrors that of the human retina. Consequently, well-defined NHP models of heritable retinal diseases, particularly cone disorders that are predictive of human conditions, are necessary to more efficiently advance new therapies for patients. We have identified 4 related NHPs at the California National Primate Research Center with visual impairment and findings from clinical ophthalmic examination, advanced retinal imaging, and electrophysiology consistent with achromatopsia. Genetic sequencing confirmed a homozygous R565Q missense mutation in the catalytic domain of PDE6C, a cone-specific phototransduction enzyme associated with achromatopsia in humans. Biochemical studies demonstrate that the mutant mRNA is translated into a stable protein that displays normal cellular localization but is unable to hydrolyze cyclic GMP (cGMP). This NHP model of a cone disorder will not only serve as a therapeutic testing ground for achromatopsia gene replacement, but also for optimization of gene editing in the macula and of cone cell replacement in general.