Comparison of immune system development in nonclinical species and humans: Closing information gaps for immunotoxicity testing and human translatability

Consideration of pathways for immunotoxicity of per- and polyfluoroalkyl substances (PFAS)

BACKGROUND

Per- and polyfluoroalkyl substances (PFAS) are of public health concern, because of their ubiquitous and extremely persistent occurrence, and depending on their structure, their bio-accumulative, mobile and toxic properties. Human health effects associated with exposure to PFAS include adverse effects on the immune system. In 2020, EFSA (the European Food Safety Authority) defined adverse effects on the immune system as the most critical effect for human health risk assessment, based on reduced antibody responses to childhood vaccines and similar effects observed in experimental animal studies. Likewise, the U.S. EPA (Environmental Protection Agency) considers PFAS-induced immunotoxicity, especially in children, as the critical effect for risk assessment. However, the mechanisms by which antibody concentrations are impacted are not completely understood. Furthermore, other targets of the immune system functions have been reported in the literature.

OBJECTIVE

The aim of this review is to explore PFAS-associated immune-related effects. This includes, relevant mechanisms that may underlie the observed effects on the immune system, immunosuppression as well as immunoenhancement, such as i) modulation of cell signalling and nuclear receptors, such as NF-κB and PPARs; ii) alteration of calcium signalling and homoeostasis in immune cells; iii) modulation of immune cell populations; iv) oxidative stress and v) impact on fatty acid metabolism & secondary effects on the immune system.

METHODS

A literature research was conducted using three databases (Web of Science, PubMed, and Scopus), which were searched in July 2021 for relevant studies published in the time frame from 2018 to 2021. In total, 487 publications were identified as potentially eligible and following expert-based judgement, articles relevant for mechanisms of PFAS induced immunotoxicity are discussed.

CONCLUSIONS

Taken together, we show that there is substantial evidence from both in vitro and in vivo experimental as well as epidemiological studies, supporting that various PFAS, not only PFOA and PFOS, affect multiple aspects of the immune system. Timing of exposure is critical, because the developing immune system is especially vulnerable to toxic insults, resulting in a higher risk of particularly adverse immune effects but also other organs later in life.

Biology and postnatal development of organ systems of cynomolgus monkeys (Macaca fascicularis)

BACKGROUND

The cynomolgus macaque has become the most used non-human primate species in nonclinical safety assessment during the past decades.

METHODS

This review summarizes the biological data and organ system development milestones of the cynomolgus macaque available in the literature.

RESULTS

The cynomolgus macaque is born precocious relative to humans in some organ systems (e.g., nervous, skeletal, respiratory, and gastrointestinal). Organ systems develop, refine, and expand at different rates after birth. In general, the respiratory, gastrointestinal, renal, and hematopoietic systems mature at approximately 3 years of age. The female reproductive, cardiovascular and hepatobiliary systems mature at approximately 4 years of age. The central nervous, skeletal, immune, male reproductive, and endocrine systems complete their development at approximately 5 to 9 years of age.

CONCLUSIONS

The cynomolgus macaque has no meaningful developmental differences in critical organ systems between 2 and 3 years of age for use in nonclinical safety assessment.

Comparative transcriptomic analysis of rabbit interscapular brown adipose tissue whitening under physiological conditions

Interscapular brown adipose tissue (iBAT) of both rabbits and humans exhibits a similar whitening phenomenon under physiological conditions. However, a detailed characterization of iBAT whitening in them is still lacking. Here, we chose rabbits as a model to gain a better understanding of the molecular signature changes during the whitening process of iBAT by transcriptomic analysis of rabbit iBAT at day 1, day 14, 1 month and 4 months after birth. We applied non-invasive MRI imaging to monitor the whitening process and correlated these changes with analysis of morphological, histological and molecular features. Principal component analysis (PCA) of differentially expressed genes delineated three major phases for the whitening process as Brown, Transition and Whitened BAT phases. RNA-sequencing data revealed that whitening of iBAT was an orchestrated process where multiple types of cells and tissues participated in a variety of physiological processes including neovascularization, formation of new nervous networks and immune regulation. Several key metabolic and signalling pathways contributed to whitening of iBAT, and immune cells and immune regulation appeared to play an overarching role.

Considerations for and against dosing rodent pups before 7 days of age in juvenile toxicology studies

This review focuses on preweaning ontogenic and developmental processes that can influence the selection of the appropriate age at which to start dosing rodent pups in juvenile animal studies (JAS). The ICH S11 guideline on 'Nonclinical Safety Testing in Support of Development of Paediatric Medicines' highlights the need to adapt the age from which animals are dosed according to the stage of development in the target organs/tissues of concern in the youngest pediatric patients. Rodents (rat or mouse) are the most common species for JAS. Despite previous practices, based on comparative ontogeny, it is rarely necessary to dose rodents younger than one week of age since postnatal day (PND)7 is appropriate to address concern for the vast majority of organs. In exceptional cases, earlier dosing (e.g., PND4) can be appropriate to address specific concern in preterm neonates and when a tissue of concern has a particularly early developmental trajectory in the rodent compared to humans. The comparative development of the CNS is particularly complex. While exposure of rodents from PND10 covers most CNS development stages relevant to human neonates, a later dosing start (yet, not later than PND14) can sometimes be appropriate to reflect specific aspects (e.g., transformation of GABAergic transmission). An extended study design including subsets of several ages can be helpful to address multiple concerns within a preweaning JAS. Such design can allow for individual assessment of each concern, whilst minimizing (potentially irrelevant) signals from tissues exposed at a developmental stage that do not match the human situation.

[Osteoimmunomodulatory effects of inorganic biomaterials in the process of bone repair]

OBJECTIVE

To review the osteoimmunomodulatory effects and related mechanisms of inorganic biomaterials in the process of bone repair.

METHODS

A wide range of relevant domestic and foreign literature was reviewed, the characteristics of various inorganic biomaterials in the process of bone repair were summarized, and the osteoimmunomodulatory mechanism in the process of bone repair was discussed.

RESULTS

Immune cells play a very important role in the dynamic balance of bone tissue. Inorganic biomaterials can directly regulate the immune cells in the body by changing their surface roughness, surface wettability, and other physical and chemical properties, constructing a suitable immune microenvironment, and then realizing dynamic regulation of bone repair.

CONCLUSION

Inorganic biomaterials are a class of biomaterials that are widely used in bone repair. Fully understanding the role of inorganic biomaterials in immunomodulation during bone repair will help to design novel bone immunomodulatory scaffolds for bone repair.

Genome editing in large animal models

Although genome editing technologies have the potential to revolutionize the way we treat human diseases, barriers to successful clinical implementation remain. Increasingly, preclinical large animal models are being used to overcome these barriers. In particular, the immunogenicity and long-term safety of novel gene editing therapeutics must be evaluated rigorously. However, short-lived small animal models, such as mice and rats, cannot address secondary pathologies that may arise years after a gene editing treatment. Likewise, immunodeficient mouse models by definition lack the ability to quantify the host immune response to a novel transgene or gene-edited locus. Large animal models, including dogs, pigs, and non-human primates (NHPs), bear greater resemblance to human anatomy, immunology, and lifespan and can be studied over longer timescales with clinical dosing regimens that are more relevant to humans. These models allow for larger scale and repeated blood and tissue sampling, enabling greater depth of study and focus on rare cellular subsets. Here, we review current progress in the development and evaluation of novel genome editing therapies in large animal models, focusing on applications in human immunodeficiency virus 1 (HIV-1) infection, cancer, and genetic diseases including hemoglobinopathies, Duchenne muscular dystrophy (DMD), hypercholesterolemia, and inherited retinal diseases.

Dose range finding approach for rodent preweaning juvenile animal studies

OBJECTIVES

Strategies for conducting juvenile dose ranging studies before definitive toxicity juvenile animal studies (JAS) have evolved, but the aim of demonstrating study design robustness and efficient animal use remains the same. The objective of dose selection is to identify a strategy to achieve consistent systemic exposure for the duration of the JAS while maintaining exposure separation between dose groups. For preweaning rodents this can prove challenging, as these studies typically treat animals over a broad period of considerable organ development.

MATERIALS AND METHODS

In our experience, over 45 rodent juvenile studies (dose range, definitive or investigative) were conducted over 20 years to support pediatric medicine development. In most cases (86%, 12/14), preweaning rodents required decreased doses of test articles than adult rodents; the majority (83%, 10/12) were due to increased systemic exposures in immature animals at the same doses. Thus, extrapolating tolerability and exposure data from adults is not ideal and should not take the place of well-designed juvenile dose range studies.

RESULTS/DISCUSSION/CONCLUSION

We propose a phased dose-range-finding approach by first conducting a tolerability phase with a few animals at a starting age corresponding to the youngest clinical starting age, spanning a wide range of doses, then a dose range phase with larger group sizes and fewer doses; both phases incorporate toxicokinetics. Often, exposure was higher in preweaning animals and decreased as animals matured postweaning (postnatal day, PND 21 and older), supporting an age-based dose adjustment strategy. Case studies demonstrate dose adjustment approaches incorporating dose increases or decreases or changes in dose frequency.

GSK2245035, a TLR7 agonist, Does Not Increase Pregnancy Loss in Cynomolgus Monkeys

GSK2245035, a small molecule Toll-like Receptor 7 (TLR7) agonist developed for immunomodulatory treatment for allergic airways disease, aimed to reduce Th2 and enhance Th1/Treg responses to aeroallergens via the local induction of type I interferons (IFNs). GSK2245035 demonstrated selectivity for potent release of type I IFNs compared to TNF-α and IL-6, with dose dependent increases in the interferon inducible chemokine, IP-10, in the nasal compartment. Implantation and parturition require pro-inflammatory processes including IFNs, Interferon Stimulated Genes, TNFα and IP-10 while pregnancy requires immune regulation to maintain maternal fetal immune tolerance, and recombinant type I IFNs induced abortions in monkeys. Due to its mechanism of action, GSK2245035 was studied at pharmacologically and clinically relevant doses in a monkey pregnancy model. Monkeys received 0, 3 or 30 ng/kg/week GSK2245035 intranasally once weekly, from Day 20 postcoitum through Day 63 postpartum. Although systemic IFN-α and IP-10 levels were approximately 14.8 or 40 -fold (respectively) above predose levels at 3 or 30 ng/kg/week, respectively, there were no effects on pregnancy and infant outcome. Non-adverse effects included increased incidence of nasal discharge, increased maternal body temperature at 30 ng/kg/week and dose-dependent increases in maternal IP-10 and IFN-α and decreased infant anti-KLH IgM and IgG titers following KLH immunization at ≥3 ng/kg/week, relative to controls. Potentially, lower IFN-α and IP-10 levels as well as once-weekly intranasal dosing vs daily subcutaneous or intramuscular dosing with recombinant type I IFNs could explain the lack of pregnancy effects; however, there was an undesired impact on offspring immune function.

The Effects of Deoxynivalenol on the Ultrastructure of the Sacculus Rotundus and Vermiform Appendix, as Well as the Intestinal Microbiota of Weaned Rabbits

Deoxynivalenol (DON) is a mycotoxin found in grains that poses a potential threat to human and animal health, and the gastrointestinal tract is the primary target organ. There are few studies focused on the toxicology of DON to rabbits, especially on the relation among DON, microbiota, and the gut-associated lymphoid tissue. A total of 30 weaned rabbits (35 d) were evenly divided into the control group and DON group (1.5 mg/kg bodyweight (BW)) based on their body weight. After a 24-day trial, the ultrastructures of the sacculus rotundus and vermiform appendix were observed using a scanning electron microscope and transmission electron microscopy. The morphology and microflora in the ileum, caecum, and colon were also examined. The results proved that the ultrastructure of the sacculus rotundus and vermiform appendix, as well as the integrity of the intestinal barrier (especially for the ileum), were impaired after DON was administrated to the rabbits. Compared to the control group, the relative abundance and diversity of the microflora decreased in all three intestinal segments in the DON group, particularly in the ileum and caecum. In conclusion, the toxic effect of DON on weaned rabbits may be performed by destroying the structure of the sacculus rotundus and vermiform appendix, as well as affecting the structure and diversity of the intestinal flora.

How repertoire data are changing antibody science

Antibodies are vital proteins of the immune system that recognize potentially harmful molecules and initiate their removal. Mammals can efficiently create vast numbers of antibodies with different sequences capable of binding to any antigen with high affinity and specificity. Because they can be developed to bind to many disease agents, antibodies can be used as therapeutics. In an organism, after antigen exposure, antibodies specific to that antigen are enriched through clonal selection, expansion, and somatic hypermutation. The antibodies present in an organism therefore report on its immune status, describe its innate ability to deal with harmful substances, and reveal how it has previously responded. Next-generation sequencing technologies are being increasingly used to query the antibody, or B-cell receptor (BCR), sequence repertoire, and the amount of BCR data in public repositories is growing. The Observed Antibody Space database, for example, currently contains over a billion sequences from 68 different studies. Repertoires are available that represent both the naive state (i.e. antigen-inexperienced) and that after immunization. This wealth of data has created opportunities to learn more about our immune system. In this review, we discuss the many ways in which BCR repertoire data have been or could be exploited. We highlight its utility for providing insights into how the naive immune repertoire is generated and how it responds to antigens. We also consider how structural information can be used to enhance these data and may lead to more accurate depictions of the sequence space and to applications in the discovery of new therapeutics.