Optimization and validation of a flow cytometric method for immunophenotyping peripheral blood lymphocytes from cynomolgus monkeys (Macaca fascicularis)

Immunohematological features of free-living Alouatta belzebul (Linnaeus, 1766) red-handed howler monkeys in the Eastern Amazon

The red-handed howler monkey (Alouatta belzebul) is one of the 35 threatened Brazilian primate species found in two highly endangered Brazilian biomes. Their Amazonian native populations have been declining due to exponential deforestation associated with human activities, especially the construction of dams. The studied population (n = 27) was located in the Belo Monte dam Area of Influence. For the first time, we presented hematological parameters and the basic profile of T (CD3) and B (BSAP PAX5) cells by immunocytochemistry. The results supported the hypothesis that the immuno-hematological profile is influenced by sex, age, and season. Eosinophils were significantly higher in females (p = 0.03), monocytes statistically greater in juveniles (p = 0.04), and total plasma protein increased significantly (p > 0.001) during the dry season. Furthermore, adults showed a statistically higher average absolute number of B lymphocytes than young individuals (p = 0.03), in contrast to T lymphocytes. Even without knowing the full history of antigenic exposure, these results not only contribute to elucidating the boundaries between health and disease but may help lay the groundwork for future research into the effects of anthropogenic stress on immune activation.

Lymphocyte subsets and immunoglobulin levels in peripheral blood from cynomolgus monkeys (Macaca fascicularis) of different age groups

Immunotoxicity assessment is an important part of non-clinical safety evaluation of biotechnology-derived pharmaceuticals. The reference ranges of evaluated parameters, which depend on the sex, age and geographical origin of animals, play a significant role in interpreting the study results. The aim of this study was to determine the reference ranges of parameters commonly used for non-clinical immunotoxicity studies in cynomolgus monkeys (Macaca fascicularis) of different ages. The percentages of CD3⁺, CD4⁺, CD8⁺, CD20⁺, CD16/56⁺ lymphocytes, and the serum levels of immunoglobulins A, M, G and E in clinically healthy cynomolgus monkeys of both sexes and different ages (37-104 months) were analysed. The lymphocyte subsets were assessed by flow cytometry and serum immunoglobulin levels were determined by enzyme-linked immunosorbent assay. Statistical analysis showed a weak rank correlation of CD3⁺, CD20⁺ lymphocyte levels with the ages of female and male cynomolgus monkeys, and no significant correlation with age for the combined data of both sexes. The serum levels of immunoglobulins A, M, G and E did not have a significant rank correlation with age for the combined data of both sexes, whereas IgA levels in females and IgG levels in males were weakly correlated with age. Overall, these results justify the use of animals aged three to eight years for non-clinical immunotoxicity evaluation of biotechnology-derived pharmaceuticals. It is important to avoid the formation of animal groups with extreme ages (three years or eight years) in one group during randomization.

Large granular lymphocytosis in a cynomolgus macaque (Macaca fascicularis) with a subclinical Trypanosoma cruzi infection

A 5.25-year-old cynomolgus macaque (Macaca fascicularis) was found to have a marked leukocytosis due to a lymphocytosis on routine quarantine laboratory data prior to inclusion in a preclinical research study. The majority of lymphocytes were characterized as intermediate to large with round to convoluted nuclei, coarse to clumped chromatin, rare prominent nucleoli, and moderate amounts of lightly basophilic cytoplasm that frequently contained small magenta granules and/or clear vacuoles. The animal had tested negative for several viruses and other etiologic agents found in nonhuman primates 1 week prior to shipment to the research facility. However, further evaluation of the blood smear revealed rare hemoflagellates, and later testing using real-time PCR and ELISA was confirmatory for Trypanosoma cruzi (T cruzi). Trypanosoma cruzi is a zoonotic pathogen responsible for Chagas disease in people and can have negative consequences on study results when positive animals are inadvertently used for preclinical research. This case report describes a marked large granular lymphocytosis in an otherwise healthy macaque as the only indication of infection with T cruzi in an animal believed to be negative for the infection. Additionally, it highlights the diagnostic limitations of screening tests to rule out diseases in animals intended to be used in preclinical studies.

Immunophenotyping: Application to Safety Assessment

A continuing education course entitled “What You Always Wanted to Know About Immunotoxicology in Pharmaceutical Development…But Were Afraid to Ask” was offered at the Society of Toxicologic Pathology (STP) 36th annual symposium in Montreal. This article summarizes some key points made during the presentation dedicated to immunophenotyping. It describes how clusters of differentiation (CDs) are well-defined antigens used to characterize cell subsets, and how lymphocyte subsets in humans and different rodent and nonrodent species can be defined by detection of various combinations of CDs. It provides an overview of immunophenotyping study design considerations and applications to safety assessment.

Method validation and reference range values for a peripheral blood immunophenotyping assay in non-human primates

A peripheral blood immunophenotyping assay was developed and validated for determination of total T-lymphocytes, helper T-lymphocytes, cytotoxic T-lymphocytes, B-lymphocytes, and natural killer cells in cynomolgus monkeys. Validation parameters included assessment of precision, linearity, antibody optimization, stability of peripheral blood samples, and stability of fixed immunophenotyping samples. Total lymphocyte populations were determined using a heterogeneous lymphocyte gating strategy consisting of CD45 fluorescent staining and side-scatter demarcation. Relative lymphocyte subset values were determined using antigen-specific gating strategies. Absolute subset concentrations for each lymphocyte subset were subsequently determined using a dual-platform methodology wherein relative lymphocyte subset values (via flow cytometry analyses) were multiplied by the absolute total lymphocyte (via hematology analyses) values. Reference ranges are presented for cynomolgus monkey, rhesus monkey, and baboon. Additional 1-year longitudinal immunophenotyping values are presented for the cynomolgus monkey. The method validation and reference ranges presented in this research provide a robust analytical methodology for determination of peripheral blood lymphocyte subsets in various non-human primate species.

An inter-laboratory retrospective analysis of immunotoxicological endpoints in non-human primates: flow cytometry immunophenotyping

Non-human primates may be the only relevant species for pharmacology or toxicology studies of certain biologics, due to lack of activity in other species. Flow cytometry immunophenotyping is often included as a minimally invasive adjunct to standard toxicity testing. A retrospective inter-laboratory analysis was conducted to assess counts and variability of the main cell types monitored in toxicity studies, and to provide guidance for conduct and interpretation of immunophenotyping assessments in cynomolgus monkeys. Univariate and multivariate models were developed. Study design factors influencing cell counts and variability were identified and a power analysis was performed. Pre-study and on-study counts were generally similar; longitudinal analysis showed little drift in mean counts or within-animal variability over time. Within-animal variability was lower than inter-animal variability. Gender was associated with small but significant differences in mean counts and variability. Age was associated with significant differences in variability. Immunophenotype definitions were associated with significant differences in mean counts and within-animal variability for most cell types. Power analysis for groups of 6-8 animals showed that differences of ≈50% in counts of T-cells, T-cell subsets, and B-cells compared to pre-treatment values may be detected; for NK cells and monocytes, differences of ≈60-90% may be detected. This review yields some general points to consider for immunophenotyping studies, i.e. (a) analysis of log-transformed cell count data and comparisons using each animal as its own reference will improve ability to detect changes, (b) the magnitude of change detectable given study group size should be considered, (c) multiplication of sampling timepoints during a study seems unnecessary, (d) consideration should be given to using only one gender, when applicable, to increase power while minimizing animal usage, and (e) the choice of immunophenotype has impacts on cell counts and variability.

Determination of Absolute Counts of Circulating Regulatory T Cells in Cynomolgus Macaques Using an Optimized Flow Cytometric Method

Regulatory T cells (Tregs) are a rare subset of lymphocytes that inhibit the activation and effector functions of T cells and are important regulators of immune responses. Although Tregs are well characterized in humans and rodents, little is known about their immunophenotyping (IP) profile in cynomolgus macaques ( Macaca fascicularis), which is an important species for pharmacological and toxicological evaluation of potential immune modulators because of their similar physiologic, genetic, and metabolic response patterns to humans. The authors have developed an immunophenotyping panel using a high-throughput 96-well microtiter plate–based assay to detect circulating Tregs (CD3+CD4+CD25hiFoxP3+) and have determined the normal range for the number of Tregs in naive healthy cynomolgus macaques to be 56.4 to 179.7 cells/µL (mean ± SEM = 113.6 ± 5.1 cells/µL; n = 25). Furthermore, the authors compared the resulting FoxP3+ Treg profiles with a CD127lo cell-surface panel (CD3+CD4+CD25hi CD127lo) and found a close correlation between the absolute numbers of CD3+CD4+CD25hiFoxP3+ and CD3+CD4+CD25hiCD127lo cells (mean ± SD = 120 ± 8.0 cells/µL). Quantification of circulating Tregs in cynomolgus macaques in this high-throughput assay may help to identify drug candidates that affect this rare, but critical, immunoregulatory cell population.