Flow cytometric characterization of lymphocyte subpopulations in the cynomolgus monkey (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.

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.

Importance of the CD3 marker for evaluating changes in rhesus macaque CD4/CD8 T-cell ratios

BACKGROUND

Until recently, there were no CD3 antibodies that crossreacted with rhesus macaque T cells. Consequently, studies relying on CD8 counts or CD4/CD8 ratios enumerated this subpopulation on the basis of CD8+ or CD8bright+ staining. We used a rhesus-specific, anti-CD3 antibody to better define the CD8+ T-cell population, and to show the effects of better measurements on CD4/CD8 ratios and changes in T cells as macaques age.

METHODS

We used three-color flow cytometry to measure CD4 and CD8 populations with and without CD3 costaining. Venous blood samples were obtained from 52 colony-bred macaques between 2 months and 9 years of age.

RESULTS

The CD8+ T cells defined by CD3 and CD8 double staining were approximately 60% of all cells that were stained by CD8 alone. Improved detection of this lymphocyte subset showed that CD4/CD8 ratios were close to the range of 1.5-2.0. Declining CD4/CD8 ratios during aging are predominantly due to decreasing CD4+ T-cell counts.

CONCLUSIONS

Better quantitation of the CD8+ T-cell population showed that the CD4/CD8 ratio was not inverted as had been reported, but is actually very similar to the values observed in human beings. Although the two species differ in the pattern of CD8 expression, the general immune system characteristics are very similar.

Upgrading of flow cytometric analysis for absolute counts, cytokines and other antigenic molecules of cynomolgus monkeys (Macaca fascicularis) by using anti-human cross-reactive antibodies

In order to effectively use cynomolgus monkeys as animal models for human diseases, more than 300 anti-human monoclonal antibodies (mAbs) were studied as to their cross-reaction with various antigens from cynomolgus monkeys (Macaca fascicularis). Two hundred twenty-nine of 339 (67.55%) anti-human mAbs that react with human antigens of CD-defined molecules, chemokine receptors, and T cell receptors were cross-reactive with the monkey antigens. Using the cross-reactive antibodies and the fluorescenced beads for calibration, the procedure for the absolute count of monkey lymphocyte subsets was developed and the mean values for CD4+ and CD8+ lymphocyte subsets in peripheral blood were 718 and 573/mm3, respectively. Moreover, intracellular cytokines, IL-2, IL-4 and IFN gamma, and intracellular apoptosis-related proteins, Bcl-2, FADD and active form of caspase-3 could be detected in peripheral blood mononuclear cells as well as various tissue cells. It is therefore practicable to detail the phenotype of leukocytes, assess the production of intracellular cytokines and enumerate T-lymphocyte subsets by using the cross-reactive human antibodies with respective antigens of cynomolgus monkeys.

A preliminary description of responses of free-ranging rhesus monkeys to brief capture experiences: behavior, endocrine, immune, and health relationships

A cohort of free-ranging rhesus monkeys has been followed since birth in 1994 on the island of Cayo Santiago, Puerto Rico. At 3 years of age, subjects were trapped and blood samples were collected after capture and prior to release the following day. Blood samples were processed for natural cytotoxicity toward xenogeneic tumors, phenotyping, and plasma hormones. Intestinal parasites were determined from fresh stool samples collected during trapping. Data were also available from the previous year for antibody titers to latent viruses prevalent in this population. Behavioral traits of each monkey were characterized using a previously developed trait scale for rhesus monkeys. Natural cytotoxicity toward both K562 and Raji targets declined from capture until release the following day. Plasma cortisol rose and plasma prolactin and growth hormone fell during the period of captivity; a rise in insulin was significant. It was expected that individual differences in behavioral traits might predict immune and hormone levels at the time of capture or changes in these parameters during the capture period. Although behavioral adjectives tended to cluster along three orthogonal dimensions (Insecurity, Irritability, and Sociability), they bore no relationship to the physiological parameters collected acutely (in vitro immune and endocrine parameters). The individual difference markers of gender and maternal rank were not related to the magnitude of the observed changes in these in vitro parameters, either. However, an in vivo measure (CMV titer) was related to individual differences in Irritability. It was concluded that the magnitude of the stress associated with capture overwhelmed the individual difference effects.

Effect of neonatal treatment with a gonadotropin releasing hormone antagonist on developmental changes in circulating lymphocyte subsets: a longitudinal study in male rhesus monkeys

We have examined changes in circulating lymphocyte subsets from the neonatal period until adulthood (4 months until 5.5 years of age) in male rhesus monkeys, and the impact of neonatal treatment with a GnRH antagonist (Ant) or Ant and androgen (Ant/And) on these parameters. Absolute numbers of lymphocytes, B cells, total T lymphocytes, and CD4+ T cells decreased, neutrophils increased, and CD8+ T cells did not change with age. WBC counts increased between 4 mo and 2 years of age and then fell to neonatal levels over the next two years. The decline of CD4 + T cells in association with stable CD8+ T cell levels resulted in an age-related decrease in the CD4+/CD8+ T cell ratio. At 4 months of age, WBC's, lymphocytes, total T cells, CD8+ T cells and B cells were lower in Ant- and Ant/And-treated animals compared to controls. With the exception of WBC counts, these values had normalized by 2 years of age. Reduced WBC levels in treated animals persisted through adulthood. CD4+ T cell levels tended to be lower in Ant-treated and higher in Ant/And-treated animals than in controls at 4 months of age. CD4+ T cells remained lower in Ant- than in Ant/And-treated animals at most ages. The higher CD4 + T cell counts in Ant/And-treated animals resulted in an elevated CD4 + /CD8 + T cell ratio that persisted until the onset of year 5. During years 5 and 6, seasonal fluctuations in WBC's and neutrophils were observed with counts being higher in the breeding (fall) than in the nonbreeding (summer) season. The data document that developmental changes in circulating immune cells in the rhesus monkey are qualitatively similar to those reported in humans, and provide further evidence that neonatal treatment of male rhesus monkeys with Ant or Ant/And may alter early programming of the immune system.

Longitudinal characterization of CD4, CD8 T-cell subsets and of haematological parameters in healthy newborns of cynomolgus monkeys

A longitudinal characterization of immune cell subpopulations (lymphocytes, CD4+ and CD8+ cells), of routine haematological parameters and of immunoglobulin serum levels was carried out in newborn Macaca fascicularis starting from 1 week up to 1 year of life. In neonates, the percentage of CD4+ lymphocytes is almost double, while the percentage of CD8+ cells is lower than that found in adult monkeys (> 5-years old). An inverted trend in the percentage of the two T-lymphocyte subpopulations was observed during the weeks following birth, with a progressive increase of circulating CD8+, paralleled by a decrease of CD4+ cell number. Consequently, the CD4/CD8 ratio slowly decreases, even if, at 12 months of life, it is still higher than that found in adult animals. Several differences were also noted between young and adult monkeys with regard to the total number of circulating CD4+ and CD8+ cells. Haematological parameters did not show consistent differences with respect to adult values. The plasma IgG level is high at birth, then decreases until 6 months of life, while the IgM and IgA values are very low during the first weeks of life but increase in the following period. Our data showed that variations of immunological (CD4+, CD8+ cells) patterns and of some haematological parameters in M. fascicularis are dependent on age. These variations should be therefore considered whenever young animals are used in experimental protocols.

Selection of monoclonal antibodies for the identification of lymphocyte surface antigens in the New World primate Saguinus oedipus oedipus (cotton top tamarin)

32 monoclonal antibodies reactive with human CD antigens were tested against tamarin peripheral blood lymphocytes, ConA blasts and lymphoblastoid B cell lines derived from tamarin cells. Reagents that cross-react with MHC class I and II, B cells (CD20, -21 and -23), monocytes (CD14) and NK cells (CD16, -56) have been identified. In addition monoclonals that cross-react with T cells (CD2, CD3), the CD4/CD8 subsets of T cells and the IL-2 receptor (CD25) are reported. A monoclonal against the beta chain of LFA-1 (CD18) cross-reacted strongly, but there was only a very poor cross-reaction with a monoclonal against the alpha chain of CD11a. Two monoclonals tested against ICAM-1(CD54) were negative.

Cynomolgus monkeys (Macaca fascicularis) in preclinical immune function safety testing: development of a delayed-type hypersensitivity procedure

A delayed-type hypersensitivity (DTH) test commonly used for humans was adapted for use with cynomolgus monkeys (Macaca fascicularis). Pilot experiments showed naive animals had poor response rates and inconsistent reactivity to the antigens. In an exploratory phase, it was determined that monkeys could be experimentally sensitized by immunization with commercially available antigens. Animals were then sensitized with various concentrations of diphtheria and tetanus toxoids, Candida, and Trichophyton in the dose-response phase. Antigens were injected intradermally (i.d.) 3 times over a 7-day period and monkeys were tested 14 days after the last injection. Responses were measured 24, 48, and 72 h post-challenge, with skin biopsies taken from two animals per group at the 24 h interval. Optimal concentrations were 1.2 Lf diphtheria, 6 Lf tetanus, 1000 PNU Candida, and 1000 PNU Trichophyton. These concentrations produced the best balance between DTH responses, homogeneity of dermal mononuclear cell infiltrate and lowest frequency of undesirable skin reactions. Positive responses were seen at 24 and 48 h post-challenge and were waning by 72 h. DTH responses were inhibited by topical corticosteroids. The final phase of these studies assessed whether sensitization of naive animals could be achieved using subcutaneous (s.c.) administration of the optimal antigen concentrations. Comparable responses to i.d. sensitization were obtained and skin sores did not develop at injection sites. These studies show that the DTH test adapted to monkeys was reproducible, minimally invasive, did not require sacrifice of the test animal, allowed repeated measurements and paralleled the reactions observed in humans.