Characterization of expanded T cell clones in healthy macaques: ontogeny, distribution and stability

Functional differences and similarities in activated peripheral blood mononuclear cells by lipopolysaccharide or phytohemagglutinin stimulation between human and cynomolgus monkeys

Background

The monkey is a primary species used in toxicological research. However, the failures of preclinical studies to predict a life-threatening “cytokine storm”, which, for instance, rapidly occurred in six healthy volunteers with the CD28 superagonist monoclonal antibody (mAb) TGN1412 in the first-in-human phase I clinical trial, have emphasized a need to clarify the differences between human and monkey immune systems.

Methods

In the present study, we analyzed and compared the lymphocyte proliferation, cytokine secretion, and gene expression profiles after phytohemagglutinin (PHA) and lipopolysaccharide (LPS) stimulation of peripheral blood mononuclear cells (PBMCs) from three healthy humans and cynomolgus monkeys (Macaca fascicularis).

Results

The results derived from comparison with the corresponding control groups showed that PHA in humans induced a stronger proliferation and wider range of cytokine secretion, along with a greater number of differently expressed genes (DEGs), than when PHA was applied in cynomolgus monkeys. The significant upregulation of genes involved in the mitotic cell cycle, including cyclin B2, TOP2A, TYMS, and CEP55, was observed in human PBMCs with PHA stimulation, while only infrequent or slight upregulation occurred in cynomolgus monkey PBMCs, which may be one of the reasons for a stronger response to PHA in humans. In contrast to PHA, LPS in both species induced a similar proliferation ratio, cytokine profile, and DEG count, suggesting that human and cynomolgus monkeys have a similar response intensity for innate immune responses. Furthermore, 38 and 20 overlapped genes under PHA and LPS stimulation, respectively, were found in both species. These overlapped DEGs were associated with the same biological functions, including DNA replication, mitosis, immune response, chemotaxis, and inflammatory response. Thus, these results might reflect the highly conserved signatures of immune responses to PHA/LPS stimulation across the primates. Moreover, there were some differences in antigen processing and presentation, and the interferon gamma (INF-γ)–mediated signaling pathway in these species detected by gene expression profile study.

Conclusions

In conclusion, this is the first study to compare data on the responses of PBMCs to PHA and LPS in humans versus cynomolgus monkeys, and these findings may provide crucial insights into translating non-human primate (NHP) studies into human trials.

Essentials for starting a pediatric clinical study (3): Dynamic changes in early development of immune system in macaque monkeys--the significance from standpoint of preclinical toxicity test using nonhuman primates

Macaque monkeys are essential laboratory animals in preclinical safety assessment for human-specific biological products including humanized antibody drug. In most case, investigators are leaving their ages out of consideration, and young individuals aged around 3 years are mainly used because of their small individual differences in biological responses to various stimulations. Since the immune system starts to develop just after birth and remarkable phenotypic and functional changes occur in various kinds of immunocompetent cells during the first few years of life in macaque monkeys, their actual immunological condition must be carefully considered in case of safety assessment of novel drugs which modulate human immune function. The early development of major immune functions of macaque monkeys is summarized as follows. These findings suggest that immunocompetent cells drastically differentiate into activated ones during early development. 1) The serum immunoglobulin contents gradually rise with increasing age up to sexual maturity. 2) The blood group-associated antibodies, anti-A and anti-B antibody, are detected around 40-days of age and antibody levels rapidly increase after one year old. 3) Infant cynomolgus monkeys obviously produce the significant levels of IgG antibody against Campylobacter jejuni within 4 weeks after infection when maternal antibody becomes undetectable (8 weeks of age). 4) The frequency of lymphocyte subpopulations expressing the resting surface phenotypes is much higher than that having activated phenotypes in neonates, and the relative population of lymphocyte subsets with resting phenotype decrease with increasing age, while the subpopulation associated with activation gradually increase with age.

CD28 extinction in human T cells: altered functions and the program of T-cell senescence

The loss of CD28 expression on T cells is the most consistent biological indicator of aging in the human immune system, and the frequency of CD28(null) T cells is a key predictor of immune incompetence in the elderly. There is also mounting evidence for the high frequency of these unusual T cells among patients with inflammatory syndromes or with chronic infections disproportionate with their age. In these pathological states, CD28(null) T cells likely represent prematurely senescent lymphocytes due to persistent immune activation. Unlike the situation in CD28 gene knockout mice that have anergic CD28(0/0) T cells, human CD28(null) T cells are functionally active, long-lived, oligoclonal lymphocytes that lack or have limited proliferative capacity. Results of replicative senescence studies show that CD28(null) T cells are derived from CD28(+) precursors that have undergone repeated stimulation, indicating that CD28 silencing underlies the program of T-cell aging. Dissection of the machinery regulating CD28 expression is paving the way in elucidating the molecular events leading to immune senescence as well as providing clues into the functional rejuvenation of senescent T cells.

Age-related telomere length dynamics in peripheral blood mononuclear cells of healthy cynomolgus monkeys measured by Flow FISH

Telomere length is a good biomarker to study the cellular senescence as well as aging of an organism, because it regulates the replicative capacity of vertebrate somatic cells. To demonstrate age-related telomere length dynamics in the peripheral blood mononuclear cells (PBMC) of the cynomolgus monkey, we introduced a novel method of measuring telomere length by fluorescence in situ hybridization with a Peptide Nucleic Acid (PNA) labelled probe and flow cytometry (Flow FISH). A highly significant correlation was observed between the intensity of telomere-specific fluorescence by Flow FISH and telomere length by Southern blot analysis (R = 0.923, n = 22). The intensity of telomere fluorescence in PBMC significantly decreased with age in 55 monkeys aged from 0 to 34 years and this decrease corresponded to the loss of 62.7 base pairs per year (R = - 0.52, P < 0.00004). We also analysed the expression of naive cell-associated markers, CD28, CD62L and CD45RA/CD62L in T lymphocytes of 47 cynomolgus monkeys. An age-related increase in the CD28- subset was observed in CD8+ T lymphocytes in monkeys less than 11 years old and in CD4+ T lymphocytes in monkeys over 23 years old, respectively. The percentage of CD62L+ subsets was significantly decreased with age in both CD4+ (R = - 0.55) and CD8+ T lymphocytes (R = - 0.73). From the comparison of telomere length among PBMC, CD62L+ and CD62L- T lymphocytes, it was clearly evident that loss of naive subsets results in the shortening of telomere length in vivo. These results show that this method can be applicable to studying the turnover and precursor-progeny of PBMC in cynomolgus monkeys as an animal model of aging.

Peripheral blood extrathymic CD4(+)CD8(+) T cells with high cytotoxic activity are from the same lineage as CD4(+)CD8(-) T cells in cynomolgus monkeys

We have previously reported that CD4/CD8 double-positive (DP) T cells with the resting memory phenotype are present in the periphery of healthy cynomolgus monkeys. In the present study, we performed functional studies on the T cells. The expression of CD4 and CD8 on DP, CD4 single-positive (SP) or CD8 SP T cells was stable in cultures with either mitogen or anti-CD3 antibody stimulation. In spite of lacking CD28 expression, DP T cells showed similar proliferative ability and apoptosis sensitivity to CD4 SP and CD8 SP T cells. DP T cells showed both helper and cytotoxic activities. Although the helper activity of DP T cells was lower than that of CD4 SP T cells, cytotoxic activity was comparable to that of CD8 SP T cells. Fresh DP T cells killed target cells mainly by the perforin-granzyme pathway. In addition, fresh DP T cells expressed a high level of mRNA for IFN-gamma and produced a high level of IFN-gamma when they were activated by anti-CD3 antibody ligation. On the other hand, several expanded DP T cell clones shared TCR V(beta) with expanded CD4 SP T cell clones, strongly suggesting that those two corresponding clones with DP and CD4 SP phenotypes might be derived from the same ancestor T cell. These results showed that the DP T cells are a novel T cell subset with functions overlapping with those of CD4 SP and CD8 SP T cells, and that they might play protective and regulatory roles in secondary immune response in cynomolgus monkeys.