Toward application of the bone marrow cell classification from human to cynomolgus monkeys and Göttingen minipigs.

<p>In 2021, a working group for the standardization of blood cell morphology (the Japanese Society for Laboratory Hematology and the Japanese Association of Medical Technologists) proposed criteria for morphological classification of erythroid and myeloid lineages in human bone marrow. A variety of laboratory animals are used in nonclinical studies, and morphological features of bone marrow cells may be unique among species. However, no definitive standard of the morphological classification of the bone marrow cells in each species has been established yet. Therefore, we investigated whether the new human criteria can be applied to the classification of myeloid and erythroid lineages in non-human primates (NHPs) and minipigs. Following observation of bone marrow smears of these animals, several insights were obtained. The human criteria indicate an oval nucleus and an indented (kidney beans-shaped) nucleus as the primary features of myelocytes and metamyelocyte, respectively, however, it was difficult to apply these criteria to NHPs in which the nucleus may be indented even in immature myelocytes or promyelocytes. Thus, metamyelocytes in NHPs are better classified by an advanced nuclear indentation (horseshoe-shaped) and tinctorial characteristics of the cytoplasm in NHPs. The human criteria for classification of the Type 1 and 2 myeloblasts are considered applicable to NHPs. In minipigs, the morphological features of nuclei during the maturation of the granulocyte linage appear to be comparable to the human classification because the nuclear indentation of the promyelocytes or myelocytes is less remarkable than in NHPs. No apparent differences were found in the erythroid linage between NHPs or minipigs and human, therefore, the human criteria are considered applicable to NHPs and minipigs.</p>