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During aging phenotypic changes in the hematopoietic system occur, and possible reason of these changes can be accumulation of gene mutations in hematopoietic stem cells or early blood progenitors. Although these mutations are mostly neutral, some may give hematopoietic stem cells and progenitor cells a proliferative advantage. In this case clonal hematopoiesis will arise, which is characterized by the formation of a genetically distinct subpopulation of blood cells. Clonal hematopoiesis may become a basis for the development of hematologic malignancies, such as acute myeloid leukemia. Clonal hematopoiesis associated genes which are most commonly mutated in acute myeloid leukemia patients are DNMT3A, TET2 and ASXL1. The prognostic significance of these gene mutations currently remains a subject of study.

Clonal hematopoiesis is a common age-dependent state accompanied by the expansion of mutant hematopoietic stem cells as a result of somatic mutations and is associated with a high risk of hematopoietic neoplasms and cardiovascular diseases. Clonal hematopoiesis in human ontogenesis occurs asymptomatically, and the fraction of mutant clones can exceed more than 2% of the total pool of circulating nucleated blood cells by age 70. Due to the variability of the accumulation rate of mutant clones, signs of clonal hematopoiesis can be observed at a younger age. Clonal hematopoiesis may act as a benign, precancerous condition and a strong factor for acute cardiovascular events such as myocardial infarction and stroke. Current evidence indicates that somatic mutations in driver genes of clonal hematopoiesis significantly increase the risk of acute conditions such as acute myeloid leukemia and acute myocardial infarction. The high mortality and morbidity of cardiovascular and cancer diseases, and their strong association with clonal hematopoiesis, make it of indeterminate potential worthy of close attention.

Recent studies in single cell RNA sequencing have improved understanding of the structure of the immune cell subpopulation in atherosclerosis. With the help of novel technologies, new subpopulations of immune cells involved in atherosclerosis have been identified. In addition, a following relatively common and strong cardiovascular risk factor has emerged: clonal hematopoiesis of indeterminate potential resulting from the accumulation of somatic mutations during life with the appearance of populations of mutant leukocyte clones. Individuals with this condition are at high risk for cardiovascular complications such as myocardial infarction and stroke, regardless of conventional risk factors. This review highlights the latest data on the study of cellular heterogeneity of immune system cells in atherosclerosis, as well as the role of clonal hematopoiesis in its development.

The number of somatic mutations among all tissues increases along with age. This process was well-studied in hematopoietic stem cells (HSCs). Some mutations lead to a proliferative advantage and expansion of HSCs to form a dominant clone. Clonal hematopoiesis is general in the elderly population. Clonal hematopoiesis of indeterminate potential (CHIP) is a more common phenomenon in the elderly and is defined as somatic mutations in clonal blood cells without any other hematological malignancies. The development of CHIP is an independent risk factor for hematological malignancies, cardiovascular diseases, and reduced overall survival. CHIP is frequently associated with mutations in DNMT3A and TET2 genes involved in DNA methylation. The epigenetic human body clocks have been developed based on the age-related changes in methylation, making it possible to detect epigenetic aging. The combination of epigenetic aging and CHUP is associated with adverse health outcomes. Further research will reveal the significance of clonal hematopoiesis and CHIP in aging, acquiring various diseases, and determining the feasibility of influencing the mutagenic potential of clones.

The paper presents new molecular data, the principles of the classification of myeloid neoplasms, and criteria for their diagnosis according to the new edition of the WHO Classification of Tumors of Hematopoietic and Lymphoid Tissues, 2017. Current concepts of clonal hematopoiesis and models of clonal evolution are presented to characterize the common features of the molecular pathogenesis of myeloid neoplasms. There are new data and general principles of diagnosis of myeloid neoplasms: Ph-negative myeloproliferative diseases, myelodysplastic syndromes, myeloid/lymphoid neoplasms with eosinophilia and rearrangements of PDGFRA, PDGFRB, FGFR1, and PCM1-JAK2, diseases from the group of myelodysplastic/myeloproliferative diseases. Emphasis is laid on the possibilities and limitations of pathological differential diagnosis when a pathologist examines bone marrow trepanobiopsy specimens in his/her routine work.