Thymalin: Activation of Differentiation of Human Hematopoietic Stem Cells

Bull Exp Biol Med. 2020 Nov;170(1):118-122. doi: 10.1007/s10517-020-05016-z. Epub 2020 Nov 25.


Thymalin is a polypeptide complex isolated from the thymus and regulating the functions of the immune system. Thymalin is effective in therapy of acute respiratory syndrome, chronic obstructive bronchitis, and other immunopathology. Thymalin increases functional activity of T lymphocytes, but the targeted molecular mechanism of its biological activity requires further study. We studied the influence of thymalin on differentiation of human hematopoietic stem cells (HSC) and expression of CD28 molecule involved in the implementation of antiviral immunity in COVID-19 infection. It was found that thymalin reduced the expression of CD44 (stem cell marker) and CD117 (molecule of the intermediate stage of HSC differentiation) by 2-3 times and increased the expression of CD28 (marker of mature T lymphocytes) by 6.8 times. This indirectly indicates that thymalin stimulated differentiation of CD117+ cells into mature CD28+T lymphocytes. It is known that in patients with severe COVID-19, the number of CD28+, CD4+, CD8+T lymphocytes in the blood decreased, which attested to a pronounced suppression of immunity. It is possible that the antiviral effect of thymalin consists in compensatory stimulation of HSC differentiation into CD28+T lymphocytes at the stage of immunity suppression in unfavorable course of viral infection. Thymalin can be considered as an immunoprotective peptide drug for the prevention of COVID-19.

Keywords: COVID-19; cell differentiation; hematopoietic stem cells; peptides; thymalin.

MeSH terms

  • CD28 Antigens / genetics
  • CD28 Antigens / metabolism
  • COVID-19 / immunology
  • COVID-19 / pathology
  • Cell Differentiation / drug effects*
  • Cell Differentiation / genetics
  • Cells, Cultured
  • Fetal Blood / cytology
  • Gene Expression Regulation / drug effects
  • Hematopoietic Stem Cells / drug effects*
  • Hematopoietic Stem Cells / pathology
  • Hematopoietic Stem Cells / physiology*
  • Humans
  • Hyaluronan Receptors / genetics
  • Hyaluronan Receptors / metabolism
  • Proto-Oncogene Proteins c-kit / genetics
  • Proto-Oncogene Proteins c-kit / metabolism
  • SARS-CoV-2 / immunology
  • T-Lymphocytes / drug effects
  • T-Lymphocytes / metabolism
  • T-Lymphocytes / physiology
  • Thymus Hormones / pharmacology*
  • Thymus Hormones / physiology


  • CD28 Antigens
  • CD44 protein, human
  • Hyaluronan Receptors
  • Thymus Hormones
  • thymalin
  • KIT protein, human
  • Proto-Oncogene Proteins c-kit