Myeloid-derived suppressor cells in COVID-19: A review.

Coronavirus disease 2019 (COVID-19) is a potentially life-threatening infection characterized by excessive inflammation, coagulation disorders and organ damage. A dysregulated myeloid cell compartment is one of the most striking immunopathologic signatures of this newly emerged infection. A growing number of studies are reporting on the expansion of myeloid cells with immunoregulatory activities in the periphery and airways of COVID-19 patients. These cells share phenotypic and functional similarities with myeloid-derived suppressor cells (MDSCs), which were first described in cancer patients. MDSCs are a heterogeneous population of pathologically activated myeloid cells that exert immunosuppressive activities against mainly effector T cells. The increased frequency of these cells in COVID-19 patients suggests that they are involved in immune regulation during this infection. In this article, we review the current findings on MDSCs in COVID-19 and discuss the complex role of these cells in the immunopathology of COVID-19.

Daunorubicin conjugated with alpha-fetoprotein selectively eliminates myeloid-derived suppressor cells (MDSCs) and inhibits experimental tumor growth.

Failure of antitumor immunity in cancer was shown to be mediated by myeloid-derived suppressor cells (MDSCs), which are considered to be one of the key factors contributing to the development of malignant diseases. Therefore, the development of pharmacological approaches to effectively eliminate MDSCs in organisms carrying growing tumors is a promising pathway for potential treatment. For this purpose we propose alpha-fetoprotein (AFP) conjugated with a cytotoxic agent as a vector molecule, specifically recognizing MDSCs. The present study was aimed at examination of this suggestion using both in vitro and in vivo approaches. MDSCs, obtained from the spleen of Ehrlich carcinoma bearing mice, selectively bound AFP labeled with fluorescein isothiocyanate. AFP conjugated to daunorubicin (AFP-DR) and DR alone showed similar in vitro cytotoxicity against the granulocytic MDSC subpopulation. The monocytic MDSC subpopulation was resistant to treatment with DR, whereas it was completely depleted in the presence of AFP-DR. Treatment of mice bearing Ehrlich carcinoma with AFP-DR resulted in reduced numbers of splenic MDSCs, normalization of NK cell levels, and inhibition of tumor growth. The obtained results demonstrate that cytotoxic conjugates based on AFP are promising anticancer drugs, which, in addition to the direct effect on tumor cells expressing receptors to AFP, may contribute to elimination of MDSCs.