Do reduced numbers of plasmacytoid dendritic cells contribute to the aggressive clinical course of COVID-19 in chronic lymphocytic leukaemia?

Scand J Immunol. 2022 Apr;95(4):e13153. doi: 10.1111/sji.13153. Epub 2022 Mar 16.


Infections with SARS-CoV-2 have been unduly severe in patients with haematological malignancies, in particular in those with chronic lymphocytic leukaemia (CLL). Based on a series of observations, we propose that an underlying mechanism for the aggressive clinical course of COVID-19 in CLL is a paucity of plasmacytoid dendritic cells (pDCs) in these patients. Indeed, pDCs express Toll-like receptor 7 (TLR7), which together with interferon-regulatory factor 7 (IRF7), enables pDCs to produce large amounts of type I interferons, essential for combating COVID-19. Treatment of CLL with Bruton's tyrosine kinase (BTK) inhibitors increased the number of pDCs, likely secondarily to the reduction in the tumour burden.

Keywords: BTK; IRF7; SARS-CoV-2; TLR7; X-linked agammaglobulinemia; toll-like receptor 7.

Publication types

  • Review

MeSH terms

  • COVID-19* / complications
  • Dendritic Cells
  • Humans
  • Interferon Regulatory Factor-7
  • Leukemia, Lymphocytic, Chronic, B-Cell* / complications
  • Leukemia, Lymphocytic, Chronic, B-Cell* / drug therapy
  • SARS-CoV-2
  • Toll-Like Receptor 7


  • IRF7 protein, human
  • Interferon Regulatory Factor-7
  • Toll-Like Receptor 7