Immunosuppression

T-cell exhaustion, MDSCs, and Treg cells are important sources of immunosuppression in patients with protracted infections, including sepsis.
Hotchkiss & Opal 2020 N Engl J Med 382: 1270-1272

Organ transplant patients maintained on immune suppressive drugs are threefold to eightfold more likely to develop cancer.
Ostrand-Rosenberg 2008

Immunosuppressive mechanisms in non-tumor cells

The immunosuppressive mechanisms that are contributed by non-tumor cells include Regulatory T Cells (Tregs) that could be attracted to some tumors by chemokines, and Myeloid-Derived Suppressor Cells (MDSCs) and their contact-dependent immunosuppression, which involves nitrogen oxide (NO) and reactive oxygen species (ROS)
Curiel et al. 2004 Nature Med. 10: 942-949
Gabrilovich et al. 2009 Nature Rev. Immunol. 9: 162-174
Gobert et al. 2009 Cancer Res. 69: 2000-2009

Immunosuppressive mechanisms in tumor cells

The immunosuppressive factors that are contributed by tumor cells include the expression of programmed cell death protein 1 (PD1) ligands; local tryptophan depletion through Indoleamine 2,3-Dioxygenase (IDO) or Tryptophan 2,3 Dioxygenase (TDO); and the production of Galectin-3 (Gal-3), which reversibly impairs T cell activation, lactic acid, adenosine, prostaglandins and transforming growth factor-beta (TGF-beta).
Uyttenhove et al. 2003 Nature Med. 9: 1269-1274
Demotte et al. 2010 Cancer Res. 70: 7476-7488
Opitz et al. 2011 Nature. 478: 197-203
Pilotte et al. 2012 Proc. Natl Acad. Sci. USA 109: 2497-2502