Natural killer cell reactivity: activation and cytolysis mechanism models, involving heat shock protein, haemopoietic histocompatibility, major histocompatibility complex and complement molecules

Roles of Extracellular HSPs as Biomarkers in Immune Surveillance and Immune Evasion

Extracellular heat shock proteins (ex-HSPs) have been found in exosomes, oncosomes, membrane surfaces, as well as free HSP in cancer and various pathological conditions, also known as alarmins. Such ex-HSPs include HSP90 (α, β, Gp96, Trap1), HSP70, and large and small HSPs. Production of HSPs is coordinately induced by heat shock factor 1 (HSF1) and hypoxia-inducible factor 1 (HIF-1), while matrix metalloproteinase 3 (MMP-3) and heterochromatin protein 1 are novel inducers of HSPs. Oncosomes released by tumor cells are a major aspect of the resistance-associated secretory phenotype (RASP) by which immune evasion can be established. The concepts of RASP are: (i) releases of ex-HSP and HSP-rich oncosomes are essential in RASP, by which molecular co-transfer of HSPs with oncogenic factors to recipient cells can promote cancer progression and resistance against stresses such as hypoxia, radiation, drugs, and immune systems; (ii) RASP of tumor cells can eject anticancer drugs, targeted therapeutics, and immune checkpoint inhibitors with oncosomes; (iii) cytotoxic lipids can be also released from tumor cells as RASP. ex-HSP and membrane-surface HSP (mHSP) play immunostimulatory roles recognized by CD91+ scavenger receptor expressed by endothelial cells-1 (SREC-1)+ Toll-like receptors (TLRs)+ antigen-presenting cells, leading to antigen cross-presentation and T cell cross-priming, as well as by CD94+ natural killer cells, leading to tumor cytolysis. On the other hand, ex-HSP/CD91 signaling in cancer cells promotes cancer progression. HSPs in body fluids are potential biomarkers detectable by liquid biopsies in cancers and tissue-damaged diseases. HSP-based vaccines, inhibitors, and RNAi therapeutics are also reviewed.

Immunomodulatory effects of radiofrequency ablation in a breast cancer model

Radiofrequency ablation (RFA), a minimally invasive surgical procedure has an increasing application in the surgical treatment of tumors. Data indicate that RFA might stimulate anti-cancer immunity possibly through the induction of necrosis and heat shock proteins (HSP) expression. This study tests a hypothesis that RFA leads to bidirectional immunoregulation. Experimental rat breast tumors were treated with RFA, surgical excision or sham operation. RFA resulted in the highest NK cells infiltration, increased HSP70 expression and activation of caspase-3 enzyme in the tumor margins. A significant reduction of the circulatory regulatory T (Treg) cells was found in both RFA- and excision-treated rats, although less pronounced in the RFA-group. The splenocyte proliferation to tumor cell lysate was stronger in the RFA-treated rats in comparison with untreated tumor-bearing rats. The potential role of self-HSP for immunomodulation was examined using in vitro proliferation assay to tetanus toxoid using human peripheral leukocytes. The response to the tetanus toxoid was significantly suppressed by HSP90 plus auto-antibodies versus HSP90 or auto-antibodies alone. In conclusion, RFA reduced the circulatory Tregs although not as efficient as tumor excision. HSPs plus natural antibodies suppress the anti-tumor response probably by stimulating Tregs. Therefore, RFA may play a role in anti-cancer therapy if combined with Tregs suppression.

Material-dependent levels of heat-shock protein 70 (hsp70) in human plasma following contact of blood with artificial surfaces

Recently, it has been shown that heat-shock protein 70 (hsp70) functions in a dual role as a chaperone and a cytokine. However, no information is available on the occurrence of hsp70 in the extracellular milieu or on its ability to modulate cellular immune response. This study shows a material-dependent increase of hsp70 levels in plasma following contact of fresh heparinized whole human blood with three different biomaterials (PVC, heparin-coated PVC, Silicone). We report a previously unknown behavior of hsp70 to act as a plasma-adsorption protein. Further, high binding capacities for hsp70 to artificial surfaces (measured by Western blotting) and elevated hsp70 levels in plasma (measured by EIA) following contact with blood correspond with a reduced hemocompatibility. The degree of surface-induced activation of blood was determined by analysis of markers for coagulation, inflammation and complement activation. These findings indicate that the selective adsorption of hsp70 on artificial surfaces and the increased hsp70 levels in plasma may be important in directing host inflammatory and immune responses. We suggest that the levels of hsp70 in human plasma may represent a new prognostic factor or a diagnostic biomarker in hemostasis research.

Hsp90 inhibition accelerates cell lysis. Anti-Hsp90 ribozyme reveals a complex mechanism of Hsp90 inhibitors involving both superoxide- and Hsp90-dependent events

The 90 kDa heat shock protein, Hsp90, is an abundant molecular chaperone participating in the cytoprotection of eukaryotic cells. Here we analyzed the involvement of Hsp90 in the maintenance of cellular integrity using partial cell lysis as a measure. Inhibition of Hsp90 by geldanamycin, radicicol, cisplatin, and novobiocin induced a significant acceleration of detergent- and hypotonic shock-induced cell lysis. The concentration and time dependence of cell lysis acceleration was in agreement with the Hsp90 inhibition characteristics of the N-terminal inhibitors, geldanamycin and radicicol. Glutathione and other reducing agents partially blocked geldanamycin-induced acceleration of cell lysis but were largely ineffective with other inhibitors. Indeed, geldanamycin treatment led to superoxide production and a change in membrane fluidity. When Hsp90 content was diminished using anti-Hsp90 hammerhead ribozymes, an accelerated cell lysis was also observed. Hsp90 inhibition-induced cell lysis was more pronounced in eukaryotic (yeast, mouse red blood, and human T-lymphoma) cells than in bacteria. Our results indicate that besides the geldanamycin-induced superoxide production, and a consequent increase in cell lysis, inhibition or lack of Hsp90 alone can also compromise cellular integrity. Moreover, cell lysis after hypoxia and complement attack was also enhanced by any type of Hsp90 inhibition used, which shows that the maintenance of cellular integrity by Hsp90 is important in physiologically relevant lytic conditions of tumor cells.

Cytokine analysis at the single cell level and lymphoproliferative responses to mycobacterial antigens in HIV-1 patients with successful virologic response to potent antiretrovirals

Immunologic parameters, known to be grossly abnormal in HIV-1-infected subjects, were analyzed in 22 patients with sustained viral load suppression (<200 copies/ml) following long-term highly active antiretroviral therapy (HAART). Responses were compared with those from 18 HIV-seronegative healthy controls. Persistent phenotypic alterations in patients' blood mononuclear cells were minimal, though the percentages of lymphocytes that could be activated to produce interleukin-2 (IL-2) remained severely depressed. Using lymphoproliferative assays, a striking deficit in the capacity of patients to respond to the common mycobacterial antigens and particularly to recombinant heat-shock proteins paralleled the absence of responses to virus p24 antigen. In view of the important immunoregulatory role of stress proteins, these findings reveal profound functional deficiencies and persistent immune dysregulation in HIV-1 patients, despite successful HAART and a considerable recovery of CD4+ lymphocyte numbers. Rational immunotherapeutic approaches should be aimed to correct the characterized immune abnormalities.