Myeloid-Derived Suppressor Cells

Myeloid-derived suppressor cells (MDSCs) are heterogeneous immature myeloid cells that have been shown to be potent immune regulatory cells in human cancer and in murine tumor models. In particular, the infiltration of MDSCs into cancer tissues is associated with poor patient prognosis and resistance to therapies. Their mechanisms of action, however, are not understood. In the current issue of Viral Immunology, O'Connor and colleagues point out that there is very little information regarding the role of MDSCs during viral infections and suggest that their involvement in these infections may be substantially underreported. Furthermore, MDSC-like cells have been phenotypically identified in several viral systems but were often not tested for suppressive activity. The authors address these issues in a review in this issue of the journal and further highlight studies that demonstrate or support a role of MDSCs or MDSC-like cells during viral infection.

Three articles in the issue focus on the development of antiviral vaccines. Chen and colleagues point out that human enterovirus 71 (EV-A71) is one of the main etiologic agents of hand, foot and mouth disease, which is prevalent in the Asia-Pacific region. The authors produced three nonstructural proteins of EV-A71 in Escherichia coli and show that all the purified fusion proteins react with IgG antibodies from EV-A71-infected patients but are only weakly recognized by IgG antibodies derived from mice or rabbits immunized by inactivated EV-A71 virus particles. The finding that the IgG antibody response against nonstructural proteins of EV-A71 is associated with viral replication suggests that these proteins could be used for the early diagnosis of EV-A71 infection or to distinguish live viral infection from inactivated vaccine immunization. In another study, Li and colleagues have addressed the problem that adenovirus-based vaccines sometimes induce strong immune responses to the vector that overshadow the response to the target antigen. The authors evaluated adenovirus vaccines expressing porcine circovirus type 2 (PCV2) capsid protein in the context of either transcriptional regulatory elements (to enhance the target gene expression) or immunostimulatory cytokine genes. The data indicate that both strategies improved the immunogenicity of the PCV2 vaccines and suggest that they could be utilized in the development of future vaccines against PCV2 infection. In a third article, Tao and colleagues have evaluated the immunostimulatory effects of N-(2-hydroxy) propyl-3-trimethylammonium chitosan chloride (HTCC) for improving the efficacy of the live attenuated hepatitis A virus (HAV) vaccine. Their data indicate that HTCC enhanced the efficacy of the live attenuated HAV vaccine demonstrating its value as a safe and potent vaccine adjuvant.

Finally, three articles in this issue of Viral Immunology address other aspects of the immune response to viral infection. Bader El Din and colleagues have evaluated the relationship between TNFα polymorphisms and the progression of hepatic fibrosis in Egyptian patients infected with hepatitis C virus (HCV) genotype 4. The authors show that two distinct TNFα polymorphisms synergistically influence the hepatic fibrosis progression and can be used as potential biomarkers to predict hepatic disease progression in chronic HCV-infected patients. Martínez-Campos and colleagues have reviewed the role of toll-like receptor (TLR)-9 on oncogenic virus-produced cancer. The authors note that oncogenic DNA viruses inhibit TLR9 expression, thereby facilitating the establishment of chronic infection by the virus. The review specifically focuses on the TLR9 signals initiated by synthetic oligodeoxynucleotide recognition on the inhibition of TLR9 expression mediated by DNA oncogenic viruses and on TLR9 expression as a relevant event in the progression to cancer. Finally, Kori and colleagues investigate the susceptibility to rubella in pregnant women attending an antenatal clinic in Central India. Rubella infection of the mother during the first trimester of pregnancy can lead to congenital rubella syndrome (CRS) with devastating consequences for the baby. The study finds that a large proportion of pregnant women at the clinic were rubella susceptible, posing a significant threat of CRS to their newborns. Clearly, robust programs for rubella immunization targeting young adult women are essential in this region of India.

I thank all the authors for their excellent contributions to the journal and all the reviewers for their efforts in maintaining the quality of articles published in this issue.