Viral inhibitors of NKG2D ligands for tumor surveillance

ABSTRACT

Introduction: Natural Killer cells (NK) are key for the innate immune response against tumors and viral infections. Several viral proteins evade host immune response and target the NK cell receptor NKG2D and its ligands.

Areas covered: This review aimed to describe the viruses and their proteins that interfere with the NKG2D receptor and their ligands, and how these interactions lead to immune evasion, host protection, and tissue damage from acute and chronic viral infections.

Expert opinion: The study of viral proteins has already impacted the field of oncology. A prime example is the HBV vaccine and the development of antiviral drugs for HIV, Hepatitis C, and the family of Herpesviridae viruses. The NKG2D system seems to be a rational therapeutic target. Nevertheless, an effective cytotoxic response by NK cells is mediated by a network of activating and inhibitory receptors, the integration of which determines if the NK cell becomes cytotoxic or permissive. Immunotherapeutic agents that increase the antitumor lytic activity of NK cells through modulating activation and inhibitory signaling of NK cells are being developed. Nevertheless, more research is needed to dissect the integrative mechanism of NK cells function to fully exploit their antitumor and antiviral effector mechanisms.

KEYWORDS:

• NK cells
• innate immunity
• viral infection
• viral proteins
• oncogenic virus

Article highlights

• Around 12% of human malignancies are related to viruses.

• Viruses have evolved mechanisms to avoid the host immune response.

• The NKG2D receptor and its ligands are frequent targets of viral proteins to evade the innate immune response.

• The NKG2D system seems to be a rational therapeutic target against viral infections and viral carcinogenesis.

• More research is needed to understand how the activating and inhibitory NK receptors cells integrate to mount an effective cytotoxic response.

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Declaration of interest

The author has no relevant affiliations or financial involvement with any organization or entity with a financial interest in or financial conflict with the subject matter or materials discussed in the manuscript. This includes employment, consultancies, honoraria, stock ownership or options, expert testimony, grants or patents received or pending, or royalties.