Cancer Immunotherapy involving Natural Killer Cells and Adenosine.

Tumor immunology is a very interesting subset of immunology as the dynamics of the immune system-tumor relationship is a long and very complicated one. Over years and years of cat-and-mouse, many immune evasion techniques have been discovered by researchers. One avenue of evasion is the release of immunosuppressive compounds by the tumor. Although tumor cells release molecules that can be recognized by the immune system and trigger a response (i.e. tumor-specific antigens (TSAs) and tumor associated antigens (TAAs)), these cells are not easy to detect. The tumor cells further ensure that these antigens are not recognized by release of immunosuppressive cytokines like IL-10 and TGF-beta (Mak and Saunders, 2011).

http://en.wikipedia.org/wiki/Metastasis

Another immunosuppressive compound is Adenosine, which is a useful molecule in the body as it is a DNA building block, a component of the main energy source in the body (ATP), and can be used to signal through one of its many receptors (A1, A2A, A2B, and A3). So it goes without saying that adenosine is present, in some form, all over the body.

Previous to the study by Beavis et al (2013), adenosine has been know to be produced from the breakdown of AMP by CD73 - a marker present on many types of cells. It has also been shown that anti-CD73 has resulted in delays in tumor expression, altogether rejection of tumor grafts in mice, inhibiting de novo carcinogensis, and preventing/reducing metastasis. In order to elucidate how exactly this immunosuppressive compound, adenosine, was suppressing tumor growth and metastasis, the authors set out to investigate adenosine in depth.

NKD2G and Allergic Inflammation

It seems to me that almost everybody nowadays has either a food allergy, seasonal allergy, or both.  Therefore, it becomes more important to understand the mechanism of allergies so that we can better treat them.  This paper examined the effect of the natural killer (NK) cell receptor NKD2G on pulmonary inflammation caused by allergic reactions. 

Allergies are a type of type 1 immune hypersensitivity (HS1).  There are two stages of HS1: sensitization and effector.  During the sensitization stage, the allergen is gathered by dendritic cells which move to the lymph node where they present the allergen to naïve Th cells.  These Th cells then provide T-cell help to B cells which release homing cytokines for other leukocytes to follow.  Other immune cells produce IL-4, IL-5 and IL-13 which facilitate isotype switching to IgE antibodies.  These antibodies then bind to receptors on the surface of basophils and mast cells.  The effector stage is the second exposure to the allergen.  The IgE antibodies bound to mast cells recognize the allergen and cause degranulation of the mast cells which have different effects depending on the tissue in which this is occurring.¹

This video might help you understand immune hypersensitivity better as well:

The first experiment performed examined how NKG2D regulated the pulmonary inflammation caused by house dust mites (HDM).  HDM extract was given to mice that lacked the NKG2D receptor (klrkl^-/-) and compared to those that had the receptor (klrkl^+/+).  As a result, klrkl^-/- mice showed a greatly reduced inflammatory response when compared to klrkl^+/+ mice.  Additionally, there was less protein exudate in the airway when measured in the bronchoalveolar lavage (BAL) and significantly diminished recruitment of neutrophils, eosinophils and lymphocytes  in klrkl^-/- mice.  Furthermore, of the CD4+ T cells that were recruited in klrkl^-/- mice, much less IL-4 and IL-13 was secreted proportionally when compared to klrkl^+/+mice.² 

NK ALERT! New Subpopulation Linked in Restriction of B-Cell Transformation by EBV

EBV, or Epstein-Barr Virus, is a pretty common and current virus that affects approximately well over ninety percent of the human adult population. The virus belongs to the herpes family meaning after the bodies defenses respond to the initial viral lytic infection, the virus remains latent in B cells till further proliferation. The virus enters our tonsils after initial transmission via the saliva¹.

Usually, in the vast majority of infected individuals, virus induced CD8⁺ T cells are responsible for the main fight against EBV infection. However, Natural Killer (NK) cells play an important role for the initial innate immune response against EBV. This paper, A Distinct Subpopulation of Human NK Cells Restricts B Cell Transformation by EBV, further explores the abilities of a specific subpopulation of NK cells in preventing B cell transformation by EBV. The specific NK subpopulation, known as CD56brightNKG2A+CD94+CD54+CD62L2, was seen by researchers to produce an interestingly high amount of IFN-γ³. IFN-γ is an important cytokine that is essential for innate and adaptive immunity when dealing with viral and intracellular bacterial infections. The importance of IFN-γ in the immune system stems in part from its ability to inhibit viral replication directly, and most importantly for its immunostimulatory and immunomodulatory effects.³ So what does this mean?

Natural Killing and Adaptive Immunity: the role of NK cells in CD8+ T cell differentiation

In the human immune response, an encounter with a pathogen results in the rapid division of immune cells which neutralize and kill viruses, bacteria and parasites. While this rapid increase in the number of immune cells in the body is necessary for a robust and effective immune response, once the pathogen has been cleared it is essential that immune cell levels be brought back down to normal. CD8⁺ T cells, also known as cytotoxic T lymphocytes (CTLs), are one type of immune cell that follows this pattern of expansion and contraction. In the presence of an antigen, CD8⁺ T cells specific for that antigen divide rapidly, seeking out and killing infected cells and pathogens. When the threat has been cleared, high levels of CD8⁺ T cells specific for a single antigen are no longer necessary, and the majority of CD8⁺ T cells die by apoptosis. The surviving CD8⁺ T cells differentiate into memory T cells, allowing the body to respond more quickly and effectively the next time it encounters the same antigen. This process is essential for maintaining immunity to diseases; the memory T cells and B cells produced after an initial exposure are the reason that, for example, you only get chicken pox once. Similarly, memory T cells and B cells enable the body to prevent infection by pathogens against which it has been vaccinated.

In a paper published in the Journal of Immunology just this week, Soderquest, et al. examine the relationship between CD8+ s and natural killer cells (NK cells) after an infection has been cleared. NK cells are an important part of innate immunity – that is, the rapid and general immune response that includes both physical barriers to infection (i.e. the skin and mucosa) and non-specific killing cells like the NK cell. During the innate immune response, NK cells identify and kill cells that are either infected with viruses or are tumorigenic. Apart from their role in the innate immune response, recent studies have shown that NK cells play an important part in the development of the more specific adaptive immune response, particularly in promoting the differentiation of CD4⁺ “helper” T cells (Th cells). In investigating the relationship between CD8⁺ T cells and NK cells, Soderquest et al. focused on the NKG2D pathway of NK cell killing. NKG2D is a protein expressed on the surface of NK cells that binds to NKG2D ligand (NKG2DL) on a target cell and induces apoptosis via the perforin/granzyme pathway. The authors of this article hypothesized that NK cells influence the development of CD8⁺ T cell-mediated adaptive immunity by killing activated CD8⁺ T cells via the NKG2D/perforin pathway.

Ring The Alarm! Granulysin’s Role in Recruiting Dendritic Cells

Our body puts up a tough fight against a constant barrage of invaders. Our first line of defense against invading pathogens is referred to as our “innate defense” and consists of a rapid response by NK, NKT and ϒδ T cells (1). These cells respond much quicker than T and B cells which are activated later if the infection persists. However, this secondary “adaptive response” requires the recruitment of dendritic cells (DCs). DCs are able to activate T and B cells highly specific for that antigen to order to mount a more focused response (1).

A recent study by Tewary et al. 2011 looks specifically at the role NK cells plays in the secondary adaptive immune response, specifically via the release of granulysin.

The GNLY gene produces the antimicrobial protein granulysin, which is initially 15 kDa in size. NK cells secrete this initial form that can be further cleaved into a smaller form, 9-kDa. The 9-kDa form is stored in the granular compartment of NK cells. The contents of the granular compartment contain toxins that cause cell death when released (degranulation) onto their pathogen targets (1) as part of the innate response.

However, a previous study also showed that GNLY participates in the adaptive response by recruiting dendritic cells (DCs), NK cells, and T cells (2), though the mechanism by which it was able to do so was unclear. Molecules that exhibit this recruitment capacity are referred to as alarmins.

In Tewary et al. 2011, the mechanism by which GNLY is able to recruit DCs and T cells and promote an immune response is elucidated.

Dodging Natural Killing: HIV Innate Immune Evasion

Image via Wikipedia Commons

HIV, the virus that causes AIDS, is the cause of one of the most far-reaching and destructive epidemics in modern times. Responsible for approximately 1.8 million deaths and more than 2.5 million new infections annually, HIV is a major public health concern, particularly in the developing world. HIV-1, the most common and virulent strain of the virus, has been studied extensively by researchers hoping to better understand the virus’s life cycle and develop treatments that disrupt its ability to infect and reproduce. One of the greatest barriers to effective treatment and clearance of HIV-1 is the virus’s astonishing capacity for immune evasion. From constant mutation to active subversion of the body's immune system, HIV is a particularly difficult pathogen to eliminate. In a paper published in PLoS: Pathogens in March of 2010, researchers from the Institut Pasteur examined one method by which HIV-1 is able to evade the natural killer (NK) cells of the innate immune system and establish a persistent infection, providing both a better understanding of HIV-1 immune evasion and a possible target for future HIV treatments.

Under normal conditions, viruses and virus particles are taken up by a subset of the host’s white blood cells known as dendritic cells (DCs). The DCs act as the immune system’s sentries, scouting the body’s tissues for foreign particles or pathogens and presenting them to other immune cells to stimulate a response. DC function is closely regulated by the interactions that take place with NK cells following infection. When inflammation occurs at the site of an infection or injuries, chemical signals known as chemokines cause NK cells to migrate to the infection site. Upon arrival, NK cells interact with DCs, sending signals that may cause the DCs to mature, and receive activating signals from the DCs. If an NK cell encounters a DC that has been infected by a virus or other intracellular pathogen, the NK cell will kill the infected cell by inducing a process known as apoptosis. When the infected DCs undergo apoptosis – also known as programmed cell death – the virus inside them can no longer replicate. This process is essential to the immune system’s ability to clear a virus from the body, particularly during the early stages of infection. However, previous research has suggested that HIV positive people are deficient in killing DCs that are infected with HIV-1, causing the infected DCs to act as a reservoir in which the virus can replicate without interference. In this paper, the researcher set out to determine the methods by which HIV-1 is able to prevent NK cells from killing infected DCs.

Something to squeak about: “Dirty” Wild Mice may be Better Models for Immunological Studies

When we become infected with a virus or develop cancerous cells, our bodily friend group expands as natural killer cells (NK) come to our defense to protect us from these nasty invaders. Like a trained body guard, the NK cells immediately respond to enhance our immune system by defending us against microbes and tumors in our bodies. They have granules in their cytoplasm which host proteins such as perforin and proteases (granzymes) which are released near a pathogen. Upon release, the perforin perforates holes in the cell membrane of the pathogen through which the granzymes and associated molecules can enter to induce apoptosis[o1] .  Interferons and macrophage-derived cytokines activate NK cells to contain viral infections while the adaptive immune response is generating antigen-specific cytotoxic T cells.

Much of what we have learned about immunological processes such as these have stemmed from research on animal models. Mice serve as an important model organism to study molecular mechanisms in immunology.  NK cells from laboratory mice respond poorly to stimuli unless the mice are treated with toll-like receptor (TLR) agonists, cytokines or infection. Previous studies indicate that NK cells are extremely low in lymph nodes (LNs), to lack perforin or granzyme B (Gzmb) and to die prematurely in cytokine absent cultures (Fehniger et al. 2007; Long 2007). This starkly contrasts with NK presence in humans which are profuse in LNs, contain perforin and Gzmb and survive better. Previously these discrepancies were attributed to the fact that the differing species had varying NK cells.  NK cells were believed to be short-lived and innate.  Recent studies, however, suggest that NK cells may be live longer than was previously thought.

Naturally killing rheumatoid arthritis

To get this semester's blogging off and running (no one wants to be the first to post on an empty blog!), here is my take on a new PNAS paper from the Cantor lab:

            Rheumatoid arthritis (RA) is an autoimmune inflammatory disease that affects around 1.3 million people in the United States. Found more commonly in women than men, this disease causes pain and swelling in the joints, and can lead to cartilage and bone loss, and joint deformity. RA is commonly treated with methotrexate, in combination with other drugs, but treatments can be expensive, with lifetime direct costs of up to $180,000 per patient (in 2010 dollars). These treatments can also have adverse side effects. The prevalence of RA in the U.S. is increasing as the population ages, suggesting a need for continued research into the causes of, and potential new therapeutics for, RA.

            At its core, RA is a disease of multiple immune cell types. One component is B cells, which produce antibodies that recognize “self” proteins found in connective tissue. A second component is “helper” T cells (also termed CD4 T cells), which help B cells produce antibody, and which contribute to an inflammatory state in the joints. A study published this week in the Proceedings of the National Academy of Sciences by Leavenworth and colleagues further refines the contribution of different CD4 T cell subsets in RA, and defines a new role for yet a third cell type, natural killer (NK) cells, in suppressing the development of RA. To do this, the authors used an experimental mouse model of RA, induced by injection of type II collagen, a prominent component of connective tissue, under the skin. This model (collagen-induced arthritis; CIA) causes many of the same symptoms as human RA, and has been used to test a number of new treatments for RA (1).