Dr. Thomas Gajewski
University of Chicago,Chicago,IL,USA
"Immunotherapeutic approaches for the treatment of melanoma, such as tumor antigen-based vaccines, can frequently boost immune responses. However, clinical responses as measured by tumor shrinkage are seen in only a minority of patients. This observation has prompted careful analysis of the tumor microenvironment for biologic correlates to clinical response and also to identify mechanisms of tumor resistance. Patients with advanced melanoma treated with antigen-specific vaccines had pre-treatment tumor biopsies analyzed by gene expression profiling. Supervised hierarchical clustering was performed based on clinical outcome. An expanded bank of tumors was analyzed to increase the sample size and better understand gene patterns.
Two major categories of melanoma metastases have been observed.
One subgroup of patient has an inflamed phenotype that includes expression of chemokines, T-cell markers, and other immunoregulatory factors. Clinical responders to melanoma vaccines appear to fall within this subset. This group also contains the highest expression of negative regulatory factors, including PD-L1, IDO, and FoxP3, suggesting that these immunosuppressive mechanisms may dominantly inhibit anti-tumor –cell function in those patients. In addition, absence of B7 expression supports classical T-cell anergy. Preclinical experiments have confirmed a critical role for these mechanisms in limiting anti-tumor T–cell efficacy in vivo, giving candidate treatment strategies for translation back into the clinic.
A second subset of patients is represented by tumors which are non-inflamed and lack chemokines for T cell recruitment. Therefore, a major barrier in these cases appears to be failed T –cell migration into tumor sites. Experimental strategies to augment T-cell migration can have important anti-tumor effects in preclinical models. The presence of the "inflamed" gene signature was associated with a type I IFN transcriptional profile, and murine experimental models have confirmed a critical role for type I IFN signaling in promoting adaptive immunity."
So,In the first subset, tumors had a suppresive nature that may be over riddden by Anti-CTLA-4 (Yervoy) and or Anti-PD-1 Therapy
The second subset was missing the "danger signal" inflammatory cytokines and chemoattractants most likely due to STAT3 signaling from the Tumor.
Stimulation of Toll-like receptor 4 (TLR-4) activates macrophages and results in the release of TNF-alpha. It is hypothesized that melanoma inhibits macrophage activation by suppressing TLR-4 signaling.
Cytokines are small proteins which allow cells of the immune system to communicate with one another via cytokine receptors expressed at the cell surface.
Activated macrophages defend against tumors by secreting cytokines to recruit secondary immune cells, presenting antigen to T cells, and by direct tumor cytotoxicity. Peritoneal macrophages harvested from melanoma-bearing mice are less cytotoxic to melanoma cells, and produce less superoxide, nitric oxide, and tumor necrosis factor-alpha (TNF-alpha) than those from nontumor-bearing mice. Similar impairment of macrophage activation occurs in vitro using media harvested from cultured melanoma cells.
Activated Macrophages secrete the following cytokines under different conditions:
IL-1,IL-12,IL-6, IFN-gamma/alpha/beta and TNF-alpha
Interleukin 6 is a pro-inflammatory cytokine and is produced in response to infection and tissue injury. IL-6 exerts its effects on multiple cell types and can act systemically.
IL-6 stimulates liver secretion of acute phase proteins
IL-6 stimulates B-lymphocytes to produce antibodies
IL-6 in concert with IL-1b causes T-cell activation
IL-6 induces STAT 3 Signaling
IL-6 Plus TGF-b induces the Th17 cell phenotype
Interleukin-1b is a pro-inflammatory cytokine which is secreted by macrophages activated by a number of stimuli including TNF-alpha, bacterial endotoxin and IL-1b itself.
IL-1b exerts its effects on many different cell types locally at the site of production and systemically (at a distance).
Interleukin-12 is a heterodimer consisting of a p35 and a p40 subunit. Both subunits are required for receptor binding and biological activity.
IL-12 stimulates growth of activated Natural Killer (NK) cells, CD8+ and CD4+ T- cells.
IL-12 increases NK and T-cell g-IFN production which shifts T-cell differentiation towards a Th1-type response.
IL-12 increases NK production of TNF-alpha which can act synergistically with IFN-gamma.
IL-12 suppresses IL-4 induced IgE production.
Tumor Necrosis Factor alpha is made by many other cells as well as macrophages, which are major sources, especially after priming by Interferon gamma.
TNF-alpha initiates a cascade of cytokines which mediate an inflammatory response. TNF-alpha effects are mediated through two types of receptor, a 75kDa TNFR-a receptor and a 55kDa TNFR-b receptor.
TNF-alpha regulates the expression of many genes in many cell types important for the host response to infection.
Macrophages, and many other cells produce these Type I interferons which act as immunomodulatory, as well as antiviral cytokines. Distinct receptor from interferon gamma, mediates overlapping or competing effects on macrophages. Cellular signalling pathways involve Jak/Stats, and other pathways.
So, if Melanoma suppresses Macrophage Activation, then the tumor microenviroment is missing IL-6, IL-1b and other cytokines.
If you look at the above micrographs, you will see that the two patients that had relapsed (10710 and 10737) Had IL-1b and IL-6 missing. The macrophages were not activated!!!! The "Danger Signal" known as inflammation was missing!
The missing combination of IL-1 and IL-6 meant there is no T-cell activation. And no induction of the Th17 phenotype. It is now becoming a lot more clearer based on Dr. Gajewski's findings.
Now might be the time for a critical re-evaluation of our overall approaches to targeting STAT3 and for developing new models for disrupting the protein in order to accomplish the goal of delivering clinically useful direct STAT3 inhibitors as novel anticancer agents in a timely manner.
“It is not the strongest of the species that survives, nor the most intelligent, but the one most responsive to change.”