Different immunotherapeutic approaches have proved to be of significant clinical value to many patients with different types of advanced cancer. However, we need more precise immunotherapies and predictive biomarkers to increase the successful response rates. The advent of next generation sequencing technologies and their applications in immuno-oncology has helped us tremendously towards this aim. We are now moving towards the realization of personalized medicine, thus, significantly increasing our expectations for a more successful management of the disease. Here, we discuss the current immunotherapeutic approaches against cancer, including immune checkpoint blockade with an emphasis on anti-PD-L1 and anti-CTLA-4 monoclonal antibodies. We also analyze a growing list of other co-inhibitory and co-stimulatory markers and emphasize the mechanism of action of the principal pathway for each of these, as well as on drugs that either have been FDA-approved or are under clinical investigation. We further discuss recent advances in other immunotherapies, including cytokine therapy, adoptive cell transfer therapy and therapeutic vaccines. We finally discuss the modulation of gut microbiota composition and response to immunotherapy, as well as how tumor-intrinsic factors and immunological processes influence the mutational and epigenetic landscape of progressing tumors and response to immunotherapy but also how immunotherapeutic intervention influences the landscape of cancer neoepitopes and tumor immunoediting.

The gastrointestinal tract is habitable by a variety of microorganisms and it is often a tissue inflicted by inflammation. Much discussion is raised in recent years about the role of microbiota in intestinal inflammation, but their role in intestinal cancer remains unclear. Here we discuss and extent our work on Drosophila melanogaster models of tumorigenesis and tumor cell invasion upon intestinal infection. In Drosophila midgut bacteria that cause enterocyte damage induce intestinal stem cell proliferation, which is diverted toward aberrant stem cell expansion upon oncogene expression to induce dysplastic tumors. In the hindgut though, oncogenes synergize with the innate immune response—not the bacterially mediated damage—to induce tumor cell invasion and dissemination to distant sites. Interestingly, our novel gene expression analysis of Drosophila hemocyte-like cells suggests commonalities with oncogenic hindgut cells in the innate immune response and the expression of matrix metalloproteinase 1 in response to bacterial infection.

Gut microbiota acts as a barrier against intestinal pathogens, but species-specific protection of the host from infection remains relatively unexplored. Taking a Koch’s postulates approach in reverse to define health-promoting microbes we find that Escherichia coli naturally colonizes the gut of healthy mice, but it is depleted from the gut of antibiotic-treated mice, which become susceptible to intestinal colonization by Pseudomonas aeruginosa and concomitant mortality. Reintroduction of fecal bacteria and E. coli establishes a high titer of E. coli in the host intestine and increases defence against P. aeruginosa colonization and mortality. Moreover, diet is relevant in this process because high sugars or dietary fat favours E. coli fermentation to lactic acid and P. aeruginosa growth inhibition. To the contrary, low sugars allow P. aeruginosa to produce the oxidative agent pyocyanin that inhibits E. coli growth. Our results provide an explanation as to why P. aeruginosa doesn’t commonly infect the human gut, despite being a formidable microbe in lung and wound infections. Author Summary: Here we interrogate the conundrum as to why Pseudomonas aeruginosa is not a clinical problem in the intestine as opposed to other tissues. P. aeruginosa interacts with Neisseria, Streptococcus, Staphylococcus and Actinomyces species found in the human lung. These are predominantly gram-positive bacteria that induce P. aeruginosa virulence. Moreover, peptidoglycan, which is abundant in gram-positive bacteria, can directly trigger the virulence of P. aeriginosa . We reasoned that P. aeruginosa might be benign in the human gut due to the inhibitory action of benign gram-negative intestinal bacteria, such as Escherichia coli . Therefore, we dissected the antagonism between E. coli and P. aeruginosa and the effect of a conventional, a fat-, a carbohydrate-and a protein-based diet in intestinal dysbiosis. Our findings support the notion that an unbalanced diet or antibiotics induces gut dysbiosis by the elimination of commensal E. coli , in addition to lactic acid bacteria, imposing a gut environment conducive to P. aeruginosa infection. Moreover, commensal E. coli provides an explanation as to why P. aeruginosa doesn’t commonly infect the human gut, despite being a formidable microbe in lung and wound infections.