Considering the Immune System during Fecal Microbiota Transplantation for Clostridioides difficile Infection.

Our understanding and utilization of fecal microbiota transplantation (FMT) has jump-started over the past two decades. Recent technological advancements in sequencing and metabolomics have allowed for better characterization of our intestinal microbial counterparts, triggering a surge of excitement in the fields of mucosal immunology and microbiology. This excitement is well founded, as demonstrated by 90% relapse-free cure rates in FMT treatment for recurrent Clostridioides difficile infections. Growing evidence suggests that in addition to bacterial factors, the host immune response during C. difficile infection greatly influences disease severity. In this review, we discuss recent advancements in understanding the interplay between immune cells and the microbiota and how they may relate to recovery from C. difficile through FMT therapy.

Immune Profiling To Predict Outcome of Clostridioides difficile Infection.

There is a pressing need for biomarker-based models to predict mortality from and recurrence of Clostridioides difficile infection (CDI). Risk stratification would enable targeted interventions such as fecal microbiota transplant, antitoxin antibodies, and colectomy for those at highest risk. Because severity of CDI is associated with the immune response, we immune profiled patients at the time of diagnosis. The levels of 17 cytokines in plasma were measured in 341 CDI inpatients. The primary outcome of interest was 90-day mortality. Increased tumor necrosis factor alpha (TNF-α), interleukin 6 (IL-6), C-C motif chemokine ligand 5 (CCL-5), suppression of tumorigenicity 2 receptor (sST-2), IL-8, and IL-15 predicted mortality by univariate analysis. After adjusting for demographics and clinical characteristics, the mortality risk (as indicated by the hazard ratio [HR]) was higher for patients in the top 25th percentile for TNF-α (HR = 8.35, P = 0.005) and IL-8 (HR = 4.45, P = 0.01) and lower for CCL-5 (HR = 0.18, P ≤ 0.008). A logistic regression risk prediction model was developed and had an area under the receiver operating characteristic curve (AUC) of 0.91 for 90-day mortality and 0.77 for 90-day recurrence. While limited by being single site and retrospective, our work resulted in a model with a substantially greater predictive ability than white blood cell count. In conclusion, immune profiling demonstrated differences between patients in their response to CDI, offering the promise for precision medicine individualized treatment.IMPORTANCEClostridioides difficile infection is the most common health care-associated infection in the United States with more than 20% patients experiencing symptomatic recurrence. The complex nature of host-bacterium interactions makes it difficult to predict the course of the disease based solely on clinical parameters. In the present study, we built a robust prediction model using representative plasma biomarkers and clinical parameters for 90-day all-cause mortality. Risk prediction based on immune biomarkers and clinical variables may contribute to treatment selection for patients as well as provide insight into the role of immune system in C. difficile pathogenesis.

Colitis-Induced Th17 Cells Increase the Risk for Severe Subsequent Clostridium difficile Infection.

Clostridium difficile infection (CDI) is the number one hospital-acquired infection in the United States. CDI is more common and severe in inflammatory bowel disease patients. Here, we studied the mechanism by which prior colitis exacerbates CDI. Mice were given dextran sulfate sodium (DSS) colitis, recovered for 2 weeks, and then were infected with C. difficile. Mortality and CDI severity were increased in DSS-treated mice compared to controls. Severe CDI is dependent on CD4+ T cells, which persist after colitis-associated inflammation subsides. Adoptive transfer of Th17 cells to naive mice is sufficient to increase CDI-associated mortality through elevated IL-17 production. Finally, in humans, the Th17 cytokines IL-6 and IL-23 associate with severe CDI, and patients with high serum IL-6 are 7.6 times more likely to die post infection. These findings establish a central role for Th17 cells in CDI pathogenesis following colitis and identify them as a potential target for preventing severe disease.

IL-33 drives group 2 innate lymphoid cell-mediated protection during Clostridium difficile infection.

Clostridium difficile (C. difficile) incidence has tripled over the past 15 years and is attributed to the emergence of hypervirulent strains. While it is clear that C. difficile toxins cause damaging colonic inflammation, the immune mechanisms protecting from tissue damage require further investigation. Through a transcriptome analysis, we identify IL-33 as an immune target upregulated in response to hypervirulent C. difficile. We demonstrate that IL-33 prevents C. difficile-associated mortality and epithelial disruption independently of bacterial burden or toxin expression. IL-33 drives colonic group 2 innate lymphoid cell (ILC2) activation during infection and IL-33 activated ILC2s are sufficient to prevent disease. Furthermore, intestinal IL-33 expression is regulated by the microbiota as fecal microbiota transplantation (FMT) rescues antibiotic-associated depletion of IL-33. Lastly, dysregulated IL-33 signaling via the decoy receptor, sST2, predicts C. difficile-associated mortality in human patients. Thus, IL-33 signaling to ILC2s is an important mechanism of defense from C. difficile colitis.

HLA class II-Restricted CD8+ T cells in HIV-1 Virus Controllers.

A paradigm shifting study demonstrated that induction of MHC class E and II-restricted CD8+ T cells was associated with the clearance of SIV infection in rhesus macaques. Another recent study highlighted the presence of HIV-1-specific class II-restricted CD8+ T cells in HIV-1 patients who naturally control infection (virus controllers; VCs). However, questions regarding class II-restricted CD8+ T cells ontogeny, distribution across different HIV-1 disease states and their role in viral control remain unclear. In this study, we investigated the distribution and anti-viral properties of HLA-DRB1*0701 and DQB1*0501 class II-restricted CD8+ T cells in different HIV-1 patient cohorts; and whether class II-restricted CD8+ T cells represent a unique T cell subset. We show that memory class II-restricted CD8+ T cell responses were more often detectable in VCs than in chronically infected patients, but not in healthy seronegative donors. We also demonstrate that VC CD8+ T cells inhibit virus replication in both a class I- and class II-dependent manner, and that in two VC patients the class II-restricted CD8+ T cells with an anti-viral gene signature expressed both CD4+ and CD8+ T cell lineage-specific genes. These data demonstrated that anti-viral memory class II-restricted CD8+ T cells with hybrid CD4+ and CD8+ features are present during natural HIV-1 infection.