Circulating IL-17 levels during the peri-transplant period as a predictor for early leukemia relapse after myeloablative allogeneic stem cell transplantation

The IL-17 family in diseases: from bench to bedside

The interleukin-17 (IL-17) family comprises six members (IL-17A-17F), and recently, all of its related receptors have been discovered. IL-17 was first discovered approximately 30 years ago. Members of this family have various biological functions, including driving an inflammatory cascade during infections and autoimmune diseases, as well as boosting protective immunity against various pathogens. IL-17 is a highly versatile proinflammatory cytokine necessary for vital processes including host immune defenses, tissue repair, inflammatory disease pathogenesis, and cancer progression. However, how IL-17 performs these functions remains controversial. The multifunctional properties of IL-17 have attracted research interest, and emerging data have gradually improved our understanding of the IL-17 signaling pathway. However, a comprehensive review is required to understand its role in both host defense functions and pathogenesis in the body. This review can aid researchers in better understanding the mechanisms underlying IL-17's roles in vivo and provide a theoretical basis for future studies aiming to regulate IL-17 expression and function. This review discusses recent progress in understanding the IL-17 signaling pathway and its physiological roles. In addition, we present the mechanism underlying IL-17's role in various pathologies, particularly, in IL-17-induced systemic lupus erythematosus and IL-17-related tumor cell transformation and metastasis. In addition, we have briefly discussed promising developments in the diagnosis and treatment of autoimmune diseases and tumors.

Alteration of the Intestinal Microbiota by Broad-Spectrum Antibiotic Use Correlates with the Occurrence of Intestinal Graft-versus-Host Disease

Patients undergoing hematopoietic stem cell transplantation (HSCT) frequently receive empiric antibiotics during the neutropenic period before engraftment. Several recent studies have shown that anaerobes in the intestine are important mediators of intestinal homeostasis, and that commensal bacteria can be potent modulators of the severity of acute graft-versus-host disease (aGVHD). However, the relationships among the type of antibiotic used during the neutropenic period, changes in the intestinal microbiota, and subsequent occurrence of aGVHD are not clear. In this study, a total of 211 patients undergoing HSCT were stratified into 3 groups: patients not treated with any antibiotics during the neutropenic period (group 1; n = 43), patients treated with cefepime only (group 2; n = 87), and patients treated with carbapenem antibiotics, defined as meropenem or prepenem with or without previous cefepime therapy (group 3; n = 81). Intestinal microbiota analyses were performed on pre- and post-HSCT stool samples, and immunophenotypic analyses were performed on pre- and post-HSCT peripheral blood samples. Among the 211 patients, 95 (45%) developed aGVHD (grade ≥II), including 54 with intestinal GVHD. The incidence of intestinal GVHD was higher in group 3 compared with group 1 and group 2 (32.1%, 11.6%, and 26.4%, respectively; P = .044). After adjusting for potentially significant variables identified by univariate analysis, multivariate analyses identified broad-spectrum antibiotic use during the neutropenic period as associated with the occurrence of intestinal GVHD (hazard ratio, 3.25; 95% confidence interval, 1.13 to 9.34; P = .029). Accordingly, loss of bacterial diversity in terms of alterations in intestinal microbiota after HSCT was observed in patients who received broad-spectrum antibiotics. Moreover, alterations in the frequencies of several intestinal bacteria phyla were associated with the occurrence of intestinal GVHD. Evaluation of circulating immune cell subsets according to type of antibiotic used during the neutropenic period revealed delayed recovery of myeloid-derived suppressor cells in the broad-spectrum antibiotic use group. Our data indicate that the use of broad-spectrum antibiotics during the neutropenic period is associated with a higher incidence of intestinal GVHD via loss of microbiome diversity. Further studies are needed to determine whether maintaining bacterial diversity can help prevent the development of aGVHD.

Matrix Metalloproteinase-9 in Monocytic Myeloid-Derived Suppressor Cells Correlate with Early Infections and Clinical Outcomes in Allogeneic Hematopoietic Stem Cell Transplantation

The recovery of myeloid-derived suppressor cells (MDSCs) and its relevance in clinical acute graft-versus-host disease (GVHD) and post-hematopoietic stem cell transplantation (HSCT) infections remain to be fully characterized. We examined the expansion of circulating monocytic (M-) MDSCs and granulocytic (G-) MDSCs at the time of engraftment in 130 patients undergoing allogeneic HSCT (allo-HSCT). Compared with the G-MDSC group, the high M-MDSC group had a higher infection rate within 100 days, along with worse 1-year cumulative incidence of treatment-related mortality (TRM) and 2-year probability of event-free survival (EFS). The frequency of M-MDSCs was associated with preceding severe mucositis. Transcriptome profiling analysis of 2 isolated MDSC subtype showed significantly greater matrix metalloproteinase-9 (MMP-9) expression in M-MDSCs than in G-MDSCs. M-MDSCs produced abundantly more MMP-9. Importantly, compared with G-MDSCs, M-MDSCs isolated from patients post-HSCT had a greater capacity to suppress T cell responses, and MMP-9 blockade more forcefully inhibited their immunosuppressive effect. MMP-9 levels also were associated with the occurrence of infections and with transplantation outcomes. Based on these findings, we identify M-MDSCs as a major contributor to infections early after allo-HSCT and worse clinical outcomes via MMP-9.

CD4 T-cell subsets and tumor immunity: the helpful and the not-so-helpful

Research over the past decade has revealed the increasingly complex biologic features of the CD4(+) T-cell lineage. This T-cell subset, which was originally defined on the basis of helper activity in antibody responses, expresses receptors that recognize peptides that have been processed and presented by specialized antigen-presenting cells. At the core of the adaptive immune response, CD4 T cells display a large degree of plasticity and the ability to differentiate into multiple sublineages in response to developmental and environmental cues. These differentiated sublineages can orchestrate a broad range of effector activities during the initiation, expansion, and memory phase of an immune response. The contribution of CD4 cells to host defense against pathogenic invasion and regulation of autoimmunity is now well established. Emerging evidence suggests that CD4 cells also actively participate in shaping antitumor immunity. Here, we outline the biologic properties of CD4 T-cell subsets with an emphasis on their contribution to the antitumor response.

The correlations between IL-17 vs. Th17 cells and cancer patient survival: a systematic review

Both IL-17 and Th17 cells have been ascribed tumor promoting as well as tumor suppressing functions. We reviewed the literature on correlations between IL-17 versus Th17 cells and survival in human cancer, following the PRISMA guidelines. Serum, formalin-fixed, paraffin-embedded (FFPE) tissue and peripheral blood samples were most frequently studied. High IL-17 quantities were correlated with poor prognosis, whereas high Th17 cell frequencies were correlated with improved prognosis. Since Th17 cells are a subpopulation of IL-17⁺ cells and had a different correlation with prognosis than total IL-17, we substantiate that a distinction should be made between Th17 and other IL-17⁺ cells.

Essentials of Th17 cell commitment and plasticity

CD4(+) T helper (Th) cells exist in a variety of epigenetic states that determine their function, phenotype, and capacity for persistence. These polarization states include Th1, Th2, Th17, and Foxp3(+) T regulatory cells, as well as the more recently described T follicular helper, Th9, and Th22 cells. Th17 cells express the master transcriptional regulator retinoic acid-related orphan receptor γ thymus and produce canonical interleukin (IL)-17A and IL-17F cytokines. Th17 cells display a great degree of context-dependent plasticity, as they are capable of acquiring functional characteristics of Th1 cells. This late plasticity may contribute to the protection against microbes, plays a role in the development of autoimmunity, and is necessary for antitumor activity of Th17 cells in adoptive cell transfer therapy models. Moreover, plasticity of this subset is associated with higher in vivo survival and self-renewal capacity and less senescence than Th1 polarized cells, which have less plasticity and more phenotypic stability. New findings indicate that subset polarization of CD4(+) T cells not only induces characteristic patterns of surface markers and cytokine production but also has a maturational aspect that affects a cell's ability to survive, respond to secondary stimulation, and form long-term immune memory.