Tracking virus-specific CD4+ T cells during and after acute hepatitis C virus infection

BACKGROUND: CD4+ T cell help is critical in maintaining antiviral immune responses and such help has been shown to be sustained in acute resolving hepatitis C. In contrast, in evolving chronic hepatitis C CD4+ T cell helper responses appear to be absent or short-lived, using functional assays. METHODOLOGY/PRINCIPAL FINDINGS: Here we used a novel HLA-DR1 tetramer containing a highly targeted CD4+ T cell epitope from the hepatitis C virus non-structural protein 4 to track number and phenotype of hepatitis C virus specific CD4+ T cells in a cohort of seven HLA-DR1 positive patients with acute hepatitis C in comparison to patients with chronic or resolved hepatitis C. We observed peptide-specific T cells in all seven patients with acute hepatitis C regardless of outcome at frequencies up to 0.65% of CD4+ T cells. Among patients who transiently controlled virus replication we observed loss of function, and/or physical deletion of tetramer+ CD4+ T cells before viral recrudescence. In some patients with chronic hepatitis C very low numbers of tetramer+ cells were detectable in peripheral blood, compared to robust responses detected in spontaneous resolvers. Importantly we did not observe escape mutations in this key CD4+ T cell epitope in patients with evolving chronic hepatitis C. CONCLUSIONS/SIGNIFICANCE: During acute hepatitis C a CD4+ T cell response against this epitope is readily induced in most, if not all, HLA-DR1+ patients. This antiviral T cell population becomes functionally impaired or is deleted early in the course of disease in those where viremia persists.

Virus-like particles induce robust human T-helper cell responses

Among synthetic vaccines, virus-like particles (VLPs) are used for their ability to induce strong humoral responses. Very little is reported on VLP-based-vaccine-induced CD4(+) T-cell responses, despite the requirement of helper T cells for antibody isotype switching. Further knowledge on helper T cells is also needed for optimization of CD8(+) T-cell vaccination. Here, we analysed human CD4(+) T-cell responses to vaccination with MelQbG10, which is a Qβ-VLP covalently linked to a long peptide derived from the melanoma self-antigen Melan-A. In all analysed patients, we found strong antibody responses of mainly IgG1 and IgG3 isotypes, and concomitant Th1-biased CD4(+) T-cell responses specific for Qβ. Although less strong, comparable B- and CD4(+) T-cell responses were also found specific for the Melan-A cargo peptide. Further optimization is required to shift the response more towards the cargo peptide. Nevertheless, the data demonstrate the high potential of VLPs for inducing humoral and cellular immune responses by mounting powerful CD4(+) T-cell help.

Segmented filamentous bacterium uses secondary and tertiary lymphoid tissues to induce gut IgA and specific T helper 17 cell responses.

Segmented filamentous bacterium (SFB) is a symbiont that drives postnatal maturation of gut adaptive immune responses. In contrast to nonpathogenic E. coli, SFB stimulated vigorous development of Peyer's patches germinal centers but paradoxically induced only a low frequency of specific immunoglobulin A (IgA)-secreting cells with delayed accumulation of somatic mutations. Moreover, blocking Peyer's patch development abolished IgA responses to E. coli, but not to SFB. Indeed, SFB stimulated the postnatal development of isolated lymphoid follicles and tertiary lymphoid tissue, which substituted for Peyer's patches as inductive sites for intestinal IgA and SFB-specific T helper 17 (Th17) cell responses. Strikingly, in mice depleted of gut organized lymphoid tissue, SFB still induced a substantial but nonspecific intestinal Th17 cell response. These results demonstrate that SFB has the remarkable capacity to induce and stimulate multiple types of intestinal lymphoid tissues that cooperate to generate potent IgA and Th17 cell responses displaying only limited target specificity.

Intestinal bacterial colonization induces mutualistic regulatory T cell responses

Mammals harbor a dense commensal microbiota in the colon. Regulatory T (Treg) cells are known to limit microbe-triggered intestinal inflammation and the CD4+ T cell compartment is shaped by the presence of particular microbes or bacterial compounds. It is, however, difficult to distinguish whether these effects reflect true mutualistic immune adaptation to intestinal colonization or rather idiosyncratic immune responses. To investigate truly mutualistic CD4+ T cell adaptation, we used the altered Schaedler flora (ASF). Intestinal colonization resulted in activation and de novo generation of colonic Treg cells. Failure to activate Treg cells resulted in the induction of T helper 17 (Th17) and Th1 cell responses, which was reversed by wild-type Treg cells. Efficient Treg cell induction was also required to maintain intestinal homeostasis upon dextran sulfate sodium-mediated damage in the colon. Thus, microbiota colonization-induced Treg cell responses are a fundamental intrinsic mechanism to induce and maintain host-intestinal microbial T cell mutualism.

The MHC-haplotype influences primary, but not memory, immune responses to an immunodominant peptide containing T- and B-cell epitopes of the caprine arthritis encephalitis virus Gag protein

In this report, we describe a short peptide, containing a T helper- and a B-cell epitope, located in the Gag protein of the caprine arthritis encephalitis virus (CAEV). This T-cell epitope is capable of inducing a robust T-cell proliferative response in vaccinated goats with different genetic backgrounds and to provide help for a strong antibody response to the B-cell epitope, indicating that it may function as a universal antigen-carrier for goat vaccines. The primary immune response of goats homozygous for MHC class I and II genes showed an MHC-dependent partitioning in rapid-high and slow-low responses, whereas the memory immune response was strong in both groups, demonstrating that a vaccine based on this immunodominant T helper epitope is capable to overcome genetic differences.

TH2 cytokines from malignant cells suppress TH1 responses and enforce a global TH2 bias in leukemic cutaneous T-cell lymphoma

PURPOSE In leukemic cutaneous T-cell lymphoma (L-CTCL), malignant T cells accumulate in the blood and give rise to widespread skin inflammation. Patients have intense pruritus, increased immunoglobulin E (IgE), and decreased T-helper (TH)-1 responses, and most die from infection. Depleting malignant T cells while preserving normal immunity is a clinical challenge. L-CTCL has been variably described as a malignancy of regulatory, TH2 and TH17 cells. EXPERIMENTAL DESIGN We analyzed phenotype and cytokine production in malignant and benign L-CTCL T cells, characterized the effects of malignant T cells on healthy T cells, and studied the immunomodulatory effects of treatment modalities in patients with L-CTCL. RESULTS Twelve out of 12 patients with L-CTCL overproduced TH2 cytokines. Remaining benign T cells were also strongly TH2 biased, suggesting a global TH2 skewing of the T-cell repertoire. Culture of benign T cells away from the malignant clone reduced TH2 and enhanced TH1 responses, but separate culture had no effect on malignant T cells. Coculture of healthy T cells with L-CTCL T cells reduced IFNγ production and neutralizing antibodies to interleukin (IL)-4 and IL-13 restored TH1 responses. In patients, enhanced TH1 responses were observed following a variety of treatment modalities that reduced malignant T-cell burden. CONCLUSIONS A global TH2 bias exists in both benign and malignant T cells in L-CTCL and may underlie the infectious susceptibility of patients. TH2 cytokines from malignant cells strongly inhibited TH1 responses. Our results suggest that therapies that inhibit TH2 cytokine activity, by virtue of their ability to improve TH1 responses, may have the potential to enhance both anticancer and antipathogen responses.

Intestinal bacteria induce TSLP to promote mutualistic T-cell responses

Thymic stromal lymphopoietin (TSLP) is constitutively expressed in the intestine and is known to regulate inflammation in models of colitis. We show that steady-state TSLP expression requires intestinal bacteria and has an important role in limiting the expansion of colonic T helper type 17 (Th17) cells. Inappropriate expansion of the colonic Th17 cells occurred in response to an entirely benign intestinal microbiota, as determined following the colonization of germ-free C57BL/6 or TSLPR(-/-) mice with the altered Schaedler flora (ASF). TSLP-TSLPR (TSLP receptor) interactions also promoted the expansion of colonic Helios(-)Foxp3(+) regulatory T cells, necessary for the control of inappropriate Th17 responses following ASF bacterial colonization. In summary, these data reveal an important role for TSLP-TSLPR signaling in promoting steady-state mutualistic T-cell responses following intestinal bacterial colonization.

ATP-gated ionotropic P2X7 receptor controls follicular T helper cell numbers in Peyer's patches to promote host-microbiota mutualism.

Microbial colonization of the gut induces the development of gut-associated lymphoid tissue (GALT). The molecular mechanisms that regulate GALT function and result in gut-commensal homeostasis are poorly defined. T follicular helper (Tfh) cells in Peyer's patches (PPs) promote high-affinity IgA responses. Here we found that the ATP-gated ionotropic P2X7 receptor controls Tfh cell numbers in PPs. Lack of P2X7 in Tfh cells enhanced germinal center reactions and high-affinity IgA secretion and binding to commensals. The ensuing depletion of mucosal bacteria resulted in reduced systemic translocation of microbial components, lowering B1 cell stimulation and serum IgM concentrations. Mice lacking P2X7 had increased susceptibility to polymicrobial sepsis, which was rescued by Tfh cell depletion or administration of purified IgM. Thus, regulation of Tfh cells by P2X7 activity is important for mucosal colonization, which in turn results in IgM serum concentrations necessary to protect the host from bacteremia.

Propionibacterium acnes promotes Th17 and Th17/Th1 responses in acne patients

Propionibacterium acnes is a Gram-positive commensal bacterium thought to be involved in the pathogenesis of acne vulgaris. Although the ability of P. acnes in the initiation of pro-inflammatory responses is well documented, little is known about adaptive immune responses to this bacterium. The observation that infiltrating immune cells consist mainly of CD4(+) T cells in the perifollicular space of early acne lesions suggests that helper T cells may be involved in immune responses caused by the intra-follicular colonization of P. acnes. A recent report showing that P. acnes can induce IL-17 production by T cells suggests that acne might be a T helper type 17 (Th17)-mediated disease. In line with this, we show in this work that, in addition to IL-17A, both Th1 and Th17 effector cytokines, transcription factors, and chemokine receptors are strongly upregulated in acne lesions. Furthermore, we found that, in addition to Th17, P. acnes can promote mixed Th17/Th1 responses by inducing the concomitant secretion of IL-17A and IFN-γ from specific CD4(+) T cells in vitro. Finally, we show that both P. acnes-specific Th17 and Th17/Th1 cells can be found in the peripheral blood of patients suffering from acne and, at lower frequencies, in healthy individuals. We therefore identified P. acnes-responding Th17/Th1 cells as, to our knowledge, a previously unreported CD4(+) subpopulation involved in inflammatory acne.

Short Peptide Vaccine Induces CD4+ T Helper Cells in Patients with Different Solid Cancers

Previous cancer vaccination trials often aimed to activate CD8(+) cytotoxic T-cell (CTL) responses with short (8-10mer) peptides and targeted CD4(+) helper T cells (TH) with HLA class II-binding longer peptides (12-16 mer) that were derived from tumor antigens. Accordingly, a study of immunomonitoring focused on the detection of CTL responses to the short, and TH responses to the long, peptides. The possible induction of concurrent TH responses to short peptides was widely neglected. In a recent phase I vaccination trial, 53 patients with different solid cancers were vaccinated with EMD640744, a cocktail of five survivin-derived short (9- or 10-mer) peptides in Montanide ISA 51VG. We monitored 49 patients and found strong CD8(+) T-cell responses in 63% of the patients. In addition, we unexpectedly found CD4(+) TH cell responses against at least two of the five short peptides in 61% (23/38) of the patients analyzed. The two peptides were recognized by HLA-DP4- and HLA-DR-restricted TH1 cells. Some short peptide-reactive (sp)CD4 T cells showed high functional avidity. Here, we show that a short peptide vaccine is able to activate a specific CD4(+) T-cell repertoire in many patients, facilitating a strong combined CD4(+)/CD8(+) T-cell response. Cancer Immunol Res; 4(1); 18-25. ©2015 AACR.