HyeMee Joo

C-Type Lectin-like Receptor LOX-1 Promotes Dendritic Cell-Mediated Class-Switched B Cell Responses

Lectin-like oxidized low-density lipoprotein receptor-1 (LOX-1) is a pattern-recognition receptor for a variety of endogenous and exogenous ligands. However, LOX-1 function in the host immune response is not fully understood. Here, we report that LOX-1 expressed on dendritic cells (DCs) and B cells promotes humoral responses. On B cells LOX-1 signaling upregulated CCR7, promoting cellular migration toward lymphoid tissues. LOX-1 signaling on DCs licensed the cells to promote B cell differentiation into class-switched plasmablasts and led to downregulation of chemokine receptor CXCR5 and upregulation of chemokine receptor CCR10 on plasmablasts, enabling their exit from germinal centers and migration toward local mucosa and skin. Finally, we found that targeting influenza hemagglutinin 1 (HA1) subunit to LOX-1 elicited HA1-specific protective antibody responses in rhesus macaques. Thus, LOX-1 expressed on B cells and DC cells has complementary functions to promote humoral immune responses.

Opposing Roles of Dectin-1 Expressed on Human Plasmacytoid Dendritic Cells and Myeloid Dendritic Cells in Th2 Polarization

Dendritic cells (DCs) can induce and control host immune responses. DC subset-dependent functional specialties and their ability to display functional plasticity, which is mainly driven by signals via pattern recognition receptors, identify DCs as immune orchestrators. A pattern recognition receptor, Dectin-1, is expressed on myeloid DCs and known to play important roles in Th17 induction and activation during fungal and certain bacterial infections. In this study, we first demonstrate that human plasmacytoid DCs express Dectin-1 in both mRNA and protein levels. More interestingly, Dectin-1–activated plasmacytoid DCs promote Th2-type T cell responses, whereas Dectin-1–activated myeloid DCs decrease Th2-type T cell responses. Such contrasting outcomes of Th2-type T cell responses by the two DC subsets are mainly due to their distinct abilities to control surface OX40L expression in response to β-glucan. This study provides new insights for the regulation of host immune responses by Dectin-1 expressed on DCs.

Functional Specialty of CD40 and Dendritic Cell Surface Lectins for Exogenous Antigen Presentation to CD8+ and CD4+ T Cells

Dendritic cells (DCs) are major antigen-presenting cells that can efficiently prime and cross-prime antigen-specific T cells. Delivering antigen to DCs via surface receptors is thus an appealing strategy to evoke cellular immunity. Nonetheless, which DC surface receptor to target to yield the optimal CD8+ and CD4+ T cell responses remains elusive. Herein, we report the superiority of CD40 over 9 different lectins and scavenger receptors at evoking antigen-specific CD8+ T cell responses. However, lectins (e.g., LOX-1 and Dectin-1) were more efficient than CD40 at eliciting CD4+ T cell responses. Common and distinct patterns of subcellular and intracellular localization of receptor-bound αCD40, αLOX-1 and αDectin-1 further support their functional specialization at enhancing antigen presentation to either CD8+ or CD4+ T cells. Lastly, we demonstrate that antigen targeting to CD40 can evoke potent antigen-specific CD8+ T cell responses in human CD40 transgenic mice. This study provides fundamental information for the rational design of vaccines against cancers and viral infections.

Induction and Activation of Human Th17 by Targeting Antigens to Dendritic Cells via Dectin-1

Recent compelling evidence indicates that Th17 confer host immunity against a variety of microbes, including extracellular and intracellular pathogens. Therefore, understanding mechanisms for the induction and activation of Ag-specific Th17 is important for the rational design of vaccines against pathogens. To study this, we employed an in vitro system in which influenza hemagglutinin (HA) 1 was delivered to dendritic cells (DCs) via Dectin-1 using anti–human Dectin-1 (hDectin-1)–HA1 recombinant fusion proteins. We found that healthy individuals maintained broad ranges of HA1-specific memory Th17 that were efficiently activated by DCs targeted with anti–hDectin-1–HA1. Nonetheless, these DCs were not able to induce a significant level of HA1-specific Th17 responses even in the presence of the Th17-promoting cytokines IL-1β and IL-6. We further found that the induction of surface IL-1R1 expression by signals via TCRs and common γ-chain receptors was essential for naive CD4+ T cell differentiation into HA1-specific Th17. This process was dependent on MyD88, but not IL-1R–associated kinase 1/4. Thus, interruptions in STAT3 or MyD88 signaling led to substantially diminished HA1-specific Th17 induction. Taken together, the de novo generation of pathogen-specific human Th17 requires complex, but complementary, actions of multiple signals. Data from this study will help us design a new and effective vaccine strategy that can promote Th17-mediated immunity against microbial pathogens.

Transcriptional Repression of IFN Regulatory Factor 7 by MYC Is Critical for Type I IFN Production in Human Plasmacytoid Dendritic Cells

Type I IFNs are crucial mediators of human innate and adaptive immunity and are massively produced from plasmacytoid dendritic cells (pDCs). IFN regulatory factor (IRF)7 is a critical regulator of type I IFN production when pathogens are detected by TLR 7/9 in pDC. However, hyperactivation of pDC can cause life-threatening autoimmune diseases. To avoid the deleterious effects of aberrant pDC activation, tight regulation of IRF7 is required. Nonetheless, the detailed mechanisms of how IRF7 transcription is regulated in pDC are still elusive. MYC is a well-known highly pleiotropic transcription factor; however, the role of MYC in pDC function is not well defined yet. To identify the role of transcription factor MYC in human pDC, we employed a knockdown technique using human pDC cell line, GEN2.2. When we knocked down MYC in the pDC cell line, production of IFN-stimulated genes was dramatically increased and was further enhanced by the TLR9 agonist CpGB. Interestingly, MYC is shown to be recruited to the IRF7 promoter region through interaction with nuclear receptor corepressor 2/histone deacetylase 3 for its repression. In addition, activation of TLR9-mediated NF-κB and MAPK and nuclear translocation of IRF7 were greatly enhanced by MYC depletion. Pharmaceutical inhibition of MYC recovered IRF7 expression, further confirming the negative role of MYC in the antiviral response by pDC. Therefore, our results identify the novel immunomodulatory role of MYC in human pDC and may add to our understanding of aberrant pDC function in cancer and autoimmune disease.

Dendritic cells and vaccine design for sexually-transmitted diseases

Dendritic cells (DCs) are major antigen presenting cells (APCs) that can initiate and control host immune responses toward either immunity or tolerance. These features of DCs, as immune orchestrators, are well characterized by their tissue localizations as well as by their subset-dependent functional specialties and plasticity. Thus, the level of protective immunity to invading microbial pathogens can be dependent on the subsets of DCs taking up microbial antigens and their functional plasticity in response to microbial products, host cellular components and the cytokine milieu in the microenvironment. Vaccines are the most efficient and cost-effective preventive medicine against infectious diseases. However, major challenges still remain for the diseases caused by sexually-transmitted pathogens, including HIV, HPV, HSV and Chlamydia. We surmise that the establishment of protective immunity in the female genital mucosa, the major entry and transfer site of these pathogens, will bring significant benefit for the protection against sexually-transmitted diseases. Recent progresses made in DC biology suggest that vaccines designed to target proper DC subsets may permit us to establish protective immunity in the female genital mucosa against sexually-transmitted pathogens.

Therapeutic HPV cancer vaccine targeted to CD40 elicits effective CD8+ T-cell immunity

In the U.S., HPV is responsible for more than 26,000 new cancer cases annually. A novel and effective immunotherapeutic vaccine against many types of HPV16-associated cancers was developed that supports targeting vaccines to dendritic cells via CD40. Human papillomavirus (HPV), particularly HPV16 and HPV18, can cause cancers in diverse anatomical sites, including the anogenital and oropharyngeal (throat) regions. Therefore, development of safe and clinically effective therapeutic vaccines is an important goal. Herein, we show that a recombinant fusion protein of a humanized antibody to CD40 fused to HPV16.E6/7 (αCD40-HPV16.E6/7) can evoke HPV16.E6/7-specific CD8+ and CD4+ T-cell responses in head-and-neck cancer patients in vitro and in human CD40 transgenic (hCD40Tg) mice in vivo. The combination of αCD40-HPV16.E6/7 and poly(I:C) efficiently primed HPV16.E6/7-specific T cells, particularly CD8+ T cells, in hCD40Tg mice. Inclusion of montanide enhanced HPV16.E6/7-specific CD4+, but not CD8+, T-cell responses. Poly(I:C) plus αCD40-HPV16.E6/7 was sufficient to mount both preventative and therapeutic immunity against TC-1 tumors in hCD40Tg mice, significantly increasing the frequency of HPV16-specific CD8+ CTLs in the tumors, but not in peripheral blood. In line with this, tumor volume inversely correlated with the frequency of HPV16.E6/7-specific CD8+ T cells in tumors, but not in blood. These data suggest that CD40-targeting vaccines for HPV-associated malignancies can provide a highly immunogenic platform with a strong likelihood of clinical benefit. Data from this study offer strong support for the development of CD40-targeting vaccines for other cancers in the future. Cancer Immunol Res; 4(10); 823–34. ©2016 AACR.

New TLR7 agonists with improved humoral and cellular immune responses.

Toll-like receptor 7 (TLR7) agonists are of interest as vaccine adjuvants and cancer therapeutics. Therefore, development of new TLR7 agonists that can efficiently promote host immune responses without evoking side effects is of great importance. Here, we describe two new compounds, J4 and F4, which elicit intracellular signaling exclusively via TLR7. Interestingly, both J4 and F4 induced less cytokine secretion (IL-1β, IL-6, IL-10, IL-12p40, TNFα, and IL-12p70) from myeloid dendritic cells (mDCs) and monocytes than CL075 and R848; however, they all generated similar levels of phenotype maturation of antigen presenting cells (APCs), including plasmacytoid DCs. We further found that J4- and F4-induced APC activation was largely dependent on the activation of NF-κB and p38. Lastly, J4 and F4 could efficiently promote B cell proliferation and plasmablast differentiation as well as antigen-specific CD8(+) T cell responses in human in vitro. Therefore, these new TLR7 agonists could be employed to facilitate the development of new therapeutics and vaccine adjuvants against cancers and microbial infections.

Dectin-1 in the control of Th2-type T cell responses.

Dendritic cells (DCs) are major antigen-presenting cells (APCs) that can induce and control host immune responses. DCs express pattern recognition receptors (PRRs), which can translate external and internal triggers into different types of T cell responses. The types of CD4+ T cell responses elicited by DCs (e.g., Th1, Th2, Th17, Th21, Th22 and regulatory T cells (Tregs)) are associated with either host immunity or inflammatory diseases, including allergic diseases and autoimmune diseases. In particular, the pathogenic functions of Th2-type T cells in allergic immune disorders have been well documented, although Th2-type T cell responses are crucial for immunity against certain parasite infections. Recent evidence also indicates that the inflammatory Th2 signatures in cancers, including breast and pancreatic cancers, are highly associated with poor clinical outcomes in patients. It is thus important to find cellular/molecular targets expressed in DCs that control such inflammatory Th2-type T cell responses. In a recent paper published in The Journal of Immunology, we demonstrated that Dectin-1 expressed on the two major human DC subsets, myeloid DCs (mDCs) and plasmacytoid DCs (pDCs), has opposing roles in the control of Th2-type CD4+ T cell responses. Dectin-1 expressed on mDCs decreases Th2-type CD4+ T cell responses, while Dectin-1 expressed on pDCs favors Th2-type CD4+ T cell responses. This finding expands our understanding of the roles of DCs and Dectin-1 expressed on DCs in the pathogenesis of Th2-associated diseases and in host immunity to microbial infections and cancers.