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.

SUMMARY 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 towards 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, which enabled their exit from germinal centers and migration towards 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.

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 antigen-specific Th17 is important for the rational design of vaccines against pathogens. To study this, we employed an in vitro system in which influenza HA1 was delivered to dendritic cells (DCs) via Dectin-1 using anti-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 significant level of HA1-specific Th17 response even in the presence of 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 were essential for naïve CD4+ T cell differentiation into HA1-specific Th17. This process was dependent on MyD88, but not IRAK1/4. 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 new and effective vaccine strategy that can promote Th17-mediated immunity against microbial pathogens.

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 (aCD40-HPV16.E6/7) can evoke HPV16.E6/7-specific CD8 þ and CD4 þ T-cell responses in head-and-neck cancer patients in vitro and in human CD40 transgenic (hCD40Tg) mice in vivo. The combination of aCD40-HPV16.E6/7 and poly(I:C) efficiently primed HPV16. E6/7-specific T cells, particularly CD8 þ T cells, in hCD40Tg mice.Inclusion of montanide enhanced HPV16.E6/7-specific CD4 þ , but not CD8þ , T-cell responses. Poly(I:C) plus aCD40-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 CD8þ 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 þ 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.

Type I interferons (IFN) are crucial mediators of human innate and adaptive immunity and are massively produced from plasmacytoid dendritic cells (pDC). IRF7 is a critical regulator of type I IFN production when pathogens are detected by Toll-like receptor (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 NCOR2/HDAC3 for its repression. In addition, activation of TLR9-mediated NF-kB 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.

Graft-versus-host disease (GVHD) is one of the major obstacles for the success of allogeneic hematopoietic stem cell transplantation. Here, we report that the interaction between OX40L and OX40 is of critical importance for both induction and progression of acute GVHD (aGVHD) driven by human T cells. Anti-human OX40L monoclonal antibody (hOX40L) treatment could thus effectively reduce the disease severity in a xenogeneic-aGVHD (x-aGVHD) model in both preventative and therapeutic modes. Mechanistically, blocking OX40L-OX40 interaction with an anti-hOX40L antibody reduces infiltration of human T cells in target organs, including liver, gut, lung, and skin. It also decreases IL-21- and TNF-producing T cell responses, while promoting regulatory T cell (Treg) responses without compromising the cytolytic activity of CD8+ T cells. Single blockade of hOX40L was thus more effective than dual blockade of IL-21 and TNF in reducing the severity of aGVHD as well as mortality. Data from this study indicate that OX40L-OX40 interactions play a central role in the pathogenesis of aGVHD induced by human T cells. Therapeutic strategies that can efficiently interrupt OX40L-OX40 interaction in patients might have potential to provide patients with an improved clinical benefit.

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.

Dendritic cells (DCs) are major antigen presenting cells that can efficiently prime and activate cellular immune responses. Delivering antigens to in vivo DCs has thus been considered as a promising strategy that could allow us to mount T cell-mediated therapeutic immunity against cancers in patients.Successful development of such types of cancer vaccines that can target in vivo DCs, however, requires a series of outstanding questions that need to be addressed. These include the proper selection of which DC surface receptors, specific DC subsets and DC activators that can further enhance the efficacy of vaccines by promoting effector T cell infiltration and retention in tumors and their actions against tumors. Supplementing these areas of research with additional strategies that can counteract tumor immune evasion mechanisms is also expected to enhance the efficacy of such therapeutic vaccines against cancers. After more than a decade of study, we have concluded that antigen targeting to DCs via CD40 to evoke cellular responses is more efficient than targeting antigens to the same types of DCs via eleven other DC surface receptors tested. In recent work, we have further demonstrated that a prototype vaccine (anti-CD40-HPV16.E6/7, a recombinant fusion protein of anti-human CD40 and HPV16.E6/7 protein) for HPV16-associated cancers can efficiently activate HPV16.E6/7-specific T cells, particularly CD8 + T cells, from the blood of HPV16 + head-and-neck cancer patients. Moreover, anti-CD40-HPV16.E6/7 plus poly(I:C) can mount potent therapeutic immunity against TC-1 tumor expressing HPV16.E6/7 protein in human CD40 transgenic mice. In this manuscript, we thus highlight our recent findings for the development of novel CD40 targeting immunotherapeutic vaccines for HPV16-associated malignancies. In addition, we further discuss several of key questions that still remain to be addressed for enhancing therapeutic immunity elicited by our prototype vaccine against HPV16-associated malignancies. Dendritic cells (DCs) are the major antigen presenting cells (APCs) that can efficiently cross-prime antigen-specific CD8 + T cells [1,2] . Such functional specialty in turn makes DCs the ideal cellular targets for the rational design of vaccine against cancers. In line with these notions, Bonifaz et al. demonstrated that antigen targeting to in vivo DCs via DEC-205 using conjugates of anti-DEC-205 and antigen is far more efficient than antigen alone at eliciting antigen-specific cellular immunity [3] .For more than a decade after the initial report on DC targeting vaccines [3] , groups of scientists have been trying to RESEARCH HIGHLIGHTCancer Cell & Microenvironment 2016; 3: e1482. doi: 10.14800/ccm.1482; © 2016 by Wenjie Yin, et al.Page 2 of 6 optimize DC-targeting vaccines by delivering antigens to different DC surface receptors. These receptors include c-type lectins (e.g., DEC205, DC-SIGN, CD207, LOX-1, DC-ASGPR, Dectin-1, DCIR, DCIR2, CLEC6, CLEC9A, and CLEC12A) [3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][...