Chun I. Yu

Broad influenza-specific CD8+ T-cell responses in humanized mice vaccinated with influenza virus vaccines

The development of novel human vaccines would be greatly facilitated by the development of in vivo models that permit preclinical analysis of human immune responses. Here, we show that nonobese diabetic severe combined immunodeficiency (NOD/SCID) beta(2) microglobulin(-/-) mice, engrafted with human CD34+ hematopoietic progenitors and further reconstituted with T cells, can mount specific immune responses against influenza virus vaccines. Live attenuated trivalent influenza virus vaccine induces expansion of CD8+ T cells specific to influenza matrix protein (FluM1) and nonstructural protein 1 in blood, spleen, and lungs. On ex vivo exposure to influenza antigens, antigen-specific CD8+ T cells produce IFN-gamma and express cell-surface CD107a. FluM1-specific CD8+ T cells can be also expanded in mice vaccinated with inactivated trivalent influenza virus vaccine. Expansion of antigen-specific CD8+ T cells is dependent on reconstitution of the human myeloid compartment. Thus, this humanized mouse model permits preclinical testing of vaccines designed to induce cellular immunity, including those against influenza virus. Furthermore, this work sets the stage for systematic analysis of the in vivo functions of human DCs. This, in turn, will allow a new approach to the rational design and preclinical testing of vaccines that cannot be tested in human volunteers.

Human CD141+ Dendritic Cells Induce CD4+ T Cells To Produce Type 2 Cytokines

Dendritic cells (DCs) play the central role in the priming of naive T cells and the differentiation of unique effector T cells. In this study, using lung tissues and blood from both humans and humanized mice, we analyzed the response of human CD1c+ and CD141+ DC subsets to live-attenuated influenza virus. Specifically, we analyzed the type of CD4+ T cell immunity elicited by live-attenuated influenza virus–exposed DCs. Both DC subsets induce proliferation of allogeneic naive CD4+ T cells with the capacity to secrete IFN-γ. However, CD141+ DCs are uniquely able to induce the differentiation of IL-4– and IL-13–producing CD4+ T cells. CD141+ DCs induce IL-4– and IL-13–secreting CD4+ T cells through OX40 ligand. Thus, CD141+ DCs demonstrate remarkable plasticity in guiding adaptive immune responses.

Reprogramming Tumor-Infiltrating Dendritic Cells for CD103+CD8+ Mucosal T-cell Differentiation and Breast Cancer Rejection.

Wu and colleagues show that intratumoral delivery of dectin-1 ligand curdlan in a humanized mouse model of breast cancer reprograms dendritic cells to induce Th1 cytokine production as well as expansion and accumulation of CD103+CD8+ mucosal T cells in tumors, leading to cancer rejection. Our studies showed that tumor-infiltrating dendritic cells (DC) in breast cancer drive inflammatory Th2 (iTh2) cells and protumor inflammation. Here, we show that intratumoral delivery of the β-glucan curdlan, a ligand of dectin-1, blocks the generation of iTh2 cells and prevents breast cancer progression in vivo. Curdlan reprograms tumor-infiltrating DCs via the ligation of dectin-1, enabling the DCs to become resistant to cancer-derived thymic stromal lymphopoietin (TSLP), to produce IL-12p70, and to favor the generation of Th1 cells. DCs activated via dectin-1, but not those activated with TLR-7/8 ligand or poly I:C, induce CD8+ T cells to express CD103 (αE integrin), a ligand for cancer cells, E-cadherin. Generation of these mucosal CD8+ T cells is regulated by DC-derived integrin αvβ8 and TGF-β activation in a dectin-1–dependent fashion. These CD103+CD8+ mucosal T cells accumulate in the tumors, thereby increasing cancer necrosis and inhibiting cancer progression in vivo in a humanized mouse model of breast cancer. Importantly, CD103+CD8+ mucosal T cells elicited by reprogrammed DCs can reject established cancer. Thus, reprogramming tumor-infiltrating DCs represents a new strategy for cancer rejection. Cancer Immunol Res; 2(5); 487–500. ©2014 AACR.

Constitutive resistance to viral infection in human CD141+ dendritic cells

Specialized human dendritic cells that resist viral infection activate T cells by relying on bystander cells for antigen production. See the related Focus by Wong et al. Divided, they conquer Dendritic cells (DCs) play a crucial role in priming T cell–driven antiviral responses. Silvin et al. have examined the paradox of how virus-infected DCs retain the ability to drive adaptive immune responses. In response to endocytic viruses, they found CD1c+ DCs to be susceptible to infection and death, whereas CD141+ DCs were not. They report that viral resistance of CD141+ DCs was conferred by the expression of an endocytic guanosine triphosphatase, RAB15, and that transfer of antigen from infected CD1c+ DCs by CD141+ DCs allowed these virus-resistant DCs to prime T cell responses. By documenting a division of labor between DC subsets that separates antigen acquisition from antigen presentation, Silvin et al. offer a solution to this long-standing puzzle. Dendritic cells (DCs) are critical for the launching of protective T cell immunity in response to viral infection. Viruses can directly infect DCs, thereby compromising their viability and suppressing their ability to activate immune responses. How DC function is maintained in light of this paradox is not understood. By analyzing the susceptibility of primary human DC subsets to viral infections, we report that CD141+ DCs have an innate resistance to infection by a broad range of enveloped viruses, including HIV and influenza virus. In contrast, CD1c+ DCs are susceptible to infection, which enables viral antigen production but impairs their immune functions and survival. The ability of CD141+ DCs to resist infection is conferred by RAB15, a vesicle-trafficking protein constitutively expressed in this DC subset. We show that CD141+ DCs rely on viral antigens produced in bystander cells to launch cross-presentation–driven T cell responses. By dissociating viral infection from antigen presentation, this mechanism protects the functional capacity of DCs to launch adaptive immunity against viral infection.

Influenza Virus and Poly(I:C) Inhibit MHC Class I-Restricted Presentation of Cell-Associated Antigens Derived from Infected Dead Cells Captured by Human Dendritic Cells

During viral infection, dendritic cells (DCs) capture infected cells and present viral Ags to CD8+ T cells. However, activated DCs might potentially present cell-associated Ags derived from captured dead cells. In this study, we find that human DCs that captured dead cells containing the TLR3 agonist poly(I:C) produced cytokines and underwent maturation, but failed to elicit autologous CD8+ T cell responses against Ags of dead cells. Accordingly, DCs that captured dead cells containing poly(I:C), or influenza virus, are unable to activate CD8+ T cell clones specific to cell-associated Ags of captured dead cells. CD4+ T cells are expanded with DCs that have captured poly(I:C)-containing dead cells, indicating the inhibition is specific for MHC class I-restricted cross-presentation. Furthermore, these DCs can expand naive allogeneic CD8+ T cells. Finally, soluble or targeted Ag is presented when coloaded onto DCs that have captured poly(I:C)-containing dead cells, indicating the inhibition is specific for dead cell cargo that is accompanied by viral or poly(I:C) stimulus. Thus, DCs have a mechanism that prevents MHC class I-restricted cross-presentation of cell-associated Ag when they have captured dead infected cells.

Humanized mice for the development and testing of human vaccines

Mouse models of human disease form a link between genetics and biology. However, mice and humans differ in many aspects of immune system biology. These differences might explain, in part, why many successful preclinical immunotherapy studies in mice turn out to be unsuccessful when used in clinical trials in humans. Pioneering studies in the late 1980s demonstrated the reconstitution of human lympho–hematopoietic cells in immunodeficient mice. Since this time, immunodeficient mice are being tested as hosts for human hematopoietic organs or cells in an effort to create an in vivo model of the complete human immune system. Such Humouse models could permit us to generate and test novel human vaccines.

Targeting dendritic cells in humanized mice receiving adoptive T cells via monoclonal antibodies fused to Flu epitopes

The targeting of vaccine antigens to antigen presenting cells (APC), such as dendritic cells (DCs), is a promising strategy for boosting vaccine immunogenicity and, in turn, protective and/or therapeutic efficacy. However, in vivo systems are needed to evaluate the potential of this approach for testing human vaccines. To this end, we examined human CD8(+) T-cell expansion to novel DC-targeting vaccines in vitro and in vivo in humanized mice. Vaccines incorporating the influenza matrix protein-1 (FluM1) antigen fused to human specific antibodies targeting different DC receptors, including DEC-205, DCIR, Dectin-1, and CD40, elicited human CD8(+) T-cell responses, as defined by the magnitude of specific CD8(+) T-cells to the targeted antigen. In vitro we observed differences in response to the different vaccines, particularly between the weakly immunogenic DEC-205-targeted and more strongly immunogenic CD40-targeted vaccines, consistent with previous studies. However, in humanized mice adoptively transferred (AT) with mature human T cells (HM-T), vaccines that performed weakly in vitro (i.e., DEC-205, DCIR, and Dectin-1) gave stronger responses in vivo, some resembling those of the strongly immunogenic CD40-targeted vaccine. These results demonstrate the utility of the humanized mouse model as a platform for studies of human vaccines.