Small Animal Models for Human Immunodeficiency Virus (HIV), Hepatitis B, and Tuberculosis: Proceedings of an NIAID Workshop.

The main advantage of animal models of infectious diseases over in vitro studies is the gain in the understanding of the complex dynamics between the immune system and the pathogen. While small animal models have practical advantages over large animal models, it is crucial to be aware of their limitations. Although the small animal model at least needs to be susceptible to the pathogen under study to obtain meaningful data, key elements of pathogenesis should also be reflected when compared to humans. Well-designed small animal models for HIV, hepatitis viruses and tuberculosis require, additionally, a thorough understanding of the similarities and differences in the immune responses between humans and small animals and should incorporate that knowledge into the goals of the study. To discuss these considerations, the NIAID hosted a workshop on 'Small Animal Models for HIV, Hepatitis B, and Tuberculosis' on May 30, 2019. Highlights of the workshop are outlined below.

"The Impact of Mycobacterium tuberculosis Immune Evasion on Protective Immunity: Implications for TB Vaccine Design" - Meeting report.

Tuberculosis (TB) is the major cause of death from infectious diseases around the world, particularly in HIV infected individuals. TB vaccine design and development have been focused on improving Bacille Calmette-Guérin (BCG) and evaluating recombinant and viral vector expressed Mycobacterium tuberculosis (Mtb) proteins, for boosting BCG-primed immunity, but these approaches have not yet yielded significant improvements over the modest effects of BCG in protecting against infection or disease. On March 7-8, 2016, the National Institute of Allergy and Infectious Diseases (NIAID) convened a workshop on "The Impact of Mtb Immune Evasion on Protective Immunity: Implications for TB Vaccine Design" with the goal of defining immune mechanisms that could be targeted through novel research approaches, to inform vaccine design and immune therapeutic interventions for prevention of TB. The workshop addressed early infection events, the impact of Mtb evolution on the development and maintenance of an adaptive immune response, and the factors that influence protection against and progression to active disease. Scientific gaps and areas of study to revitalize and accelerate TB vaccine design were discussed and prioritized. These included a comprehensive evaluation of innate and Mtb-specific adaptive immune responses in the lung at different stages of disease; determining the role of B cells and antibodies (Abs) during Mtb infection; development of better assays to measure Mtb burden following exposure, infection, during latency and after treatment, and approaches to improving current animal models to study Mtb immunogenicity, TB disease and transmission.

Decreased CD4 expression by polarized T helper 2 cells contributes to suboptimal TCR-induced phosphorylation and reduced Ca2+ signaling.

Polarized Th1 and Th2 cells expressing the same TCR produce distinct biochemical responses to ligand engagement. Compared to Th1 cells, Th2 cells show altered substrate tyrosine phosphorylation and a diminished or transient Ca2+ response. Here we demonstrate that agonist stimulation of Th1 cells leads to the predominant appearance of fully phosphorylated (p23) TCR zeta, substantial phosphorylation of zeta-associated protein 70 (ZAP-70), and strong elevation of intracellular Ca2+, whereas agonist stimulation of Th2 cells expressing an identical TCR results in an elevated p21:p23 TCR zeta ratio, little or no detectable ZAP-70 phosphorylation, and a more limited elevation in intracellular Ca2+. Th2 cells consistently had twofold lower surface CD4 expression as compared to Th1 cells with the same TCR. When CD4 levels in Th2 cells were raised to Th1 levels using retroviral gene transfer, the transduced cells showed greater generation of p23 phospho-zeta, measurable phosphorylation of ZAP-70, and increased Ca2+ responses. These findings suggest that the apparent qualitative differences in TCR signaling characterizing Th1 versus Th2 cells are largely the result of modest quantitative variation in CD4 expression, with decreased CD4 expression playing a significant role in attenuating the proximal signaling responsiveness of Th2 cells to TCR ligands.

Distinct contributions of different CD40 TRAF binding sites to CD154-induced dendritic cell maturation and IL-12 secretion.

The mechanisms by which CD40 controls the maturation and antigen presentation functions of dendritic cells (DC) remains largely undefined in this critical cell type. To examine this question, we have employed retroviral transduction of primary bone marrow-derived mouse DC. Mutation of the distinct binding sites for TNF receptor-associated factor 6 (TRAF6) and for TRAF 2, 3, and 5 in the CD40 cytoplasmic domain revealed their independent contributions to DC maturation and activation of NF-kappaB. In contrast, disruption of the TRAF6 but not the TRAF 2,3,5 binding site markedly decreased IL-12 p40 secretion along with p38 and JNK activation in response to CD154 stimulation. These data document a clear bifurcation of the CD40 signaling cascade in primary DC at the level of the receptor's two distinct and autonomous TRAF binding sites, and reveal the predominant role of the TRAF6 binding site in CD40-induced pro-inflammatory cytokine production by these cells.