Peroxisome deficiency underlies failures in hepatic immune cell development and antigen presentation in a severe Zellweger disease model

Peroxisome biogenesis disorders (PBDs) represent a group of metabolic conditions that cause severe developmental defects. Peroxisomes are essential metabolic organelles, present in virtually every eukaryotic cell and mediating key processes in immunometabolism. To date, the full spectrum of PBDs remains to be identified, and the impact PBDs have on immune function is unexplored. This study presents a characterization of the hepatic immune compartment of a neonatal PBD mouse model at single-cell resolution to establish the importance and function of peroxisomes in developmental hematopoiesis. We report that hematopoietic defects are a feature in a severe PBD murine model. Finally, we identify a role for peroxisomes in the regulation of the major histocompatibility class II expression and antigen presentation to CD4+ T cells in dendritic cells. This study adds to our understanding of the mechanisms of PBDs and expands our knowledge of the role of peroxisomes in immunometabolism.

Using model systems to unravel host-Pseudomonas aeruginosa interactions

Using model systems in infection biology has led to the discoveries of many pathogen-encoded virulence factors and critical host immune factors to fight pathogenic infections. Studies of the remarkable Pseudomonas aeruginosa bacterium that infects and causes disease in hosts as divergent as humans and plants afford unique opportunities to shed new light on virulence strategies and host defence mechanisms. One of the rationales for using model systems as a discovery tool to characterise bacterial factors driving human infection outcomes is that many P. aeruginosa virulence factors are required for pathogenesis in diverse different hosts. On the other side, many host signalling components, such as the evolutionarily conserved mitogen-activated protein kinases, are involved in immune signalling in a diverse range of hosts. Some model organisms that have less complex immune systems also allow dissection of the direct impacts of innate immunity on host defence without the interference of adaptive immunity. In this review, we start with discussing the occurrence of P. aeruginosa in the environment and the ability of this bacterium to cause disease in various hosts as a natural opportunistic pathogen. We then summarise the use of some model systems to study host defence and P. aeruginosa virulence.

The diverse roles of C-type lectin-like receptors in immunity

Our understanding of the C-type lectin-like receptors (CTLRs) and their functions in immunity have continued to expand from their initial roles in pathogen recognition. There are now clear examples of CTLRs acting as scavenger receptors, sensors of cell death and cell transformation, and regulators of immune responses and homeostasis. This range of function reflects an extensive diversity in the expression and signaling activity between individual CTLR members of otherwise highly conserved families. Adding to this diversity is the constant discovery of new receptor binding capabilities and receptor-ligand interactions, distinct cellular expression profiles, and receptor structures and signaling mechanisms which have expanded the defining roles of CTLRs in immunity. The natural killer cell receptors exemplify this functional diversity with growing evidence of their activity in other immune populations and tissues. Here, we broadly review select families of CTLRs encoded in the natural killer cell gene complex (NKC) highlighting key receptors that demonstrate the complex multifunctional capabilities of these proteins. We focus on recent evidence from research on the NKRP1 family of CTLRs and their interaction with the related C-type lectin (CLEC) ligands which together exhibit essential immune functions beyond their defined activity in natural killer (NK) cells. The ever-expanding evidence for the requirement of CTLR in numerous biological processes emphasizes the need to better understand the functional potential of these receptor families in immune defense and pathological conditions.

Abstract 2111: Mobilization of memory natural killer cells in cancer immunotherapy

Introduction: Immunological memory has long been exclusively attributed to T and B lymphocytes; however, we now know that natural killer (NK) cells also possess an analogous function. Studies of Rag-1-deficient mice (Rag1-/-), which lack T and B cells, provided evidence of NK cell-mediated immunological memory. As NK cells also possess a natural capacity to eliminate tumor cells, we set out to define the role of NK cell memory in anti-cancer immune responses using NK cell-targeted cancer immunotherapy through immunization.

Methods: Rag1-/- mice (n=15) were immunized with the E749-57 RAHNIVYTIF (R9F) peptide from Human Papillomavirus 16, using the proprietary DepoVax (DPX) vaccine formulation, (IMV, Inc., NS Canada). Age-matched Rag1-/- mice (n=15) treated with the DPX vehicle alone served as controls. Sixteen days after immunization, all mice were flank-injected with C3 tumor cells, which express the R9F antigen. Tumor appearance and tumor growth rates were recorded. To test the requirement for Perforin, Rag1/Prf1/- mice (n=15) or age-matched Rag1-/- (n=15) were similarly immunized and tumor challenge. To determine the antigen specificity of NK cell memory, Rag1-/- mice (n=15) were immunized with the chicken-ovalbumin model antigen OVA257-265 SIINFEKL (DPX-SIINFEKL) or DPX vehicle (n=15). Mice for these experiments were implanted with C3 cells that express the ovalbumin gene and present the SIINFEKL antigen (C3-OVA cells). For all groups, tumor appearance and tumor growth rates were recorded.

Results: Rag1-/- mice vaccinated with DPX-R9F had better protection against C3 tumor development, with 60% remaining tumor-free in comparison to the DPX vehicle control cohort, in which all mice developed tumors. Additionally, the tumor growth rate in DPX-R9F immunized mice was significantly slower than in the control cohort. Perforin has a key role in mediating the observed anti-tumor responses as Rag1/Prf1/- mice vaccinated with DPX-R9F had less tumor protection compared to the Rag1-/- mice, of which only 20% remained tumor-free. Finally, we found 60% of mice immunized with DPX-SIINFEKL and challenged with C3-OVA remained tumor-free, indicating that tumor protection could be induced by distinct antigens.

Conclusions: Our preliminary results suggest that DPX-R9F or DPX-SIINFEKL immunization induces antigen-specific protection against tumor development in mice in a T cell- and B cell-independent manner. These immunizations appear to induce memory NK cells to mount antigen-specific antitumor responses that rely on Perforin as an effector molecule. By demonstrating that memory NK cells have a role in protection against tumor development, future cancer immunotherapies could be improved by priming not only T cells but also NK cells, proposing a therapeutic approach with better patient outcomes and improving, at the same time, the safety profile of these immunotherapies.

Citation Format: Daniel Medina-Luna, Gayani Gamage, Michal Scur, Haggah Zein, Brendon Parsons, Andrew P. Makrigiannis. Mobilization of memory natural killer cells in cancer immunotherapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2111.

Modulation of the cell membrane lipid milieu by peroxisomal β-oxidation induces Rho1 signaling to trigger inflammatory responses

Phagocytosis, signal transduction, and inflammatory responses require changes in lipid metabolism. Peroxisomes have key roles in fatty acid homeostasis and in regulating immune function. We find that Drosophila macrophages lacking peroxisomes have perturbed lipid profiles, which reduce host survival after infection. Using lipidomic, transcriptomic, and genetic screens, we determine that peroxisomes contribute to the cell membrane glycerophospholipid composition necessary to induce Rho1-dependent signals, which drive cytoskeletal remodeling during macrophage activation. Loss of peroxisome function increases membrane phosphatidic acid (PA) and recruits RhoGAPp190 during infection, inhibiting Rho1-mediated responses. Peroxisome-glycerophospholipid-Rho1 signaling also controls cytoskeleton remodeling in mouse immune cells. While high levels of PA in cells without peroxisomes inhibit inflammatory phenotypes, large numbers of peroxisomes and low amounts of cell membrane PA are features of immune cells from patients with inflammatory Kawasaki disease and juvenile idiopathic arthritis. Our findings reveal potential metabolic markers and therapeutic targets for immune diseases and metabolic disorders.

NKR-P1B expression in gut-associated innate lymphoid cells is required for the control of gastrointestinal tract infections

Helper-type innate lymphoid cells (ILC) play an important role in intestinal homeostasis. Members of the NKR-P1 gene family are expressed in various innate immune cells, including natural killer (NK) cells, and their cognate Clr ligand family members are expressed in various specialized tissues, including the intestinal epithelium, where they may play an important role in mucosal-associated innate immune responses. In this study, we show that the inhibitory NKR-P1B receptor, but not the Ly49 receptor, is expressed in gut-resident NK cells, ILC, and a subset of γδT cells in a tissue-specific manner. ILC3 cells constitute the predominant cell subset expressing NKR-P1B in the gut lamina propria. The known NKR-P1B ligand Clr-b is broadly expressed in gut-associated cells of hematopoietic origin. The genetic deletion of NKR-P1B results in a higher frequency and number of ILC3 and γδT cells in the gut lamina propria. However, the function of gut-resident ILC3, NK, and γδT cells in NKR-P1B-deficient mice is impaired during gastrointestinal tract infection by Citrobacter rodentium or Salmonella typhimurium, resulting in increased systemic bacterial dissemination in NKR-P1B-deficient mice. Our findings highlight the role of the NKR-P1B:Clr-b recognition system in the modulation of intestinal innate immune cell functions.