Siglecs as Therapeutic Targets in Cancer

Hypersialylation is a common post-translational modification of protein and lipids found on cancer cell surfaces, which participate in cell-cell interactions and in the regulation of immune responses. Sialic acids are a family of nine-carbon α-keto acids found at the outermost ends of glycans attached to cell surfaces. Given their locations on cell surfaces, tumor cells aberrantly overexpress sialic acids, which are recognized by Siglec receptors found on immune cells to mediate broad immunomodulatory signaling. Enhanced sialylation exposed on cancer cell surfaces is exemplified as “self-associated molecular pattern” (SAMP), which tricks Siglec receptors found on leukocytes to greatly down-regulate immune responsiveness, leading to tumor growth. In this review, we focused on all 15 human Siglecs (including Siglec XII), many of which still remain understudied. We also highlighted strategies that disrupt the course of Siglec-sialic acid interactions, such as antibody-based therapies and sialic acid mimetics leading to tumor cell depletion. Herein, we introduced the central roles of Siglecs in mediating pro-tumor immunity and discussed strategies that target these receptors, which could benefit improved cancer immunotherapy.

Naive and in vitro-activated primary mouse CD8+ T cells retain in vivo immune responsiveness after electroporation-based CRISPR/Cas9 genetic engineering

CRISPR/Cas9 technology has revolutionized genetic engineering of primary cells. Although its use is gaining momentum in studies on CD8+ T cell biology, it remains elusive to what extent CRISPR/Cas9 affects in vivo function of CD8+ T cells. Here, we optimized nucleofection-based CRISPR/Cas9 genetic engineering of naive and in vitro-activated primary mouse CD8+ T cells and tested their in vivo immune responses. Nucleofection of naive CD8+ T cells preserved their in vivo antiviral immune responsiveness to an extent that is indistinguishable from non-nucleofected cells, whereas in vitro activation of CD8+ T cells prior to nucleofection led to slightly impaired expansion/survival. Of note, different target proteins displayed distinct decay rates after gene editing. This is in stark contrast to a comparable period of time required to complete gene inactivation. Thus, for optimal experimental design, it is crucial to determine the kinetics of the loss of target gene product to adapt incubation period after gene editing. In sum, nucleofection-based CRISPR/Cas9 genome editing achieves efficient and rapid generation of mutant CD8+ T cells without imposing detrimental constraints on their in vivo functions.

Inhaled Particulate Matter Affects Immune Responsiveness of Human Lung Phagocytes to Mycobacteria

The influence of smoke- or air pollution-derived cytoplasmic particulate matter (PM) can be detrimental and lead to failed lung immunity. We investigated mycobacterial uptake, intracellular replication, and soluble immune mediator responses of human bronchoalveolar lavage cells (BALC) loaded with/without PM, to infection with mycobacterial strains. We observed that only BALC containing PM display an ex vivo phenotypic profile dominated by spontaneous interleukin (IL) -10 production. PM loaded BALC retained the ability to phagocytose both Mycobacterium bovis Bacille Calmette Guérin (BCG) and Mycobacterium tuberculosis (M.tb) ΔleuDΔpanCD at equal efficacy as clear non-PM loaded BALC. However, immune responsiveness, such as the production of IL-6 (p=0.015) and tumor necrosis factor (TNF)-α (p= 0.0172) immediately post M.bovis BCG infection, were dramatically lower in black BALC loaded with PM versus clear non-PM loaded BALC. By 24 hour post infection, differential immune responses to M.bovis BCG between black versus clear BALC waned, and instead, production of IL-6 (p= 0.03) and IL-1α (p= 0.04 ) by black BALC were lower versus clear BALC following M.tb ΔleuDΔpanCD infection. Considering that TNFα and IL-6 are characterized as critical to host protection against mycobacteria, our findings suggest that BALC loaded with inhaled PM, display lower levels of anti-mycobacterial mediators, and that the response magnitude differs according to infective mycobacterial strain. Even though this did not translate into altered mycobacterial killing at early time points post infection, the long-term impact of such changes remains to be established.

Could Antigen Presenting Cells Represent a Protective Element during SARS-CoV-2 Infection in Children?

Antigen Presenting Cells (APC) are immune cells that recognize, process, and present antigens to lymphocytes. APCs are among the earliest immune responders against an antigen. Thus, in patients with COVID-19, a disease caused by the newly reported SARS-CoV-2 virus, the role of APCs becomes increasingly important. In this paper, we dissect the role of these cells in the fight against SARS-CoV-2. Interestingly, this virus appears to cause a higher mortality among adults than children. This may suggest that the immune system, particularly APCs, of children may be different from that of adults, which may then explain differences in immune responses between these two populations, evident as different pathological outcome. However, the underlying molecular mechanisms that differentiate juvenile from other APCs are not well understood. Whether juvenile APCs are one reason why children are less susceptible to SARS-CoV-2 requires much attention. The goal of this review is to examine the role of APCs, both in adults and children. The molecular mechanisms governing APCs, especially against SARS-CoV-2, may explain the differential immune responsiveness in the two populations.

A Proteome-Wide Immunoinformatics Tool to Accelerate T-Cell Epitope Discovery and Vaccine Design in the Context of Emerging Infectious Diseases: An Ethnicity-Oriented Approach

Emerging infectious diseases (EIDs) caused by viruses are increasing in frequency, causing a high disease burden and mortality world-wide. The COVID-19 pandemic caused by the novel SARS-like coronavirus (SARS-CoV-2) underscores the need to innovate and accelerate the development of effective vaccination strategies against EIDs. Human leukocyte antigen (HLA) molecules play a central role in the immune system by determining the peptide repertoire displayed to the T-cell compartment. Genetic polymorphisms of the HLA system thus confer a strong variability in vaccine-induced immune responses and may complicate the selection of vaccine candidates, because the distribution and frequencies of HLA alleles are highly variable among different ethnic groups. Herein, we build on the emerging paradigm of rational epitope-based vaccine design, by describing an immunoinformatics tool (Predivac-3.0) for proteome-wide T-cell epitope discovery that accounts for ethnic-level variations in immune responsiveness. Predivac-3.0 implements both CD8+ and CD4+ T-cell epitope predictions based on HLA allele frequencies retrieved from the Allele Frequency Net Database. The tool was thoroughly assessed, proving comparable performances (AUC ~0.9) against four state-of-the-art pan-specific immunoinformatics methods capable of population-level analysis (NetMHCPan-4.0, Pickpocket, PSSMHCPan and SMM), as well as a strong accuracy on proteome-wide T-cell epitope predictions for HIV-specific immune responses in the Japanese population. The utility of the method was investigated for the COVID-19 pandemic, by performing in silico T-cell epitope mapping of the SARS-CoV-2 spike glycoprotein according to the ethnic context of the countries where the ChAdOx1 vaccine is currently initiating phase III clinical trials. Potentially immunodominant CD8+ and CD4+ T-cell epitopes and population coverages were predicted for each population (the Epitope Discovery mode), along with optimized sets of broadly recognized (promiscuous) T-cell epitopes maximizing coverage in the target populations (the Epitope Optimization mode). Population-specific epitope-rich regions (T-cell epitope clusters) were further predicted in protein antigens based on combined criteria of epitope density and population coverage. Overall, we conclude that Predivac-3.0 holds potential to contribute in the understanding of ethnic-level variations of vaccine-induced immune responsiveness and to guide the development of epitope-based next-generation vaccines against emerging pathogens, whose geographic distributions and populations in need of vaccinations are often well-defined for regional epidemics.