Yuki Kinjo

Background: 21-valent pneumococcal conjugate vaccine (PCV21) is under evaluation, in comparison to PCV20, for the routine immunization among adults aged 65-year in Japan. Methods: Serotype distribution of isolates and the incidence of invasive pneumococcal disease (IPD) in adults were monitored yearly, and the case numbers of IPD or pneumococcal community-acquired pneumonia (pCAP) preventable by immunization with PCV20 or PCV21 were estimated according to the reported vaccine efficacy and it’s duration in older adults. Data from our study of nationwide adult IPD surveillance and a multicenter study of pCAP were used.Results: The mean annual incidence of adult patients with IPD caused by all serotypes in the 65-year age group, which declined during COVID-19 pandemic period, returned to 89% of that before pandemic in 2025. The proportion of PCV20-nonPCV21 serotype was 8.5% in adults aged 65 years during the period of 2023–2025. At a current vaccination coverage rate of 40%, the numbers of preventable IPD cases (person per year) by PCV20 and PCV21 were 36 and 53, respectively. The preventable numbers of pCAP cases (person per year) by PCV20 and PCV21 were 2,821 and 4,765, respectively. The preventable number of pCAP cases was approximately 80 to 90 times higher than that of IPD cases.Conclusion: Our data indicate that PCV21 is 1.5–1.7 time more preventable than those of PCV20 in adults aged 65 years in Japan. PCV20 should be considered in case of increased adult IPD cases with PCV20–nonPCV21 serotype.

Due to the COVID-19 pandemic, the importance of developing effective vaccines has received more attention than ever before. To maximize the effects of vaccines, it is important to select adjuvants that induce strong and rapid innate and acquired immune responses. Invariant natural killer T (iNKT) cells, which constitute a small population among lymphocytes, bypass the innate and acquired immune systems through the rapid production of cytokines after glycolipid recognition; hence, their activation could be used as a vaccine strategy against emerging infectious diseases. Additionally, the diverse functions of iNKT cells, including enhancing antibody production, are becoming more understood in recent years. In this review, we briefly describe the functional subset of iNKT cells and introduce the glycolipid antigens recognized by them. Furthermore, we also introduce novel vaccine development taking advantages of iNKT cell activation against infectious diseases.

Invariant natural killer T (iNKT) cells are innate-like T lymphocytes that express an invariant T cell receptor α chain and contribute to bridging innate and acquired immunity with rapid production of large amounts of cytokines after stimulation. Among effecter subsets of iNKT cells, follicular helper NKT (NKT_FH) cells are specialized to help B cells. However, the mechanisms of NKT_FHcell differentiation remain to be elucidated. In this report, we studied the mechanism of NKT_FHcell differentiation induced by pneumococcal surface protein A and α-galactosylceramide (P/A) vaccination. We found that Gr-1⁺cells helped iNKT cell proliferation and NKT_FHcell differentiation in the spleen by producing interleukin-27 (IL-27) in the early phase after vaccination. The neutralization of IL-27 impaired NKT_FHcell differentiation, which resulted in compromised antibody production and diminished protection againstStreptococcus pneumoniaeinfection by the P/A vaccine. Our data indicated that Gr-1⁺cell–derived IL-27 stimulated mitochondrial metabolism, meeting the energic demand required for iNKT cells to differentiate into NKT_FHcells. Interestingly, Gr-1⁺cell–derived IL-27 was induced by iNKT cells via interferon-γ production. Collectively, our findings suggest that optimizing the metabolism of iNKT cells was essential for acquiring specific effector functions, and they provide beneficial knowledge on iNKT cell–mediated vaccination-mediated therapeutic strategies.

Whole-biofilm imaging at single-cell resolution is necessary for system-level analysis of cellular heterogeneity, identification of key matrix component functions and response to immune cells and antimicrobials. To this end, we developed a whole-biofilm clearing and imaging method, termed instantaneous clearing of biofilm (iCBiofilm). iCBiofilm is a simple, rapid, and efficient method involving the immersion of biofilm samples in a refractive index-matching medium, enabling instant whole-biofilm imaging with confocal laser scanning microscopy. We also developed non-fixing iCBiofilm, enabling live and dynamic imaging of biofilm development and actions of antimicrobials. iCBiofilm is applicable for multicolor imaging of fluorescent proteins, immunostained matrix components, and fluorescence labeled cells in biofilms with a thickness of several hundred micrometers. iCBiofilm is scalable from bacterial to fungal biofilms and can be used to observe biofilm-neutrophil interactions. iCBiofilm therefore represents an important advance for examining the dynamics and functions of biofilms and revisiting bacterial and fungal biofilm formation.

Biofilms are surface-bound microbial communities that are typically embedded in a matrix of self-produced extracellular polymeric substances and can cause chronic infections. Extracellular DNA is known to play a crucial role in biofilm development in diverse bacteria; however, the existence and function of RNA are poorly understood. Here, we show that RNA contributes to the structural integrity of biofilms formed by the human pathogen Staphylococcus aureus. RNase A dispersed both fresh and mature biofilms, indicating the importance of RNA at various stages. RNA-sequencing analysis demonstrated that the primary source of RNA in the biofilm matrix was the Brain Heart Infusion medium (>99.32%). RNA purified from the medium promoted biofilm formation. Microscopic and molecular interaction analyses demonstrated that polysaccharides were critical for capturing and stabilizing external RNA in biofilms, which contributes to biofilm organization. These findings provide a basis for exploring the role of externally derived substances in bacterial biofilm organization.

Background: Vulvovaginal candidiasis is a common superficial candidiasis; however, a host’s immunological mechanism against vaginal Candida infection remains unknown. Objectives: In this study, we aimed to elucidate the effect of iNKT cell activation on vulvovaginal candidiasis. Methods: Using a vulvovaginal candidiasis model with estrogenized mice, we evaluated the fungal burden and number of leukocyte infiltrations in the vaginal lavage of wild-type C57BL/6J mice after Candida albicans inoculation. One day before C. albicans inoculation, α-galactosylceramide (the α-GalCer group) or sterile phosphate-buffered saline (the sham group) was intraperitoneally injected into the mice. We also evaluated the level of antimicrobial peptide S100A8 in the vaginal lavage and analyzed the correlation between S100A8 concentration and the number of vaginal leukocyte infiltrations. Moreover, the number of uterine and vaginal immune cells were evaluated using flow cytometry. Results: The number of vaginal leukocyte infiltrations was significantly higher in the α-GalCer group than in the sham group 3 days after C. albicans inoculation. In addition, the fungal burden was significantly lower in the α-GalCer group than the sham group at 7 days after inoculation. In the analysis of S100A8 concentration of vaginal lavage, there were no significant differences between these two groups, although S100A8 concentration and the number of vaginal leukocyte infiltrations were positively correlated in the α-GalCer group. Moreover, the number of vaginal iNKT cells, NK cells and CD8⁺ T-cells was significantly higher in the α-GalCer group 3 days after inoculation. Conclusions: α-GalCer-stimulated iNKT cells likely play a protective role against vulvovaginal candidiasis.

Cutibacterium modestum is a new species coined in 2020 as the fifth species of genus Cutibacterium, which includes Cutibacterium acnes. The species is predicted as a minor but common member of skin microbiome and includes a group tentatively named as “Propionibacterium humerusii”. The description of the species has been provided only with a single strain. To establish the characteristics of C. modestum and search for possible disease-related subtypes, we investigated the biochemical characteristics of eight live strains and performed in silico comparison of nine genomes. The common features, which included the morphology of Gram-stain positive short rods, the negativity of phenylalanine arylamidase, and several unique MALDI-TOF MS spectral peaks, were considered useful in laboratory identification. Pairwise comparisons of the genomes by in silico DNA–DNA hybridization showed similarity values of 98.1% or larger, which were far higher than the subspecies cutoff of 79–80%. The 16S rRNA gene sequences of thirteen isolates and genomes were identical. Their recA gene sequences were identical except for two strains, HM-510 (HL037PA2) and Marseille-P5998, which showed unique one-nucleotide polymorphisms. The biochemical features using API kits were slightly different among the isolates but far closer than those of the nearest other species, C. acnes and Cutibacterium namnetense. Spectra of MALDI-TOF mass spectrometry showed slight differences in the presence of m/z 10,512 (10 kD chaperonin GroS) and three other peaks, further clustering the eight isolates into three subtypes. These results indicated that these isolates did not separate to form subspecies-level clusters, but subtyping is possible by using recA gene sequences or MALDI-TOF mass spectrometry spectra. Moreover, this work has confirmed that a group “P. humerusii” is included in C. modestum.

Editorial: Host-Pathogen Interactions During Pneumococcal Infection