The role of antigen availability during B cell induction and its effect on sustained memory and antibody production after infection and vaccination-lessons learned from the SARS-CoV-2 pandemic.

The importance of antibodies, particularly neutralizing antibodies, has been known for decades. When examining the immune responses against a pathogen after a vaccination or infection it is easier to measure the levels of antigen-specific antibodies than the T-cell response, but it does not give the whole picture. The levels of neutralizing antibodies are harder to determine but give a better indication of the quality of the antibody response. The induction of long-lived antibody-secreting plasma cells is crucial for a persistent humoral immune response, which has been shown for example after vaccination with the vaccinia vaccine, where antibody levels have been shown to persist for decades. With the SARS-CoV-2 pandemic ravaging the world for the past years and the monumental effort in designing and releasing novel vaccines against the virus, much effort has been put into analysing the quantity, quality, and persistence of antibody responses.

Determining SARS-CoV-2 non-infectivity state-A brief overview.

From the beginning of the COVID-19 pandemic, it has claimed over 6 million lives, and globally the pandemic rages with detrimental consequences, with the emergence of new more infectious and possibly virulent variants. A clinical obstacle in this battle has been to determine when an infected individual has reached a non-infectious state. Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) can be transmitted under diverse circumstances, and various rules and regulations, along with different testing methods, have been applied in an attempt to confine the transmission. However, that has proven to be a difficult task. In this review, we take together recently published data on infectivity and transmission of SARS-CoV-2 and have combined it with the clinical experience that physicians in Iceland have accumulated from the pandemic. In addition, we suggest guidelines for determining when patients with COVID-19 reach a non-infectious state based on a combination of clinical experience, scientific data, and proficient use of available tests. This review has addressed some of the questions regarding contagiousness and immunity against SARS-CoV-2.

HSCT in two brothers with CGD arising from mutations in CYBC1 corrects the defect in neutrophil function.

Homozygous mutations in cytochrome b-245 chaperone 1 (CYBC1) have been recently described as causing recurrent infections and inflammatory disease in an Icelandic cohort and a patient from Saudi Arabia, by destabilising the dimerisation of gp91phox with p22phox, manifesting as phenotypic chronic granulomatous disease (CGD). Haematopoietic stem cell transplantation is the treatment of choice in CGD, though experience of transplantation in this subtype of CGD is limited to a brief description in one patient. We provide clinical and transplant data for two Icelandic brothers with CGD due to homozygous p.Tyr2Ter mutations in CYBC1, demonstrating maintained cure of the immune defect 11 years post-transplant in one brother, and death in the peri-transplant period for the other.

Detailed Multiplex Analysis of SARS-CoV-2 Specific Antibodies in COVID-19 Disease.

A detailed understanding of the antibody response against SARS-CoV-2 is of high importance, especially with the emergence of novel vaccines. A multiplex-based assay, analyzing IgG, IgM, and IgA antibodies against the receptor binding domain (RBD), spike 1 (S1), and nucleocapsid proteins of the SARS-CoV-2 virus was set up. The multiplex-based analysis was calibrated against the Elecsys® Anti-SARS-CoV-2 assay on a Roche Cobas® instrument, using positive and negative samples. The calibration of the multiplex based assay yielded a sensitivity of 100% and a specificity of 97.7%. SARS-CoV-2 specific antibody levels were analyzed by multiplex in 251 samples from 221 patients. A significant increase in all antibody types (IgM, IgG, and IgA) against RBD was observed between the first and the third weeks of disease. Additionally, the S1 IgG antibody response increased significantly between weeks 1, 2, and 3 of disease. Class switching appeared to occur earlier for IgA than for IgG. Patients requiring hospital admission and intensive care had higher levels of SARS-CoV-2 specific IgA levels than outpatients. These findings describe the initial antibody response during the first weeks of disease and demonstrate the importance of analyzing different antibody isotypes against multiple antigens and include IgA when examining the immunological response to COVID-19.

TREM-1+ Macrophages Define a Pathogenic Cell Subset in the Intestine of Crohn's Disease Patients.

BACKGROUND AND AIMS: Uncontrolled activation of intestinal mononuclear phagocytes [MNPs] drives chronic inflammation in inflammatory bowel disease [IBD]. Triggering receptor expressed on myeloid cells 1 [TREM-1] has been implicated in the pathogenesis of IBD. However, the role of TREM-1+ cell subsets in driving IBD pathology and the link with clinical parameters are not understood. We investigated TREM-1 expression in human intestinal MNP subsets and examined blocking TREM-1 as a potential IBD therapy. METHODS: TREM-1 gene expression was analysed in intestinal mucosa, enriched epithelial and lamina propria [LP] layers, and purified cells from controls and IBD patients. TREM-1 protein on immune cells was assessed by flow cytometry and immunofluorescence microscopy. Blood monocyte activation was examined by large-scale gene expression using a TREM-1 agonist or LP conditioned media [LP-CM] from patients in the presence or absence of TREM-1 and tumour necrosis factor [TNF] antagonist antibodies. RESULTS: TREM-1 gene expression increases in intestinal mucosa from IBD patients and correlates with disease score. TREM-1+ cells, which are mainly immature macrophages and CD11b+ granulocytes, increase among LP cells from Crohn's disease patients and their frequency correlates with inflammatory molecules in LP-CM. LP-CM from Crohn's disease patients induces an inflammatory transcriptome in blood monocytes, including increased IL-6 expression, which is reduced by simultaneous blocking of TREM-1 and TNF. CONCLUSIONS: High intestinal TREM-1 expression, reflecting a high frequency of TREM-1+ immature macrophages and TREM-1+CD11b+ granulocytes, is linked to the deleterious inflammatory microenvironment in IBD patients. Therefore, blocking the TREM-1 pathway, especially simultaneously with anti-TNF therapy, has potential as a new IBD therapy.

Correction: A patient-derived xenograft pre-clinical trial reveals treatment responses and a resistance mechanism to karonudib in metastatic melanoma.

On Pubmed, the name of co-author Roger Olofsson Bagge appeared incorrectly as "Bagge RO" instead of "Olofsson Bagge, Roger". This has been corrected in the PDF and HTML versions.

Long-Lived Plasma Cells in Mice and Men.

Even though more than 30 years have passed since the eradication of smallpox, high titers of smallpox-specific antibodies are still detected in the blood of subjects vaccinated in childhood. In fact, smallpox-specific antibody levels are maintained in serum for more than 70 years. The generation of life-long immunity against infectious diseases such as smallpox and measles has been thoroughly documented. Although the mechanisms behind high persisting antibody titers in the absence of the causative agent are still unclear, long lived plasma cells (LLPCs) play an important role. Most of the current knowledge on LLPCs is based on experiments performed in mouse models, although the amount of data derived from human studies is increasing. As the results from mouse models are often directly extrapolated to humans, it is important to keep in mind that there are differences. These are not only the obvious such as the life span but there are also anatomical differences, for instance the adiposity of the bone marrow (BM) where LLPCs reside. Whether these differences have an effect on the function of the immune system, and in particular on LLPCs, are still unknown. In this review, we will briefly discuss current knowledge of LLPCs, comparing mice and humans.

A patient-derived xenograft pre-clinical trial reveals treatment responses and a resistance mechanism to karonudib in metastatic melanoma.

Karonudib (TH1579) is a novel compound that exerts anti-tumor activities and has recently entered phase I clinical testing. The aim of this study was to conduct a pre-clinical trial in patient-derived xenografts to identify the possible biomarkers of response or resistance that could guide inclusion of patients suffering from metastatic melanoma in phase II clinical trials. Patient-derived xenografts from 31 melanoma patients with metastatic disease were treated with karonudib or a vehicle for 18 days. Treatment responses were followed by measuring tumor sizes, and the models were categorized in the response groups. Tumors were harvested and processed for RNA sequencing and protein analysis. To investigate the effect of karonudib on T-cell-mediated anti-tumor activities, tumor-infiltrating T cells were injected in mice carrying autologous tumors and the mice treated with karonudib. We show that karonudib has heterogeneous anti-tumor effect on metastatic melanoma. Thus, based on the treatment responses, we could divide the 31 patient-derived xenografts in three treatment groups: progression group (32%), suppression group (42%), and regression group (26%). Furthermore, we show that karonudib has anti-tumor effect, irrespective of major melanoma driver mutations. Also, we identify high expression of ABCB1, which codes for p-gp pumps as a resistance biomarker. Finally, we show that karonudib treatment does not hamper T-cell-mediated anti-tumor responses. These findings can be used to guide future use of karonudib in clinical use with a potential approach as precision medicine.

Long-lived plasma cells in human bone marrow can be either CD19+ or CD19.

Long-lived plasma cells secreting vaccinia-specific antibodies are detected in human bone marrow >35 years after the eradication of smallpox.Long-lived plasma cells secreting vaccinia-specific antibodies are still able to express the B-lymphocyte antigen CD19.

An Antibody Against Triggering Receptor Expressed on Myeloid Cells 1 (TREM-1) Dampens Proinflammatory Cytokine Secretion by Lamina Propria Cells from Patients with IBD.

BACKGROUND: Triggering receptor expressed on myeloid cells 1 (TREM-1) is a potent amplifier of inflammation. Recently, the antimicrobial peptide PGLYRP-1 was shown to be the ligand of TREM-1. Here, the ability of an anti-TREM-1 antibody to dampen the release of proinflammatory cytokines by colon lamina propria cells (LPCs) from patients with IBD was investigated and correlated with PGLYRP-1 levels. METHODS: Biopsies from patients with ulcerative colitis (UC, n = 45) or Crohn's disease (CD, n = 26) were compared with those from individuals undergoing colonoscopy for other reasons (n = 17). TREM-1 expression was analyzed on myeloid cells by flow cytometry. Cell culture experiments with LPCs were used to analyze PGLYRP-1 and inflammatory cytokine levels and assess the effect of anti-TREM-1 on cytokine secretion. RESULTS: The frequency of TREM-1-expressing neutrophils and recruited macrophages was higher in inflamed than in noninflamed biopsies. The PGLYRP-1 level in inflamed tissue was higher than in noninflamed tissue; it was produced primarily by neutrophils, and its level correlated with the secretion of proinflammatory cytokines. Secretion of myeloperoxidase, tumor necrosis factor-α, interleukin-1ß, and interleukin-8 by LPCs stimulated with the potent TREM-1 agonist consisting of PGLYRP-1 complexed with peptidoglycan was reduced in the presence of anti-TREM-1. Moreover, a blocking effect of anti-TREM-1 was apparent when LPCs from a subset of inflamed individuals with elevated PGLYRP-1 were stimulated with killed bacteria. CONCLUSIONS: An anti-TREM-1 antibody can dampen secretion of proinflammatory cytokines in inflamed patients with elevated PGLYRP-1. Moreover, PGLYRP-1 + myeloperoxidase is a potential biomarker for predicting the effect of anti-TREM-1 therapy.

Hyporesponsiveness following booster immunization with bacterial polysaccharides is caused by apoptosis of memory B cells.

BACKGROUND: Repeated immunizations with polysaccharide (PS) vaccines cause hyporesponsiveness through undefined mechanisms. We assessed the effects of a PS booster on immune responses, frequency, and survival of PS-specific B-cell subpopulations in spleen and bone marrow. METHODS: Neonatal mice were primed with meningococcus serotype C (MenC) conjugate MenC-CRM(197)+CpG1826, boosted with MenC-CRM(197), MenC-PS, or saline; subsequently, bromodeoxyuridine (BrdU) was injected daily intraperitoneally. MenC-PS-specific cells were labeled with fluorescent MenC-PS and phenotyped by flow cytometry. RESULTS: After MenC-PS booster, proliferating (BrdU(+)) MenC-PS-specific naive B cells (CD138(-)/B220(+); P = .0003) and plasma cells (CD138(+)/B220(-); P = .0002) in spleen were fewer than after saline booster. BrdU(+) MenC-PS-specific plasma cells were also reduced in bone marrow (P = .0308). Compared to saline, MenC-PS booster reduced BrdU(+) IgG(+) MenC-PS-specific B cells in spleen (P = .0002). Twelve hours after the MenC-PS booster, an increased frequency of apoptotic (AnnexinV(+)) MenC-PS-specific B cells in spleen was observed compared with MenC-CRM(197) (P = .0286) or saline (P = .001) boosters. CONCLUSIONS: We demonstrated that the MenC-PS booster significantly reduced the frequency of newly activated MenC-PS-specific B cells-mostly switched IgG(+) memory cells-by driving them into apoptosis. It shows directly that apoptosis of PS-specific memory cells is the cause of PS-induced hyporesponsiveness. These results should be taken into account prior to consideration of the use of PS vaccines.

Concomitant administration of Mycobacterium bovis BCG with the meningococcal C conjugate vaccine to neonatal mice enhances antibody response and protective efficacy.

Mycobacterium bovis BCG is administered to human neonates in many countries worldwide. The objective of the study was to assess if BCG could act as an adjuvant for polysaccharide-protein conjugate vaccines in newborns and thereby induce protective immunity against encapsulated bacteria in early infancy when susceptibility is high. We assessed whether BCG could enhance immune responses to a meningococcal C (MenC) conjugate vaccine, MenC-CRM(197), in mice primed as neonates, broaden the antibody response from a dominant IgG1 toward a mixed IgG1 and IgG2a/IgG2b response, and increase protective efficacy, as measured by serum bactericidal activity (SBA). Two-week-old mice were primed subcutaneously (s.c.) with MenC-CRM(197). BCG was administered concomitantly, a day or a week before MenC-CRM(197). An adjuvant effect of BCG was observed only when it was given concomitantly with MenC-CRM(197), with increased IgG response (P = 0.002) and SBA (8-fold) after a second immunization with MenC-CRM(197) without BCG, indicating increased T-cell help. In neonatal mice (1 week old) primed s.c. with MenC-CRM(197) together with BCG, MenC-polysaccharide (PS)-specific IgG was enhanced compared to MenC-CRM(197) alone (P = 0.0015). Sixteen days after the second immunization with MenC-CRM(197), increased IgG (P < 0.05), IgG1 (P < 0.05), IgG2a (P = 0.06), and IgG2b (P < 0.05) were observed, and only mice primed with MenC-CRM(197) plus BCG showed affinity maturation and detectable SBA (SBA > 128). Thus, vaccination with a meningococcal conjugate vaccine (and possibly with other conjugates) may benefit from concomitant administration of BCG in the neonatal period to accelerate and enhance production of protective antibodies, compared to the current infant administration of conjugate which follows BCG vaccination at birth.

Neonatal immune response and serum bactericidal activity induced by a meningococcal conjugate vaccine is enhanced by LT-K63 and CpG2006.

Neonates have a poorly developed immune system. Therefore it is important to develop vaccination strategies that induce protective immunity and immunological memory against pathogens early in life. The immunogenicity of a meningococcal serogroup C polysaccharide conjugate (MenC-CRM(197)) was assessed in neonatal mice, and effects of LT-K63 and CpG2006 and immunisation routes were compared. Neonatal mice were primed subcutaneously (s.c.) or intranasally (i.n.) with MenC-CRM(197) with or without LT-K63 or CpG2006 and re-immunised 16 and 30 days later by the same route and formulation. Antibody levels were measured and generation of immunological memory assessed by affinity maturation and kinetics of the Ab response. Serum bactericidal activity (SBA) was measured to evaluate protective efficacy. The second and third dose of MenC-CRM(197) mixed with either LT-K63 or CpG2006 induced a rapid increase in MenC-specific IgG antibodies, to levels higher than elicited by MenC-CRM(197) alone (P<0.01) and in unimmunised mice (P<0.001), indicating efficient generation of memory by priming through both s.c. and i.n. routes. SBA was detected after three s.c. immunisations with MenC-CRM(197) s.c. alone. However, only two doses of MenC-CRM(197)+LT-K63 or MenC-CRM(197)+CpG2006 were needed to induce SBA levels>16. LT-K63 and CpG2006 enhanced neonatal antibody responses, affinity maturation, immunological memory to the conjugate MenC-CRM(197) and protective immunity. These results encourage the development of neonatal vaccination strategies to induce protective immunity and immunological memory against meningococcal disease.