High seroprevalence but short-lived immune response to SARS-CoV-2 infection in Paris.

Although the COVID-19 pandemic peaked in March/April 2020 in France, the prevalence of infection is barely known. Using high-throughput methods, we assessed herein the serological response against the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) of 1847 participants working in three sites of an institution in Paris conurbation. In May-July 2020, 11% (95% confidence interval [CI]: 9.7-12.6) of serums were positive for IgG against the SARS-CoV-2 N and S proteins, and 9.5% (95% CI: 8.2-11.0) were neutralizer in pseudo-typed virus assays. The prevalence of seroconversion was 11.6% (95% CI: 10.2-13.2) when considering positivity in at least one assay. In 5% of RT-qPCR positive individuals, no systemic IgGs were detected. Among immune individuals, 21% had been asymptomatic. Anosmia (loss of smell) and ageusia (loss of taste) occurred in 52% of the IgG-positive individuals and in 3% of the negative ones. In contrast, 30% of the anosmia-ageusia cases were seronegative, suggesting that the true prevalence of infection may have reached 16.6%. In sera obtained 4-8 weeks after the first sampling, anti-N and anti-S IgG titers and neutralization activity in pseudo-virus assay declined by 31%, 17%, and 53%, resulting thus in half-life of 35, 87, and 28 days, respectively. The population studied is representative of active workers in Paris. The short lifespan of the serological systemic responses suggests an underestimation of the true prevalence of infection.

Standardized whole blood stimulation improves immunomonitoring of induced immune responses in multi-center study.

Functional immune responses are increasingly important for clinical studies, providing in depth biomarker information to assess immunotherapy or vaccination. Incorporating functional immune assays into routine clinical practice has remained limited due to challenges in standardizing sample preparation. We recently described the use of a whole blood syringe-based system, TruCulture®, which permits point-of-care standardized immune stimulation. Here, we report on a multi-center clinical study in seven FOCIS Centers of Excellence to directly compare TruCulture to conventional PBMC methods. Whole blood and PBMCs from healthy donors were exposed to LPS, anti-CD3 anti-CD28 antibodies, or media alone. 55 protein analytes were analyzed centrally by Luminex multi-analyte profiling in a CLIA-certified laboratory. TruCulture responses showed greater reproducibility and improved the statistical power for monitoring differential immune response activation. The use of TruCulture addresses a major unmet need through a robust and flexible method for immunomonitoring that can be reproducibly applied in multi-center clinical studies. ONE SENTENCE SUMMARY: A multi-center study revealed greater reproducibility from whole blood stimulation systems as compared to PBMC stimulation for studying induced immune responses.

Human MAIT cells are xenobiotic-resistant, tissue-targeted, CD161hi IL-17-secreting T cells.

Mucosal-associated invariant T (MAIT) cells are very abundant in humans and have antimicrobial specificity, but their functions remain unclear. MAIT cells are CD161(hi)IL-18Rα(+) and either CD4(-)CD8(-) (DN) or CD8αß(int) T cells. We now show that they display an effector-memory phenotype (CD45RA(-)CD45RO(+)CD95(hi)CD62L(lo)), and their chemokine receptor expression pattern (CCR9(int)CCR7(-)CCR5(hi)CXCR6(hi)CCR6(hi)) indicates preferential homing to tissues and particularly the intestine and the liver. MAIT cells can represent up to 45% of the liver lymphocytes. They produce interferon-γ and Granzyme-B as well as high levels of interleukin-17 after phorbol myristate acetate + ionomycin stimulation. Most MAIT cells are noncycling cells (< 1% are Ki-67(+)) and express the multidrug resistance transporter (ABCB1). As expected from this phenotype, MAIT cells are more resistant to chemotherapy than other T-cell populations. These features might also allow MAIT cells to resist the xenobiotics potentially secreted by the gut bacteria. We also show that this population does not appear to have antiviral specificity and that CD8 MAIT cells include almost all the ABCB1(+)CD161(hi) CD8 T cells. Together with their already known abundance and antimicrobial specificity, the gut-liver homing characteristics, high expression of ABCB1, and ability to secrete interleukin-17 probably participate in the antibacterial properties of MAIT cells.

High numbers of differentiated effector CD4 T cells are found in patients with cancer and correlate with clinical response after neoadjuvant therapy of breast cancer.

CD4(+) T cells influence tumor immunity in complex ways that are not fully understood. In this study, we characterized a population of human differentiated effector CD4(+) T cells that is defined by low levels of the interleukin (IL)-2 and IL-7 receptors (CD25(-)CD127(-)). We found that this cell population expands in patients with various types of cancer, including breast cancer, to represent 2% to 20% of total CD4(+) blood T lymphocytes as compared with only 0.2% to 2% in healthy individuals. Notably, these CD25(-)CD127(-)CD4 T cells expressed effector markers such as CD244 and CD11b with low levels of CD27, contrasting with the memory phenotype dominating this population in healthy individuals. These cells did not cycle in patients, nor did they secrete IL-10 or IL-17, but instead displayed cytotoxic features. Moreover, they encompassed oligoclonal expansions paralleling an expansion of effector CD8(+) T cells that included tumor antigen-specific T cells. During neoadjuvant chemotherapy in patients with breast cancer, we found that the increase in CD25(-)CD127(-) CD4(+) T cells correlated with tumor regression. This observation suggested that CD4(+) T cells included tumor antigen-specific cells, which may be generated by or participate in tumor regressions during chemotherapy. In summary, our results lend support to the hypothesis that CD4(+) T cells are involved in human antitumor responses.

Specific MAIT cell behaviour among innate-like T lymphocytes in critically ill patients with severe infections.

PURPOSE: In between innate and adaptive immunity, the recently identified innate-like mucosal-associated invariant T (MAIT) lymphocytes display specific reactivity to non-streptococcal bacteria. Whether they are involved in bacterial sepsis has not been investigated. We aimed to assess the number and the time course of circulating innate-like T lymphocytes (MAIT, NKT and γδ T cells) in critically ill septic and non-septic patients and to establish correlations with the further development of intensive care unit (ICU)-acquired infections. METHODS: We prospectively enrolled consecutive patients with severe sepsis and septic shock. Controls were critically ill patients with non-septic shock and age-matched healthy subjects. Circulating innate-like lymphocytes were enumerated using a flow cytometry assay at day 1, 4 and 7. RESULTS: One hundred and fifty six patients (113 severe bacterial infections, 36 non-infected patients and 7 patients with severe viral infections) and 26 healthy subjects were enrolled into the study. Patients with severe bacterial infections displayed an early decrease in MAIT cell count [median 1.3/mm(3); interquartile range (0.4-3.2)] as compared to control healthy subjects [31.1/mm(3) (12.1-45.2)], but also to non-infected critically ill patients [4.3/mm(3) (1.4-13.2)] (P < 0.0001 for all comparisons). In contrast NKT and γδ T cell counts did not differ between patients groups. The multivariate analysis identified non-streptococcal bacterial infection as an independent determinant of decrease in MAIT cell count. Furthermore, the incidence of ICU-acquired infections was higher in patients with persistent MAIT cell depletion. CONCLUSIONS: This large human study provides valuable information about MAIT cells in severe bacterial infections. The persistent depletion of MAIT cells is associated with the further development of ICU-acquired infections.

Age-related patterns in human myeloid dendritic cell populations in people exposed to Schistosoma haematobium infection.

BACKGROUND: Urogenital schistosomiasis is caused by the helminth parasite Schistosoma haematobium. In high transmission areas, children acquire schistosome infection early in life with infection levels peaking in early childhood and subsequently declining in late childhood. This age-related infection profile is thought to result from the gradual development of protective acquired immunity. Age-related differences in schistosome-specific humoral and cellular responses have been reported from several field studies. However there has not yet been a systematic study of the age-related changes in human dendritic cells, the drivers of T cell polarisation. METHODS: Peripheral blood mononuclear cells were obtained from a cohort of 61 Zimbabwean aged 5-45 years with a S. haematobium prevalence of 47.5%. Two subsets of dendritic cells, myeloid and plasmacytoid dendritic cells (mDCs and pDCs), were analyzed by flow cytometry. FINDINGS: In this population, schistosome infection levels peaked in the youngest age group (5-9 years), and declined in late childhood and adulthood (10+ years). The proportions of both mDCs and pDCs varied with age. However, for mDCs the age profile depended on host infection status. In the youngest age group infected people had enhanced proportions of mDCs as well as lower levels of HLA-DR on mDCs than un-infected people. In the older age groups (10-13 and 14-45 years) infected people had lower proportions of mDCs compared to un-infected individuals, but no infection status-related differences were observed in their levels of HLA-DR. Moreover mDC proportions correlated with levels of schistosome-specific IgG, which can be associated with protective immunity. In contrast proportions of pDCs varied with host age, but not with infection status. CONCLUSIONS: Our results show that dendritic cell proportions and activation in a human population living in schistosome-endemic areas vary with host age reflecting differences in cumulative history of exposure to schistosome infection.