Induction into viable but non culturable state and outgrowth heterogeneity of Listeria monocytogenes is affected by stress history and type of growth.

Exposure to sublethal stresses related to food-processing may induce a heterogenous mixture of cells that co-exist, comprising healthy, sublethally injured, dormant and dead cells. Heterogeneity in survival capacity and dormancy of single cells may impede the detection of foodborne pathogens. In this study, we exposed Listeria monocytogenes Scott A strain, to peracetic acid (PAA; 20-40 ppm) and to acidic conditions (hydrochloric (HCl) and acetic (AA) acid, adjusted to pH 2.7-3.0, to evaluate the resuscitation capacity and outgrowth kinetics of metabolically active cells in two different media. Injury and the viable-but-non-culturable (VBNC) status of cells were assessed by flow cytometry using CFDA (metabolically active) and PI (dead) staining. Stressed CFDA+PI- cells were sorted on Tryptic Soy (TS) Agar or in TS broth, both supplemented with 0.6 % Yeast Extract (TSAYE or TSBYE), to evaluate culturability. Resuscitation capacity of CFDA+PI-sorted cells (10 events/well) was monitored by visual inspection on TSAYE and by optical density measurement in TSBYE for 5 days. Sorting of L. monocytogenes viable cells (CFDA+PI-) in Ringer's solution on TSAYE and TSBYE showed 100 % recovery in both media (control condition), while the mean lag time in TSBYE was 9.6 h. Treatment with 20 ppm PAA for 90 and 180 min resulted in 74.79 % and 85.82 % of non-culturable cells in TSBYE and increased the average lag time to 41.7 h and 43.8 h, respectively, compared to the control (9.6 h). The longest average lag time (79.5 h) was detected after treatment with 30 ppm PAA for 90 min, while at the same condition sorting of CFDA+PI- cells resulted in 95.05 % and 93.94 % non-culturable cells on TSAYE and TSBYE, respectively. The highest percentage of wells with non-culturable cells (96.17 %) was detected on TSAYE after treatment with 40 ppm PAA for 30 min. Fractions of VBNC cells were detected in TSBYE after treatment with HCl pH 3.0 for 60 and 240 min, and in TSAYE and TSBYE after exposure to AA pH 2.7. Treatment with AA pH 2.7 for 150-300 min increased the range of recorded lag time values compared to 60 min, from 8.6 h up to 13.3 h, as well as the mean lag times in TSBYE. Modelling of the outgrowth kinetics comparing the two types of stress (oxidative vs acid) and the two systems of growth (colonial vs planktonic) revealed that low starting concentrations hindered the detection of viable L. monocytogenes cells, either due to VBNC induction or cell heterogeneity.

4th Summer School in Immuno-Oncology, July 1st-3rd, 2021, Athens, Greece.

The 4th Summer School in Immuno-Oncology was held from July 1st-July 3rd as a web meeting. Many eminent researchers and leading oncologists from Europe and the USA working on basic, translational and clinical cancer research participated, presented, and discussed the most recent advances in cancer immunology and immunotherapy. Besides sharing the newest information in the field of cancer immunology and immunotherapy, the meeting also focused on the actual translation of new knowledge acquired in the lab to the clinical setting; particular emphasis was given to the mode of action of novel therapeutic modalities and to biomarkers helpful for treatment decision-making, as well as to means that may improve cancer immunotherapeutic protocols used for the treatment of a variety of malignancies. The main topics presented by the speakers included: (1) mechanisms of tumor immune evasion and resistance; (2) host-tumor interactions and means to regulate antitumor immunity; (3) exploitation of new biomarkers and tumor or immune signatures able to potentially guide therapeutic interventions; (4) emerging therapeutic modalities for cancer treatment and specific immunotherapeutics for thoracic, genito-urinary, gastrointestinal, skin and breast cancers; and (5) innovative treatment options and alternatives to minimize the toxic adverse events of cancer immunotherapy.

Aberrant Plasma Cell Contamination of Peripheral Blood Stem Cell Autografts, Assessed by Next-Generation Flow Cytometry, Is a Negative Predictor for Deep Response Post Autologous Transplantation in Multiple Myeloma; A Prospective Study in 199 Patients.

High-dose chemotherapy with autologous stem cell support (ASCT) is the standard of care for eligible newly diagnosed Multiple Myeloma (MM) patients. Stem cell graft contamination by aberrant plasma cells (APCs) has been considered a possible predictive marker of subsequent clinical outcome, but the limited reports to date present unclear conclusions. We prospectively estimated the frequency of graft contamination using highly sensitive next-generation flow cytometry and evaluated its clinical impact in 199 myeloma patients who underwent an ASCT. Contamination (con+) was detected in 79/199 patients at a median level 2 × 10-5. Its presence and levels were correlated with response to induction treatment, with 94%, 71% and 43% achieving CR, VGPR and PR, respectively. Importantly, con+ grafts conferred 2-fold and 2.8-fold higher patient-risk of not achieving or delaying reaching CR (4 vs. 11 months) and MRD negativity (5 vs. 18 months) post ASCT, respectively. Our data also provide evidence of a potentially skewed bone marrow (BM) reconstitution due to unpurged grafts, since con+ derived BM had significantly higher prevalence of memory B cells. These data, together with the absence of significant associations with baseline clinical features, highlight graft contamination as a potential biomarker with independent prognostic value for deeper responses, including MRD negativity. Longer follow-up will reveal if this corresponds to PFS or OS advantage.

Recovery of Innate Immune Cells and Persisting Alterations in Adaptive Immunity in the Peripheral Blood of Convalescent Plasma Donors at Eight Months Post SARS-CoV-2 Infection.

Persisting alterations and unique immune signatures have been previously detected in the peripheral blood of convalescent plasma (CP) donors at approximately two months after initial SARS-CoV-2 infection. This article presents the results on the sequential analysis of 47 CP donors at a median time of eight months (range 7.5-8.5 months) post infection, as assessed by flow cytometry. Interestingly, our results show a significant variation of the relevant immune subset composition among CP donors. Regarding innate immunity, both non-classical monocytes, and CD11b- granulocytes had fully recovered at eight months post COVID-19 infection. Intermediate monocytes and natural killer (NK) cells had already been restored at the two-month evaluation and remained stable. Regarding adaptive immunity, the COVID-19-related skewed Th1 and Th2 cell polarization remained at the same levels as in two months. However, low levels of total B cells were detected even after eight months from infection. A persisting reduction of CD8+ Tregs and changes in the NKT cell compartment were also remarkable. CP donors present with a unique immune landscape at eight months post COVID-19 infection, which is characterized by the notable restoration of the components of innate immunity along with a persisting imprint of SARS-CoV-2 in cells of the adaptive immunity.

SARS-CoV-2 Infection Is Asymptomatic in Nearly Half of Adults with Robust Anti-Spike Protein Receptor-Binding Domain Antibody Response.

Between June and November 2020, we assessed plasma antibodies against severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) nucleocapsid protein in 4996 participants (aged 18-82 years, 34.5% men) from the National and Kapodistrian University of Athens. The weighted overall prevalence was 1.6% and monthly prevalence correlated with viral RNA-confirmed SARS-CoV-2 infections in Greece, in the same period. Notably, 49% of seropositive cases reported no history of SARS-CoV-2 infection-related clinical symptoms and 33% were unsuspected of their previous infection. Additionally, levels of anti-SARS-CoV-2 antibodies against the spike-protein receptor-binding domain were similar between symptomatic and asymptomatic individuals, irrespective of age and gender. Using Food and Drug Administration Emergency Use Authorization-approved assays, these results support the need for such studies on pandemic evaluation and highlight the development of robust humoral immune responses even among asymptomatic individuals. The high percentage of unsuspected/asymptomatic active cases, which may contribute to community transmission for more days than that of cases who are aware and self-isolate, underscores the necessity of measures across the population for the efficient control of the pandemic.

Peripheral Blood Immune Profiling of Convalescent Plasma Donors Reveals Alterations in Specific Immune Subpopulations Even at 2 Months Post SARS-CoV-2 Infection.

Immune profiling of patients with COVID-19 has shown that SARS-CoV-2 causes severe lymphocyte deficiencies (e.g., lymphopenia, decreased numbers, and exhaustion of T cells) and increased levels of pro-inflammatory monocytes. Peripheral blood (PB) samples from convalescent plasma (CP) donors, COVID-19 patients, and control subjects were analyzed by multiparametric flow cytometry, allowing the identification of a wide panel of immune cells, comprising lymphocytes (T, B, natural killer (NK) and NKT cells), monocytes, granulocytes, and their subsets. Compared to active COVID-19 patients, our results revealed that the immune profile of recovered donors was restored for most subpopulations. Nevertheless, even 2 months after recovery, CP donors still had reduced levels of CD4+ T and B cells, as well as granulocytes. CP donors with non-detectable levels of anti-SARS-CoV-2-specific antibodies in their serum were characterized by higher Th9 and Th17 cells, which were possibly expanded at the expense of Th2 humoral immunity. The most noticeable alterations were identified in previously hospitalized CP donors, who presented the lowest levels of CD8+ regulatory T cells, the highest levels of CD56+CD16- NKT cells, and a promotion of a Th17-type phenotype, which might be associated with a prolonged pro-inflammatory response. A longer follow-up of CP donors will eventually reveal the time needed for full recovery of their immune system competence.

Deep Phenotyping Reveals Distinct Immune Signatures Correlating with Prognostication, Treatment Responses, and MRD Status in Multiple Myeloma.

Despite recent advances, Multiple Myeloma (MM) remains an incurable disease with apparent heterogeneity that may explain patients' variable clinical outcomes. While the phenotypic, (epi)genetic, and molecular characteristics of myeloma cells have been thoroughly examined, there is limited information regarding the role of the bone marrow (BM) microenvironment in the natural history of the disease. In the present study, we performed deep phenotyping of 32 distinct immune cell subsets in a cohort of 94 MM patients to reveal unique immune profiles in both BM and peripheral blood (PB) that characterize distinct prognostic groups, responses to induction treatment, and minimal residual disease (MRD) status. Our data show that PB cells do not reflect the BM microenvironment and that the two sites should be studied independently. Adverse ISS stage and high-risk cytogenetics were correlated with distinct immune profiles; most importantly, BM signatures comprised decreased tumor-associated macrophages (TAMs) and erythroblasts, whereas the unique Treg signatures in PB could discriminate those patients achieving complete remission after VRd induction therapy. Moreover, MRD negative status was correlated with a more experienced CD4- and CD8-mediated immunity phenotype in both BM and PB, thus highlighting a critical role of by-stander cells linked to MRD biology.

Seroprevalence of Antibodies against SARS-CoV-2 among the Personnel and Students of the National and Kapodistrian University of Athens, Greece: A Preliminary Report.

Due to early implementation of public health measures, Greece had low number of SARS-CoV-2 infections and COVID-19 severe incidents in hospitalized patients. The National and Kapodistrian University of Athens (ΝΚUA), especially its health-care/medical personnel, has been actively involved in the first line of state responses to COVID-19. To estimate the prevalence of antibodies (Igs) against SARS-CoV-2 among NKUA members, we designed a five consecutive monthly serosurvey among randomly selected NKUA consenting volunteers. Here, we present the results from the first 2500 plasma samples collected during June-July 2020. Twenty-five donors were tested positive for anti-SARS-CoV-2 Igs; thus, the overall seroprevalence was 1.00%. The weighted overall seroprevalence was 0.93% (95% CI: 0.27, 2.09) and varied between males [1.05% (95% CI: 0.18, 2.92)] and females [0.84% (95% CI: 0.13, 2.49)], age-groups and different categories (higher in participants from the School of Health Sciences and in scientific affiliates/faculty members/laboratory assistants), but no statistical differences were detected. Although focused on the specific population of NKUA members, our study shows that the prevalence of anti-SARS-CoV-2 Igs for the period June-July 2020 remained low and provides knowledge of public health importance for the NKUA members. Given that approximately one in three infections was asymptomatic, continuous monitoring of the progression of the pandemic by assessing Ig seroprevalence is needed.

Ex Vivo Models Simulating the Bone Marrow Environment and Predicting Response to Therapy in Multiple Myeloma.

Multiple myeloma (MM) remains incurable despite the abundance of novel drugs. As it has been previously shown, preclinical 2D models fail to predict disease progression due to their inability to simulate the microenvironment of the bone marrow. In this review, we focus on 3D models and present all currently available ex vivo MM models that fulfil certain criteria, such as development of complex 3D environments using patients' cells and ability to test different drugs in order to assess personalized MM treatment efficacy of various regimens and combinations. We selected models representing the top-notch ex vivo platforms and evaluated them in terms of cost, time-span, and feasibility of the method. Finally, we propose where such a model can be more informative in a patient's treatment timeline. Overall, advanced 3D preclinical models are very promising as they may eventually offer the opportunity to precisely select the optimal personalized treatment for each MM patient.