Motion of hydrogen bonds in diluted HDO/D2O solutions: direct probing with 150 fs resolution

An experiment is described to study temporal variations of the hydrogen bond length in diluted HDO/D2O solutions. The principles of this laser spectroscopic experiment are explained first. The construction of a laser source generating 150 fs pulses in the 2.5-4.5 microns spectral region at a 10 microJ power level is detailed next. The OH stretching band is reproduced for different excitation frequencies and different pump-probe delay times. A theory, based on statistical mechanics of nonlinear optical processes, is proposed to calculate the lowest two spectral moments. An effect is reported, the delay dependent vibrational solvatochromism. It is shown how this effect can be exploited to follow temporal variations of the OH...O bond length directly, in real time. The corresponding time scales are of the order of 700 fs. No bond oscillations are observed.

Antibody-dependent cellular cytotoxicity (ADCC) is mediated by genetically modified antigen-specific human T lymphocytes

In the context of transplantation, donor and virus-specific T-lymphocyte infusions have demonstrated the dramatic potential of T cells as immune effectors. Unfortunately, most attempts to exploit the T-cell immune system against nonviral malignancies in the syngeneic setting have been disappointing. In contrast, treatments based on monoclonal antibodies (Abs) have been clinically successful and have demonstrated the clinical relevance of several antigens as therapeutic targets and the importance of the antibody-dependent cellular cytotoxicity (ADCC) pathway. In the present study, we considered the possibility of arming specific T cells with a receptor that would enable them to mediate ADCC. After transduction with a CD16/gamma receptor gene, CD4(+) and CD8(+) cytotoxic T lymphocytes displayed stable expression of the CD16 receptor at their surface. In the absence of Ab, CD16/gamma expression did not affect the capacity of specific T lymphocytes to kill their target following "natural" T-cell receptor recognition. When tested against the autologous B-lymphoblastoid cell line (BLCL) coated with anti-CD20 mAb, the newly expressed Fc receptor enabled the T cells to kill the BLCL through ADCC. Adoptive transfer of such newly designed immune effector may be considered to increase antibody efficiency by harnessing the immune potential of T cells.

Recognition of leukemic blasts by HLA-DPB1-specific cytotoxic T cell clones: a perspective for adjuvant immunotherapy post-bone marrow transplantation

There is increasing evidence that the immune response plays a role in the prevention of leukemic relapses after allogeneic bone marrow transplantation (BMT). Producing this effect (referred to as the graft-versus-leukemia reaction or GVL) is a current goal of clinical transplantation. At present, all protocols rely on the injection of donor T cells with unknown specificities. In keeping with this approach, we recently proposed the use of a single allogeneic T cell clone transfected with the HSv-tk gene to target an HLA-DPB1 mismatch in the GVH direction. For this strategy to be successful, HLA-DP antigens must be expressed on leukemic cells, which should be recognised by the HLA-DP-specific T cell clone and subsequently destroyed. In the present study, differential expression of HLA-DR, -DQ and -DP was tested by fluorescence using monoclonal antibodies on a panel of 46 acute myeloid leukemias (AML), 28 acute lymphoblastic leukemias (ALL) and 31 chronic lymphocytic leukemias of B cell origin (B-CLL). The vast majority of leukemic cells expressed HLA-DP antigens although with considerable variability. HLA-DPB1 genotyped leukemic cells were used as target cells for an HLA-DPB1*0401-specific T cell clone. Specific recognition of leukemic blasts was demonstrated for 11 out of 11 B-CLL, 11 out of 19 AML and nine out of 16 ALL. These data show that most leukemic blasts are accessible to direct lysis by allogeneic HLA-DP-specific T cells.

Acute graft-versus-host disease after bone marrow transplantation with a single HLA-DPB1*1001 mismatch: involvement of different TCRBV subsets

HLA-DP incompatibility is not considered as an exclusion criterion for bone marrow donors, because such incompatibility was not shown to affect significantly the risk for acute graft-versus-host disease (GVHD). In line with this clinical observation, it was proposed that in the context of bone marrow transplantation, HLA-DP determinants did not function as transplantation antigens in the same way as HLA-A, -B or -DR. In contrast to the above conclusion, we recently demonstrated the presence of HLA-DPB1*0501 specific T cell clones in a skin biopsy of a patient who developed aGVHD after receiving a bone marrow transplant (BMT) in which the only mismatched allele in the GVHD direction was HLA-DPB1*0501. At that time, this case was unique and occurred in a relatively uncommon graft setting where the patient received purified CD34+ BM cells from an unrelated donor. In the present study, we analyzed the immunological events associated with an aGVHD which occurred in the context of a 'regular' allogeneic BMT involving a single HLA-DPB1*1001 mismatch between donor and recipient in the GVHD direction. To this end, we analyzed several amplified T cell subsets present within a T cell line derived from a skin biopsy performed at the onset of GVHD. Our results demonstrated that T cell populations belonging to the TCRBV2, TCRB6.7, TCRBV14 and TCRBV17 subsets were specific for the HLA-DPB1*1001 mismatched allele. These data strengthen and generalize our first conclusion that a single HLA-DP mismatch between donor and recipient can activate a strong T cell response in vivo and consequently challenge the notion that HLA-DP incompatibility should not be taken into account in the choice of BM donors. Moreover, they also underline the idea that HLA-DP antigens may represent an interesting immune target for future therapeutic approaches.

Purification of Ag-specific T lymphocytes after direct peripheral blood mononuclear cell stimulation followed by CD25 selection. I. Application to CD4(+) or CD8(+) cytomegalovirus phosphoprotein pp65 epitope determination

The two main constraints that currently limit a broader usage of T cell therapy against viruses are the delay required to obtain specific T cells and the safety of the selection procedure. In the present work we developed a generally applicable strategy that eliminates the need for APC for timing reasons, and the need for infectious viral strains for safety concerns. As a model, we used the selection of T lymphocytes specific for the immunodominant CMV phosphoprotein pp65. PBMC from healthy seropositive donors were first depleted of IL-2R alpha-chain CD25(+) cells and were then stimulated for 24-96 h with previously defined peptide Ags or with autologous PBMC infected with a canarypox viral vector encoding the total pp65 protein (ALVAC-pp65). Subsequent immunomagnetic purification of newly CD25-expressing cells allowed efficient recovery of T lymphocytes specific for the initial stimuli, i.e., for the already known immunodominant epitope corresponding to the peptides used as a model or for newly defined epitopes corresponding to peptides encoded by the transfected pp65 protein. Importantly, we demonstrated that direct PBMC stimulation allowed recovery not only of CD8(+) memory T lymphocytes, but also of the CD4(+) memory T cells, which are known to be crucial to ensure persistence of adoptively transferred immune memory. Finally, our analysis of pp65-specific T cells led to the identification of several new helper and cytotoxic epitopes. This work thus demonstrates the feasibility of isolating memory T lymphocytes specific for a clinically relevant protein without the need to prepare APC, to use infectious viral strains, or to identify immunodominant epitopes.

The T cell repertoire selected in vitro against EBV: diversity, specificity, and improved purification through early IL-2 receptor alpha-chain (CD25)-positive selection

Polyclonal T cell lines specific for EBV proteins have proved efficient in preventing EBV-related immunoblastic lymphoma after allogeneic bone marrow transplantation. To gain insight into the composition of the EBV-specific T cell repertoire that ensured patient protection, we performed for the first time an extensive characterization of eight cytotoxic T cell lines selected in vitro against EBV-transformed autologous lymphoblastoid cell lines (BLCL). These T cell lines consist of 50-100 distinct T cell clones, of which 32-96% are specific for autologous BLCL. Moreover, we demonstrate that reactivities against only five EBV proteins (BZLF1, BMLF1, EBNA-3A, EBNA-3C, and LMP2) cover 86% (32/37) of the specificities detected. In addition, we describe an improved method of T cell harvesting using a CD25 selection procedure which reduces the time required to obtain specific T cells and improves the purity of EBV-specific T cells, thus showing promise for use in adoptive transfer protocols.

The French prospective multisite registry on sudden unexpected infant death (OMIN): rationale and study protocol

INTRODUCTION

Even after 'back-to-sleep' campaigns, sudden unexpected infant death (SUID) continues to be the leading cause of death for infants 1 month to 1 year old in developed countries, with devastating social, psychological and legal implications for families. To sustainably tackle this problem and decrease the number of SUIDs, a French SUID registry was initiated in 2015 to (1) inform prevention with standardised data, (2) understand the mechanisms leading to SUID and the contribution of the already known or newly suggested risk factors and (3) gather a multidisciplinary group of experts to coordinate and develop innovative and urgent research in the SUID area.

METHODS AND ANALYSIS

This observational multisite prospective observatory includes all cases of sudden unexpected deaths in children younger than 2 years occurring in the French territory covered by the 35 participating French referral centres. From these cases, various data concerning sociodemographic conditions, death scene, personal and family medical history, parental behaviours, sleep environment, clinical examinations, biological and imagery investigations and autopsy are systematically collected. These data will be complemented as of 2018 with a biobank of diverse biological samples (blood, hair, urine, faeces and cerebrospinal fluid), with other administrative health-related data (health claim reimbursements and hospital admissions) and socioenvironmental data. Insights from exploratory descriptive statistics and thematic analysis will be combined for the design of targeted strategies to effectively reduce preventable infant deaths.

ETHICS AND DISSEMINATION

The French sudden unexpected infant death registry (Observatoire National des Morts Inattendues du Nourrisson registry;OMIN) was approved in 2015 by the French Data Protection Authority in clinical research (Commission Nationale de l'Informatique et des Libertés: number 915273) and by an independent ethics committee (Groupe Nantais d'Ethique dans le Domaine de la Santé: number 2015-01-27). Results will be discussed with associations of families affected by SUID, caregivers, funders of the registry, medical societies and researchers and will be submitted to international peer-reviewed journals and presented at international conferences.

Long-term preservation of antibody-dependent cellular cytotoxicity (ADCC) of natural killer cells amplified in vitro from the peripheral blood of breast cancer patients after chemotherapy

Twenty percent of breast cancer adenocarcinomas overexpress the oncogene c-erb-2 that is recognized by the humanized anti-Her2/neu monoclonal antibody Herceptin. Results from clinical studies suggest that antibody-dependent cellular cytotoxicity (ADCC) is involved in the clinical response of Herceptin-treated patients. The purpose of the current study was to evaluate the possibility of amplifying in vitro the CD3-/CD16+ natural killer (NK) cell subset that mediates ADCC from breast cancer patients after chemotherapy. Peripheral blood mononuclear cells from six breast cancer patients taken 2 months after chemotherapy completion were co-cultured with an autologous irradiated Epstein-Barr virus-transformed B-lymphoblastoid cell line (LCL) in the presence of interleukin-2 (IL-2) for 4-6 weeks. These LCL + IL2 activated cultures (ACs) were tested for ADCC potential, and their CD3/CD16 NK proportion was quantified. Among the ACs, the proportion of CD3-/CD16+ NK cells increased up to 64% over the first 2 weeks of culture and the ACs continued to expand for 1 month thereafter. Control and patient ACs displayed ADCC activity (tested in the presence of Rituximab against the autologous LCL to take into account any possible effect of inhibitory NK receptors) as well as against the MCF-7(Her2/neu) breast cancer cell line in the presence of Herceptin. This ADCC activity was maintained during the entire culture period. In conclusion, chemotherapy in breast cancer patients does not obviate the possibility of amplifying in vitro the NK cell subset that mediates ADCC. Consequently, adoptive transfer of lymphocytes mediating ADCC can be considered using this protocol to test its benefit in patients under Herceptin treatment.

Propagation of ultrawideband short pulses of terahertz radiation through submillimeter-diameter circular waveguides

We report experimental investigations in which quasi-optical methods were used to efficiently couple freely propagating, optoelectronically generated, subpicosecond pulses of terahertz (THz) radiation into submillimeter circular metal tubes (waveguides) and, consequently, to measure the transmitted pulses from these waveguides. We observe very dispersive low-loss propagation over the frequency band from 0.65 to 3.5 THz, with frequency-dependent group velocities nu(g) ranging from c/4 to c and phase velocities nu(p) from 4c to c , where nu(g)nu(p)=c(2) . The linearly polarized incoming THz pulses couple significantly only into the TE(11) , TM(11) , and TE(12) modes of the utilized 24- and 4-mm-long stainless-steel tubes, with inside diameters of 240 and 280microm , respectively.

Generation of intense highly coherent femtosecond pulses in the mid infrared

Highly coherent mid-infrared femtosecond pulses, tunable between 2.5 and 4.4 mum, and with an average energy and duration between 2.6 and 3.6 microm of 11 microJ and 200fs, respectively, have been produced by an optical parametric amplifier setup driven at 1kHz by a 400- microJ , 800-nm pulse from a Ti:sapphire amplifier. In this system, first tunable moderate-energy femtosecond pulses in the near infrared are produced by continuum amplification in beta -barium borate, and subsequently the near-infrared pulses are amplified and frequency mixed with 800-nm radiation in potassium titanyl phosphate to produce intense tunable mid-infrared pulses. The time-bandwidth product of the mid-infrared pulses is 0.28+/-0.02 over the whole high-energy tuning range. Experimental results are compared with numerical simulations and a simple model.

Efficient transduction and selection of human T-lymphocytes with bicistronic Thy1/HSV1-TK retroviral vector produced by a human packaging cell line

BACKGROUND

T-cells expressing the HSV1-TK suicide gene can be used for the control of graft-versus-host disease following allogeneic stem cell transplantation. To develop clinical trials based on such a strategy, we have generated under good manufacturing procedures a novel 'split genome' human packaging cell line (1704 cells).

METHODS

To minimize the risk of generating replication-competent retroviruses, pol was truncated to remove sequences overlapping with env. To improve retroviral infection and selection of transduced T-cells, high titers of GALV-pseudotyped retroviral particles harboring a bicistronic Thy1-IRES-TK vector coding for the CD90 GPI-anchored membrane molecule were produced by 1704 cells.

RESULTS

Using 1704 cell supernatant and an optimized transduction protocol, approximately 50% of primary T-cells were transduced and could then be purified (approximately 95%) using clinical-grade immunomagnetic beads directed against CD90. Over 96% of these OKT3/IL-2-activated CD90(+)-selected T-cells were killed by ganciclovir. Cell proliferation and cytokine production of transduced T-cells and HLA-restricted cytotoxicity of transduced T-cell clones were identical to those of their non-transduced counterparts cultured under the same conditions.

CONCLUSIONS

GALV-pseudotyped retroviral particles harboring a bicistronic Thy1-IRES-TK vector allow efficient transduction and rapid selection of human T-cells under conditions applicable for clinical trials using the new human 1704 packaging cell line.

Upregulation of adhesion molecules on leukemia targets improves the efficacy of cytotoxic T cells transduced with chimeric anti-CD19 receptor

T lymphocytes engineered to express chimeric antigen receptors (CARs) interact directly with cell surface molecules, bypassing MHC antigen presentation dependence. We generated human anti-CD19ζ CAR cytotoxic T lymphocytes and cytokine-induced killer cells and studied their sensitivity to the expression of adhesion molecules for the killing of primary B-lineage acute lymphoblastic leukemia (B-ALL) targets. Despite a very low basal expression of surface adhesion molecules, B-ALL blasts were lysed by the anti-CD19ζ-CAR transduced effectors as expected. We next investigated the regulatory role of adhesion molecules during CAR-mediated cytolysis. The blocking of these accessory molecules strongly limited the chimeric effector's cytotoxicity. Thereafter, B-ALL cells surface adhesion molecule level expression was induced by IFN-γ or by the combined use of CD40L and IL-4 and the cells were submitted to anti-CD19ζ-CAR transduced effectors lysis. Upregulation of adhesion molecules expression by blasts potentiated their killing. The improved cytotoxicity observed was dependent on target surface expression of adhesion molecules, particularly CD54. Taken together, these results indicate that adhesion molecules, and principally CD54, are involved in the efficiency of recognition by effector chimeric ζ. These observations have potential implications for the design of immunotherapy treatment approaches for hematological malignancies and tumors based on the adoption of CAR effector cells.

Exploration of the lysis mechanisms of leukaemic blasts by chimaeric T-cells

Adoptive transfer of specific cytotoxic T lymphocytes (CTL) and Cytokine Induced Killer Cells (CIK) following genetic engineering of T-cell receptor zeta hold promising perspective in immunotherapy. In the present work we focused on the mechanisms of anti-tumor action of effectors transduced with an anti-CD19 chimaeric receptor in the context of B-lineage acute lymphoblastic leukemia (B-ALL). Primary B-ALL blasts were efficiently killed by both z-CD19 CTL and z-CD19 CIK effectors. The use of death receptor mediated apoptosis of target cells was excluded since agonists molecules of Fas and TRAIL-receptors failed to induce cell death. Perforin/granzyme pathway was found to be the mechanism of chimaeric effectors mediated killing. Indeed, cytolytic effector molecules perforin as well as granzymes were highly expressed by CTL and CIK. CD19 specific stimulation of transduced effectors was associated with degranulation as attested by CD107 membrane expression and high IFN-gamma and TNF-alpha release. Moreover inhibitors of the perforin-based cytotoxic pathway, Ca(2+)-chelating agent EGTA and Concanamycin A, almost completely abrogated B-ALL blast killing. In conclusion we show that the cytolysis response of z-CD19 chimaeric effectors is predominantly mediated via perforin/granzyme pathway and is independent of death receptors signaling in primary B-ALL.

Cascaded second-order effects in the femtosecond regime in beta-barium borate: self-compression in a visible femtosecond optical parametric oscillator

Cascaded second-order effects are studied in the femtosecond regime in beta-barium borate by use of the Z-scan technique. Large nonlinear phase shifts can be obtained near the second-harmonic-generation phasematching condition for a Ti:sapphire laser. Solution of the nonlinear propagation equations for femtosecond pulses yields good agreement with experiment and also demonstrates that the description of cascaded effects by an effective nonlinear refractive index is no longer valid in the ultrafast domain and that these effects are less efficient for ultrashort pulses. The cascade-induced negative nonlinear phase shift in beta-barium borate is shown to be responsible for the self-compression observed in a prismless femtosecond visible optical parametric oscillator.

Selection of Epstein-Barr virus specific cytotoxic T lymphocytes can be performed with B lymphoblastoid cell lines created in serum-free media

Epstein-Barr Virus (EBV)-transformed B lymphoblastoid cell lines (BLCL) are currently used for numerous applications in cellular immunology. Where protocols destined for clinical application are concerned, the final choice of assay is made according to a risk/benefit ratio analysis. In this balance the use of xenogenic or allogenic serum has always been a major concern, as it carries both an infectious and an immunological risk. So far, it is unknown whether serum can be omitted from the entire BLCL selection procedure. In addition, as BLCL have been described as heterogeneous, serum deprivation may affect their antigen-presenting capacity. In the present study, BLCL were generated in the absence or presence of fetal calf serum (referred to as BLCL0 or BLCL(FCS), respectively). Next, in order to assess the antigen-presenting capacity of these cells, we compared the ability of BLCL0 and BLCL(FCS) cells to stimulate the EBV-specific repertoire of the corresponding donor's peripheral blood mononuclear cells in vitro. Our results showed that addition of serum was not essential for BLCL infection and culture, and that as far as we could determine, BLCL0 cells were as effective as BLCL(FCS) in reactivating the EBV-specific T-cell repertoire in vitro. Notably, FCS-specific T-lymphocytes can be detected among the BLCL(FCS)-specific CD4+-CTL. Not only was this latter observation unexpected for an EBV-seropositive donor, but it implied that the BLCL had captured and processed the corresponding FCS-derived solubles antigens; taken together our results emphasized the interest of the possibility to generate BLCL0, both for research and for clinical applications.

A model for thermal exchange in axons during action potential propagation

Several experiments have shown that during propagation of the action potential in axons, thermal energy is locally exchanged. In this paper, we use a simple model based on statistical physics to show that an important part of this exchange comes from the physics of the effusion. We evaluate, during the action potential propagation, the variation of internal energy and of the energy associated with the chemical potential of the effusion of water and ions to extract the thermal energy exchanged. The temperature exchanged is then evaluated on the area where the action potential is active. Results give a good correspondence between experimental work and this model, showing that an important part of the thermal energy exchange comes from the statistical cooling power of the effusion.

Viral DNA contamination is responsible for Epstein-Barr virus detection in cytotoxic T lymphocytes stimulated in vitro with Epstein-Barr virus B-lymphoblastoid cell line

Epstein-Barr virus (EBV)-transformed B-lymphoblastoid cell lines (LCLs) are used to prepare human EBV-specific T lymphocytes (EBV-CTL) in vitro. Within an LCL, up to 5-7% the cells release infectious EBV, and this has fostered safety concerns for therapeutic applications because of the exposure of T cells to EBV. The release of infectious viruses can be prevented by ganciclovir, but this drug may seriously affect LCL growth. In the wake of these concerns, the present work was designed to compile safety data on EBV-CTL preparation for the purpose of submission to a regulatory agency. We showed that further to supernatant exclusion, the number of EBV genome copies (EBVc) associated with the EBV-CTL always made up a constant proportion of the EBVc number detected in the culture supernatant. In addition, such was the case whether infectious virus could be produced by the LCL or not, suggesting that the EBV signal detected was due to a DNA contamination rather than an infection. Furthermore, we demonstrated that the number of EBVc associated with the EBV-CTL was highly sensitive to DNAse treatment, and finally that EBVc could no longer be detected after the EBV-CTL had been amplified in the absence of LCL. Consequently, during in vitro EBV-CTL preparation, either T cells cannot be infected or they die rapidly after EBV infection.

T cell repertoire and Epstein-Barr virus-specific T cell response in chronic active Epstein-Barr virus infection: a case study

In a patient with chronic active Epstein-Barr virus infection associated with vasculitis and fulminant CD4+ T cell lymphoproliferative disorder, we probed the peripheral blood mononuclear cells (PBMC) for the presence of an EBV-specific T cell repertoire and tested the possible relationship between the lymphocytic infiltrate and the EBV-specific T cell response. Our results give credence to the presence of an apparently normal EBV-specific memory T cell response after in vitro reactivation of the patient's PBMC with autologous infected B lymphoblastoid cell lines. In keeping with the characterization of the vasculitis, certain T cell subsets were detected after expansion of skin lesion-infiltrating lymphocytes and were found to be infected with EBV. These particular T cell expansions were neither the effectors nor the targets of the in vitro reactivated EBV-specific T cells, thus excluding a simple relationship between EBV, the skin lesions, and the T cell expansions frequently observed in these patients.

Preparation of Genetically Homogeneous Antigen-Specific Thymidine Kinase Positive T-Lymphocyte Clones for the Control of Alloreactivity Post-Bone Marrow Transplantation

We have previously proposed the use of HLA-specific T-cell clones transduced with a suicide gene to produce an allogeneic effect that can be controlled after allogeneic bone marrow transplantation. Procedures described so far to obtain specific T-cells transduced with a suicide gene have led to the recovery of heterogeneous polyclonal T-cells with a limited level of purity. We have therefore developed an approach to select specific T-cell clones in which the suicide transgene is inserted at a unique site of the genome, and used it to produce CD(+)-cytotoxic HLA-DP-specific T-cell clones. Immunization was performed by a one-way mixed lymphocyte culture and responder T lymphocytes were transduced at day 16, 6 days after the second stimulation. Transductions were carried out using gibbon ape leukemia virus (GALV)-pseudotyped retroviral particles harboring a bicistronic Thy-1/TK vector produced by TEFLY GA16-pKM4 clone 34 packaging cells. Three to 5 days later, CD90 immunomagnetic selection and cloning were performed on the transduced T cells. Our results demonstrate that this procedure led to the recovery of T-cell clones, the majority of which had the expected specificity and a single site of transgene insertion. Such clonotransgenic T-cell populations represent suitable tools to drive a defined alloreaction that can be controlled after bone marrow transplantation.

The risk of COVID-19 in IBD patients is increased by urban living and is not influenced by disease activity or intravenous biologics

Background

Patients with inflammatory bowel disease (IBD) may have a modified immune response to SARS-CoV-2. The objectives were to evaluate the prevalence of COVID-19 in patients treated with infliximab or vedolizumab, to analyze the factors associated with the infection, the impact of treatments and trough levels.

Methods

Patients with IBD treated with intravenous biologics in 14 French centers were included between March and June 2020 and followed-up for 6 months. Blood samples were collected for serologies and trough levels. The analysis of factors associated with COVID-19 was conducted in a matched 1:1 case-control sub-study with positive patients.

Results

In total, 1026 patients were included (74.9% infliximab). Over the follow-up period, 420 patients reported the occurrence of COVID-19 symptoms; 342 had been tested of whom 18 were positive. At the end of follow-up, 38 patients had a positive serology. Considering both nasal tests and serologies together, 46 patients (4.5%) had been infected. The risk of COVID-19 was related neither to the use of treatments (whatever the trough levels) nor to disease activity. Infections were more frequent when using public transport or living in flats in urban areas.

Conclusions

The prevalence rate of COVID-19 in this IBD population treated with intravenous infliximab or vedolizumab was the same as the one in the French population before the start of the vaccination campaign. The risk was increased by urban living and was not influenced by disease activity or biologics. Sanitary barrier measures remain the best way to protect against SARS-CoV-2 in patients with IBD in biological therapy.