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Alphaviruses are emerging positive-stranded RNA viruses which replicate and transcribe their genomes in membranous organelles formed in the cell cytoplasm. The nonstructural protein 1 (nsP1) is responsible for viral RNA capping and gates the replication organelles by assembling into monotopic membrane-associated dodecameric pores. The capping pathway is unique to Alphaviruses; beginning with the N 7 methylation of a guanosine triphosphate (GTP) molecule, followed by the covalent linkage of an m 7 GMP group to a conserved histidine in nsP1 and the transfer of this cap structure to a diphosphate RNA. Here, we provide structural snapshots of different stages of the reaction pathway showing how nsP1 pores recognize the substrates of the methyl-transfer reaction, GTP and S-adenosyl methionine (SAM), how the enzyme reaches a metastable postmethylation state with SAH and m 7 GTP in the active site, and the subsequent covalent transfer of m 7 GMP to nsP1 triggered by the presence of RNA and postdecapping reaction conformational changes inducing the opening of the pore. In addition, we biochemically characterize the capping reaction, demonstrating specificity for the RNA substrate and the reversibility of the cap transfer resulting in decapping activity and the release of reaction intermediates. Our data identify the molecular determinants allowing each pathway transition, providing an explanation for the need for the SAM methyl donor all along the pathway and clues about the conformational rearrangements associated to the enzymatic activity of nsP1. Together, our results set ground for the structural and functional understanding of alphavirus RNA-capping and the design of antivirals.

Alphaviruses are emerging positive stranded RNA virus which replicate and transcribe their genomes in membranous organelles formed in the cell cytoplasm. The non-structural protein 1 (nsP1) is responsible for RNA capping and the gating of replication organelles by assembling into monotopic membrane-associated dodecameric pores (Jones R. et al. Nature 2021). The capping path is unique for Alphavirus; beginning with the N7 methylation of a GTP molecule, followed by the covalent linkage of a m7GMP group to a conserved histidine in nsP1 and the transfer of this cap structure to a diphosphate RNA (Ahola T. et al. PNAS 1995). Here we provide structural snapshots of different stages of the reaction pathway showing how nsP1 pores recognize the substrates of the methyl-transfer reaction, GTP and SAM, how it reaches a metastable post-methylation state with SAH and m7GTP in the active site, the subsequent covalent transfer of m7GMP to nsP1 and post-reaction conformational changes triggering the opening of the pore. In addition, we biochemically characterize the capping reaction, demonstrating specificity for the RNA substrate and the reversibility of the cap transfer resulting in decapping activity and the release of intermediates of the reaction. Our data identify the molecular determinants allowing each pathway transition, provide explanation for the need for the SAM methyl donor all along the pathway and new clues about the conformational rearrangements associated to the enzymatic activity of nsP1. Together our results set new ground for the structural and functional understanding of alphavirus RNA-capping and the design of antivirals.Significance statementHere we present biochemical and structural characterization of the capping pathway carried out by the Chikungunya virus nsP1 capping pores. We provide five Cryo-EM structures representative of the different steps of the reaction. These structures reveal the molecular determinants and dynamics associated with the alphavirus capping process. In addition, we biochemically show the RNA capping specificity and the reversibility of the reaction which allow nsP1 to cap and decap RNAs and to release intermediates of the reaction. These data provide a new biochemical clues on the enzymatic activity of nsP1 capping pores and a new structural landscape that will be instrumental for the design of effective antivirals targeting the viral RNA capping for blocking the infection.

SummaryThe yeast Ty1 retrotransposon integrates upstream of genes transcribed by RNA polymerase III (Pol III). Specificity of integration is mediated by an interaction between the Ty1 integrase (IN1) and Pol III, currently uncharacterized at the atomic level. Here, we report cryo-EM structures of Pol III in complex with IN1, revealing a 16-residue segment at the IN1 C-terminus that contacts Pol III subunits AC40 and AC19, an interaction that we validate by in vivo mutational analysis. Unexpectedly, IN1 binding associates with insertion of subunit C11 C-terminal Zn-ribbon into the Pol III funnel, which provides atomic evidence for a two-metal mechanism during RNA cleavage. Moreover, unstructured regions of subunits C53 and C37 reorganize close to C11, likely explaining the connection between the C37/C53 heterodimer and C11 during transcription reinitiation. Our results suggest that IN1 binding induces a Pol III configuration that favors chromatin residence, thus improving the likelihood of Ty1 integration.

Introduction Tisagenlecleucel (tisa-cel) is a second generation, CD19-targeted Chimeric Antigen Receptor (CAR) T-cell therapy for relapsed or refractory (R/R) large B-cell lymphoma (LBCL). The pivotal phase 2 trial JULIET included 93 patients and reported an overall response rate (ORR) of 52% and a complete response rate of 40% among treated patients. However, very little is known regarding its safety and efficacy in the commercial or real-world setting as well as from an intention-to-treat perspective. In our study, we report clinical outcomes of patients with R/R LBCL treated with commercial tisa-cel in 10 Spanish institutions. Methods Data were collected retrospectively from all consecutive patients with R/R LBCL who underwent apheresis for tisa-cel at a Spanish site from December 2018 until June 2020. Evaluable patients included those who received a CAR-T infusion and had at least 1 month of follow-up. Adverse events after infusion were graded according to the ASTCT consensus and efficacy outcomes were assessed according to the Lugano criteria. Efficacy outcomes were calculated in the patients who received a CAR T-cell infusion and in all patients who underwent apheresis for tisa-cel (intention-to-treat). Results During the study period 91 patients with R/R LBCL underwent apheresis for tisa-cel. At the study cutoff, 69 (76%) patients had received a CAR T-cell infusion whereas 22 (24%) had not due to progressive disease (n=10, 45%), pending manufacturing process (n=7, 32%), out of specification (OOS) or manufacturing failure (n=4, 18%), or others (n=1, 5%). Sixty-one patients had at least the first disease response evaluation at 1-month post-infusion. Baseline characteristics of the whole cohort and the infused patients are summarized in Table 1. Among infused patients, median age was 57 years (range 24-77) and 65% were male. Most of the patients had a high-risk International Prognostic Index score (62%), an advanced stage at diagnosis (91%) and were refractory to the previous therapy (80%). Median follow-up after CAR T-cell infusion was 4 months (1-16). Fifty-six patients (81%) received bridging therapy before infusion, including chemotherapy in most cases (n=51, 91%). All patients received fludarabine and cyclophosphamide as lymphodepleting chemotherapy. Median time from apheresis to infusion was 53 days (range 29-225). Median infused cell dose was 2.2 x 108 CAR positive viable T-cells (range 0.4-4.2 x 108). Eleven (16%) products were considered OOS although 45% of them were infused. Among the infused patients, 47 (68%) and 9 (13%) developed any grade of cytokine release syndrome (CRS) and neurotoxicity, respectively. Grade >2 CRS and neurotoxicity events occurred in 3 (4%) and 0 patients, respectively. Tocilizumab was administered to 21 (30%) patients and steroids to 13 (19%) patients. Nine (13%) patients required admission to the Intensive Care Unit. By day 100, 2 (3%) patients experienced non-relapse mortality. Other adverse events including infections and tumor lysis syndrome are summarized in table 2. Best response achieved among the infused patients included complete remission in 17 (28%) patients and partial remission in 22 (36%) patients, with an ORR of 64%. Stable disease and progressive disease were the best response in 4 (7%) and 18 (29%) patients, respectively. Considering all patients who underwent apheresis, CR and PR were obtained in 19% and 24% (ORR 43%), respectively. Median progression-free survival (PFS) and overall survival (OS) for infused patients were 3 months (95%CI 2.1-3.4) and 8 months (95%CI 5.7-10.8), respectively. In the univariate analysis, patients with ECOG score >1 (HR 4.3 95%CI 1.5 - 40.9) (p < 0.001) and IPI score >2 (HR 4.8 95%CI 1.6 - 14.4) (p = 0.002) were associated with lower PFS while an ECOG score >1 was also associated with lower OS (HR 3.4 95%CI 1.15 - 34.4) (p = 0.04). In the intention-to-treat analysis for all patients who underwent apheresis, median PFS and OS from apheresis were 4 months (95%CI 2.8-5.8) and 9 months (95%CI 5.8-11.8), respectively. Conclusions Treatment with tisa-cel was able to induce disease response with a good toxicity profile in a population of patients with LBCL treated in a European country. Poor performance status at the time of CAR T-cell infusion was associated with lower PFS and OS. Disclosures Iacoboni: Novartis, Gilead, Celgene, Roche: Honoraria. Guerreiro:Novartis: Honoraria. Mussetti:Novartis, Gilead: Honoraria, Research Funding. Sancho:Roche, Janssen, Celgene, Novartis, Gilead, Sandoz, Mundipharma y Takeda; Advisory y/o consultor para Roche, Janssen, Celgene, Novartis, Gilead, Sandoz, Celltrion y Kern-Pharma.: Honoraria. Hernani:Gilead: Honoraria. Sureda Balari:Takeda: Consultancy, Honoraria, Speakers Bureau; Celgene/Bristol-Myers Squibb: Consultancy, Honoraria; Merck Sharpe and Dohme: Consultancy, Honoraria, Speakers Bureau; Sanofi: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Gilead/Kite: Consultancy, Honoraria; Janssen: Consultancy, Honoraria; Incyte: Consultancy; Celgene: Consultancy, Honoraria; BMS: Speakers Bureau; Roche: Honoraria. Martin Garcia-Sancho:Celgene, Eusa Pharma, Gilead, iQuone, Kyowa Kirin, Roche, Morphosys: Consultancy; Roche, Celgene, Janssen, Servier, Gilead: Honoraria. Kwon:Jazz: Consultancy, Honoraria; Gilead: Consultancy, Honoraria; Novartis: Consultancy, Honoraria; Pfizer: Consultancy, Honoraria. Reguera:Celgene, Novartis: Consultancy; Novartis, Gilead: Honoraria. Barba:Novartis, Celgene, Gilead, Pfizer, Amgen, Roche: Honoraria.

Chikungunya virus (CHIKV) nonstructural protein 1 (nsP1) harbors the methyltransferase (MTase) and guanylyltransferase (GTase) activities needed for viral RNA capping and represents a promising antiviral drug target. We compared the antiviral efficacies of nsP1 inhibitors belonging to the MADTP, CHVB, and FHNA series (69-fluoro- homoneplanocin A [FHNA], its 39-keto form, and 69-b-fluoro-homoaristeromycin). Cell-based phenotypic cross-resistance assays revealed that the CHVB and MADTP series had similar modes of action that differed from that of the FHNA series. In biochemical assays with purified Semliki Forest virus and CHIKV nsP1, CHVB compounds strongly inhibited MTase and GTase activities, while MADTP-372 had a moderate inhibitory effect. FHNA did not directly inhibit the enzymatic activity of CHIKV nsP1. The first-oftheir- kind molecular-docking studies with the cryo-electron microscopy (cryo-EM) structure of CHIKV nsP1, which is assembled into a dodecameric ring, revealed that the MADTP and CHVB series bind at the S-adenosylmethionine (SAM)-binding site in the capping domain, where they would function as competitive or noncompetitive inhibitors. The FHNA series was predicted to bind at the secondary binding pocket in the ring-aperture membrane-binding and oligomerization (RAMBO) domain, potentially interfering with the membrane binding and oligomerization of nsP1. Our cell-based and enzymatic assays, in combination with molecular docking and mapping of compound resistance mutations to the nsP1 structure, allowed us to group nsP1 inhibitors into functionally distinct classes. This study identified druggable pockets in the nsP1 dodecameric structure and provides a basis for the rational design, optimization, and combination of inhibitors of this unique and promising antiviral drug target., K.K. was supported by the Marie Sklodowska-Curie ETN European Training Network “ANTIVIRALS” (EU grant agreement 642434). M.G.G. was supported by funding from the Oncode Institute, the Netherlands. R.J. and J.R. were supported by the ATIP-Avenir program and the Bettencourt Shueller Foundation. M.-J.P.-P. acknowledges the financial support of AEI (grant PID2019-105117RR-C22).

International audience

Positive-sense single-stranded RNA viruses, such as coronaviruses, flaviviruses and alphaviruses, carry out transcription and replication inside virus-induced membranous organelles within host cells1,2,3,4,5,6,7. The remodelling of the host-cell membranes for the formation of these organelles is coupled to the membrane association of viral replication complexes and to RNA synthesis. These viral niches allow for the concentration of metabolites and proteins for the synthesis of viral RNA, and prevent the detection of this RNA by the cellular innate immune system8. Here we present the cryo-electron microscopy structure of non-structural protein 1 (nsP1) of the alphavirus chikungunya virus, which is responsible for RNA capping and membrane binding of the viral replication machinery. The structure shows the enzyme in its active form, assembled in a monotopic membrane-associated dodecameric ring. The structure reveals the structural basis of the coupling between membrane binding, oligomerization and allosteric activation of the capping enzyme. The stoichiometry—with 12 active sites in a single complex—redefines viral replication complexes as RNA synthesis reactors. The ring shape of the complex implies it has a role in controlling access to the viral organelle and ensuring the exit of properly capped viral RNA. Our results provide high-resolution information about the membrane association of the replication machinery of positive-sense single-stranded RNA viruses, and open up avenues for the further characterization of viral replication on cell membranes and the generation of antiviral agents., This work has been supported by the Bettencourt Shueller Fondation and an ATIP-Avenir grant (CNRS/INSERM).

B ackground: ARI0002h is an academic autologous CAR T-cell product with a 4-1BB co-stimulatory domain and a humanized single chain variable fragment targeting BCMA, which is being tested in the CARTBCMA-HCB-01 clinical trial for patients (pts) with RRMM (NCT04309981). A fractionated infusion of 3x10 6 CAR+ cells (ARI0002h)/kg (10/30/60%) was administered after lymphodepletion regimen (LR). A second dose of 3x10 6 CAR+ cells/kg was planned starting at 4 months after the first dose, with or without LR according to persistence of CAR-T in peripheral blood (PB). Clinical results have been submitted in a separate abstract (#147188); here we present the correlative biological studies performed and related to disease response. Methods: ARI0002h production data were obtained and analyzed, including % CAR transduction in the final product (FP) by flow cytometry (FC). PB samples were obtained at inclusion and sequentially after infusion. Bone marrow (BM) samples were obtained at inclusion, at d28, d100 and at 6 months (m), to evaluate BCMA expression on plasma cells (PCs) and minimal residual disease (MRD) by next generation flow (NGF) with 10 -6 sensitivity. Apheresis, FP, and PB/BM samples on d28 were analyzed for T-cell subpopulations and surface markers. Persistence of ARI0002h was evaluated in PB after infusion by PCR. If a second infusion was administered, CART detection after 3 and 7d was also checked. Plasmatic soluble BCMA (sBCMA) was determined by ELISA prior to infusion, at d28 and if a relapse was observed. Human anti-human antibodies (HAHAs) were evaluated at d100 (using FC on transduced HEK cells). Clinical and response data were collected for analysis. Results: Mean BCMA molecules/cell on malignant BM PC at inclusion were 1306 (SD ±889) with non-significant (NS) correlation with response at d100. Thirty-three apheresis were obtained and transduced, with a median manufacturing time of 11d (range 9-14). All FP were successfully obtained at first attempt but one, which could be produced with a second apheresis. The mean % transduction of ARI0002h on autologous T cells was 56% (SD ±25). A higher CD4/CD8 ratio in the apheresis was correlated with achievement of stringent complete response (sCR) (p=0.003); this association was not observed in the FP. Moreover, T-cell subpopulations in the FP did not correlate with response (Figure 1A). A significant increase of PD-1 (p=0.0001), TIGIT (p=0.037) and LAG3 (p=0.003) expression was observed in CD4 CAR-T cells, as well as PD-1 in CD8 (p=0.0001), between the FP and d28 PB paired samples; similar results were observed in BM CAR-T cells at d28, except for LAG3 (Figure 1B). ARI0002h CAR-T cells showed maximum PB expansion at 14d (range 7d - 5m). Among pts with 3 and 6 m follow-up, 54% and 24% had evidence of CAR+ T cells in PB, with a median persistence of 4m (range 2-not reached). Expansion levels by PCR and PB persistence did not correlate with MM response. 22 out of 27 eligible pts (81%) received a 2 nd dose, with a subsequent CART expansion in 10 of 20 (50%) evaluable pts; LR was readministered in only 30% of these 10 pts. B-cell aplasia was observed in all pts concurring with CART expansion (Figure 1C). Also, a decline in B-cell counts was observed in some pts after reinfusion, with no association with response. Patients with detectable sBCMA at inclusion became sBCMA negative in all the subsequent tested samples at d28 and d100. None of these pts have relapsed. 27 pts had MRD assessed at day +100. In 3, the BM was severely hemodiluted and inadequate for MRD testing. Of 24 MRD-evaluable pts, 22 (92%) were MRD-negative (59% were negative at a sensitivity of 1x10 -6, 36% at 1x10 -5 and 5% at 1x10 -4), and 2 were MRD positive (one BCMA positive and another with BCMA undetermined result). Only 1 of 27 (4%) evaluable pts had positive HAHAs at day 100. CAR-T cells were undetectable at day 70 in this patient, but after receiving a 2 nd dose at m4 a short-lasted expansion was observed. Despite that, the patient deepened the response from partial response (PR) (d100) to very good PR (m6). Conclusion: ARI0002h production is fast and feasible. The peak of CART expansion occurs after 14d of infusion and also in some pts after reinfusion, regardless of LR, which suggests that LR may not be mandatory to allow further expansion after booster dose. Responses obtained are deep and construct immunogenicity seems to be low. Figure 1 Figure 1. Disclosures Gonzalez-Calle: BMS, Janssen, Amgen: Honoraria. Cabañas: Sanofi: Honoraria; BMS: Consultancy, Honoraria; Janssen: Consultancy, Honoraria. Reguera: Janssen, Kite/Gilead, Novartis: Speakers Bureau; BMS-Celgene, Novartis: Membership on an entity's Board of Directors or advisory committees. Rodríguez-Otero: Regeneron: Honoraria; Celgene-BMS, Janssen, Amgen, Sanofi, GSK, Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees. Rosinol: Janssen, Celgene, Amgen and Takeda: Honoraria. Moraleda: Pfizer: Other: Educational Grants, Research Funding; Sanofi: Other: Educational Grants, Research Funding; MSD: Other: Educational Grants, Research Funding; ROCHE: Consultancy, Honoraria, Other: Educational Grants, Research Funding; Takeda: Consultancy, Honoraria, Other: Educational Grants, Research Funding; Sandoz: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Other: Educational Grants, Research Funding; Gilead: Consultancy, Honoraria, Other: Educational Grants, Research Funding; Jazz Pharmaceuticals: Consultancy, Honoraria, Other: Educational Grants, Research Funding; NovoNordisk: Other: Educational Grants, Research Funding; Janssen: Other: Educational Grants, Research Funding; Celgene: Other: Educational Grants, Research Funding; Amgen: Other: Educational Grants, Research Funding. Prósper: Oryzon: Honoraria; Janssen: Honoraria; BMS-Celgene: Honoraria, Research Funding. Mateos: Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene - Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sea-Gen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria; GSK: Honoraria; Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; Bluebird bio: Honoraria; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Regeneron: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees. Paiva: Bristol-Myers Squibb-Celgene, Janssen, and Sanofi: Consultancy; Adaptive, Amgen, Bristol-Myers Squibb-Celgene, Janssen, Kite Pharma, Sanofi and Takeda: Honoraria; Celgene, EngMab, Roche, Sanofi, Takeda: Research Funding. Fernandez de Larrea: GSK: Honoraria; Takeda: Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; Sanofi: Consultancy; Janssen: Consultancy, Honoraria, Research Funding.

BACKGROUND AND OBJECTIVES CD19-directed chimeric antigen receptor (CAR)-T-cell therapy is associated with early cytopenia in approx. 80% of patients and late cytopenia in 40% of patients. To date, the transfusion profile of patients undergoing these therapies has not been described. Our objectives are: To define the transfusion profile of CAR-T therapy in our setting.To evaluate clinical variables related to the intensity and duration of cytopenias. METHODOLOGY This is an observational, prospective, single centre study. Adult patients with lymphoproliferative disorders and acute lymphoblastic leukaemia proposed for CAR-T therapy from August 2019 to March 2021 were included. RESULTS 68 patients were included in the CAR-T cell therapy program. Table 1 describes patients characteristics. Forty-seven received CART therapy, apheresis was not performed in 7 cases (progression n=6, withdrawal of consent n=1), product was not infused in 9 patients due to disease progression and 5 patients are awaiting infusion. Cytokine release syndrome (CRS) occurred in 79% of patients, 25% developed grade≥2 and median time to onset was 2 days (IQR, 1-4 days). Immune effector cell-associated neurotoxicity syndrome (ICANS) occurred in 33% of patients, 16% were grade≥3 and median time to onset was 7 days (IQR, 6-8 days). Median duration of hospital admission was 14 days (IQR, 12 to 21 days). None of the 47 infused patients had neutropenia or anemia in the transfusion range prior to lymphodepletion. 94% (44/47) developed grade ≥3 neutropenia, with a median duration of 14.5 days (IQR, 9.75 to 36 days). G-CSF was administered to 21 patients, with a median time on G-CSF of 115 days (IQR, 27-258 days). A total of 239 red blood cells units (RBC) have been transfused, median 3.5 RBC/patient (IQR, 0 to 7.5 RBC / patient). 70% of this consumption occurred in the first 30 days after infusion. Before CAR T cell infusion, 2 patients had a platelet count 20x10 9/L was 17 days (IQR, 4-54 days) and > 50x10 9/L was 39 days (IQR, 20-79 days). 62% of patients received ≤2 platelet concentrates (PC). However, 21% had long-term thrombocytopenia (> 30 days). This group received a median of 15 PC (IQR, 12-27). The amount of PC used was 198, 52% were administered in the first 30 days. Eltrombopag was indicated in 9 of the 25 patients with grade ≥3 thrombocytopenia, doses never exceeded 75 mg/day. No serious bleeding (WHO grade ≥2) was observed. Factors related to severe thrombocytopenia were female (74% vs 42%, p=0.036), CRS (61% vs 0%, p=0.019), ICANS (80% vs 43%, p=0.020) and use of steroids (92% vs 67%, p=0.003). We found no relationship with underlying disease or status, prior treatment lines, prior autologous transplantation, CAR-T product, duration of lymphopenia, time and duration of CRS or ICANS. With a median follow-up of 167 days (IQR, 73-303 days), 26% of patients died, causes of death were infections n=2 and disease progression n=10. Three months after the procedure, there were 30 evaluable patients for response and 64% remained in remission (47% CR, 17% PR). CONCLUSIONS A high percentage of patients receiving CAR T cell therapy present long-term cytopenias. Reserves of irradiated blood components must be foreseen. Development of CRS and ICANS could be prognostic factors for the development of long-term grade ≥3 thrombocytopenia. Studies are needed on the use of thrombopoietin receptor agonists to reduce the duration of thrombocytopenia, although effective doses could be higher than those used in idiopathic immune thrombocytopenia. Figure 1 Figure 1. Disclosures Reguera: Janssen, Kite/Gilead, Novartis: Speakers Bureau; BMS-Celgene, Novartis: Membership on an entity's Board of Directors or advisory committees. Perez-Simon: JANSSEN, TAKEDA, PFIZER, JAZZ, BMS, AMGEN, GILEAD: Other: honorarium or budget for research projects and/or participation in advisory boards and / or learning activities and / or conferences.

Background: ARI0002h is an academic lentiviral autologous second-generation CAR T-cell product with a 4-1BB co-stimulatory domain and a humanized single chain variable fragment targeting BCMA. In pre-clinical studies, ARI0002h has demonstrated potent in vitro and in vivo activity. Here, we report the first safety and efficacy results of the CARTBCMA-HCB-01 multicenter clinical trial for patients with relapsed/refractory multiple myeloma (RRMM) (NCT04309981) who received ARI0002h in 5 Spanish centers. Methods: Patients (pts) aged 18-75 years old with RRMM were eligible for this study if they had measurable disease, as assessed by M-protein or serum free light chain levels, received ≥2 prior regimens, including a proteasome inhibitor, an immunomodulatory drug (lenalidomide or pomalidomide) and an anti-CD38 antibody, and were refractory to the last line of treatment. Bridging therapy was allowed after apheresis. Cyclophosphamide (300 mg/m 2) and fludarabine (30 mg/m 2) on days -6 to -3 were used as lymphodepletion regimen. The targeted dose was 3x10 6/kg CAR+cells (range 1.2-3x10 6) and was administered in a fractionated manner (10%/30%/60%), with at least 24h between infusions. A second dose of 3x10 6 CAR+ cells/kg was planned at least 4 months after the first dose in pts who had any response and had not presented MM progression or serious complications after the first administration, with or without repeated lymphodepletion depending on the persistence of CAR-T cells. Primary objectives were overall response rate (ORR; at less partial response -PR-) within 3 months of the first infusion and rate of cytokine release syndrome (CRS) and/or neurological toxicity in the first 30 days. Response was assessed as per IMWG criteria and bone marrow minimal residual disease (MRD) was analyzed by next-generation flow. Adverse events (AEs) were graded using CTCAE v5.0. CRS and neurotoxicity were graded according to the American Society for Transplantation and Cellular Therapy (ASTCT) criteria. Results: As of July 19 th, 35 pts (median age 61 years) with RRMM were included in the trial. Four pts could not receive ARI-0002h due to MM progression before apheresis (2 pts) or treatment (2 pts) and one pt died of a fungal infection. Therefore, 30 pts received ARI0002h cells (modified intention-to-treat population), of which 47% received bridging therapy. The main characteristics of these pts and previous treatments are described in Table 1. Median CAR-T cell production time was 11 days (range 9-14) with a 100% manufacture success. Median follow-up after ARI0002h administration for surviving pts was 8 months (range 2-12). The ORR of 27 evaluable pts at 3 months was 96%, with a stringent complete remission (sCR) rate of 44.4% (Table 1) and very good partial response (VGPR) observed in 18.6% of pts. Median time to first response was one month. All pts achieved at least a PR and only one patient progressed after 4 months exclusively with extramedullary disease. Of 25 MRD-evaluable pts at day +100, 92% were MRD-negative. Median progression-free survival (PFS) and overall survival (OS) were not reached and the 6-month PFS and OS rates were 92.1% (Figure 1) and 95.8%, respectively. AEs reported in >70% of pts were CRS (87%; grade [gr] 3/4 0%; gr 1 73%), neutropenia (97%; gr 3/4 100%), anemia (85%; gr 3/4 43%), and thrombocytopenia (79%; gr 3/4 70%). Median duration of CRS was 4 days (range 1-12). No CAR-T cell-related neurotoxicity cases were reported. Tocilizumab and corticosteroids were administered in 76% (mainly for persistent grade 1 CRS) and 12% of pts, respectively. One death occurred due to unrelated causes (cranial traumatism). ARI0002h cells demonstrated peak expansion on day 14 (range 7-100 days). Among the pts with 3 and 6 months follow-up, 54% and 24% had measurable CAR+ T cells in peripheral blood, respectively. 22 out of 27 eligible pts (81%) have already received the second dose (range 1.2-3x10 6 CAR+ cells/kg). Median time after first infusion was 4 months; 36% received a second lymphodepletion. No relevant toxicities after second infusions were reported. Responses deepened over time and at 6 months, 5 pts who had reached PR achieved VGPR and one improved from VGPR to sCR. Conclusion: ARI0002h is the first European academic CAR T-cell for RRMM that has demonstrated excellent feasibility in a clinical trial, with deep and durable responses and a favorable safety profile, including the absence of neurotoxicity. Figure 1 Figure 1. Disclosures Fernandez de Larrea: Takeda: Honoraria, Research Funding; Amgen: Consultancy, Honoraria, Research Funding; BMS: Consultancy, Honoraria, Research Funding; GSK: Honoraria; Sanofi: Consultancy; Janssen: Consultancy, Honoraria, Research Funding. Gonzalez-Calle: BMS, Janssen, Amgen: Honoraria. Cabañas: Janssen: Consultancy, Honoraria; BMS: Consultancy, Honoraria; Sanofi: Honoraria. Rodriguez-Otero: Janssen: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Clínica Universidad de Navarra: Current Employment; Celgene-BMS: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Consultancy, Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Consultancy; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Kite: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria; Regeneron: Honoraria. Reguera: BMS-Celgene, Novartis: Membership on an entity's Board of Directors or advisory committees; Janssen, Kite/Gilead, Novartis: Speakers Bureau. Corral: Novartis: Consultancy; Gileqd: Honoraria; Gilead: Consultancy. Paiva: Bristol-Myers Squibb-Celgene, Janssen, and Sanofi: Consultancy; Adaptive, Amgen, Bristol-Myers Squibb-Celgene, Janssen, Kite Pharma, Sanofi and Takeda: Honoraria; Celgene, EngMab, Roche, Sanofi, Takeda: Research Funding. Rosinol: Janssen, Celgene, Amgen and Takeda: Honoraria. Ortiz-Maldonado: Kite, Novartis, BMS, Janssen: Honoraria. Perez-Simon: JANSSEN, TAKEDA, PFIZER, JAZZ, BMS, AMGEN, GILEAD: Other: honorarium or budget for research projects and/or participation in advisory boards and / or learning activities and / or conferences. Prósper: BMS-Celgene: Honoraria, Research Funding; Janssen: Honoraria; Oryzon: Honoraria. Moraleda: Pfizer: Other: Educational Grants, Research Funding; Sanofi: Other: Educational Grants, Research Funding; MSD: Other: Educational Grants, Research Funding; ROCHE: Consultancy, Honoraria, Other: Educational Grants, Research Funding; Takeda: Consultancy, Honoraria, Other: Educational Grants, Research Funding; Sandoz: Consultancy, Honoraria; Novartis: Consultancy, Honoraria, Other: Educational Grants, Research Funding; Gilead: Consultancy, Honoraria, Other: Educational Grants, Research Funding; Jazz Pharmaceuticals: Consultancy, Honoraria, Other: Educational Grants, Research Funding; NovoNordisk: Other: Educational Grants, Research Funding; Janssen: Other: Educational Grants, Research Funding; Celgene: Other: Educational Grants, Research Funding; Amgen: Other: Educational Grants, Research Funding. Mateos: Adaptive Biotechnologies: Honoraria, Membership on an entity's Board of Directors or advisory committees; GSK: Honoraria; Bluebird bio: Honoraria; Oncopeptides: Honoraria, Membership on an entity's Board of Directors or advisory committees; Sea-Gen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Roche: Honoraria, Membership on an entity's Board of Directors or advisory committees; Oncopeptides: Honoraria; Regeneron: Honoraria, Membership on an entity's Board of Directors or advisory committees; Takeda: Honoraria, Membership on an entity's Board of Directors or advisory committees; Amgen: Honoraria, Membership on an entity's Board of Directors or advisory committees; Celgene - Bristol Myers Squibb: Honoraria, Membership on an entity's Board of Directors or advisory committees; AbbVie: Honoraria; Sanofi: Honoraria, Membership on an entity's Board of Directors or advisory committees; Pfizer: Honoraria, Membership on an entity's Board of Directors or advisory committees; Janssen: Honoraria, Membership on an entity's Board of Directors or advisory committees.

Introduction: Axicabtagene ciloleucel (axi-cel) and tisagenlecleucel (tisa-cel) are the two autologous anti-CD19 chimeric antigen receptors T cells commercially approved in Europe for relapsed/refractory (R/R) DLBCL. We performed a retrospective study to evaluate patients characteristics, efficacy and safety for axi-cel and tisa-cel in a large cohort of patients within the GETH-TC (Spanish Group of Stem Transplantation and Cell Therapy)-GELTAMO (Spanish Group of Lymphoma and Autologous Stem Cell Transplantation). Methods: Ten Spanish centers contributed data. Data were collected retrospectively from consecutive patients with DLBCL in whom apheresis was performed for axi-cel or tisa-cel treatment. CRS and ICANS were graded with the ASTCT consensus criteria. Response was assessed according to the Lugano criteria. Patients included had at least 30 days of follow-up. Results: A total of 268 patients with R/R DLBCL underwent apheresis for axi-cel (n=123) and tisacel (n=145) from Nov-2018 to May-2021, of which 232 (86%) received CART-cell infusion (n=110, 89% and n=122, 84%, respectively). Reasons for not undergoing infusion were progression in 10 cases, tumor lysis syndrome in 1, infection in 1, and CR after bridging therapy in 1 for the axi-cel cohort, and progression in 21 (4 after manufacture failure), psychiatric disorder in 1, and post-apheresis cerebral hemorrhage in 1 case for the tisa-cel cohort. Time between apheresis and infusion was 41 days (IQR 40-56) and 49 days (IQR 46-62) (p=0.006), respectively. Characteristics at baseline, apheresis and at lymphodepletion are summarized in Tables 1 and 2. Median age was 60 (range 19-79), 61% of patients were male, most of them treated for DLBCL NOS (66%). There were no significant differences between patients intended to be treated with axi-cel and tisa-cel. 82% of the infused patients received bridging therapy. At apheresis and at lymphodepletion ECOG performance status score was 0-1 in 93% and 91%, and 7 and 32 patients were in response, respectively. The overall response rates (ORRs) at 1 month and 3 months were 65% and 56%, respectively, with 34% and 45% achieving a complete response (CR), respectively. In the intention-to-treat analysis, with a median follow-up of 9 months (IQR 5-15), EFS and OS at 9 months was 44% (95%CI 38-51)(Figure 1) and 59% (95%CI 53-66) with a median EFS and OS of 6 months and 11 months, respectively. At lymphodepletion, characteristics of infused patients and disease were not significantly different between axi-cel and tisa-cel cohorts. Rates of CRS, CRS grade 3-4, ICANS, ICANS grade 3-4 were 89% and 71% (p=0.001), 10% and 7% (p=0.34), 42% and 16% (p=0.001), 20% and 4% (p=0.001) for the axi-cel and tisa-cel cohorts, respectively. ICU admission was needed in 25% and 15% of patients (p=0.06), respectively. Non-relapse mortality at days 100 were 2.5% and 1.4%, and at day 180, 5.4% and 2.2% (p=0.08) for the axi-cel and tisa-cel groups, respectively. With a median follow-up of 8 months for patients who received infusion with axi-cel and 12 months for patients infused with tisa-cel, EFS and OS at 12 months were 48% and 33% (p=0.33), and 53% and 50% (p=0.27), respectively, with a median EFS of 11 and 6 months and a median OS of 13 and 12 months, respectively. In the multivariate analysis, the only factor associated with poor PFS was having ECOG-PS ≥2 at lymphodepletion (HR13, p=0.03). No factors were identified as associated independently to OS. Factors associated to CRS grade 3-4 were IPI score 4-5 at lymphodepletion (OR 1.4, p=0.03) and ECOG-PS ≥2 at apheresis (OR 1.5, p=0.03). For ICANS grade 3-4, factors associated were the use of axi-cel (OR 8, p=0.04) and diagnosis of HG double/triple hit lymphoma (OR 9, p=0.022). Conclusions:This multicentric analysis describes one of the largest real-life cohorts of patients treated with axi-cel and tisa-cel for R/R aggressive B cell lymphoma in Europe. Results are comparable to those from the pivotal studies and other large real-life experiences. Up to now, patients included for one or other product in Spain do not differ significantly in terms of baseline characteristics, and within this setting, results are comparable between both products in terms of efficacy. The use of axi-cel was associated to higher rates of CRS and especially, severe forms of ICANS. However, mortality associated to toxicity were low and not significantly different between both cohorts. Figure 1 Figure 1. Disclosures Kwon: Novartis, Celgene, Gilead, Pfizer: Consultancy, Honoraria. Iacoboni: BMS/Celgene, Gilead, Novartis, Janssen, Roche: Honoraria. Reguera: Janssen, Kite/Gilead, Novartis: Speakers Bureau; BMS-Celgene, Novartis: Membership on an entity's Board of Directors or advisory committees. Lopez Corral: Gilead, Novartis: Consultancy, Honoraria. Guerreiro: Novartis, Gilead: Consultancy, Honoraria. Caballero: Novartis, Gilead: Honoraria. Ortiz-Maldonado: Kite, Novartis, BMS, Janssen: Honoraria. Sanchez: Janssen, Jazz Pharmaceuticals, Gilead, Novartis, Amgen: Consultancy. Sancho: Roche, Janssen, Celgene-BMS, Gilead, Novartis, Takeda: Honoraria, Speakers Bureau; Roche, Janssen, Celgene-BMS, Gilead, Novartis, Incyte, Beigene: Speakers Bureau. Bastos-Oreiro: Janssen: Honoraria, Speakers Bureau; F. Hoffmann-La Roche: Honoraria, Research Funding, Speakers Bureau; Takeda: Speakers Bureau; Novartis: Honoraria, Speakers Bureau; BMS-Celgene: Honoraria, Speakers Bureau; Gilead: Honoraria; Kite: Speakers Bureau. Oarbeascoa: Gilead: Honoraria, Speakers Bureau. Mussetti: Gilead: Other: Unspecified, Research Funding; Novartis: Honoraria, Other: Unspecified; Takeda: Honoraria. Bailen: Gilead, Pfizer: Speakers Bureau. Martin Garcia-Sancho: Takeda: Honoraria; Novartis: Consultancy; Incyte: Consultancy; Celgene/BMS: Consultancy; Celgene: Honoraria, Other: travel; Roche: Consultancy, Honoraria, Other: Travel/Accommodations/Expenses; Janssen: Honoraria, Research Funding; Servier: Consultancy, Honoraria, Other: Travel/Accommodations/Expenses; Gilead: Consultancy, Honoraria; Morphosys: Consultancy; Kyowa Kirin: Consultancy; Clinigen: Consultancy; Eusa Pharma: Consultancy; Kern Pharma: Other: TRAVEL, ACCOMMODATIONS, EXPENSES (paid by any for-profit health care company). Barba: Amgen, Celgene, Gilead, Incyte, Jazz Pharmaceuticals, MSD, Novartis, Pfizer and Roche, Jazz Phar,aceuticals: Honoraria; Cqrlos III heqlth Institute, aSOCIACION espanola contra el cancer, PERIS: Research Funding.

Background: Chimeric antigen receptor-engineered (CAR) T-cell therapy remains associated with significant toxicities including cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome (ICANS). Recently, the recombinant IL-1 receptor antagonist anakinra has emerged as a promising approach after failure of tocilizumab and corticosteroids to treat CRS/ICANS (Norelli, Nat Med 2018; Giavridis, Nat Med 2018). Here, we describe the safety and efficacy of two anakinra dose regimens to treat refractory CRS and/or ICANS after CAR T-cell therapy. Methods: We retrospectively analyzed data from 26 patients with B-cell or plasma cell malignancies treated at 9 institutions with anakinra for CRS and/or ICANS after CAR T-cell therapy. Details regarding CAR T-cell product and disease type are shown in the Table. CRS/ICANS grade was determined by applying the ASTCT criteria at the time of peak symptom severity. We defined response to anakinra as an improvement in CRS and/or ICANS symptoms per the attending physician's evaluation. Results: Patients, disease, and CAR T-cell product are shown in the Table. Anakinra was administered at 100-200mg/day subcutaneously (SC) in 13 patients (pts) (50%; low-dose), or at 8mg/kg/day SC or intravenously (IV) in 13 pts (50%; high-dose). Most pts were treated with anakinra for steroid-refractory ICANS (n=23); two pts were treated for tocilizumab-refractory CRS (n=2) and one for both (n=1). All but one patient received anakinra concurrently with corticosteroids. Median peak CRS and ICANS grade by ASTCT criteria was 2 (range, 1-4), and 4 (range, 0-5), respectively. Median CRS and ICANS duration was 5 days (range, 1-10) and 15.5 days (range, 1-38), respectively. Median time from CAR T-cell infusion to anakinra initiation was 9 days (range, 5-31). The median duration of anakinra treatment was 8.5 days (range, 1-47). The median time to anakinra initiation from CRS or ICANS onset was comparable in pts receiving high-dose compared to low-dose anakinra (4 versus 4 days, respectively; p=0.8). Comparable peak CRS (median grade, 2 versus 2, p=0.9) and ICANS (median grade, 4 versus 4, p=0.2) were measured in both groups. Other toxicity-directed therapies were administered in 8 pts receiving low-dose anakinra (siltuximab, n=8; intrathecal chemotherapy, n=2, etoposide n=1). The only infectious event reported after anakinra initiation was HHV6 encephalitis (n=1). Two pts with infections confirmed prior to anakinra initiation died after anakinra treatment: CMV pneumonia (n=1), Escherichia coli bacteremia (n=1). In one patient the anakinra administration route was changed from SC to IV due to a subcutaneous hematoma; in one patient anakinra was discontinued due to elevated liver enzymes. We observed anti-tumor responses (partial or complete) to CAR T-cell therapy in 15 pts (58%; B-ALL, n=1/1; DLBCL, n=9/15; MCL, n=3/4; MM; n=1/1; PMBCL, n=1/3), including complete responses in 11 pts (42%). In high-dose anakinra pts, the ORR was 77% (complete response, 53%). CRS/ICANS improvement was observed after anakinra initiation in 73% of pts with a median duration of treatment of 3 days (range 1-7). Higher response rates were seen in pts who received high-dose compared to low-dose anakinra (100% versus 46%, respectively; p=0.005) and the non-relapse mortality rate at day 30 was significantly lower in pts treated with high-dose anakinra compared to low-dose anakinra (0% versus 69%; p=0.001%). In addition, a shorter time to anakinra initiation from CRS or ICANS onset was associated with CRS/ICANS improvement (median, 2 versus 5 days in responders versus non-responders, respectively; p=0.04). Conclusion After failure of tocilizumab and/or corticosteroids, early administration of high-dose anakinra (8mg/kg/day IV or SC) was associated with rapid resolution of CRS/ICANS symptoms after use of tocilizumab and/or corticosteroids, with a manageable toxicity profile, and with a non-relapse mortality rate at day 30 of 0%. In contrast, 38% of patients treated with low-dose anakinra died from infections. We observed complete responses to CAR T-cell therapy in pts treated with high-dose anakinra, suggesting limited impact on in vivo CAR-T cell function. In summary, high-dose anakinra is a feasible and promising approach after failure of conventional CRS and ICANS-directed therapies. Prospective trials of anakinra to prevent or treat CRS and ICANS are ongoing. Figure 1 Figure 1. Disclosures Barba: Amgen, Celgene, Gilead, Incyte, Jazz Pharmaceuticals, MSD, Novartis, Pfizer and Roche, Jazz Phar,aceuticals: Honoraria; Cqrlos III heqlth Institute, aSOCIACION espanola contra el cancer, PERIS: Research Funding. Iacoboni: BMS/Celgene, Gilead, Novartis, Janssen, Roche: Honoraria. Kwon: Novartis, Celgene, Gilead, Pfizer: Consultancy, Honoraria. Bailen: Gilead, Pfizer: Speakers Bureau. Reguera: Janssen, Kite/Gilead, Novartis: Speakers Bureau; BMS-Celgene, Novartis: Membership on an entity's Board of Directors or advisory committees. Corral: Gilead: Consultancy; Novartis: Consultancy; Gileqd: Honoraria. Ortiz-Maldonado: Kite, Novartis, BMS, Janssen: Honoraria. Maziarz: Allovir: Consultancy, Research Funding; Novartis: Consultancy, Other: Data and Safety Monitoring board, Research Funding; Vor Pharma: Other: Data and Safety Monitoring Board; Incyte Corporation: Consultancy, Honoraria; Bristol-Myers, Squibb/Celgene,, Intellia, Kite: Honoraria; Artiva Therapeutics: Consultancy; CRISPR Therapeutics: Consultancy; Omeros: Research Funding; Intellia: Honoraria; Athersys: Other: Data and Safety Monitoring Board, Patents & Royalties. Shadman: Mustang Bio, Celgene, Bristol Myers Squibb, Pharmacyclics, Gilead, Genentech, Abbvie, TG Therapeutics, Beigene, AstraZeneca, Sunesis, Atara Biotherapeutics, GenMab: Research Funding; Abbvie, Genentech, AstraZeneca, Sound Biologics, Pharmacyclics, Beigene, Bristol Myers Squibb, Morphosys, TG Therapeutics, Innate Pharma, Kite Pharma, Adaptive Biotechnologies, Epizyme, Eli Lilly, Adaptimmune , Mustang Bio and Atara Biotherapeutics: Consultancy. Green: Seagen Inc.: Research Funding; bristol myers squibb: Membership on an entity's Board of Directors or advisory committees, Patents & Royalties, Research Funding; Cellectar Biosciences: Research Funding; GSK: Membership on an entity's Board of Directors or advisory committees; Janssen Biotech: Membership on an entity's Board of Directors or advisory committees, Research Funding; Juno Therapeutics: Patents & Royalties, Research Funding; Legend Biotech: Consultancy; Neoleukin Therapeutics: Membership on an entity's Board of Directors or advisory committees; Seattle Genetics: Membership on an entity's Board of Directors or advisory committees, Research Funding; SpringWorks Therapeutics: Research Funding. Chow: ADC Therapeutics: Current holder of individual stocks in a privately-held company, Research Funding; AstraZeneca: Research Funding. Hirayama: Novartis: Honoraria; Bristol Myers Squibb: Honoraria. Maloney: Kite, a Gilead Company, Juno, and Celgene: Research Funding; A2 Biotherapeutics: Consultancy; BioLineRx, Juno, Celgene, Kite, a Gilead Company, Gilead, Novartis, and Pharmacyclics: Honoraria; A2 Biotherapeutics: Divested equity in a private or publicly-traded company in the past 24 months; Juno: Patents & Royalties. Turtle: AstraZeneca: Consultancy, Research Funding; Nektar Therapeutics: Consultancy, Research Funding; Precision Biosciences: Current holder of stock options in a privately-held company, Other: Scientific Advisory Board; Caribou Biosciences: Consultancy, Current holder of stock options in a privately-held company, Other: Scientific Advisory Board; Eureka Therapeutics: Current holder of stock options in a privately-held company, Other: Scientific Advisory Board; Arsenal Bio: Current holder of stock options in a privately-held company, Other: Scientific Advisory Board; Century Therapeutics: Consultancy, Other: Scientific Advisory Board; T-CURX: Other: Scientific Advisory Board; Myeloid Therapeutics: Current holder of stock options in a privately-held company, Other: Scientific Advisory Board; Asher Bio: Consultancy; Amgen: Consultancy; PACT Pharma: Consultancy; TCR2 Therapeutics: Research Funding; Juno Therapeutics/BMS: Patents & Royalties: Right to receive royalties from Fred Hutch for patents licensed to Juno Therapeutics, Research Funding; Allogene: Consultancy. Gauthier: Janssen: Membership on an entity's Board of Directors or advisory committees; Legend Biotech: Membership on an entity's Board of Directors or advisory committees; Multerra Bio: Consultancy; Larvol: Consultancy; JMP: Consultancy; Eusapharma: Consultancy.

Introduction Brexucabtagene autoleucel (brexu-cel) is a second generation, CD19-targeted Chimeric Antigen Receptor (CAR) T-cell therapy approved for relapsed or refractory (R/R) mantle cell lymphoma (MCL). The pivotal phase 2 trial ZUMA-2 enrolled 74 patients and infused 68, with an overall response rate (ORR) of 85% (complete response rate, 59%) among all patients who underwent apheresis (intention-to-treat, ITT). Grade 3 or higher cytokine release syndrome (CRS) and neurologic events occurred in 15% and 31% of patients, respectively. However, very little is known regarding its safety and efficacy in the real-world setting. In our study, we report clinical outcomes of patients with R/R MCL treated with commercial brexu-cel. Methods Data were collected retrospectively from all consecutive patients with R/R MCL who underwent apheresis for brexu-cel at 7 European sites, in 3 different countries, from start of the Compassionate Use Program in Europe (February 2020) until June 2021. Evaluable patients included those who received a CAR-T infusion and had at least 1 month of follow-up. Adverse events after infusion were graded according to the ASTCT consensus and efficacy outcomes were assessed according to Lugano criteria. Efficacy outcomes were calculated in the patients who received a CAR T-cell infusion and in all patients who underwent apheresis for brexu-cel (ITT). Results During the study period 28 patients with R/R MCL underwent apheresis for brexu-cel. At data cutoff, 19 (68%) patients had received a CAR T-cell infusion whereas 9 (32%) had not due to progressive disease (n=4), pending manufacturing process (n=4) or achieving a complete response with bridging (n=1). Baseline characteristics of the whole cohort and the infused patients are summarized in Table 1. Among infused patients, median age was 67 years (range 51-78) and 89% were male. Most of the patients had a high-risk simplified Mantle Cell Lymphoma International Prognostic Index score (63%), an advanced stage (84%) and 32% had received a prior autologous stem cell transplant. Median follow-up after CAR T-cell infusion was 5 months (range 1-10). Fifteen patients (79%) received bridging therapy after apheresis, including ibrutinib in 8/15 (53%) patients, immunochemotherapy in 7/15 (47%) and radiotherapy in 6/15 (40%). Half the patients (53%) had progressive disease as best response to bridging; 4 (27%) patients had stable disease, 2 (13%) partial response and 1 (7%) achieved a complete response. Median time from apheresis to brexu-cel delivery was 30 days (range 22-48) and median time from apheresis to infusion was 42 days (range 28-77). Among the infused patients, 17 (89%) and 12 (63%) developed any grade of CRS and neurotoxicity, respectively. Grade >2 CRS and neurotoxicity events occurred in 1 (5%) and 5 (26%) patients, respectively. Tocilizumab was administered to 16 (84%) patients and steroids to 12 (63%) patients. Two (11%) patients required admission to the Intensive Care Unit for grade 4 neurotoxicity and septic shock, respectively. At data cutoff, all infused patients were alive except for 1 patient who died due to progressive disease. Other adverse events are summarized in table 2. Best response achieved among the infused patients included complete remission in 13 (68%) patients and partial remission in 4 (21%) patients, with an ORR of 89%. Stable disease and progressive disease were the best response in 1 (5%) patient each. Median progression-free survival (PFS) and overall survival (OS) for infused patients were not reached with the current follow-up (Figure 1); estimated 6-month OS was 91% (95%CI 50.8-98.6) and 6-month PFS was 83% (95%CI 55.4-94.2). Three (16%) patients progressed at days 14, 33 and 90 post-infusion. In the univariate analysis, the percentage of patients with complete response was consistent across key subgroups with high-risk features (including blastoid morphology and TP53 mutation). Response rate and survival analysis by ITT will be presented at the meeting when all products still undergoing manufacturing are complete. Conclusion This multicenter, international study confirms that treatment with brexu-cel in patients with R/R MCL in the real-world setting has very promising efficacy, including in high-risk patients. The early safety profile was manageable and similar to the pivotal trial. Longer follow-up is needed to better assess long-term efficacy and ITT analysis. Figure 1 Figure 1. Disclosures Iacoboni: BMS/Celgene, Gilead, Novartis, Janssen, Roche: Honoraria. Chiappella: Takeda: Other: advisory board; Clinigen: Other: lecture fee, advisory board; Novartis: Other: lecture fee; Gilead Sciences: Other: lecture fee, advisory board; Janssen: Other: lecture fee, advisory board; Roche: Other: lecture fee, advisory board; Servier: Other: lecture fee; Celgene Bristol Myers Squibb: Other: lecture fee, advisory board; Astrazeneca: Other: lecture fee; Incyte: Other: lecture fee. Corral: Gileqd: Honoraria; Gilead: Consultancy; Novartis: Consultancy. Bastos-Oreiro: BMS-Celgene: Honoraria, Speakers Bureau; Gilead: Honoraria; Janssen: Honoraria, Speakers Bureau; F. Hoffmann-La Roche: Honoraria, Research Funding, Speakers Bureau; Takeda: Speakers Bureau; Novartis: Honoraria, Speakers Bureau; Kite: Speakers Bureau. Schmidt: Novartis: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses; Kite/Gilead: Consultancy, Honoraria, Other: Travel, Accommodations, Expenses, Research Funding; Takeda: Consultancy, Other: Travel, Accommodations, Expenses; BMS: Consultancy, Other: Travel, Accommodations, Expenses; Bayer Healthcare: Research Funding; Janssen: Other: Travel, Accommodations, Expenses. Carpio: Regeneron, TAKEDA, Celgene, Novartis: Consultancy, Membership on an entity's Board of Directors or advisory committees, Other: Travels and accommodation. Reguera: Janssen, Kite/Gilead, Novartis: Speakers Bureau; BMS-Celgene, Novartis: Membership on an entity's Board of Directors or advisory committees. Kwon: Gilead: Honoraria. Martín García-Sancho: Janssen: Honoraria, Research Funding; Novartis: Consultancy; Gilead: Consultancy, Honoraria; Celgene: Consultancy, Honoraria; Roche: Consultancy, Honoraria. Zinzani: Beigene: Other, Speakers Bureau; MSD: Consultancy, Other: Advisory board, Speakers Bureau; TG Therapeutics: Other: Advisory board, Speakers Bureau; TAKEDA: Other: Advisory board, Speakers Bureau; ROCHE: Other, Speakers Bureau; EUSAPHARMA: Consultancy, Other, Speakers Bureau; SANDOZ: Other: Advisory board; SERVIER: Other: Advisory board, Speakers Bureau; BMS: Other: Advisory board, Speakers Bureau; JANSSEN-CILAG: Other: Advisory board, Speakers Bureau; GILEAD: Other: Advisory board, Speakers Bureau; CELLTRION: Other: Advisory board, Speakers Bureau; KYOWA KIRIN: Other, Speakers Bureau; NOVARTIS: Consultancy, Other, Speakers Bureau; ADC Therap.: Other; Incyte: Other, Speakers Bureau; VERASTEM: Consultancy, Other: Advisory board, Speakers Bureau. Subklewe: Pfizer: Consultancy, Speakers Bureau; Janssen: Consultancy; Takeda: Speakers Bureau; Klinikum der Universität München: Current Employment; Gilead: Consultancy, Research Funding, Speakers Bureau; Miltenyi: Research Funding; MorphoSys: Research Funding; Novartis: Consultancy, Research Funding, Speakers Bureau; Roche: Research Funding; Seattle Genetics: Consultancy, Research Funding; BMS/Celgene: Consultancy, Research Funding, Speakers Bureau; Amgen: Consultancy, Research Funding, Speakers Bureau. Barba: Novartis: Honoraria; Pfizer: Honoraria; Gilead: Honoraria; BMS: Honoraria; Amgen: Honoraria.

[u'Rats and mice sometimes transmit hantaviruses, a family of microbes that can cause deadly human diseases. For example, the Hantaan virus leads to haemorrhagic fevers that are potentially fatal. There are no vaccine or even drugs against these infections.', u'To multiply, viruses must insert their genetic material inside a cell. While the body often detects and destroys foreign genetic information, hantaviruses can still evade our defences. Molecules called nucleoproteins bind to the viral genome, hiding it away in long helices called nucleocapsids. When the virus needs to replicate, an enzyme opens up the nucleocapsid, reads and copies the genetic code, and then closes the helix. Yet, researchers know little about the details of this process, or even the structure of the nucleocapsid.', u'Here, Arragain et al. use a method called cryo-electron microscopy to examine and piece together the exact 3D structure of the Hantaan virus nucleocapsid. This was possible because the new technique allows scientists to observe biological molecules at an unprecedented, near atomic resolution. The resulting model reveals that the viral genome nests into a groove inside the nucleocapsid. It also shows that specific interactions between nucleoproteins stabilise the helix. Finally, the model helps to provide hypotheses on how the enzyme could read the genome without breaking the capsid.', u'Mapping out the structure and the interactions of the nucleocapsid is the first step towards finding molecules that could destabilise the helix and neutralise the virus: this could help fight both the Hantaan virus and other members of its deadly family.'], Negative-strand RNA viruses condense their genome into helical nucleocapsids that constitute essential templates for viral replication and transcription. The intrinsic flexibility of nucleocapsids usually prevents their full-length structural characterisation at high resolution. Here, we describe purification of full-length recombinant metastable helical nucleocapsid of Hantaan virus (Hantaviridae family, Bunyavirales order) and determine its structure at 3.3 Å resolution by cryo-electron microscopy. The structure reveals the mechanisms of helical multimerisation via sub-domain exchanges between protomers and highlights nucleotide positions in a continuous positively charged groove compatible with viral genome binding. It uncovers key sites for future structure-based design of antivirals that are currently lacking to counteract life-threatening hantavirus infections. The structure also suggests a model of nucleoprotein-polymerase interaction that would enable replication and transcription solely upon local disruption of the nucleocapsid.

Summary Segmented negative-strand RNA virus (sNSV) polymerases transcribe and replicate the viral RNA (vRNA) within a ribonucleoprotein particle (RNP). We present cryo-EM and X-ray structures of, respectively, apo- and vRNA bound La Crosse orthobunyavirus (LACV) polymerase that give atomic-resolution insight into how such RNPs perform RNA synthesis. The complementary 3′ and 5′ vRNA extremities are sequence specifically bound in separate sites on the polymerase. The 5′ end binds as a stem-loop, allosterically structuring functionally important polymerase active site loops. Identification of distinct template and product exit tunnels allows proposal of a detailed model for template-directed replication with minimal disruption to the circularised RNP. The similar overall architecture and vRNA binding of monomeric LACV to heterotrimeric influenza polymerase, despite high sequence divergence, suggests that all sNSV polymerases have a common evolutionary origin and mechanism of RNA synthesis. These results will aid development of replication inhibitors of diverse, serious human pathogenic viruses., Graphical Abstract, Highlights • Bunyavirus polymerase binds its complementary 3′ and 5′ vRNA ends in distinct sites • 5′ vRNA binding allosterically structures and activates the polymerase catalytic site • Distinct template/product exit tunnels explain RNA synthesis in a circularized RNP • Monomeric bunyavirus and trimeric influenza polymerases are structurally similar, The structure of the monomeric bunyavirus polymerase reveals that divergent segmented negative-strand RNA virus polymerases have a common overall architecture, explains how viral RNA binding allosterically regulates polymerase activity, and suggests a replication model that could apply to all related RNA viruses.

Cell surface aminopeptidase N (APN) is a membrane-bound ectoenzyme that hydrolyzes proteins and peptides and regulates numerous cell functions. APN participates in tumor cell expansion and motility, and is a target for cancer therapies. Small drugs that bind to the APN active site inhibit catalysis and suppress tumor growth. APN is also a major cell entry receptor for coronavirus, which binds to a region distant from the active site. Three crystal structures that we determined of human and pig APN ectodomains defined the dynamic conformation of the protein. These structures offered snapshots of closed, intermediate and open APN, which represent distinct functional states. Coronavirus envelope proteins specifically recognized the open APN form, prevented ectodomain progression to the closed form and substrate hydrolysis. In addition, drugs that bind the active site inhibited both coronavirus binding to cell surface APN and infection; the drugs probably hindered APN transition to the virus-specific open form. We conclude that allosteric inhibition of APN functions occurs by ligand suppression of ectodomain motions necessary for catalysis and virus cell entry, as validated by locking APN with disulfides. Blocking APN dynamics can thus be a valuable approach to development of drugs that target this ectoenzyme., GM was a recipient of a La Caixa fellowship. JR was supported by the Juan de la Cierva program and RR by NIH grant 2P01AI054456-06A1. The work was supported by grants from the Spanish Ministry of Science (BFU2011-23940 and BIO2014-52683-R to JMC).

Highlights • Bunyavirus and arenavirus are important public health threats. • Bunyavirus and arenavirus molecular biology, common and differential features. • Implications of LACV L protein structure for understanding viral RNA synthesis. • Current state and future perspectives on bunya- and arenavirus antivirals., Bunyaviridae and Arenaviridae virus families include an important number of highly pathogenic viruses for humans. They are enveloped viruses with negative stranded RNA genomes divided into three (bunyaviruses) or two (arenaviruses) segments. Each genome segment is coated by the viral nucleoproteins (NPs) and the polymerase (L protein) to form a functional ribonucleoprotein (RNP) complex. The viral RNP provides the necessary context on which the L protein carries out the biosynthetic processes of RNA replication and gene transcription. Decades of research have provided a good understanding of the molecular processes underlying RNA synthesis, both RNA replication and gene transcription, for these two families of viruses. In this review we will provide a global view of the common features, as well as differences, of the molecular biology of Bunyaviridae and Arenaviridae. We will also describe structures of protein and protein-RNA complexes so far determined for these viral families, mainly focusing on the L protein, and discuss their implications for understanding the mechanisms of viral RNA replication and gene transcription within the architecture of viral RNPs, also taking into account the cellular context in which these processes occur. Finally, we will discuss the implications of these structural findings for the development of antiviral drugs to treat human diseases caused by members of the Bunyaviridae and Arenaviridae families.

In the coronavirus (CoV), the envelope spike (S) glycoprotein is responsible for CoV cell entry and host-to-host transmission. The S is a multifunctional glycoprotein that mediates both attachment of CoV particles to cell surface receptor molecules as well as membrane penetration by fusion. Receptor-binding domains (RBD) have been identified in the S of diverse CoV; they usually contain antigenic determinants targeted by antibodies that neutralize CoV infections. To penetrate host cells, the CoV can use various cell surface molecules, although they preferentially bind to ectoenzymes. Several crystal structures have determined the folding of CoV RBD and the mode by which they recognize cell entry receptors. Here we review the CoV-receptor complex structures reported to date, and highlight the distinct receptor recognition modes, common features, and key determinants of the binding specificity. Structural studies have established the basis for understanding receptor recognition diversity in CoV, its evolution and the adaptation of this virus family to different hosts. CoV responsible for recent outbreaks have extraordinary potential for cross-species transmission; their RBD bear large platforms specialized in recognition of receptors from different species, which facilitates host-to-host circulation and adaptation to man., GM is a PhD fellow of the La Caixa Foundation International Fellowship Program (La Caixa/CNB). The work was supported by a grant from the Spanish Ministry of Science (BFU2011-23940 to JMC). We acknowledge support by the European Synchrotron Research Facility through the BAG-Madrid project.

The nucleoprotein (NP) of segmented negative-strand RNA viruses such as Orthomyxo-, Arena-, and Bunyaviruses coats the genomic viral RNA and together with the polymerase forms ribonucleoprotein particles (RNPs), which are both the template for replication and transcription and are packaged into new virions. Here we describe the crystal structure of La Crosse Orthobunyavirus NP both RNA free and a tetrameric form with single-stranded RNA bound. La Crosse Orthobunyavirus NP is a largely helical protein with a fold distinct from other bunyavirus genera NPs. It binds 11 RNA nucleotides in the positively charged groove between its two lobes, and hinged N - and C-terminal arms mediate oligomerization, allowing variable protein–protein interface geometry. Oligomerization and RNA binding are mediated by residues conserved in the Orthobunyavirus genus. In the twofold symmetric tetramer, 44 nucleotides bind in a closed ring with sharp bends at the NP–NP interfaces. The RNA is largely inaccessible within a continuous internal groove. Electron microscopy of RNPs released from virions shows them capable of forming a hierarchy of more or less compact irregular helical structures. We discuss how the planar, tetrameric NP–RNA structure might relate to a polar filament that upon supercoiling could be packaged into virions. This work gives insight into the RNA encapsidation and protection function of bunyavirus NP, but also highlights the need for dynamic rearrangements of the RNP to give the polymerase access to the template RNA.

The N-terminal S1 region of the transmissible gastroenteritis virus (TGEV) spike (S) glycoprotein contains four antigenic sites (C, B, D and A, from the N- to the C-terminal end) and is engaged in host-cell receptor recognition. The most N-terminal portion of the S1 region, which comprises antigenic sites C and B, is needed for the enteric tropism of TGEV, whereas the major antigenic site A at the C-terminal moiety is required for both respiratory and enteric cell tropism, and is engaged in recognition of the aminopeptidase N (APN) receptor. This study determined the kinetics for binding of a soluble S1 protein to the APN protein. Moreover, the S1 region of the TGEV S protein was dissected, with the aim of identifying discrete modules displaying unique antigenic sites and receptor-binding functions. Following protease treatments and mammalian cell expression methods, four modules or domains (D1–D4) were defined at the S1 region. Papain treatment identified an N-terminal domain (D1) resistant to proteolysis, whereas receptor binding defined a soluble and functional APN receptor-binding domain (D3). This domain was recognized by neutralizing antibodies belonging to the antigenic site A and therefore could be used as an immunogen for the prevention of viral infection. The organization of the four modules in the S1 region of the TGEV S glycoprotein is discussed.

Negative strand RNA viruses (NSVs), which may have segmented (sNSV) or non-segmented genomes (nsNSV) are responsible for numerous serious human infections such as Influenza, Measles, Rabies, Ebola, Crimean Congo Haemorrhagic Fever and Lassa Fever. Their RNA-dependent RNA polymerases transcribe and replicate the nucleoprotein coated viral genome within the context of a ribonucleoprotein particle. We review the first high resolution crystal and cryo-EM structures of representative NSV polymerases. The heterotrimeric Influenza and single-chain La Crosse orthobunyavirus polymerase structures (sNSV) show how specific recognition of both genome ends is achieved and is required for polymerase activation and how the sNSV specific ‘cap-snatching’ mechanism of transcription priming works. Vesicular Stomatitis Virus (nsNSV) polymerase shows a similar core architecture but has different flexibly linked C-terminal domains which perform mRNA cap synthesis. These structures pave the way for a more complete understanding of these complex, multifunctional machines which are also targets for anti-viral drug design.

In the spherical virion of the parvovirus minute virus of mice, several amino acid side chains of the capsid were previously found to be involved in interactions with the viral single-stranded DNA molecule. We have individually truncated by mutation to alanine many (ten) of these side chains and analyzed the effects on capsid assembly, stability and conformation, viral DNA encapsidation, and virion infectivity. Mutation of residues Tyr-270, Asp-273, or Asp-474 led to a drastic reduction in infectivity. Mutant Y270A was defective in capsid assembly; mutant D273A formed stable capsids, but it was essentially unable to encapsidate the viral DNA or to externalize the N terminus of the capsid protein VP2, a connected conformational event. Mutation of residues Asp-58, Trp-60, Asn-183, Thr-267, or Lys-471 led to a moderate reduction in infectivity. None of these mutations had an effect on capsid assembly or stability, or on the DNA encapsidation process. However, those five mutant virions were substantially less stable than the parental virion in thermal inactivation assays. The results with this model spherical virus indicate that several capsid residues that are found to be involved in polar interactions or multiple hydrophobic contacts with the viral DNA molecule contribute to preserving the active conformation of the infectious viral particle. Their effect appears to be mediated by the non-covalent interactions they establish with the viral DNA. In addition, at least one acidic residue at each DNA-binding region is needed for DNA packaging.

Twenty-eight amino acid residues involved in most noncovalent interactions between trimeric protein subunits in the capsid of the parvovirus minute virus of mice were truncated individually to alanine, and the effects on capsid assembly, thermostability, and conformation were analyzed. Only seven side chains were essential for protein subunit recognition. These side chains virtually corresponded with those that either buried a large hydrophobic surface on trimer association or formed buried intertrimer hydrogen bonds or salt bridges. The seven residues are evolutionarily conserved, and they define regularly spaced spots on a thin equatorial belt surrounding each trimer. Truncation of the many side chains that were dispensable for assembly, including those participating in solvent-accessible polar interactions, did not substantially affect capsid thermostability either. However, the interfacial residues located at the base of the pores delineating the capsid five-fold axes participated in a heat-induced conformational rearrangement associated with externalization of the capsid protein N terminus, and they were needed for infectivity. Thus, at the subunit interfaces of this model virus capsid, only key residues involved in the strongest interactions are critical for assembly and stability, but additional residues fulfill other important biological roles.

We have analyzed the in vitro disassembly of the capsid of the minute virus of mice, and the stability of capsid chimeras carrying heterologous epitope insertions. Upon heating in a physiological buffer, empty capsids formed by 60 copies of protein VP2 underwent first a reversible conformational change with a small enthalpy change detected by fluorescence. This change was associated with, but not limited to, externalization of the VP2 N terminus. Irreversible capsid dissociation as detected by changes in fluorescence, hemagglutination activity, and electrophoretic mobility occurred at much higher temperatures. Differential scanning calorimetry in the same conditions indicated that the dissociation/denaturation transition involved a high enthalpy change and proceeded through one or more intermediates. In contrast, in the presence of 1.5 M guanidinium chloride, heat-induced disassembly fitted a two-state irreversible process. Both thermally and chemically induced dissociation/denaturation yielded a form that had lost a part of the tertiary structure, but still retained the native secondary structure. Data from chemical dissociation indicates this form may correspond to a molten globule-like monomeric state of the capsid protein. All five antigenic peptide insertions attempted in exposed loops, despite being perhaps among the least disruptive, led to defects in folding/assembly of the capsid and, in most cases, to reduced capsid stability against thermal dissociation. The results with one of the simplest viral capsids reveal a complex pathway for disassembly, and a reduction in capsid assembly and stability upon insertion of peptides, even within the most exposed capsid loops.

Negative strand RNA virus (NSV) genomes are never free, but always found assembled with multiple copies of their nucleoprotein, as RNPs. A flurry of papers describing the X-ray crystal structures of several segmented NSV nucleoproteins have recently appeared. The most significant feature of these various structures is that the arms that are used to oligomerize the nucleoproteins on their genome RNAs are highly flexible, permitting these RNPs to assume virtually unlimited geometries. The structural flexibility of segmented NSV RNPs is undoubtedly important in all aspects of their biology, including genome replication and circularization, and the selection of one copy of each segment for packaging into virus particles.

The L polymerase of bunyaviruses replicates and transcribes the viral genome. While replication products are faithful copies of the uncapped genomic RNA, transcription products contain capped 5′ extensions which had been cleaved from host cell mRNAs. For La Crosse virus (LACV; genus Orthobunyavirus ), the nuclease responsible for host cell mRNA cleavage is located at the N terminus of the L protein, with an active site of five conserved amino acids (H34, D52, D79, D92, and K94) surrounding two Mn 2+ ions (J. Reguera, F. Weber, and S. Cusack, PLoS Pathog. 6:e1001101, 2010). Here, we present reverse genetics systems and L mutants enabling us to study bunyaviral genome replication in the absence of transcription. Transcription was evaluated with an enhanced minigenome system consisting of the viral polymerase L, nucleocapsid protein N, a negative-sense minigenome, and—to alleviate antiviral host responses—a dominant-negative mutant (PKRΔE7) of the antiviral kinase protein kinase R (PKR). The transcriptional activity was strongly reduced by mutation of any of the five key amino acids, and the H34K, D79A, D92A, and K94A LACV L mutants were almost entirely silent in transcription. The replication activity of the L mutants was measured by packaging of progeny minigenomes into virus-like particles (VLPs). All mutant L proteins except K94A retained full replication activity. To test the broader applicability of our results, we introduced the homolog of mutation D79A (D111A) into the L sequence of Rift Valley fever virus (RVFV; genus Phlebovirus ). As for LACV D79A, the RVFV D111A was incapable of transcription but fully active in replication. Thus, we generated mutants of LACV and RVFV L polymerases that are specifically deficient in transcription. Genome replication by bunyavirus polymerases can now be studied in the absence of transcription using convenient reverse genetics systems.

The coronaviruses (CoVs) are enveloped viruses of animals and humans associated mostly with enteric and respiratory diseases, such as the severe acute respiratory syndrome and 10–20% of all common colds. A subset of CoVs uses the cell surface aminopeptidase N (APN), a membrane-bound metalloprotease, as a cell entry receptor. In these viruses, the envelope spike glycoprotein (S) mediates the attachment of the virus particles to APN and subsequent cell entry, which can be blocked by neutralizing antibodies. Here we describe the crystal structures of the receptor-binding domains (RBDs) of two closely related CoV strains, transmissible gastroenteritis virus (TGEV) and porcine respiratory CoV (PRCV), in complex with their receptor, porcine APN (pAPN), or with a neutralizing antibody. The data provide detailed information on the architecture of the dimeric pAPN ectodomain and its interaction with the CoV S. We show that a protruding receptor-binding edge in the S determines virus-binding specificity for recessed glycan-containing surfaces in the membrane-distal region of the pAPN ectodomain. Comparison of the RBDs of TGEV and PRCV to those of other related CoVs, suggests that the conformation of the S receptor-binding region determines cell entry receptor specificity. Moreover, the receptor-binding edge is a major antigenic determinant in the TGEV envelope S that is targeted by neutralizing antibodies. Our results provide a compelling view on CoV cell entry and immune neutralization, and may aid the design of antivirals or CoV vaccines. APN is also considered a target for cancer therapy and its structure, reported here, could facilitate the development of anti-cancer drugs., Author Summary The cell surface aminopeptidase N (APN), a membranebound metalloprotease target for cancer therapy, is a major cell entry receptor for coronaviruses (CoVs), agents that cause important respiratory and enteric diseases. In some CoVs, the virus envelope spike glycoprotein (S) mediates attachment of the virus particles to the host APN protein and cell entry, which is blocked by antibodies that prevent CoV infections. The crystal structures of the S proteins of two porcine CoV in complex with the pig APN (pAPN) or with a neutralizing antibody shown here, reveal how some CoV bind to its cell surface APN receptor and how antibodies prevent receptor binding and infection. The report uncovers a unique virus-receptor recognition mode that engages a glycan N-linked to the pAPN ectodomain, revealing structural determinants of the receptor-binding specificity in CoVs. Neutralizing antibodies target viral residues used for binding to the APN receptor and entry into host cells, showing that efficient CoV neutralization requires immune responses focused toward key receptor binding motifs in the virus envelope. These structural insights, together with the structure of the APN ectodomain, provide a compelling view of relevant cell membrane processes related to infectious diseases and cancer.

Bunyaviruses are a large family of segmented RNA viruses which, like influenza virus, use a cap-snatching mechanism for transcription whereby short capped primers derived by endonucleolytic cleavage of host mRNAs are used by the viral RNA-dependent RNA polymerase (L-protein) to transcribe viral mRNAs. It was recently shown that the cap-snatching endonuclease of influenza virus resides in a discrete N-terminal domain of the PA polymerase subunit. Here we structurally and functionally characterize a similar endonuclease in La Crosse orthobunyavirus (LACV) L-protein. We expressed N-terminal fragments of the LACV L-protein and found that residues 1-180 have metal binding and divalent cation dependent nuclease activity analogous to that of influenza virus endonuclease. The 2.2 Å resolution X-ray crystal structure of the domain confirms that LACV and influenza endonucleases have similar overall folds and identical two metal binding active sites. The in vitro activity of the LACV endonuclease could be abolished by point mutations in the active site or by binding 2,4-dioxo-4-phenylbutanoic acid (DPBA), a known influenza virus endonuclease inhibitor. A crystal structure with bound DPBA shows the inhibitor chelating two active site manganese ions. The essential role of this endonuclease in cap-dependent transcription was demonstrated by the loss of transcriptional activity in a RNP reconstitution system in cells upon making the same point mutations in the context of the full-length LACV L-protein. Using structure based sequence alignments we show that a similar endonuclease almost certainly exists at the N-terminus of L-proteins or PA polymerase subunits of essentially all known negative strand and cap-snatching segmented RNA viruses including arenaviruses (2 segments), bunyaviruses (3 segments), tenuiviruses (4–6 segments), and orthomyxoviruses (6–8 segments). This correspondence, together with the well-known mapping of the conserved polymerase motifs to the central regions of the L-protein and influenza PB1 subunit, suggests that L-proteins might be architecturally, and functionally equivalent to a concatemer of the three orthomyxovirus polymerase subunits in the order PA-PB1-PB2. Furthermore, our structure of a known influenza endonuclease inhibitor bound to LACV endonuclease suggests that compounds targeting a potentially broad spectrum of segmented RNA viruses, several of which are serious or emerging human, animal and plant pathogens, could be developed using structure-based optimisation., Author Summary Bunyaviruses are a large family of RNA viruses that include serious human, animal and plant pathogens. The viral RNA-dependent RNA polymerase (L-protein) is responsible for replication and transcription of the viral RNA, but apart from its central polymerase domain, it is poorly characterized. Like influenza virus polymerase, bunyavirus L-proteins employ a cap-snatching mechanism to transcribe viral mRNAs, by which host mRNAs are endonucleolytically cleaved as a source of short capped primers. Influenza polymerase endonuclease has recently been located at the PA subunit N-terminus. Here we show biochemically and by crystal structure determination that a similar two-manganese dependent nuclease exists at the N-terminus of La Crosse orthobunyavirus L-protein, whose function is required for cap-dependent transcription. By sequence analysis we show that similar endonuclease signature motifs exist in almost all known segmented RNA, cap-snatching viruses including arenaviruses, bunyaviruses, tenuiviruses and orthomyxoviruses. This suggests that the polymerases of these viruses might share a conserved global architecture with the L-protein being equivalent to a concatenation of the orthomxyovirus PA-PB1-PB2 subunits. We also propose that broad spectrum drugs targeting the endonuclease domain of such viruses could be developed, as exemplified by our structure of the LACV endonuclease complexed with a known influenza endonuclease inhibitor.

Segmented negative strand RNA viruses of the arena-, bunya- and orthomyxovirus families uniquely carry out viral mRNA transcription by the cap-snatching mechanism. This involves cleavage of host mRNAs close to their capped 5′ end by an endonuclease (EN) domain located in the N-terminal region of the viral polymerase. We present the structure of the cap-snatching EN of Hantaan virus, a bunyavirus belonging to hantavirus genus. Hantaan EN has an active site configuration, including a metal co-ordinating histidine, and nuclease activity similar to the previously reported La Crosse virus and Influenza virus ENs (orthobunyavirus and orthomyxovirus respectively), but is more active in cleaving a double stranded RNA substrate. In contrast, Lassa arenavirus EN has only acidic metal co-ordinating residues. We present three high resolution structures of Lassa virus EN with different bound ion configurations and show in comparative biophysical and biochemical experiments with Hantaan, La Crosse and influenza ENs that the isolated Lassa EN is essentially inactive. The results are discussed in the light of EN activation mechanisms revealed by recent structures of full-length influenza virus polymerase., Author Summary Segmented negative strand viruses (sNSV) such as Influenza, Lassa or Hantaan viruses are responsible for a large number of severe human infectious diseases. Currently, there are vaccines and antiviral treatments available for influenza but none for the infections caused by other sNSV. All carry out transcription by the cap-snatching mechanism, which requires the action of a metal ion dependent endonuclease (EN), a domain within their large viral polymerases. Here we provide the crystal structure of the Hantaan virus (family Bunyaviridae) and Lassa virus (family Arenaviridae) cap-snatching ENs in complex with manganese and a comparative functional study of their catalytic activity. Despite the high structural homology between the two ENs a few changes in the active site, involving a catalytic histidine, cause a different binding of the metal ions with dramatic consequences for their in vitro activity. Hantaan EN binds the metal ions as Influenza A (family Orthomyxoviridae) and LACV (family Bunyaviridae) ENs and all three are active in vitro. In contrast Lassa virus EN is inactive in the same experimental conditions. We can now classify sNSV into two functionally distinct groups (His+ and His- ENs), providing a broad view of the sNSV cap-snatching ENs properties that will be determinant for the comprehensive development of broad-spectrum antiviral drugs. These results also have implications for the viral transcription regulation in the light of recent studies on full-length sNSV polymerases.

infected cells. Nevertheless, there is a limited knowledge of the biochemical events occurring in host cells and in the biochemistry of the infection. Infections by CoVs cause alterations in host cells in transcription and translation patterns, in the cell cycle, in the cytoskeleton, and in apoptosis pathways. In addition, in the host, CoV infection may cause inflammation, alterations of the immune response, of cytokine and chemokine levels, of interferon (INF)-induced gene expression and of stress responses, and modification of coagulation pathways. This chapter will focus on selected biochemical aspects of CoV replication and transcription with special attention to the interaction between cell and viral factors.

The connection between nuclear transport and morphogenesis of a large macromolecular entity has been investigated using the karyophylic capsid of the parvovirus minute virus of mice (MVM) as a model. The VP1 (82 kDa) and VP2 (63 kDa) proteins forming the T = 1 icosahedral MVM capsid at the respective 1:5 molar ratio of synthesis, could be covalently cross-linked with dimethyl suberimidate into two types of oligomeric assemblies, which were present at stoichiometric amounts in infected cell extracts and purified viral particles. The larger species contained VP1 and corresponded in size (200 kDa) to a heterotrimer of one VP1 and two VP2 subunits. The smaller species contained VP2 only and corresponded in size (180 kDa) to a homotrimer. The introduction of bulky residues or the truncation of side-chains involved in multiple interactions at the interfaces between trimers of VPs in the MVM capsid, produced the accumulation of trimeric intermediates that were competent in nuclear translocation but not in capsid assembly. These results indicate that MVM maturation proceeds by cytoplasmic oligomerization of the capsid subunits into two types of trimers, which are the assembly intermediates competent to translocate across the nuclear membrane. Consistent with this conclusion, mutations at basic residues that inactivate a previously identified beta-stranded nuclear localization motif, which notably are not involved in inter or intra-subunit contacts, led to cytoplasmic retention of the two types of trimers, with no evidence for other assembly intermediates. Although a fraction of the VP1-containing trimers were translocated into the nucleus driven by the conventional nuclear transport signal of VP1 N terminus, their further assembly in the absence of the VP2-only trimers yielded large molecular mass amorphous aggregates. Therefore, the nuclear transport stoichiometry of assembly intermediates may exert a morphogenetic quality control on macromolecular complexes like the MVM capsid.