A Dual-Approach Strategy to Optimize the Safety and Efficacy of Anti-Zika Virus Monoclonal Antibody Therapeutics.

Antibody-dependent enhancement of infection (ADE) is clinically relevant to Dengue virus (DENV) infection and poses a major risk to the application of monoclonal antibody (mAb)-based therapeutics against related flaviviruses such as the Zika virus (ZIKV). Here, we tested a two-tier approach for selecting non-cross-reactive mAbs combined with modulating Fc glycosylation as a strategy to doubly secure the elimination of ADE while preserving Fc effector functions. To this end, we selected a ZIKV-specific mAb (ZV54) and generated three ZV54 variants using Chinese hamster ovary cells and wild-type (WT) and glycoengineered ΔXF Nicotiana benthamiana plants as production hosts (ZV54CHO, ZV54WT, and ZV54ΔXF). The three ZV54 variants shared an identical polypeptide backbone, but each exhibited a distinct Fc N-glycosylation profile. All three ZV54 variants showed similar neutralization potency against ZIKV but no ADE activity for DENV infection, validating the importance of selecting the virus/serotype-specific mAbs for avoiding ADE by related flaviviruses. For ZIKV infection, however, ZV54CHO and ZV54ΔXF showed significant ADE activity while ZV54WT completely forwent ADE, suggesting that Fc glycan modulation may yield mAb glycoforms that abrogate ADE even for homologous viruses. In contrast to the current strategies for Fc mutations that abrogate all effector functions along with ADE, our approach allowed the preservation of effector functions as all ZV54 glycovariants retained antibody-dependent cellular cytotoxicity (ADCC) against the ZIKV-infected cells. Furthermore, the ADE-free ZV54WT demonstrated in vivo efficacy in a ZIKV-infection mouse model. Collectively, our study provides further support for the hypothesis that antibody-viral surface antigen and Fc-mediated host cell interactions are both prerequisites for ADE, and that a dual-approach strategy, as shown herein, contributes to the development of highly safe and efficacious anti-ZIKV mAb therapeutics. Our findings may be impactful to other ADE-prone viruses, including SARS-CoV-2.

Human Anti-Ace2 Monoclonal Antibodies as Pan-Sarbecovirus Prophylactic Agents

Background: Human monoclonal antibodies from convalescent individuals that target the SARS-CoV-2 spike protein have been deployed as therapeutics against SARS-CoV-2. However, nearly all of these antibodies have been rendered obsolete by SARS-CoV-2 variants that evolved to resist similar, naturally occurring antibodies. Moreover, Most SARS-CoV-2 specific antibodies are inactive against divergent sarbecoviruses Methods: By immunizing mice that carry human immunoglobulin variable gene segments we generated a suite of fully human monoclonal antibodies that bind the human ACE2 receptor (hACE2) rather than the viral spike protein and were engineered to lack effector functions such as ADCC. Result(s): These ACE2 binding antibodies block infection by all hACE2 binding sarbecoviruses, including emergent SARS-CoV-2 variants, with a potency that of the most potent spike binding therapeutic antibodies. Structural and biochemical analyses revealed that the antibodies target an hACE2 epitope that engages SARS-CoV-2 spike. Importantly, the antibodies do not inhibit hACE2 enzymatic activity, nor do they induce ACE depletion from cell surfaces. The antibodies exhibit favorable pharmacology in human ACE2 knock in mice and provide near complete protection of hACE2 knock-in mice against SARS-CoV-2 infection. Conclusion(s): ACE2 binding antibodies should be useful prophylactic and treatment agents against any current and future SARS-CoV-2 variants, as well as hACE2-binding sarbecoviruses that might emerge as future pandemic threats.

SIGLEC-9 RESTRAINS ANTIBODY-DEPENDENT NK CELL CYTOTOXICITY AGAINST SARS-CoV-2

Background: SARS CoV 2 infection alters the immunological profiles of natural killer (NK) cells. However, whether NK anti-viral functions (direct cytotoxicity and/or antibody-dependent cell cytotoxicity (ADCC)) are impaired during severe COVID-19 and what host factors modulate these functions remain unclear. Method(s): Using functional assays, we examined the ability of NK cells from SARS-CoV-2 negative controls (n=12), mild COVID-19 patients (n=26), and hospitalized COVID-19 patients (n=41) to elicit direct cytotoxicity and ADCC [NK degranulation by flow] against cells expressing SARS-CoV-2 antigens. SARS-CoV- 2 N antigen plasma load was measured using an ultra-sensitive Simoa assay. We also phenotypically characterized the baseline expression of NK activating (CD16 and NKG2C), maturation (CD57), and inhibitory (NKG2A and the glyco-immune negative checkpoint Siglec-9) by flow cytometry. Finally, an anti-Siglec-9 blocking antibody was used to examine the impact of Siglec-9 expression on anti-SARS-CoV-2-specific ADCC [degranulation and target cell lysis]. Result(s): NK cells from hospitalized COVID-19 patients degranulate less against SARS-CoV-2-antigen-expressing cells (in direct cytolytic and ADCC assays) than did cells from mild COVID-19 patients or negative controls (Fig. 1A). The lower NK degranulation was associated with higher plasma levels of SARS-CoV-2 N-antigen (P<=0.02). Phenotypic and functional analyses showed that NK cells expressing Siglec-9 elicited higher ADCC than Siglec-9- NK cells (P<0.05;Fig. 1B). Consistently, Siglec-9+ NK cells expressed an activated and mature phenotype with higher expression of CD16, CD57, and NKG2C, and lower expression of NKG2A, than Siglec-9- NK cells (P<=0.03). These data are consistent with the concept that the NK cell subpopulation expressing Siglec-9 is highly activated and cytotoxic. However, the Siglec-9 molecule itself is an inhibitory receptor that restrains NK cytotoxicity during cancer and other infections. Indeed, blocking Siglec-9 significantly enhanced the ADCC-mediated NK degranulation and lysis of SARS-CoV-2-antigen-positive target cells (P<=0.05;Fig. 1C). Conclusion(s): These data support a model (Fig. 1D) in which the Siglec-9+ CD56dim NK subpopulation is cytotoxic even while being restrained by the inhibitory effects of Siglec-9. However, alleviating the Siglec-9-mediated restriction on NK cytotoxicity can further improve NK immune surveillance and presents an opportunity to develop novel immunotherapeutic tools against SARS-CoV-2 infected cells. (Figure Presented).

Adaptive Immunity Dysregulation Is Associated to the Development of Long Covid

Background: The pathogenetic mechanisms behind the development of long- COVID (LC) are largely unknown. Because both plasma SARS-CoV-2 RNAemia and dysregulated immunity have been correlated with COVID-19 severity, we evaluated whether they are associated with LC. Method(s): We consecutively enrolled unvaccinated hospitalized COVID-19 patients during acute-COVID-19 (T0) in March-October 2020 who either developed LC at a follow-up visit 2-3 months from virologic clearance (T1) or did not. LC was defined as persistence >=2 months after recovery of >=1 symptom: anosmia, dysgeusia, fever, gastrointestinal symptoms, dyspnoea, fatigue, musculoskeletal pain, muscle weakness, brain fog. We measured: SARS-CoV-2 RNAemia (RT-qPCR, log10(copies/mL)), magnitude (ELISA, AUC) and functionality (pseudovirus neutralization, ID50;Fc-mediated functions, %ADCC) of SARS-CoV-2-specific antibodies, SARS-CoV-2-specific B and CD4-T-cells (Immunophenotype, AIM and ICS assays). Result(s): We enrolled 48 COVID-19 individuals, 38/48 (79.2%) developed LC (LC+) and 10 did not (LC-). LC+ and LC- had similar co-morbidities and symptoms in the acute phase (Fig.1A), and the majority showed a radiologically documented SARS-CoV-2 pneumonia. The SARS-CoV-2 RNAemia did not differ between groups at both time points. The levels of RBD-specific Abs, as well as their functionality, appeared to increase over time in the LC- group but not in the LC+ (Fig.1B-D). Similarly, a trend towards increased RBD-specific B-cells was observed over time in the LC- group but not in LC+ (Fig.1E). B-cell immunophenotyping showed a significant increase over time of classical memory B cells (MBCs) at the expenses of activated MBCs (Fig.1F-G) as well as an IgA class-switching in the LC- group compared to LC+ (Fig.1H-I). Furthermore, LC+ showed a faster decline of SARS-CoV-2-specific (CD69+CD137+) CD4- TEMRA and CD4-TEM (Fig.1L-M). Finally, IFN-gamma-producing TREG of LC- individuals increased over time (Fig.1N). Conclusion(s): Acutely ill, hospitalized COVID-19 patients developing LC feature a dysregulated SARS-CoV-2-specific humoral as well as B- and T-cell response, in both magnitude and functionality, suggesting a link between dysregulated SARS-CoV-2-specific adaptive immunity and LC development. The fine understanding of the factors contributing to such dysregulation in LC patients is strongly needed, that might further inform targeted therapeutic interventions. (Figure Presented).

SARS-CoV-2 Spike Expression at the Surface of Infected Primary Human Airway Epithelial Cells.

Different serological assays were rapidly generated to study humoral responses against the SARS-CoV-2 Spike glycoprotein. Due to the intrinsic difficulty of working with SARS-CoV-2 authentic virus, most serological assays use recombinant forms of the Spike glycoprotein or its receptor binding domain (RBD). Cell-based assays expressing different forms of the Spike, as well as pseudoviral assays, are also widely used. To evaluate whether these assays recapitulate findings generated when the Spike is expressed in its physiological context (at the surface of the infected primary cells), we developed an intracellular staining against the SARS-CoV-2 nucleocapsid (N) to distinguish infected from uninfected cells. Human airway epithelial cells (pAECs) were infected with authentic SARS-CoV-2 D614G or Alpha variants. We observed robust cell-surface expression of the SARS-CoV-2 Spike at the surface of the infected pAECs using the conformational-independent anti-S2 CV3-25 antibody. The infected cells were also readily recognized by plasma from convalescent and vaccinated individuals and correlated with several serological assays. This suggests that the antigenicity of the Spike present at the surface of the infected primary cells is maintained in serological assays involving expression of the native full-length Spike.

COVID-19 convalescent plasma: Mechanisms of action and rationale for use: A narrative review

The use of convalescent plasma (CP) transfusions for patients with coronavirus disease 2019 (COVID-19) has gained great interest during the severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) pandemic. This review aims at summarizing the literature on the potential mechanisms of action of COVID-19 CP (CCP) and the rationale for use. A narrative review of the literature was conducted using PubMed, Google Scholar, and the Cochrane Database through October 2020. The rationale of CCP deployment was based on historical use in other outbreaks and pandemics and the emergent need at the time of lack of proven therapies and vaccines. There are many proposed mechanisms of action including direct neutralization and suppression of viremia, antibody-dependent cellular cytotoxicity, modification of the inflammatory response, restoration of the coagulation factors, immunomodulation of the hypercoagulable state and the potential role of ABO naturally occurring iso-agglutinins. Many donor, product, and patient factors can impact the response to CCP, such as antibody titer in the CCP product, CCP dose, frequency of administration, the severity of underlying illness, and the timing of administration from time of disease onset. Based on current evidence, CCP appears to be safe. However, it remains unknown whether it impacts the improvement of clinical symptoms, time to death, and all-cause mortality. In conclusion, the use of CCP offers quick access as an empirical therapy when specific therapies are not available or under development. Ongoing clinical trials are expected to add to the breadth of knowledge on the safety and efficacy of CCP use in patients with COVID-19.Copyright © 2021 AME Publishing Company.

Impact Of Plant Based Vaccines On Covid-19

Human life has always been under a constant threat to emerging deadly viruses, Covid-19 is the newest. This deadliest virus become pandemic within a short span of time and brought great amount of concern to fight against it and overcome dynamic challenges. It demands the speedy manufacture of vaccines and drugs at the industrial level. A conventional vaccine is effective but has risk of being infected with foreign agents;to overcome this problem plant based vaccine is superior alternative. The VLPs are generated by recombinant technology and consumed orally and functionally plant cell distributes the antigen. The process consumes time, cost effective, easily conveyed and mucosal immunity induction. Benefit of plant counteract, they are free from any corruption and has minute risk of anomalous responses. VLPs are more stable than conventional vaccines and have immense potential to treat diseases. It contains few bioethical issues, such as transferring of allergens to humans. It requires the safe sites and skilled staff for the smooth administration of operations. Copyright © 2022 Wolters Kluwer Medknow Publications. All rights reserved.

Determinants of Placental Transfer of HSV-specific Antibodies and the Impact of SARS-CoV-2 Coinfection

Background. Primary versus recurrent herpes simplex virus 1 or 2 (HSV-1 or HSV-2) infection during pregnancy carries a higher risk of neonatal herpes. Murine and clinical studies demonstrate that antibody dependent cellular cytotoxicity (ADCC) provides greater protection against disseminated neonatal disease. To quantify relative transfer of HSV specific Abs with different functions and targets and whether SARS-CoV-2 coinfection modified transfer, we conducted a prospective cohort study of mother-infant dyads prior to and during COVID-19. Methods. Total and HSV lysate, glycoprotein D (gD) and glycoprotein B (gB)-specific IgG, IgG1 and IgG3, nAbs and ADCC were quantified in paired 3rd trimester maternal and cord blood. IgG1 and IgG3 subclass and gD or gB-specific Abs were isolated by column purification and glycan profiles were assessed using mass spectrometry. The pre-COVID study population included 21 term and 15 preterm dyads who were HSV seropositive and the pri-COVID cohort included 25 HSV seropositive term dyads whose mothers were also SARS-CoV-2 PCR and COVID Ab positive at delivery. Results. HSV-specific Ab and neutralizing Ab transfer ratio (TR) were higher in term compared to preterm pre-COVID dyads (all p< 0.05), but the ADCC TR was < 1.0 for both groups. To determine if the low ADCC TR reflected antigenic target, subclass and/or glycans, we enriched for anti-gD and anti-gB specific and IgG1 and IgG3 Abs. The anti-gD Abs were exclusively IgG, had only neutralizing activity and had glycans associated with FcRn binding. In contrast, anti-gB Abs were both IgG1 and IgG3;had both neutralizing and ADCC activity and expressed glycans associated with both FcRn and FcgammaRIIIa binding. There was no significant difference in HSV-specific IgG TR in pre-COVID vs COVID dyads (0.42) but the nAb TR was lower (p=0.018) and ADCC TR higher (p< 0.001) in COVID compared to pre-COVID patients. Placental immunohistochemistry showed an increased colocalization of FcRn and FcgammaRIIIA in SARS-CoV-2 positive mothers, which would favor transfer of ADCC Abs. Conclusion. Defining the determinants of ADCC transfer has implications for future vaccine and monoclonal Ab strategies to prevent/treat neonatal herpes. We speculate that increasing the transfer of ADCC may be a key element in providing immune protection.

Antibody-dependent cellular cytotoxicity against SARS-CoV-2 Omicron sub-lineages is reduced in convalescent sera regardless of infecting variant.

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) Omicron BA.4 and BA.5 variants caused major waves of infections. Here, we assess the sensitivity of BA.4 to binding, neutralization, and antibody-dependent cellular cytotoxicity (ADCC) potential, measured by FcγRIIIa signaling, in convalescent donors infected with four previous variants of SARS-CoV-2, as well as in post-vaccination breakthrough infections (BTIs) caused by Delta or BA.1. We confirm that BA.4 shows high-level neutralization resistance regardless of the infecting variant. However, BTIs retain activity against BA.4, albeit at reduced titers. BA.4 sensitivity to ADCC is reduced compared with other variants but with smaller fold losses compared with neutralization and similar patterns of cross-reactivity. Overall, the high neutralization resistance of BA.4, even to antibodies from BA.1 infection, provides an immunological mechanism for the rapid spread of BA.4 immediately after a BA.1-dominated wave. Furthermore, although ADCC potential against BA.4 is reduced, residual activity may contribute to observed protection from severe disease.

Phenotype of SARS-CoV-2 Specific T and B Cells in Lymph Nodes of Patients With ESRD

Background: In patients with end-stage renal disease (ESRD), mean antibody concentrations following SARS-CoV-2 vaccination are lower than in the general population, which correlates with the risk of COVID-19 disease. For a high-affinity antibody response, germinal centre responses in lymph nodes (LN) are critical. However, current knowledge on SARS-CoV-2 specific B and T cell responses is almost exclusively based on peripheral blood (PB) mononuclear cells (MNC). Previous studies have shown that LN MNC differ substantially from their PB counterparts. We aim to study the functional and phenotypical differences between PB-and LN-derived SARS-CoV-2 specific B and T cells after vaccination in ESRD patients and compare these with their counterparts after infection. Method(s): MNC were isolated from PB and paired non-draining LN of ESRD patients, retrieved during kidney transplantation. Ten patients who received SARS-CoV-2 vaccination and five who suffered COVID-19 disease were included. SARS-CoV-2 spike specific T cells were phenotyped using HLA class I dextramers and for SARS-CoV-2 spike specific B cells spike-tetramers were used. Also, antibody levels and functions like neutralization of infectivity, phagocytosis, antibody-dependent cellular cytotoxicity and complement-mediated lysis of pathogens of infected cells were measured. Result(s): An example of the SARS-CoV-2 specific T and B cell phenotyping in PB MNC of healthy controls is shown. Whether these cells are detectable in the non-draining LN of ESRD patients after SARS-CoV-2 vaccination or infection and if they functionally and phenotypically correlate with paired PB MNC is yet to be determined. Conclusion(s): We aim to gain an invaluable insight into the underlying T-and B-cellcentred immunological processes in LN of ESRD patients in order to understand and optimize vaccine response.

Quantitative PBMC ADCC bioassay and ADCC reporter bioassays for immunotherapy and SARS-CoV-2 monoclonal antibody development

Fc effector function is one of the main mechanisms of action (MoA) for therapeutic monoclonal antibodies (mAbs). Quantitative measurement of antibody-dependent cellular cytotoxicity (ADCC) is critically required for understanding the Fc function in mAb drug development. Despite the increasing interest and clinical success of the mAb therapeutic, it has been highly challenging to measure their ADCC activity in a reproducible and quantitative manner due to the lack of consistency in current methods that are based on primary PBMCs or NK cells and use tedious assay procedures. To improve ADCC assay precision so they can be validated as potency assay in cGMP laboratories, we developed reporter based ADCC bioassays using engineered effector cell line stably expressing a luciferase reporter and FcγRIIIa (V or F variant) to replace primary PBMC to overcome the assay variation. The ADCC reporter bioassays have been validated according to ICH guidelines by many laboratories and are demonstrated to be suitable for product release and stability studies in a quality-controlled environment. For early research and antibody characterization, we developed an improved PBMC ADCC assay using ADCC-prequalified PBMCs and engineered HiBiT target cells so they can measure the target specific lysis in ADCC. The PBMCs used in the study are isolated from prescreened blood donors and QC tested in ADCC assay. When HiBiT target cells are incubated with an antibody and PBMCs, HiBiT are released to the culture medium where it binds to LgBiT in the detection reagent to form a functional NanoBiT luciferase to generate luminescence signal. This new PBMC ADCC bioassay is simple, homogenous, highly sensitive, and gives a robust assay window. We demonstrate that it can quantitatively measure the potency for mAb drugs in cancer immunotherapy (e.g., rituximab, trastuzumab), and for anti-SARS-CoV-2 spike antibodies in antiviral drug development. Additionally, it shows antibody potency comparable with the ADCC reporter bioassay. In summary, the new PBMC ADCC bioassay using HiBiT target cells can be a valuable tool for early antibody discovery and characterization and also for method bridging study with ADCC reporter bioassay.

Antigenic target, antibody subclass, function and glycans and SARS-CoV-2 coinfection impact the placental transfer of herpes simplex virus antibodies

Primary versus recurrent herpes simplex virus 1 or 2 (HSV-1 or HSV- 2) infection during pregnancy carries a higher risk of neonatal herpes suggesting that placental transfer of antibodies protects against transmission and infection. Murine and clinical studies demonstrate that antibody-dependent cellular cytotoxicity (ADCC) provides greater protection than neutralizing antibodies (nAbs) against disseminated neonatal disease. To quantify the relative transfer of HSV-specific Abs with different functions and targets and whether SARS-CoV-2 coinfection modified transfer, we conducted a prospective cohort study of mother-infant dyads prior to and during COVID-19. Total and HSV lysate, glycoprotein D (gD) and glycoprotein B (gB)- specific IgG, IgG1 and IgG3, nAbs, and ADCC were quantified in paired 3rd trimester maternal and cord blood. Transfer ratios (TR) were defined as cord: maternal Ab levels. IgG1 and IgG3 subclass and gD or gB-specific Abs were isolated by column purification and glycan profiles were assessed using mass spectrometry. The pre-COVID study population included 21 term and 15 preterm dyads who were HSV-1 (± HSV-2) seropositive (+) enrolled between 2018-2019 and the peri- COVID cohort included 25 HSV-1 (±HSV-2)+term dyadswhosemothers were also SARS-CoV-2 PCR and COVID Ab+ at delivery;14 were asymptomatic and 11 had mild-moderate COVID disease. None of the mothers had active genital HSV lesions during delivery. HSV-specific IgG, IgG1, and IgG3 TR were higher in term compared to preterm pre-COVID dyads (all p< 0.05). Similarly, the neutralizing Ab TR was 2.4[1.5, 4.0] in term vs 0.8[0.6, 1] in preterm (median [95%CI], p< 0.0001) but the ADCC TR was < 1.0 for both groups. To determine if the low ADCC TR reflected antigenic target, subclass, and/or glycans, we enriched for anti-gD and anti-gB specific and IgG1 and IgG3 Abs. These envelope glycoproteins are primary targets of neutralizing and ADCC responses, respectively. The anti-gD Abs were exclusively IgG1 and had only neutralizing activity. In contrast, anti-gB Abs were both IgG1 and IgG3;the IgG1 gB Abs had both neutralizing and ADCC activity whereas the IgG3 were only neutralizing. The anti-gD Abs were enriched for glycans associated with an affinity for FcRn, whereas anti-gB Abs expressed glycans associated with both FcRn and FcγRIIIa (receptor-associated with ADCC activity) binding. There was no significant difference in HSV-specific IgG TR in pre-COVID vs COVID dyads (0.42) but the nAb TR was lower (p = 0.018) and ADCC TR higher (p<0.001) in COVID compared to pre-COVID patients. Studies are in progress to assess whether this reflects increased placental colocalization of FcRn and FcgRIIIA, which would favor the transfer of ADCCAbs or modified Fc glycans. ADCC Abs transfer relatively inefficiently compared to nAbs, particularly in preterm infants and this may contribute to an increased risk of HSV disease. ADCC Ab transfer increased with SARS-CoV-2 coinfection, which may reflect differences in glycans and/or alterations in the placental architecture. Defining the determinants of ADCC transfer has implications for future vaccine and monoclonal Ab strategies to prevent/treat neonatal herpes. We speculate that increasing the transfer of ADCC may be a key element in providing immune protection.

Response of lymphopenic apheresis platelet donors to COVID-19 vaccination

Background: Recent studies have shown that several frequent apheresis platelet donors (more than 20 donations/year for several years) have CD4+ T cell counts below the normal limit (<400 cells/μl) while the levels of other blood cell types (including B cells) remain normal. This lymphopenia does not appear to be associated with an increased susceptibility to infections and cancers, suggesting that it does not affect immune function of the platelet donors with low CD4+ T cell counts. Aims: To assess the immune capacity of apheresis platelet donors with lymphopenia by taking advantage of the recent SARS-CoV-2 vaccination campaign. Methods: Forty-three apheresis platelet donors who donate at least five times per year were recruited. At least half of these participants were frequent donors and were thus more likely to have low CD4+ T cell counts. Their baseline CD4+ T cell count was determined by flow cytometry. The levels of antibodies targeting the SARS-CoV-2 Spike receptor binding domain (RBD) were measured by ELISA before and after vaccination. The level of antibodies against native full-length Spike was determined by flow cytometry using transfected cells expressing different Spike variants of concern (D614G, Delta, Omicron). The avidity of RBD antibodies produced after the first and second dose of vaccine was determined using a modified ELISA in which a chaotropic agent (urea 8 M) was added. The functional properties of vaccine-elicited SARSCoV- 2 antibodies were measured using ADCC and neutralization assays. Results: Of the 43 participants, 27 had pre-vaccination CD4+ T cell counts below 400 cells/μl (low CD4 group) and 16 participants had CD4+ T cell counts in the normal range (400-1600 CD4/μl;normal CD4 group). The levels of RBD-binding antibody did not significantly differ between the low and normal CD4 groups for all three isotypes (IgG, IgA and IgM) after the first and second doses of vaccine. As expected given the maturation of immune response, the avidity of RBD-binding antibodies present in the plasma collected after the second dose of vaccine was significantly higher than that measured in plasma recovered after the first dose. However, the increase was of similar magnitude in both CD4 groups. Recognition of the three Spike variants, as measured by flow cytometry, did not differ significantly between the low and normal CD4 groups. Finally, the antibody(Fc)- mediated effector function (measured by ADCC using cells expressing the wild type Spike) and neutralization capacity of the three variants of concern were comparable for the two groups, after receiving two vaccine doses. Summary/Conclusions: Our data show that low CD4+ T cell counts in apheresis platelet donors do not impair their response to antigenic challenge such as COVID-19 vaccination. This finding is consistent with the previously lack of increased susceptibility of platelet donors with lymphopenia to infections and cancers. Work remains to be done to understand the physiological mechanism behind the low number of CD4+ T cells in the peripheral blood of several plateletpheresis donors.

IMPAIRED CYTOTOXIC IMMUNE RESPONSE and EBV REACTIVATION in PATIENTS with LONG COVID19

Background: About 10% of individuals with mild infection with SARS-CoV-2 suffer from Long COVID-19, defined as signs and symptoms developed during or following COVID-19 that continue for more than twelve weeks and cannot be explained by an alternative diagnosis. In this study, we analyzed the ADCC response and the reactivation of CMV and EBV in Long COVID-19 syndrome, in comparison with patients who completely recovered from mild COVID-19 Methods: 30 patients with Long COVID-19 (Long COVID-19) and 20 individuals who suffered mild COVID-19 and were completely recovered (Recovered) were recruited for this study. Specific anti-SARS-CoV-2 IgG titers were analyzed by direct ELISA and their neutralizing capability was measured by using pseudovirus neutralization assay. Phenotype of CD4+ and CD8+ T cells, NK, NKT, and B cells in peripheral blood was analyzed by flow cytometry. ADCC activity was analyzed using rituximab-coated Raji cells as target. EBV and CMV reactivation in plasma was analyzed by qPCR. Results: 1) 86.6% and 55.50% participants were female in Long COVID-19 and Recovered cohorts, respectively. Median age at COVID-19 diagnosis was 42y(IQR 37-46) and 45y (IQR 28-57), respectively. 2) Similar levels of CD4+ T cells were observed in both groups. However, Tregs were increased 2.8-fold in Long COVID-19 participants (p=0.0007). 3) CD8+ T cells, CD8+TCRγδ and CD8+TCRγδ were increased 1.3-(p=0.0005), 2.0-(p=0.049), and 2.5-fold (p=0.005) in Long COVID-19 individuals. 4) Expression of CD56 in NK cells and CD3-CD56+CD16+ cells were increased 1.7-(p=0.0005) and 1.7-fold (p=0.032) in Long COVID-19, respectively. 5) Specific anti-SARS-CoV-2 IgG titers were increased 2.3-fold in Long COVID-19 individuals (p=0.02) and their neutralizing capacity was increased 4.2-fold (p=0.034) in this cohort. However, ADCC activity was decreased 1.4-fold (p=0.0044). 6) Resting memory B cells were increased 2.3-fold during Long COVID-19, whereas plasmablasts were reduced 3.1-fold. 7) EBV was reactivated in 33.3% of Long COVID-19 individuals (p<0.0001), whereas CMV was not reactivated in any individual. Conclusion: Despite high levels of neutralizing antibodies and cytotoxic immune populations, an impaired antibody-dependent cytotoxic activity was observed in PBMCs from individuals with Long COVID-19. This defective cytotoxic immune response may impede viral clearance, which may also contribute to EBV reactivation observed in these individuals, thereby influencing on the persistent COVID-19 symptoms.

CD64 GENE-MODIFIED PRIMARY NK CELLS LOADED with ANTI-HIV bNAbs TRIGGER HIGH ADCC

Background: As part of a combined HIV CURE immuno-therapy strategy, we transduced primary human NK cells with the high affinity CD64 Fc receptor and pre-loaded them with HIV-specific bNAbs. We named these chimeric NK cells "NuKES" (NK Enhancement Strategy) for their augmented capacity to mediate ADCC and their potential clinical application as an autologous primary NK cell immuno-therapy against HIV. Methods: We transduced primary NK cells from control donors with a lentivirus expressing human CD64 in the presence or absence of irradiated K562 feeder cells expressing co-stimulatory molecules (CD40, 4-1BB) and/or cytokine pre-stimulation (IL-2, IL-21, IL-15). CD64 expressing NK cells were CFSE labeled and expanded ex vivo or FACS sorted at various times post transduction to high purity. CD64 expressing NK cells were then pre-loaded with HIV-specific bNAbs and tested in a functional ADCC CD107a degranulation assay against HIV-1 infected autologous CD4+ primary T cells. Results: After pre-stimulation with cytokines and/or irradiated K562 Feeder Cells, we could routinely achieve (n=5) greater than 40% CD64 expression in primary human NK cells (Day 14 post-transduction shown in Figure 1A). NK cells maintained strong proliferation potential with greater than 6 cells divisions beyond 10 days post transduction as determined by CFSE dilution (Day 10 post-transduction shown in Figure 1B). Phenotypically, CD64 transduced NK cells were similar to control NK cells and possessed strong expression of CD56, CD16, CD69 with intermediate levels of the NK maturation marker CD57. CD64 transduced NK cells could be successfully pre-loaded with HIV-specific bNAbs and possessed an enhanced capacity (GMFI of 2,014 versus 276) to retain 10-1074 for several hours as compared to control NK cells (Figure 1C). Functionally, CD64 transduced NK cells showed a significant two-fold increase in ADCC-triggered degranulation capacity against autologous HIV-1 infected CD4+ primary T cells compared to control NK cells after pre-loading with HIV-specific bNAbs (27.6% versus 13.2% CD107a). Conclusion: Primary human NK cells can be successfully transduced with CD64 and expanded ex vivo to high purity. Preparation of bNAbs specific NuKES represent a viable autologous NK immuno-therapy approach against HIV-1 with potential adaptation for added disease targets (i.e., COVID, Cancer) moving forward.

A LONG-INTERVAL VACCINE REGIMEN LEADS to STRONG HUMORAL RESPONSES AGAINST SARS-CoV-2

Background: While the standard regimen of the BNT162b2 mRNA vaccine includes two doses administered three weeks apart, some public health authorities decided to space them in a context of vaccine scarcity. This decision raised concerns about vaccine efficacy, notably against the many circulating variants. In this study, we analyzed the longitudinal humoral responses from before the first dose to 4 months after the second dose in a cohort of SARS-CoV-2 naïve and previously infected (PI) individuals, with an interval of sixteen weeks between the two doses. We compared these responses to those elicited in individuals receiving the three weeks dose interval. Methods: We measured the level of antibodies recognizing SARS-CoV-2 Spike or its receptor-binding domain, and the capacity of these antibodies to neutralize several variants of concern (VOCs) and other human coronaviruses. We also measured B cell responses and Fc-mediated effector functions (ADCC) elicited by vaccination. Results: We observed that in PI individuals, the first dose led to strong humoral responses that could not be significantly improved further upon administration of a second dose. In the naïve individual's group, the first dose induced weak neutralizing activity but strong Fc-mediated functions and the administration of the second dose 16 weeks after led to a significant increase of humoral responses, achieving similar levels to those measured in PI individuals. In both groups, we observed that plasmas were able to recognize and neutralize the Spike of different VOCs but also SARS-CoV-1. Conclusion: Our results show that individuals that received the extended BNT162b2 vaccine interval developed strong humoral responses. For the naïve donors, these responses were superior to those elicited by the three-week dose interval and comparable to the PI responses after one or two doses.

SARS-CoV-2 PLASMA VIREMIA and DYSREGULATED IMMUNITY in SEVERE COVID-19

Background: Critical COVID-19 occurs ca. 7d from symptoms onset, and is associated to immune dysregulation as well as SARS-CoV-2 detection in plasma (i.e. viremia). We hereby sought to detail the association between SARS-CoV-2 viremia measured at the end of the first week of disease and immune phenotypes/function in COVID-19 patients. Methods: We consecutively enrolled patients hospitalized in the acute phase of ascertained SARS-CoV-2 pneumonia. In this disease stage, we studied SARS-CoV-2 viremia (RT-PCR) and cytokines (MACSPlex), HLA-DR+CD38+ activated, GRZB+PRF+ pro-cytolitic T-cells, intracellular cytokine production (IL-2, IFNγ, TNFα, IL-4, IL-17A) after SARS-CoV-2 challenge (S-N-M-peptide pool). Simultaneous Th1-cytokines production (polyfunctionality) and amount (iMFI) was assessed. Humoral response: anti-S1/S2 IgG, anti-RBD total-Ig, IgM, IgA, IgG1 and IgG3 (ELISA), pseudoviruses neutralization (ID50) and Fc-mediated functions (%ADCC). Results: Out of 54 patients, 27 had detectable viremia (V+). Albeit comparable age and co-morbidities, V+ patients more frequently required non-invasive/invasive ventilatory support (p=0.035), with a trend to higher death (p=0.099) vs patients with undetectable viremia (V-)(Fig.1A). V+ displayed higher circulating IFN-α (p=0.002) and IL-6 (0.003), lower activated HLA-DR+CD38+CD4 (p=0.01) and CD8 (p=0.02), with no differences in GRZB+PRF+ T-cells. V+ featured reduced SARS-CoV-2-specific cytokine-producing T-cells, reaching significance for IFNγ+CD4 (p=0.02), TNFα+CD8, IL-4+CD8 (p=0.04) (Fig.1B-C), with lower bi-and tri-functional SARS-CoV-2-specific CD4 Th1, reaching significance for IL-2+TNFα+CD4 (p=0.03) (Fig.1D). A trend towards lower cytokines iMFI in bi-and tri-functional SARS-CoV-2-specific CD4 Th1 was observed in V+, reaching significance for IL-2+TNFα+CD4, p=0.004. V+ displayed lower anti-S IgG, anti-RBD total-Ig, IgM, IgG1 and IgG3 (Fig.1E), with lower ID50 and %ADCC vs V-(Fig.1F-G). Conclusion: Hospitalized COVID-19 patients with detectable plasma SARS-CoV-2 RNA in the acute phase of disease present worse outcome, higher inflammatory cytokines, fewer activated and SARS-CoV-2-specific polyfunctional T-cells, suggesting a link between SARS-CoV-2 viremia at the end of the first stage of disease and immune dysregulation. Whether high ab initium viral burden and/or intrinsic host factors contribute to a delayed and/or exhausted immune response in severe COVID-19 remains to be elucidated, to further inform strategies of targeted therapeutic interventions.

TEMPORAL ASSOCIATIONS of B and T CELL IMMUNITY in A 16-WEEK INTERVAL BNT162b2 REGIMEN

Background: Spacing of the BNT162b2 mRNA doses beyond the standard 3-week interval raised concerns about vaccine efficacy. We longitudinally analyzed B cell, T cell and humoral responses to two BNT162b2 mRNA doses administered 16 weeks apart in 43 SARS-CoV-2 naïve and previously-infected (PI) donors. We examined blood samples at five time points from baseline to 4 months post second dose. Methods: We used high-parameter flow cytometry to study: i) receptor binding domain (RBD)-specific B cells;ii) Spike (S)-specific CD4 and CD8 T cells by activation-induced marker (AIM) assay;iii) S-specific CD4 and CD8 T cells by intracellular staining (ICS) assay. We measured humoral responses by ELISA, neutralization and ADCC assays. We did supervised and unsupervised (FlowSOM) analyses of B and T cell subsets, and temporal association analyses. Results: We observed partial attrition of B and T cell responses between doses at a memory time point 12 weeks post first dose. RBD-specific B cell kinetics differed between cohorts: the first dose led to their robust increase in PI but small magnitude in naïve. The second dose had little effect in PI but briskly expanded RBD-specific B cells in naïve, leading to convergence between cohorts. Robust T cell responses, with a dominance of CD4 over CD8 responses, were universally induced and did not significantly differ in magnitude after either dose, although there was a trend for a gain in CD8 responses after the second dose in naïve. Unsupervised and supervised analyses of S-specific CD4 T cells showed that the first dose was sufficient to generate highly diverse CD4 subsets, including robust populations of follicular T helper cells. The second dose did not elicit new subsets but lead to convergent phenotypic and functional profiles between PI and naïve with qualitative shifts. Integrated analyses of antigen-specific responses showed immune component-specific associations over-time, with early CD4 responses post-first dose (but not at late time points) strongly correlating with B cell responses after the second dose. In contrast, CD8 responses post second dose correlated with CD4 responses at the same time point. Conclusion: The 16-week interval schedule is associated with robust, multi-faceted recall cellular responses after the second dose, consistent with highly functional immune memory. The early induction of robust CD4 responses and their associations with longer-term B cell and humoral immunity support their central role in the efficacy of this vaccine regimen.