Neutralizing Antibody Research Articles

Standardization, validation, and comparative evaluation of a convenient surrogate recombinant vesicular stomatitis virus plaque reduction test for quantification of Hantaan orthohantavirus (HTNV) neutralizing antibodies

Hantaan orthohantavirus (HTNV) is responsible for severe hemorrhagic fever with renal syndrome (HFRS), which has a case fatality rate of 1% to 10%. Currently, the inactive vaccine licensed in endemic areas elicit low levels of neutralizing antibodies (NAbs). Early NAbs administration is helpful for patients recovery from HFRS. Therefore, measuring NAbs is crucial for evaluating the immune response following infection or vaccination. The golden standard for HTNV NAbs measurement is the focus reduction neutralization test (FRNT), which typically requires skilled technicians and is performed under high biosafety containment facility. Here, we established a surrogate NAbs titration method with replication-competent vesicular stomatitis virus (VSV) bearing HTNV glycoprotein (rVSV-HTNV-GP) based plaque reduction neutralization test (PRNT). Then compared and correlated this method with the authentic HTNV based FRNT, and applied it to measure the NAbs level in 47 serum samples from HFRS patients, healthy donors and inactive vaccine recipients. We observed positive correlations between two neutralization assays among HFRS patients and inactive vaccine recipients (R2 = 0.5994 and 0.3440, respectively) and confirmed the clear specificity with healthy donors without vaccinated and reproducibility with three more assays. Our results suggest that rVSV-HTNV-GP based PRNT is a reliable lower-biosafety level surrogate for HTNV NAbs evaluation, which is easy to perform with higher sensitivity.Graphical abstract

Vitamin D as an Adjuvant Immune Enhancer to SARS-Cov-2 Vaccine.

The SARS-CoV-2 vaccine is an important keystone in fighting against the virus. The vaccination alone could not prevent all SARS-CoV-2 viral infections or even its spread, especially after the emergence of newly mutant strains. The immune response to the SARS-CoV-2 vaccines varies greatly from one person to another. Age, along with adequate micronutrients, especially vitamin D, are major factors influencing immunity. We aimed to analyze SARS-CoV-2 vaccine neutralization potency and the total IgG antibodies along with 25-hydroxy-cholecalciferol concentrations in a cohort of healthy Egyptian vaccinated adults. 196 individuals were included; 145 females and 51 males, with an age range between 22 and 59 years old, from the first time of vaccination and over 16weeks long. Three blood samples were taken from each individual at three time points; before the 1st dose of vaccination, before the 2nd dose of vaccination, and after 8 weeks of complete vaccination. The samples were analyzed using a chemiluminescent immunoassay to measure vitamin D level and titer of neutralizing and IgG antibodies. A lower level of neutralizing antibodies was detected in deficient and insufficient vitamin D-vaccinated individuals. However, a sufficient titer was detected in individuals with normal vitamin D. Vitamin D deficiency is associated with a suppressed immune response against SARS-CoV-2 despite vaccination. Thus, we made inquiries about using vitamin D as an adjuvant to SARS-CoV-2 vaccination, and its relation with the production of anti-SARS-CoV-2 antibodies.

A SARS-CoV-2 vaccine on an NIR-II/SWIR emitting nanoparticle platform.

The COVID-19 pandemic caused a global health crisis that resulted in millions of deaths. Effective vaccines have played central roles in curtailing the pandemic. Here, we developed a down-converting near-infrared IIb (NIR-IIb; 1500 to 1700 nanometers) luminescent, pure NaErF4@NaYF4 rare-earth nanoparticle (pEr) as vaccine carriers. The pEr nanoparticles were coated with three layers of cross-linked biocompatible polymers (pEr-P3; ~55 nanometers) and conjugated to the receptor binding domain (RBD) of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) spike protein. Upon subcutaneous injection of the pEr-P3-RBD nanovaccine in mice, in vivo NIR-IIb imaging revealed active vaccine trafficking and migration to lymph nodes through lymphatic vessels. Two doses of the adjuvant-free vaccine elicited long-lasting (>7 months) high titers of serum viral neutralization antibody and anti-RBD immunoglobulin G, along with robust RBD-specific germinal center B cells and T follicular helper cells. We devised in vivo NIR-II molecular imaging of RBD-specific cells in lymph nodes, opening noninvasive assessments of vaccine-elicited immune responses longitudinally.

SARS-CoV-2 outbreak in lions, tigers, and hyenas at Denver Zoo.

In late 2019, SARS-CoV-2 spilled over from an animal host into humans, where it efficiently spread, resulting in the COVID-19 pandemic. Through both natural and experimental infections, we learned that many animal species are susceptible to SARS-CoV-2. Importantly, animals in close proximity to humans, including companion, farmed, and those at zoos and aquariums, became infected, and many studies demonstrated transmission to/from humans in these settings. In this study, we first review the literature of SARS-CoV-2 infections in tigers and lions and compare species, sex, age, virus and antibody detection assay, and types, frequency, and length of clinical signs, demonstrating broad heterogeneity among infections. We then describe a SARS-CoV-2 outbreak in lions, tigers, and hyenas at Denver Zoo in late 2021. Animals were tested for viral RNA (vRNA) for 4 months. Lions had significantly more vRNA in nasal swabs than both tigers and hyenas, and many individual lions experienced viral recrudescence after weeks of undetectable vRNA. Infectious virus was correlated with high levels of vRNA and was more likely to be detected earlier during infection. Four months post-infection, all tested animals generated robust neutralizing antibody titers. Animals were infected with Delta lineage AY.20 identical to a variant circulating at less than 1% in Colorado humans at that time, suggesting a single spillover event from an infected human spread within and between species housed at the zoo. Better understanding of epidemiology and susceptibility of SARS-CoV-2 infections in animals is critical to limit the current and future spread and protect animal and human health.IMPORTANCESurveillance and experimental testing have shown many animal species, including companion, wildlife, and conservatory, are susceptible to SARS-CoV-2. Early in the COVID-19 pandemic, big cats at zoological institutions were among the first documented cases of naturally infected animals; however, challenges in the ability to collect longitudinal samples in zoo animals have limited our understanding of SARS-CoV-2 kinetics and clearance in these settings. We measured SARS-CoV-2 infections over 4 months in lions, tigers, and hyenas at Denver Zoo and detected viral RNA, infectious virus, neutralizing antibodies, and recrudescence after initial clearance. We found lions had longer and higher levels of virus compared to the other species. All animals were infected by a rare viral lineage circulating in the human population, suggesting a single spillover followed by interspecies transmission. These data are important in better understanding natural SARS-CoV-2 spillover, spread, and infection kinetics within multiple species of zoo animals.

Rapid restoration of potent neutralization activity against the latest Omicron variant JN.1 via AI rational design and antibody engineering

The rapid evolution of the viral genome has led to the continual generation of new variants of SARS-CoV-2. Developing antibody drugs with broad-spectrum and high efficiency is a long-term task. It is promising but challenging to develop therapeutic neutralizing antibodies (nAbs) through in vitro evolution based on antigen-antibody binding interactions. From an early B cell antibody repertoire, we isolated antibody 8G3 that retains its nonregressive neutralizing activity against Omicron BA.1 and various other strains in vitro. 8G3 protected ACE2 transgenic mice from BA.1 and WA1/2020 virus infection without adverse clinical manifestations and completely cleared viral load in the lungs. Similar to most IGHV3-53 antibodies, the binding sites of 8G3 and ACE2 largely overlap, enabling competition with ACE2 for binding to RBD. By comprehensively considering the binding free energy changes of the antigen-antibody complexes, the biological environment of their interactions, and the evolutionary direction of the antibodies, we were able to select 50 mutants. Among them, 11 were validated by experiments showing better neutralizing activities. Further, a combination of four mutations were identified in 8G3 that increased its neutralization potency against JN.1, the latest Omicron mutant, by approximately 1,500-fold, and one of the mutations led to an improvement in activity against multiple variants to a certain extent. Together, we established a procedure of rapid selection of neutralizing antibodies with potent SARS-CoV-2 neutralization activity. Our results provide a reference for engineering neutralizing antibodies against future SARS-CoV-2 variants and even other pandemic viruses.

A truncated pre-F protein mRNA vaccine elicits an enhanced immune response and protection against respiratory syncytial virus

The Food and Drug Administration (FDA) has approved vaccines designed by GSK, Pfizer and Moderna to protect high-risk populations against respiratory syncytial virus (RSV). These vaccines employ the pre-fusion F (pre-F) protein as the immunogen. In this study, we explored an mRNA vaccine based on a modified pre-F protein called LC2DM-lipid nanoparticle (LC2DM-LNP). This vaccine features a truncated version of the pre-F protein that is anchored to the cell membrane. Our experiments in young and old female mice revealed that the LC2DM-LNP vaccine elicited robust neutralizing antibody titers. Moreover, LC2DM-LNP prompted a Th1-skewed T-cell immune response in female rodent models. Female cotton rats immunized with LC2DM-LNP demonstrated strong immunity to RSV, without signs of vaccine-enhanced respiratory disease (VERD), even in cases of breakthrough infection. Importantly, when administered to pregnant female cotton rats, LC2DM-LNP ensured the transfer of pre-F-specific antibodies to the offspring and provided protection against RSV without increasing lung inflammation. Our findings suggest that LC2DM-LNP could serve as an alternative RSV vaccine candidate for high-risk groups.

The oncolytic adenovirus TILT-123 with pembrolizumab in platinum resistant or refractory ovarian cancer: the phase 1a PROTA trial.

Immune checkpoint inhibitors have demonstrated modest efficacy as a monotherapy in ovarian cancer. Originally developed to improve efficacy of T-cell therapies such as immune checkpoint inhibitors and adoptive cell transfer, TILT-123 (Ad5/3-E2F-D24-hTNFα-IRES-hIL-2) is a serotype chimeric oncolytic adenovirus encoding tumor necrosis factor alpha and interleukin-2. Here we report results from phase 1a of PROTA, a single-arm, multicentre dose escalation trial with TILT-123 and pembrolizumab in female patients with platinum resistant or refractory ovarian cancer (NCT05271318). The primary endpoint was safety. Secondary endpoints included efficacy, tolerability, virus persistence and anti-viral immunity. Patients (n = 15) received intravenous and intraperitoneal and/or intratumoral injections of TILT-123 as well as intravenous pembrolizumab. Treatment was well tolerated, and no dose-limiting toxicities were observed. The most frequent adverse events were fever (40%), fatigue (40%) and nausea (40%). Disease control was achieved in 64% of evaluable patients (9/14). Median progression-free survival and overall survival were 98 and 190 days respectively. Clinical responses were associated with higher serum anti-adenovirus neutralizing antibody titer at baseline and post-treatment. The phase 1b investigating TILT-123, pembrolizumab and PEGylated liposomal doxorubicin in a similar patient population is underway.

Efficient Identification of Monoclonal Antibodies Against Rift Valley Fever Virus Using High-Throughput Single Lymphocyte Transcriptomics of Immunized Mice

Background: Rift Valley fever virus (RVFV) is a zoonotic virus that poses a significant threat to both livestock and human health and has caused outbreaks in endemic regions. In humans, most patients experience a febrile illness; however, in some patients, RVF disease may result in hemorrhagic fever, retinitis, or encephalitis. While several veterinary vaccines are being utilized in endemic countries, currently, there are no licensed RVF vaccines or therapeutics for human use. Neutralizing antibodies specifically targeting vulnerable pathogen epitopes are promising candidates for prophylactic and therapeutic interventions. In the case of RVFV, the surface glycoproteins Gc and Gn, which harbor neutralizing epitopes, represent the primary targets for vaccine and neutralizing antibody development. Methods: We report the implementation of advanced 10x Genomics technology, enabling high-throughput single-cell analysis for the identification of rare and potent antibodies against RVFV. Following the immunization of mice with live attenuated rMP-12-GFP virus and successive Gc/Gn boosts, memory B cell populations (both general and antigen-specific) were sorted from splenocytes by flow cytometry. Deep sequencing of the antibody repertoire at a single-cell resolution, together with bioinformatic analyses, was applied for BCR pair selection based on their abundance and specificity. Results: Twenty-three recombinant monoclonal antibodies (mAbs) were selected and expressed, and their antigen-binding capacities were characterized. About half of them demonstrated specific binding to their cognate antigen with relatively high binding affinities. Conclusions: These antibodies could be used for the future development of efficacious therapeutics, as well as for studying virus-neutralizing mechanisms. The current study, in which the single-cell sequencing approach was implemented for the development of antibodies targeting the RVFV surface proteins Gc and Gn, demonstrates the effective applicability of this technique for antibody discovery purposes.

Corrigendum: A self-assembled nanoparticle vaccine elicits effective neutralizing antibody response against EBV infection

Corrigendum: A self-assembled nanoparticle vaccine elicits effective neutralizing antibody response against EBV infection

The immunogenicity of PRV ΔgE/TK/UL49.5 three-gene-deleted vaccine in mice

BackgroundPseudorabies (PR) caused by the re-emerging of pseudorabies virus (PRV) variant has outbroken among PRV vaccine immunized swine in many pig farms, which has caused serious social and economic consequences since the end of 2011. The PRV UL49.5 protein can inactivate the transporter associated with antigen processing (TAP), thereby downregulating the cell surface expression of swine leukocyte antigen class I (SLA-I) to evade host immune surveillance.MethodsIn this study, based on the PRV ΔgE/TK strain, PRV ΔgE/TK/UL49.5 triple gene deletion strain was constructed through homologous recombination and deletion of the PRV UL49.5 gene by the Cre-LoxP system. Its growth curve and effect on SLA-I transcription level were determined. Preliminary studies were carried out on serum neutralizing antibody levels, IFN-γ and IL-4 cytokines levels in mice immunized with PRV ΔgE/TK/UL49.5, and the viral load and challenge protection in mice tissues after challenge.ResultsThe growth characteristics of PRV ΔgE/TK/UL49.5 strain were similar to those of PRV ΔgE/TK strain. The level of SLA-I was returned to normal after the deletion of PRV UL49.5 gene. The immunization of PRV ΔgE/TK/UL49.5 did not affect the weight gain of mice. Immunized mice could induce high levels of serum neutralization antibodies and immune cytokines, including IFN-γ and IL-4, which could provide complete protection against virulent PRV challenge. No obvious pathological damage was observed in lung, brain and trigeminal ganglion of mice immunized with PRV ΔgE/TK/UL49.5, and the tissue viral load was the lowest.ConclusionsPRV ΔgE/TK/UL49.5 strain can induce enhanced immunogenicity and had the potential to be used as a candidate strain.

Pan-caspase inhibitors induce secretion of HIV-1 latency reversal agent lymphotoxin-alpha from cytokine-primed NK cells

The persistence of HIV-1 latency reservoirs in CD4+ T cells is a significant obstacle for curing HIV-1. Shock-and-kill strategies, which aim to reactivate latent HIV-1 followed by cytotoxic clearance, have shown limited success in vivo due to insufficient efficacy of latency reversal agents (LRAs) and off-target effects. Natural killer (NK) cells, with their ability to mediate cytotoxicity independent of antigen specificity, offer a promising avenue for enhancing the shock-and-kill approach. Previously, we observed that pan-caspase inhibitors induce NK cells to secrete an LRA in vitro. Here, we aimed to identify this LRA using a targeted proteomic approach. We identified lymphotoxin-α (LTα) as the key LRA secreted by NK cells following pan-caspase inhibitor treatment. LTα was shown to significantly induce HIV-1 LTR promoter activity, a hallmark of viral reactivation. Neutralization of LTα effectively abolished the observed LRA activity, confirming its central role. Moreover, cytokine-primed but not resting human primary NK cells exhibited LRA activity that could be neutralized with LTα neutralizing antibodies. Finally, pan-caspase inhibitor treatment did not decrease the ability of the cytokine-primed NK cells to kill target cells. These findings demonstrate that cytokine-primed NK cells, through LTα secretion, can effectively reactivate latent HIV-1 following pan-caspase inhibitor treatment, without compromising NK cell cytotoxicity. This highlights a potential enhancement strategy utilizing NK cells for shock-and-kill approaches in HIV-1 cure research.

Neutralizing antibody responses to three XBB protein vaccines in older adults

The ongoing COVID-19 pandemic has underscored the importance of strong immune defenses against emerging SARS-CoV-2 variants. While COVID-19 vaccines containing XBB subvariants have proven effective in neutralizing new SARS-CoV-2 variants, a gap remains in knowledge regarding neutralizing antibody responses in older adults aged >65 years against these newly emerged variants. This study was therefore undertaken to investigate and compare neutralizing antibody responses to three XBB-containing protein-based vaccines (trivalent XBB.1.5 vaccine, bivalent Omicron XBB vaccine, and tetravalent XBB.1 vaccine) head-to-head in 90 individuals aged >65 years. The results showed that all three XBB-containing vaccines substantially enhanced the neutralizing antibody response, with 100% of vaccinees having detectable antibody titers against ancestral D614G and variants BA.5, XBB.1.5, JN.1, KP.2, and KP.3 after booster immunization. Subsequent analysis indicated that the trivalent XBB.1.5 and tetravalent XBB.1 vaccines elicited higher levels of neutralizing antibodies compared to the bivalent Omicron XBB vaccine. The KP.2 and KP.3 variants displayed antibody resistance comparable to the JN.1 variant. Older adults produce similar neutralizing antibody responses to the vaccines regardless of their underlying medical conditions. These findings indicate that booster vaccination with XBB-containing vaccines can effectively elicit strong neutralizing responses against a number of SARS-CoV-2 variants in older adults over 65 years, which will help guide vaccine strategies in this elderly population.

Atezolizumab neutralizing assay development: a novel way of evaluating assay cutpoint after sample pretreatment

Atezolizumab, a biotherapeutic monoclonal antibody directed against PD-L1, has been shown to be efficacious in multiple oncology indications. In clinical trials, a subset of patients developed anti-atezolizumab antibodies, necessitating the development of a neutralizing antibody (NAb) assay. A bead-based sample pretreatment method was developed to reduce high levels of therapeutic in patient serum samples. Untreated sample variability is reduced by this sample pretreatment, based on this, a novel approach was taken for determining an appropriate assay decision threshold (cutpoint). The therapeutic was added to the samples to mimic typical patient samples. The resulting assay was successfully validated and applied to sample analysis from multiple clinical trials.

A Decrease of Antibodies Against SARS-CoV-2 Antigens Does Not Reflect a Decrease of Neutralization Rate: A Prospective Study to Evaluate Kinetic and Dynamic Humoral Immune Response After Vaccination During Pregnancy.

Despite being at increased risk for severe COVID-19, pregnant women were initially excluded from vaccine clinical trials, which limited data regarding vaccine effectiveness and protection in this group. Aiming to better understand the immune response to vaccination during pregnancy, we compared the kinetics and titers of neutralizing and IgG antibodies generated against SARS-CoV-2 during vaccination with BNT162b2 (Pfizer-BioNTech) or CoronaVac (Sinovac Biotech) in a cohort of pregnant women. We evaluated participants before vaccination and 30 days after each vaccine dose, using a multiplex bead assay to measure IgG antibodies against SARS-CoV-2 antigens (total spike, spike-1, spike-2, receptor binding domain, and nucleocapsid) and a live virus fluorescence reduction neutralization assay (FRNA) to quantify neutralizing antibodies. Our data showed that vaccination resulted in a robust humoral response, with a considerable increase in the levels of IgG and neutralizing antibodies after the first vaccine dose and a sustained neutralizing response after the vaccine boost. In addition, antispike IgG assays presented a slight decrease after the second dose, while the neutralization rate remained stable. Immune response to the SARS-CoV-2 vaccine in pregnant women demonstrated an important increase in neutralizing antibodies.

Antibody responses in omicron BF.7-infected patients vaccinated with inactivated SARS-CoV-2.

Our study aimed to investigate antibody responses in omicron BF.7-infected patients after being vaccinated with inactivated SARS-CoV-2. Blood serum samples were collected every 2-7d, 1 w before infection, during the acute infection period and recovery period, and every month after recovery to detect IgG, IgM, IgA, neutralizing antibodies, and neutralizing antibodies against different omicrons in the acute phase. The levels of IgG, IgA and neutralizing antibodies increased sharply at 6-7d after infection, and the levels of IgG and neutralizing antibodies peaked rapidly within 1-2 w, lasting for 3-4 w, and the antibody levels gradually decreased at 4-8 w after infection. The level of neutralizing antibodies against the wild-type strain SARS-CoV-2 was much greater than that against the variant strains during the acute infection period. After being infected with omicron BF.7, the IgG and neutralizing antibodies in inactivated SARS-CoV-2-vaccinated individuals increase sharply 6-7 days after infection, which is earlier than those in the initial WT SARS-CoV-2 infection, and the peak time within 1-2 w is shorter. The levels of IgG, neutralizing antibody, and IgA antibodies are high, and the levels of IgM antibodies are low; however, the neutralizing antibodies are mainly against the wild-type strain of SARS-CoV-2.

Development and immunogenicity evaluation of attenuated Salmonella typhimurium delivering porcine Deltacoronavirus S1 gene.

Porcine deltacoronavirus (PDCoV) is a swine enteropathogenic coronavirus that causes severe diarrhea in piglets, the development of novel vaccines is of great value in the prevention and control of PDCoV. Here, we selected attenuated Salmonella typhimurium SL7207 to deliver pVAX1-S1, resulting in the oral vaccine strain, SL7207 (pVAX1-S1). In immunized mice, SL7207 (pVAX1-S1) induced PDCoV-specific humoral IgG, IgA, neutralizing antibodies, mucosal sIgA, up-regulation of CD8+ T cells, and increased levels of Th1 cytokines (IFN-γ and IL-2). In piglets, SL7207 (pVAX1-S1) induced high levels of PDCoV-specific humoral IgG and neutralizing antibodies but no detectable IgA, and only low levels of mucosal sIgA. SL7207 (pVAX1-S1) also promoted T cell differentiation into CD4+ and CD8+ T cells, and increased the expression level of IFN-γ and IL-4 in peripheral blood. Challenge experiments in piglets showed SL7207 (pVAX1-S1) alleviated diarrhea, decreased fecal virus load and intestinal lesions compared with control groups. In conclusion, this study systematically evaluated the immunogenicity and feasibility of attenuated Salmonella typhimurium delivering PDCoV S1 gene, which will provide helpful reference information for further exploration of novel PDCoV oral vaccine.

Immunogenicity of yellow fever vaccine co-administered with 13-valent pneumococcal conjugate vaccine in rural Gambia: A cluster-randomised trial.

Because booster doses of pneumococcal conjugate vaccine (PCV) may be given at a similar time to yellow fever vaccine (YF), it is important to assess the immune response to YF when co-administered with PCV. This has been investigated during a reduced-dose PCV trial in The Gambia. In this phase 4, parallel-group, cluster-randomized trial, healthy infants aged 0-10weeks were randomly allocated to receive either a two-dose schedule of PCV13 with a booster dose co-administered with YF vaccine at age 9months (1+1 co-administration) or YF vaccine administered separately at age 10months (1+1 separate) or the standard three early doses of PCV13 with YF vaccine at age 9months (3+0 separate). Blood samples were collected 28-35days post-vaccination and YF neutralizing antibody (NA) titres were measured. Proportions with seroprotective YF NA titres≥1:8 were calculated with 95% confidence intervals (CI). Non-inferiority was demonstrated if the lower limit of the CI for the difference in proportions between the co-administration and separate groups was greater than-10%. Forty-eight, 66, and 98 participants enrolled in 3+0 separate, 1+1 co-administration, and 1+1 separate groups respectively had NA results. Per protocol analysis of the 3+0 separate, 1+1 co-administration, 1+1 separate, and the combined 1+1 separate and 3+0 separate groups found that 81%, 85%, 92%, and 88% of participants respectively had YF NA titres ≥1:8. Results were similar with analysis by intention-to-treat. The difference in proportions comparing 1+1 co-administration and 1+1 separate groups was -7% (95% CI, -18% to 3%). The difference between 1+1 co-administration and 3+0 separate groups was 4% (95% CI, -10% to 15%). There was no statistical difference in the YF seroresponse when the YF vaccine was co-administered with PCV or administered separately. No evidence was found of the non-inferiority of the seroresponse to YF vaccine when co-administered with PCV13. The levels of YF NA attaining seroprotection (NT ≥1:8) were high in all groups. PCV13 co-administered with YF vaccine at 9months does not affect seroresponse to YF vaccine. http://www.isrctn.org/ - ISRCTN72821613.

Assessing Torquetenovirus (TTV) as a Biomarker for Immune Responses to SARS-CoV-2 mRNA Vaccines in People Living with HIV and Healthy Individuals

Background: Torquetenovirus (TTV) viremia is increasingly recognized as a marker of immune competence. In the context of COVID-19, TTV viral load (VL) has been shown to predict anti-Spike antibody levels in severely immunocompromised patients. This study aimed to evaluate whether pre-vaccine TTV VL could predict humoral and cellular immune responses to SARS-CoV-2 mRNA vaccines in people living with HIV (PLWH) and healthy individuals (HP). Methods: TTV VL was measured via real-time PCR in serum samples collected before the second and third doses of mRNA vaccines in 93 PLWH and 48 HP (second dose) and 255 PLWH and 48 HP (third dose). Immune responses were assessed through anti-SARS-CoV-2 receptor-binding domain (RBD) IgG, neutralizing antibodies, and IFN-γ release. Statistical analyses included correlation studies between TTV VL and vaccine-induced immune responses. Results: TTV VL did not significantly correlate with anti-RBD IgG or neutralizing antibody levels in either cohort; highlighting its limited predictive value for humoral responses in relatively immunocompetent populations. However, a strong inverse correlation was observed between TTV VL and IFN-γ release after the third, but not the second, vaccine dose. These findings suggest that higher TTV VL, indicative of reduced immune competence, may impair T-cell-mediated immunity to vaccines. Conclusions: In virologically suppressed PLWH and HP, TTV VL is not a reliable predictor of humoral immune responses to COVID-19 vaccines. However, its inverse relationship with cellular responses warrants further investigation in more immunosuppressed populations. These results reinforce the continuum model of TTV VL as a biomarker, with predictive utility increasing alongside the degree of immunosuppression

Effectiveness and Immunogenicity of the MMR Vaccine Against SARS-CoV-2 Among Healthcare Workers

The purpose of this study was to evaluate the effectiveness and immunogenicity of the measles–mumps–rubella (MMR) vaccine against SARS-CoV-2 in healthcare workers at one medical institution. The effectiveness of the MMR vaccine against SARS-CoV-2 was evaluated in overall healthcare workers (HCWs). In addition, neutralizing antibodies to SARS-CoV-2 were measured according to the subjects’ measles immunity status with serum samples collected before the coronavirus disease 2019 pandemic period. The effectiveness of the MMR vaccine for SARS-CoV-2 in all HCWs and measles IgG-positive subjects was 34% (adjusted odds ratio [aOR] = 1.20, 95% confidence interval [CI] = 0.53–2.70) and 34% (aOR = 0.66, CI = 0.38–18.4), respectively. The neutralizing antibody levels for SARS-CoV-2 were low in all groups regardless of the measles immune status. The MMR vaccine alone may not provide sufficient protection against SARS-CoV-2.

Comparison of neuraminidase inhibiting antibody responses elicited by egg- and cell-derived influenza vaccines.

An immunogenicity sub-study was performed within a clinical trial comparing the effectiveness of egg, cell, and recombinant hemagglutinin (HA)-derived influenza vaccines during the 2018-2019 and 2019-2020 influenza seasons. NAI and neutralizing antibody titers against the A(H1N1)pdm09 and A(H3N2) components of the vaccines were measured in pre- and post-vaccination sera. Responses to the N1 component of eIIV and cIIV were different in both study years 1 and 2 whereas response rate and antibody titers to the N2 component of egg and cell culture-derived vaccines were similar. For example, 43.5% of eIIV and no cIIV recipients had four-fold NAI titer increases in year 1. There was a weak positive correlation between responses to N1 and N2 for both vaccine types but no correlation between NAI and HA-specific neutralizing antibody responses. Recombinant HA vaccine that does not contain NA served as a specificity control; NAI antibody titers did not increase in recipients except in two individuals presumed to have subclinical infection. Antibody responses to NA following vaccination with eIIV and cIIV were not the same; although the responses to the N1 and N2 components of eIIV were similar, there were fewer responders to N1 than N2 of cIIV. Studies to determine the impact of NA immunity on influenza vaccine effectiveness are warranted.