Immunity to SARS-CoV-2: What Do We Know and Should We Be Testing for It?

Validation of a Pseudovirus Neutralization Assay for Severe Acute Respiratory Syndrome Coronavirus 2: A High-Throughput Method for the Evaluation of Vaccine Immunogenicity

The evaluation of coronavirus disease 2019 (COVID-19) vaccine immunogenicity remains essential as the severe acute respiratory syncytial virus 2 (SARS-CoV-2) pandemic continues to evolve and as additional variants emerge. Neutralizing antibodies are a known correlate of protection for SARS-CoV-2 vaccines. A pseudovirus neutralization (PNT) assay was developed and validated at Novavax Clinical Immunology Laboratories to allow for the detection of neutralizing antibodies in vaccine clinical trial sera. The PNT assay was precise, accurate, linear, and specific in measuring SARS-CoV-2 neutralization titers in human serum for ancestral strain and the Omicron subvariants BA.5 and XBB.1.5, with an overall geometric coefficient of variation of ≤43.4%, a percent relative bias within the expected range of -60% to 150%, and a linearity value of R2 > 0.98 for all three strains. This pseudovirus assay will be useful for the analysis of vaccine clinical trial samples to assess vaccine immunogenicity. Future work will focus on modifying the assay for emerging variants, including XBB.1.16, EG.5.1, BA.2.86, and any other variants that emerge in the ongoing pandemic.

Testing for SARS-CoV-2: lessons learned and current use cases

SUMMARYThe emergence and worldwide dissemination of SARS-CoV-2 required both urgent development of new diagnostic tests and expansion of diagnostic testing capacity on an unprecedented scale. The rapid evolution of technologies that allowed testing to move out of traditional laboratories and into point-of-care testing centers and the home transformed the diagnostic landscape. Four years later, with the end of the formal public health emergency but continued global circulation of the virus, it is important to take a fresh look at available SARS-CoV-2 testing technologies and consider how they should be used going forward. This review considers current use case scenarios for SARS-CoV-2 antigen, nucleic acid amplification, and immunologic tests, incorporating the latest evidence for analytical/clinical performance characteristics and advantages/limitations for each test type to inform current debates about how tests should or should not be used.

Validation of a severe acute respiratory syndrome coronavirus 2 microneutralization assay for evaluation of vaccine immunogenicity

As variants of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) continue to emerge, assessment of vaccine immunogenicity remains a critical factor to support continued vaccination. To this end, an in vitro microneutralization (MN50) assay was validated to quantitate SARS-CoV-2 neutralizing antibodies against prototype and variant strains (Beta, Delta, Omicron BA.1, Omicron BA.5, and XBB.1.5) in human serum. For the prototype strain, the MN50 assay met acceptance criteria for inter-/intra-assay precision, specificity, linearity, and selectivity. The assay was robust against changes to virus/serum incubation time, cell seeding density, virus content per well, cell passage number, and serum interference. Analyte in serum samples was stable up to five freeze/thaw cycles and for up to 12 months of storage at -80 ± 10 °C. Similar results were observed for the variant-adapted MN50 assays. The conversion factor to convert assay result units to WHO international standard units (IU/mL) was determined to be 0.62 for the prototype strain. This MN50 assay will be useful for vaccine immunogenicity analyses in clinical trial samples, enabling assessment of vaccine immunogenicity for ancestral and variant strains as variant-adapted vaccines are developed.

SARS-CoV-2 membrane protein-specific antibodies from critically ill SARS-CoV-2-infected individuals interact with Fc receptor-expressing cells but do not neutralize the virus

The membrane (M) glycoprotein of SARS-CoV-2 is one of the key viral proteins regulating virion assembly and morphogenesis. Immunologically, the M protein is a major source of peptide antigens driving T cell responses, and most individuals who have been infected with SARS-CoV-2 make antibodies to the N-terminal, surface-exposed peptide of the M protein. We now report that although the M protein is abundant in the viral particle, antibodies to the surface-exposed N-terminal epitope of M do not appear to neutralize the virus. M protein-specific antibodies do, however, activate antibody-dependent cell-mediated cytotoxicity and cytokine secretion by primary human natural killer cells. Interestingly, while patients with severe or mild disease make comparable levels of M antigen-binding antibodies, M-specific antibodies from the serum of critically ill patients are significantly more potent activators of antibody-dependent cell-mediated cytotoxicity than antibodies found in individuals with mild or asymptomatic infection.

Humoral and Cellular Immune Response after Three Doses of Sinopharm [Vero Cell]-Inactivated COVID-19 Vaccine in Combination with SARS-CoV-2 Infection Leads to Hybrid Immunity

BACKGROUND

Several vaccines against COVID-19 have been developed and licensed to enhance the immune response against SARS-CoV-2. Similarly, previous infection with SARS-CoV-2 has been shown to provide significant protection against severe infection and hospitalization.

METHODS

We investigated the effect of three doses of the Sinopharm vaccine and SARS-CoV-2 infection on the specific immune response in 103 volunteers, measuring neutralizing antibodies, anti-S1 IgG, anti-RBD IgM, anti-N IgM, anti-N IgG antibodies, and INF γ.

RESULTS

Our results showed that the presence of cardiovascular diseases increased the level of anti-N-IgG antibodies, while endocrinological diseases decreased the level of neutralizing antibodies and anti-N IgG antibodies, suggesting that these diseases alter the effect of vaccine-induced immunity. In addition, there was a significant decrease in anti-S1 IgG levels at 6 months and in anti-N IgG levels 18 months post-infection, while neutralizing antibodies and INF γ levels were constant at 3, 6, and 18 months post-infection.

CONCLUSIONS

Our results confirm the emergence of hybrid immunity, which is the strongest and most durable compared to natural immunity or vaccine-induced immunity. Significant positive correlations were found between humoral and cellular immunity markers: neutralizing antibodies, anti-S1 IgG and anti-N IgG antibodies, and INF γ, indicating a unique coordinated response specific to COVID-19.

Comprehensive, comparative evaluation of 25 automated SARS-CoV-2 serology assays

IMPORTANCE

We have previously highlighted the fact that hundreds of SARS-CoV-2 serology tests were released months after the onset of the COVID-19 pandemic. Of the hundreds of studies investigating the test kits' performance, few were comparative reports, using the same comprehensive sample set across multiple tests. Recently, we reported a comparative assessment of 35 rapid diagnostic tests (RDTs) or microtiter plate enzyme immunoassays (EIA) for use in low- and middle-income countries, using a large sample set from individuals with a history of COVID-19. Only a few tests meet WHO Target Product Profile performance requirements. This study reports on the performance of a further 25 automated SARS-CoV-2 immunoassays using the same panel of samples. The results highlight the better analytical and clinical performance of automated serology test kits compared with RDTs, and the importance of independent comparative assessments to inform the use and procurement of these tests for both diagnostic and epidemiological investigations.

Hook Effect in Semiquantitative SARS-CoV-2 Antispike Total Antibody Assay

OBJECTIVES

The hook effect is a common preanalytical error that results in falsely decreased analyte concentrations in immunoassays. We present here an example in a semiquantitative SARS-CoV-2 antispike total antibody assay and report the incidence of this error at our institution.

METHODS

All specimens with initial results within the reportable range of the assay were diluted. Results with higher results upon dilution were determined to have the hook effect. In a subset of specimens, these results were also confirmed as elevated on an alternative SARS-CoV-2 antibody assay.

RESULTS

Over 1 month, 12 (9.1%) of 132 results were within the analytical measuring range of the assay. Of these, 11 showed the hook effect and required dilution to obtain accurate results. These represented 8.3% of our total testing volume.

CONCLUSIONS

The hook effect was detected in a semiquantitative SARS-CoV-2 antispike total antibody assay at a high incidence. This error results in observed concentrations much lower than is accurate. Laboratories should be aware of this issue and consider manually diluting specimens within the reportable range of the assay to detect this issue.

T cell responses to COVID-19 infection and vaccination in patients with multiple sclerosis receiving disease-modifying therapy

BACKGROUND

Multiple sclerosis (MS) is a neurological disorder marked by accumulating immune-mediated damage to the central nervous system. The dysregulated immune system in MS combined with immune effects of disease-modifying therapies (DMTs) used in MS treatment could alter responses to infections, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that causes coronavirus disease 2019 (COVID-19). Most of the literature on immune response to SARS-CoV-2 infection and COVID-19 vaccination, in both the general population and patients with MS on DMTs, has focused on humoral immunity. However, immune response to COVID-19 involves multiple lines of defense, including T cells.

OBJECTIVE AND METHODS

We review innate and adaptive immunity to COVID-19 and expand on the role of T cells in mediating protective immunity against SARS-CoV-2 infection and in responses to COVID-19 vaccination in MS.

RESULTS

Innate, humoral, and T cell immune responses combat COVID-19 and generate protective immunity. Assays detecting cytokine expression by T cells show an association between SARS-CoV-2-specific T cell responses and milder/asymptomatic COVID-19 and protective immune memory.

CONCLUSION

Studies of COVID-19 immunity in people with MS on DMTs should ideally include comprehensive assessment of innate, humoral, and T cell responses.

A machine learning model for predicting serum neutralizing activity against Omicron SARS-CoV-2 BA.2 and BA.4/5 sublineages in the general population

Supervised machine learning (ML) methods have been used to predict antibody responses elicited by COVID-19 vaccines in a variety of clinical settings. Here, we explored the reliability of a ML approach to predict the presence of detectable neutralizing antibody responses (NtAb) against Omicron BA.2 and BA.4/5 sublineages in the general population. Anti-SARS-CoV-2 receptor-binding domain (RBD) total antibodies were measured by the Elecsys® Anti-SARS-CoV-2 S assay (Roche Diagnostics) in all participants. NtAbs against Omicron BA.2 and BA4/5 were measured using a SARS-CoV-2 S pseudotyped neutralization assay in 100 randomly selected sera. A ML model was built using the variables of age, vaccination (number of doses) and SARS-CoV-2 infection status. The model was trained in a cohort (TC) comprising 931 participants and validated in an external cohort (VC) including 787 individuals. Receiver operating characteristics analysis indicated that an anti-SARS-CoV-2 RBD total antibody threshold of 2300 BAU/mL best discriminated between participants either exhibiting or not detectable Omicron BA.2 and Omicron BA.4/5-Spike targeted NtAb responses (87% and 84% precision, respectively). The ML model correctly classified 88% (793/901) of participants in the TC: 717/749 (95.7%) of those displaying ≥2300 BAU/mL and 76/152 (50%) of those exhibiting antibody levels <2300 BAU/mL. The model performed better in vaccinated participants, either with or without prior SARS-CoV-2 infection. The overall accuracy of the ML model in the VC was comparable. Our ML model, based upon a few easily collected parameters for predicting neutralizing activity against Omicron BA.2 and BA.4/5 (sub)variants circumvents the need to perform not only neutralization assays, but also anti-S serological tests, thus potentially saving costs in the setting of large seroprevalence studies.

A research and development (R&D) roadmap for broadly protective coronavirus vaccines: A pandemic preparedness strategy

Broadly protective coronavirus vaccines are an important tool for protecting against future SARS-CoV-2 variants and could play a critical role in mitigating the impact of future outbreaks or pandemics caused by novel coronaviruses. The Coronavirus Vaccines Research and Development (R&D) Roadmap (CVR) is aimed at promoting the development of such vaccines. The CVR, funded by the Bill & Melinda Gates Foundation and The Rockefeller Foundation, was generated through a collaborative and iterative process, which was led by the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota and involved 50 international subject matter experts and recognized leaders in the field. This report summarizes the major issues and areas of research outlined in the CVR and identifies high-priority milestones. The CVR covers a 6-year timeframe and is organized into five topic areas: virology, immunology, vaccinology, animal and human infection models, and policy and finance. Included in each topic area are key barriers, gaps, strategic goals, milestones, and additional R&D priorities. The roadmap includes 20 goals and 86 R&D milestones, 26 of which are ranked as high priority. By identifying key issues, and milestones for addressing them, the CVR provides a framework to guide funding and research campaigns that promote the development of broadly protective coronavirus vaccines.

SARS-CoV-2-reactive antibody waning, booster effect and breakthrough SARS-CoV-2 infection in hematopoietic stem cell transplant and cell therapy recipients at one year after vaccination

The kinetics of SARS-CoV-2 reactive IgG antibodies after full vaccination and booster in allogeneic and autologous stem cell transplantation (allo-HSCT, ASCT) and chimeric antigen receptor T-cell therapy (CAR-T) are of utmost importance for estimating risk of infection. A prospective multicenter registry-based cohort study, conducted from December 2020 to July 2022 was used to analyze antibody waning over time, booster effect and the relationship of antibody response and breakthrough infection in 572 recipients (429 allo-HSCT, 121 ASCT and 22 CAR-T cell therapy). A significant decline in antibody titers was observed at 3 and 6 months after full vaccination in recipients without pre-vaccine SARS-CoV-2 infection, whereas recipients infected prior to vaccination showed higher and stable antibody titers over time. In poor responders, a booster dose was able to increase antibody titers in 83% of allo-HSCT and 58% of ASCT recipients but not in CART-T cell recipients [0%] (p < 0.01). One-year cumulative incidence of breakthrough infection was 15%, similar among cell therapy procedures. Immunosuppressive drugs at the time of vaccination [hazard ratio (HR) 1.81, p = 0.0028] and reduced intensity conditioning (HR 0.49, p = 0.011) were identified as the only conditions associated with different risk of breakthrough infection in allo-HSCT recipients. Antibody titers were associated with breakthrough infection and disease severity. No death was observed among the 72 breakthrough infections. Antibody level decay after the first two vaccine doses was common except in recipients with pre-vaccination SARS-CoV-2 infection. Poorly responding allo-HSCT recipients showed a response advantage with the booster as compared to ASCT and, especially, the null response found in CAR-T cell recipients. Antibody titers were positively correlated with the risk of breakthrough SARS-CoV-2 infection which was mainly driven by the immunosuppression status.

Extracellular Vesicle-Based SARS-CoV-2 Vaccine

Messenger ribonucleic acid (RNA) vaccines are mainly used as SARS-CoV-2 vaccines. Despite several issues concerning storage, stability, effective period, and side effects, viral vector vaccines are widely used for the prevention and treatment of various diseases. Recently, viral vector-encapsulated extracellular vesicles (EVs) have been suggested as useful tools, owing to their safety and ability to escape from neutral antibodies. Herein, we summarize the possible cellular mechanisms underlying EV-based SARS-CoV-2 vaccines.

Wild-type SARS-CoV-2 neutralizing immunity decreases across variants and over time but correlates well with diagnostic testing

Importance

The degree of immune protection against severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) variants provided by infection versus vaccination with wild-type virus remains unresolved, which could influence future vaccine strategies. The gold-standard for assessing immune protection is viral neutralization; however, few studies involve a large-scale analysis of viral neutralization against the Omicron variant by sera from individuals infected with wild-type virus.

Objectives

1) To define the degree to which infection versus vaccination with wild-type SARS-CoV-2 induced neutralizing antibodies against Delta and Omicron variants.2) To determine whether clinically available data, such as infection/vaccination timing or antibody status, can predict variant neutralization.

Methods

We examined a longitudinal cohort of 653 subjects with sera collected three times at 3-to-6-month intervals from April 2020 to June 2021. Individuals were categorized according to SARS-CoV-2 infection and vaccination status. Spike and nucleocapsid antibodies were detected via ADVIA Centaur^® (Siemens) and Elecsys^® (Roche) assays, respectively. The Healgen Scientific^® lateral flow assay was used to detect IgG and IgM spike antibody responses. Pseudoviral neutralization assays were performed on all samples using human ACE2 receptor-expressing HEK-293T cells infected with SARS-CoV-2 spike protein pseudotyped lentiviral particles for wild-type (WT), B.1.617.2 (Delta), and B.1.1.529 (Omicron) variants.

Results

Vaccination after infection led to the highest neutralization titers at all timepoints for all variants. Neutralization was also more durable in the setting of prior infection versus vaccination alone. Spike antibody clinical testing effectively predicted neutralization for wild-type and Delta. However, nucleocapsid antibody presence was the best independent predictor of Omicron neutralization. Neutralization of Omicron was lower than neutralization of either wild-type or Delta virus across all groups and timepoints, with significant activity only present in patients that were first infected and later immunized.

Conclusions

Participants having both infection and vaccination with wild-type virus had the highest neutralizing antibody levels against all variants and had persistence of activity. Neutralization of WT and Delta virus correlated with spike antibody levels against wild-type and Delta variants, but Omicron neutralization was better correlated with evidence of prior infection. These data help explain why 'breakthrough' Omicron infections occurred in previously vaccinated individuals and suggest better protection is observed in those with both vaccination and previous infection. This study also supports the concept of future SARS-CoV-2 Omicron-specific vaccine boosters.

A performance comparison of two (electro) chemiluminescence immunoassays for detection and quantitation of serum anti-spike antibodies according to SARS-CoV-2 vaccination and infections status

The information provided by SARS-CoV-2 spike (S)-targeting immunoassays can be instrumental in clinical-decision making. We compared the performance of the Elecsys® Anti-SARS-CoV-2 S assay (Roche Diagnostics) and the LIAISON® SARS-CoV-2 TrimericS IgG assay (DiaSorin) using a total of 1176 sera from 797 individuals, of which 286 were from vaccinated-SARS-CoV-2/experienced (Vac-Ex), 581 from vaccinated/naïve (Vac-N), 147 from unvaccinated/experienced (Unvac-Ex), and 162 from unvaccinated/naïve (Unvac-N) individuals. The Roche assay returned a higher number of positive results (907 vs. 790; p = 0.45; overall sensitivity: 89.3% vs. 77.6%). The concordance between results provided by the two immunoassays was higher for sera from Vac-N (ϰ: 0.58; interquartile ranges [IQR]: 0.50-0.65) than for sera from Vac-Ex (ϰ: 0.19; IQR: -0.14 to 0.52) or Unvac-Ex (ϰ: 0.18; IQR: 0.06-0.30). Discordant results occurred more frequently among sera from Unvac-Ex (34.7%) followed by Vac-N (14.6%) and Vac-Ex (2.7%). Antibody levels quantified by both immunoassays were not significantly different when <250 (p = 0.87) or <1000 BAU/ml (p = 0.13); in contrast, for sera ≥1000 BAU/ml, the Roche assay returned significantly higher values than the DiaSorin assay (p < 0.008). Neutralizing antibody titers (NtAb) were measured in 127 sera from Vac-Ex or Vac-N using a S-pseudotyped virus neutralization assay of Wuhan-Hu-1, Omicron BA.1, and Omicron BA.2. The correlation between antibody levels and NtAb titers was higher for sera from Vac-N than those from Vac-Ex, irrespective of the (sub)variant considered. In conclusion, neither qualitative nor quantitative results returned by both immunoassays are interchangeable. The performance of both assays was found to be greatly influenced by the vaccination and SARS-CoV-2 infection status of individuals.

Durability of humoral and cell-mediated immune response after SARS-CoV-2 mRNA vaccine administration

Vaccination against the SARS-Cov-2 virus is an effective way to protect against the disease and the severe course of COVID-19. Forty-nine fully vaccinated with mRNA vaccines (BNT162b2 or mRNA-1273) SARS-CoV-2 infection-naïve volunteers aged 33-89 were enrolled in the study. Evaluation of the cellular and humoral immune response was performed within 1 to 3 months (T1) and 6-9 months (T2) after the second injection, and within 2-3 months (T3) after a booster dose. Additionally, a comparative analysis of the specific immune status was made between two age groups-below 60 (n = 22) and over 60 (n = 27) years. SARS-CoV-2-specific T-cell response was evaluated by IFN-γ-producing spot forming cells (SFCs) using a standardized ELISPOT assay. Virus neutralizing antibodies (VNA) against SARS-CoV-2 were measured by a blocking ELISA test and spike protein specific IgG (S-IgG) and IgA (S-IgA) antibodies-by semiquantitative ELISA. IFN-γ-producing SFCs, S-IgG, S-IgA and VNA significantly decreased 6-9 months after the second dose. After the third injection S-IgG and S-IgA markedly increased compared to T2 and reached the levels at T1. Of note, the highest values of VNA were observed at T3. No differences in the tested immune parameters were found between the two age groups. Data obtained showed that for a long period-6-9 months after a full course of immunization with mRNA vaccine, immune reactivity is present, but both cellular and humoral immune responses gradually decrease. The administration of a third dose mainly restores the specific humoral immune response against the SARS-CoV-2 virus.

Immunological Studies to Understand Hybrid/Recombinant Variants of SARS-CoV-2

The zoonotic SARS-CoV-2 virus was present before the onset of the pandemic. It undergoes evolution, adaptation, and selection to develop variants that gain high transmission rates and virulence, resulting in the pandemic. Structurally, the spike protein of the virus is required for binding to ACE2 receptors of the host cells. The gene coding for the spike is known to have a high propensity of mutations, as a result generating numerous variants. The variants can be generated by random point mutations or recombination during replication. However, SARS-CoV-2 can also produce hybrid variants on co-infection of the host by two distinct lineages of the virus. The genomic sequences of the two variants undergo recombination to produce the hybrid variants. Additionally, these sub-variants also contain numerous mutations from both the parent variants, as well as some novel mutations unique to the hybrids. The hybrid variants (XD, XE, and XF) can be identified through numerous techniques, such as peak PCR, NAAT, and hybrid capture SARS-CoV-2 NGS (next generation sequencing) assay, etc., but the most accurate approach is genome sequencing. There are numerous immunological diagnostic assays, such as ELISA, chemiluminescence immunoassay, flow-cytometry-based approaches, electrochemiluminescence immunoassays, neutralization assays, etc., that are also designed and developed to provide an understanding of the hybrid variants, their pathogenesis, and other reactions. The objective of our study is to comprehensively analyze the variants of SARS-CoV-2, especially the hybrid variants. We have also discussed the techniques available for the identification of hybrids, as well as the immunological assays and studies for analyzing the hybrid variants.

Recapping the Features of SARS-CoV-2 and Its Main Variants: Status and Future Paths

Over the two years that we have been experiencing the Severe Acute Respiratory Syndrome Coronavirus-2 (SARS-CoV-2) pandemic, our challenges have been the race to develop vaccines and the difficulties in fighting against new variants due to the rapid ability of the virus to evolve. In this sense, different organizations have identified and classified the different variants that have been emerging, distinguishing between variants of concern (VOC), variants of interest (VOI), or variants under monitoring (VUM). The following review aims to describe the latest updates focusing on VOC and already de-escalated variants, as well as to describe the impact these have had on the global situation. Understanding the intrinsic properties of SARS-CoV-2 and its interaction with the immune system and vaccination is essential to make out the underlying mechanisms that have led to the appearance of these variants, helping to determine the next steps for better public management of this pandemic.

Serologic response to a third dose of an mRNA-based SARS-CoV-2 vaccine in lung transplant recipients

Lung transplant recipients have an increased risk for severe coronavirus disease 2019 (COVID-19) due to infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). A third dose of a SARS-CoV-2 vaccine has been recommended for all solid organ transplant recipients, but data from lung transplant recipients specifically are scarce. In this study, the serologic response to a third dose of an mRNA-based SARS-CoV-2 vaccine was measured in 78 lung transplant recipients. Sixty-two percent (n = 48) had a serological response to vaccination, which was significantly higher than after the second vaccine dose (27 patients (35%); p = 0.0013). A positive serologic response was associated with having had COVID-19 (p = 0.01), and higher serum IgG level and complement mannose binding lectin pathway activity prior to vaccination (p = 0.04 and p = 0.03, respectively). Serologic response was not associated with the dose of mycophenolate mofetil or prednisone or other immune status parameters. Eleven patients (14%) developed COVID-19 after the second or third vaccine dose, but this did not associate with serologic response after the second vaccine dose (9% in patients who developed COVID-19 versus 39% in patients who did not develop COVID-19 (p = 0.09)), or with serologic response above cut-off values associated with clinical protection in previous studies. In conclusion, the response to mRNA-based SARS-CoV-2 vaccines in lung transplant recipients improves significantly after a third vaccine dose. Factors associated with a positive serologic response are having had COVID-19 prior to vaccination, and serum IgG and complement mannose binding lectin pathway activity prior to vaccination. Serologic response did not associate with clinical protection against COVID-19 in this study.

Peripheral lymphocyte subset counts predict antibody response after SARS-CoV-2 mRNA-BNT162b2 vaccine in cancer patients: results from the Vax-On-Profile study

Background

The adaptive immune response following COVID-19 vaccination is essential for humoral immunogenicity and clinical protection against symptomatic infections. We present the results of circulating lymphocyte profiling and their correlation with antibody response in cancer patients tested serologically six months after receiving a two-dose schedule of mRNA-BNT162b2 vaccine.

Methods

Absolute counts of lymphocyte subsets were determined using peripheral blood immunophenotyping. We collected samples for flow cytometry analysis alongside quantitative detection of IgG antibodies against the receptor-binding domain (RBD) of the SARS-CoV-2 Spike protein (S1). An IgG titer ≥ 50 AU/mL defined a positive seroconversion response.

Results

311 patients were evaluable for lymphocyte profiling and serologic testing. A preliminary multivariate analysis revealed that cytotoxic chemotherapy was the most consistent factor associated with lower counts of all lymphocyte subpopulations. T helper and B cells were found to be useful in predicting the occurrence of a positive seroconversion response using ROC curve analysis. A significant positive linear correlation was shown when anti-RBD-S1 IgG titers were compared to these lymphocyte subset counts. Univariate analysis indicated that antibody titers and seroconversion rates were significantly improved in the high-level T and B cell subgroups. Multivariate analysis confirmed these significant interactions, as well as the negative predictive value of immunosuppressive corticosteroid therapy.

Conclusions

These findings suggest that simple and widely available peripheral counts of T helper and B cells correlate with humoral response to mRNA-BNT162b2 vaccine in actively treated cancer patients. Upon validation, our results could provide additional insights into the predictive assessment of vaccination efficacy.

Humoral response after a third and fourth dose of mRNA-based SARS-CoV-2 vaccine in previously seronegative kidney transplant recipients

Growing evidence shows diminished response to mRNA-based SARS-CoV‑2 vaccination in kidney transplant recipients. We aimed to investigate the seroconversion rate after a 3rd and 4th dose of mRNA vaccination in kidney transplant recipients without prior antibody response to two or three vaccination doses.This retrospective study included 324 prevalent kidney transplant recipients of a single tertiary transplantation center of which 157 remained seronegative, defined as anti-spike-RBD-IgG antibody titer < 7.1 BAU/ml, after two doses of mRNA-based SARS-CoV‑2 vaccination. Maintenance immunosuppression was not changed. The median patient age was 60.6 years (IQR 51.4-68.1 years), 66.9% were male. Positivity for anti-spike-RBD-IgG (≥ 7.1 BAU/ml) was measured 4-5 weeks after administration of a 3rd and 4th vaccine dose.Seroconversion rates were 63.9% after a 3rd dose and 29.3% after a 4th dose of vaccine. Cumulative prevalence of seropositivity was 51.5% after 2 doses, 80.5% after 3 doses and 84.2% after 4 doses.In conclusion, seroconversion can be achieved in the majority of the kidney transplant recipients by administrating three or four doses of mRNA vaccine without changing maintenance immunosuppression.