SARS-CoV-2 evolution has increased resistance to monoclonal antibodies and first-generation COVID-19 vaccines: Is there a future therapeutic role for soluble ACE2 receptors for COVID-19?

COVID-19 has caused calamitous health, economic and societal consequences. Although several COVID-19 vaccines have received full authorization for use, global deployment has faced political, financial and logistical challenges. The efficacy of first-generation COVID-19 vaccines is waning and breakthrough infections are allowing ongoing transmission and evolution of SARS-CoV-2. Furthermore, COVID-19 vaccine efficacy relies on a functional immune system. Despite receiving three primary doses and three or more heterologous boosters, some immunocompromised patients may not be adequately protected by COVID-19 vaccines and remain vulnerable to severe disease. The evolution of new SARS-CoV-2 variants has also resulted in the rapid obsolescence of monoclonal antibodies. Convalescent plasma from COVID-19 survivors has produced inconsistent results. New drugs such as Paxlovid (nirmatrelvir/ritonavir) are beyond the reach of low- and middle-income countries. With widespread use of Paxlovid, it is likely nirmatrelvir-resistant clades of SARS-CoV-2 will emerge in the future. There is thus an urgent need for new effective anti-SARS-CoV-2 treatments. The in vitro efficacy of soluble ACE2 against multiple SARS-CoV-2 variants including omicron (B.1.1.529), was recently described using a competitive ELISA assay as a surrogate marker for virus neutralization. This indicates soluble wild-type ACE2 receptors are likely to be resistant to viral evolution. Nasal and inhaled treatment with soluble ACE2 receptors has abrogated severe disease in animal models of COVID-19. There is an urgent need for clinical trials of this new class of antiviral therapeutics, which could complement vaccines and Paxlovid.

The autoimmune rheumatological presentation of Common Variable Immunodeficiency Disorders with an overview of genetic testing

Primary immunodeficiency Disorders (PIDS) are rare, mostly monogenetic conditions which can present to a number of specialties. Although infections predominate in most PIDs, some individuals can manifest autoimmune or inflammatory sequelae as their initial clinical presentation. Identifying patients with PIDs can be challenging, as some can present later in life. This is often seen in patients with Common Variable Immunodeficiency Disorders (CVID), where symptoms can begin in the sixth or even seventh decades of life. Some patients with PIDs including CVID can initially present to rheumatologists with autoimmune musculoskeletal manifestations. It is imperative for these patients to be identified promptly as immunosuppression could lead to life-threatening opportunistic infections in these immunocompromised individuals. These risks could be mitigated by prior treatment with subcutaneous or intravenous (SCIG/IVIG) immunoglobulin replacement or prophylactic antibiotics. Importantly, many of these disorders have an underlying genetic defect. Individualized treatments may be available for the specific mutation, which may obviate or mitigate the need for hazardous broad-spectrum immunosuppression. Identification of the genetic defect has profound implications not only for the patient but also for affected family members, who may be at risk of symptomatic disease following an environmental trigger such as a viral infection. Finally, there may be clinical clues to the underlying PID, such as recurrent infections, the early presentation of severe or multiple autoimmune disorders, as well as a relevant family history. Early referral to a clinical immunologist will facilitate appropriate diagnostic evaluation and institution of treatment such as SCIG/IVIG immunoglobulin replacement. This review comprises three sections; an overview of PIDs, focusing on CVID, secondly genetic testing of PIDs and finally the clinical presentation of these disorders to rheumatologists.

Phenotypic spectrum in a family with a novel RAC2 p.I21S dominant-activating mutation

Objectives

Dominant-activating (DA) lesions in RAC2 have been reported in 18 individuals to date. Some have required haematopoietic stem cell transplantation (HSCT) for their (severe) combined immunodeficiency syndrome phenotype. We aimed to investigate clinical and cellular features of a kindred harbouring a novel variant in RAC2 p.Ile21Ser (I21S) to better understand DA lesions' phenotypic spectrum.

Methods

Clinical and immunological information was collated for seven living individuals from the same kindred with RAC2 p.I21S. We evaluated neutrophil morphology, RAC2 protein expression and superoxide production using freshly isolated neutrophils stimulated with phorbol-12-myristate-13-acetate (PMA) and N-formyl-MetLeuPhe (fMLP).

Results

Patient 1 (P1, aged 11, male) has a history of bacterial suppurative otitis media, viral and bacterial cutaneous infections. P1's siblings (P2, P3), mother (P4), maternal aunt (P5) and uncle (P6) have similar infection histories. P1's maternal cousin (P7) presented with Burkitt's lymphoma at age 9. All affected individuals are alive and none has required HSCT to date. They have chronic lymphopenia affecting the CD4+T and B-cell compartments. P1-3 have isolated reduction in IgM levels whereas the adults universally have normal immunoglobulins. Specific antibody responses are preserved. Affected individuals have neutrophil vacuolation, and their neutrophils have enhanced superoxide production compared to healthy controls.

Conclusion

RAC2 p.I21S is an activating variant causing notable morphological and functional abnormalities similar to other reported DA mutations. This novel variant expands the broad clinical phenotypic spectrum of RAC2 DA lesions, emphasising the need to tailor clinical management according to patients' disease phenotype and severity.

Detection of interferon alpha and beta receptor subunit 1 (IFNAR1) loss-of-function Glu386∗ variant by tri-allelic genotyping

Mutations of the human interferon alpha and beta receptor subunit 1 (IFNAR1) gene are associated with severe viral infections. Individuals homozygous for the Glu386∗ variant have impaired type I interferon signalling and can suffer severe illness when exposed to certain viruses and live attenuated virus vaccines. Glu386∗ heterozygotes are clinically unaffected, but can pass the variant allele to their descendants. We aimed to develop an assay that can identify IFNAR1 Glu386∗ homozygotes and heterozygotes to support urgent clinical diagnosis, and that can use dried blood spots (DBS) sent at ambient temperature to overcome geographical logistical challenges in the South Pacific region. The tri-allelic genotyping assay interrogates a single nucleotide polymorphism (rs201609461) located in IFNAR1. The reference allele G encodes for wild-type IFNAR1. Minor alleles A (c.1156G>A) and T (c.1156G>T) encode for Glu386Lys and a truncated IFNAR1 protein (p.Glu386∗), respectively. Synthetic oligonucleotides were mixed in equal molar ratio to create six different genotypes which were randomly assigned to 960 genotyping reactions by R software. Three different fluorescence probes were designed to discriminate the three alleles (G, T and A) within a pair of flanking primers in a single genotyping reaction. The assay discriminated all three alleles using DBS from Guthrie cards randomly spiked with synthetic oligonucleotides. We correctly identified all the different genotypes in 960 reactions in these blinded experiments. These findings validate the genotyping assay for rapidly identifying the IFNAR1 Glu386∗ variant from DBS.

Challenges for gene editing in common variable immunodeficiency disorders: Current and future prospects

The original CRISPR Cas9 gene editing system and subsequent innovations offers unprecedented opportunities to correct severe genetic defects including those causing Primary Immunodeficiencies (PIDs). Common Variable Immunodeficiency Disorders (CVID) are the most frequent symptomatic PID in adults and children. Unlike many other PIDs, patients meeting CVID criteria do not have a definable genetic defect and cannot be considered to have an inborn error of immunity (IEI). Patients with a CVID phenotype carrying a causative mutation are deemed to have a CVID-like disorder consequent to an IEI. Patients from consanguineous families often have highly penetrant early-onset autosomal recessive forms of CVID-like disorders. Individuals from non-consanguineous families may have autosomal dominant CVID-like disorders with variable penetrance and expressivity. This essay explores the potential clinical utility as well as the current limitations and risks of gene editing including collateral genotoxicity. In the immediate future the main application of this technology is likely to be the in vitro investigation of epigenetic and polygenic mechanisms, which are likely to underlie many cases of CVID and CVID-like disorders. In the longer-term, the CRISPR Cas9 system and other gene-based therapies could be utilized to treat CVID-like disorders, where the underlying IEI is known.

Soluble wild-type ACE2 molecules inhibit newer SARS-CoV-2 variants and are a potential antiviral strategy to mitigate disease severity in COVID-19

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the virus responsible for coronavirus disease of 2019 (COVID-19), has caused havoc around the world. While several COVID-19 vaccines and drugs have been authorized for use, these antiviral drugs remain beyond the reach of most low- and middle-income countries. Rapid viral evolution is reducing the efficacy of vaccines and monoclonal antibodies and contributing to the deaths of some fully vaccinated persons. Others with normal immunity may have chosen not to be vaccinated and remain at risk if they contract the infection. Vaccines may not protect some immunodeficient patients from SARS-CoV-2, who are also at increased risk of chronic COVID-19 infection, a dangerous stalemate between the virus and a suboptimal immune response. Intra-host viral evolution could rapidly lead to the selection and dominance of vaccine and monoclonal antibody-resistant clades of SARS-CoV-2. There is thus an urgent need to develop new treatments for COVID-19. The NZACE2-Pātari project, comprising modified soluble angiotensin-converting enzyme 2 (ACE2) molecules, seeks to intercept and block SARS-CoV-2 infection of the respiratory mucosa. In vitro data presented here show that soluble wild-type ACE2 molecules retain the ability to effectively block the Spike (S) glycoprotein of SARS-CoV-2 variants including the ancestral Wuhan, delta (B.1.617.2) and omicron (B.1.1.529) strains. This therapeutic strategy may prove effective if implemented early during the nasal phase of the infection and may act synergistically with other antiviral drugs such as Paxlovid to further mitigate disease severity.

The Rapidly Expanding Genetic Spectrum of Common Variable Immunodeficiency-Like Disorders

The understanding of common variable immunodeficiency disorders (CVID) is in evolution. CVID was previously a diagnosis of exclusion. New diagnostic criteria have allowed the disorder to be identified with greater precision. With the advent of next-generation sequencing (NGS), it has become apparent that an increasing number of patients with a CVID phenotype have a causative genetic variant. If a pathogenic variant is identified, these patients are removed from the overarching diagnosis of CVID and are deemed to have a CVID-like disorder. In populations where consanguinity is more prevalent, the majority of patients with severe primary hypogammaglobulinemia will have an underlying inborn error of immunity, usually an early-onset autosomal recessive disorder. In nonconsanguineous societies, pathogenic variants are identified in approximately 20% to 30% of patients. These are often autosomal dominant mutations with variable penetrance and expressivity. To add to the complexity of CVID and CVID-like disorders, some genetic variants such as those in TNFSF13B (transmembrane activator calcium modulator cyclophilin ligand interactor) predispose to, or enhance, disease severity. These variants are not causative but can have epistatic (synergistic) interactions with more deleterious mutations to worsen disease severity. This review is a description of the current understanding of genes associated with CVID and CVID-like disorders. This information will assist clinicians in interpreting NGS reports when investigating the genetic basis of disease in patients with a CVID phenotype.

Selective IgA Deficiency May Be an Underrecognized Risk Factor for Severe COVID-19

SARS-CoV-2, the agent responsible for COVID-19, has wreaked havoc around the globe. Hundreds of millions of individuals have been infected and well over six million have died from COVID-19. Many COVID-19 survivors have ongoing physical and psychiatric morbidity, which will remain for the rest of their lives. Early in the pandemic, it became apparent that older individuals and those with comorbidities including obesity, diabetes mellitus, coronary artery disease, hypertension, and renal and pulmonary disease were at increased risk of adverse outcomes. It is also clear that some immunodeficient patients, such as those with innate or T cell-immune defects, are at greater risk from COVID-19. Selective IgA deficiency (sIgAD) is generally regarded as a mild disorder in which most patients are asymptomatic because of redundancy in protective immune mechanisms. Recent data indicate that patients with sIgAD may be at high risk of severe COVID-19. SARS-CoV-2 gains entry primarily through the upper respiratory tract mucosa, where IgA has a critical protective role. This may underlie the vulnerability of sIgAD patients to adverse outcomes from COVID-19. This perspective highlights the need for ongoing research into mucosal immunity to improve COVID-19 treatments for patients with sIgAD.

Critical role of diagnostic SARS-CoV-2 T cell assays for immunodeficient patients

After almost 3 years of intense study, the immunological basis of COVID-19 is better understood. Patients who suffer severe disease have a chaotic, destructive immune response. Many patients with severe COVID-19 produce high titres of non-neutralising antibodies, which are unable to sterilise the infection. In contrast, there is increasing evidence that a rapid, balanced cellular immune response is required to eliminate the virus and mitigate disease severity. In the longer term, memory T cell responses, following infection or vaccination, play a critical role in protection against SARS-CoV-2.Given the pivotal role of cellular immunity in the response to COVID-19, diagnostic T cell assays for SARS-CoV-2 may be of particular value for immunodeficient patients. A diagnostic SARS-CoV-2 T cell assay would be of utility for immunocompromised patients who are unable to produce antibodies or have passively acquired antibodies from subcutaneous or intravenous immunoglobulin (SCIG/IVIG) replacement. In many antibody-deficient patients, cellular responses are preserved. SARS-CoV-2 T cell assays may identify breakthrough infections if reverse transcriptase quantitative PCR (RT-qPCR) or rapid antigen tests (RATs) are not undertaken during the window of viral shedding. In addition to utility in patients with immunodeficiency, memory T cell responses could also identify chronically symptomatic patients with long COVID-19 who were infected early in the pandemic. These individuals may have been infected before the availability of reliable RT-qPCR and RAT tests and their antibodies may have waned. T cell responses to SARS-CoV-2 have greater durability than antibodies and can also distinguish patients with infection from vaccinated individuals.

SARS-CoV-2 Omicron: Light at the End of the Long Pandemic Tunnel or Another False Dawn for Immunodeficient Patients?

COVID-19 has had a disastrous impact on the world. Apart from at least 6 million deaths, countless COVID-19 survivors are suffering long-term physical and psychiatric morbidity. Hundreds of millions have been plunged into poverty caused by economic misery, particularly in developing nations. Early in the pandemic, it became apparent certain groups of individuals such as the elderly and those with comorbidities were more likely to suffer severe disease. In addition, patients with some forms of immunodeficiency, including those with T-cell and innate immune defects, were at risk of poor outcomes. Patients with immunodeficiencies are also disadvantaged as they may not respond optimally to COVID-19 vaccines and often have pre-existing lung damage. SARS-CoV-2 Omicron (B.1.529) and its subvariants (BA.1, BA.2, etc) have emerged recently and are dominating COVID-19 infections globally. Omicron is associated with a reduced risk of hospitalization and appears to have a lower case fatality rate compared with previous SARS-CoV-2 variants. Omicron has offered hope the pandemic may finally be coming to an end, particularly for vaccinated, healthy individuals. The situation is less clear for individuals with vulnerabilities, particularly immunodeficient patients. This perspective offers insight into potential implications of the SARS-CoV-2 Omicron variant for patients with immunodeficiencies.

SARS-CoV-2 the ASIA virus (autoimmune/autoinflammatory syndrome induced by adjuvants), the risk of infertility and vaccine hesitancy

INTRODUCTION

COVID-19 has had a calamitous impact on the global community. The current death toll far exceeds 6 million and large numbers of patients are experiencing long-term medical and psychiatric morbidity from the infection. The immunopathology of severe COVID-19 is now better understood. In severely affected patients, there is a chaotic, destructive immune response triggered by SARS-CoV-2, where autoimmunity features prominently.

AREAS COVERED

COVID-19 vaccines ensure a coordinated, balanced immune response to future SARS-CoV-2 infection. The rapid global deployment of effective COVID-19 vaccines has been hindered by financial, logistical and political barriers. Of concern is increasing vaccine hesitancy caused by unfounded conspiracy theories of vaccine adverse effects, often fueled by misinformation and disinformation on social media.

EXPERT OPINION

This perspective discusses the potential impact of the so-called autoimmune/autoinflammatory syndrome caused by adjuvants (ASIA) on COVID-19 vaccine uptake. Proponents of the ASIA syndrome have inappropriately linked infertility to HPV vaccines and have recently suggested antigenic cross-reactivity between SARS-CoV-2 and ovarian follicles. COVID-19 vaccines have also been linked to ASIA and unfounded fear of infertility is a leading cause of vaccine hesitancy. Vaccine hesitancy caused by spurious disorders such as ASIA are likely to harm individuals and delay global vaccination efforts leading to emergence of vaccine and monoclonal antibody resistant mutants, thereby prolonging the COVID-19 pandemic.

A loss-of-function IFNAR1 allele in Polynesia underlies severe viral diseases in homozygotes

Globally, autosomal recessive IFNAR1 deficiency is a rare inborn error of immunity underlying susceptibility to live attenuated vaccine and wild-type viruses. We report seven children from five unrelated kindreds of western Polynesian ancestry who suffered from severe viral diseases. All the patients are homozygous for the same nonsense IFNAR1 variant (p.Glu386*). This allele encodes a truncated protein that is absent from the cell surface and is loss-of-function. The fibroblasts of the patients do not respond to type I IFNs (IFN-α2, IFN-ω, or IFN-β). Remarkably, this IFNAR1 variant has a minor allele frequency >1% in Samoa and is also observed in the Cook, Society, Marquesas, and Austral islands, as well as Fiji, whereas it is extremely rare or absent in the other populations tested, including those of the Pacific region. Inherited IFNAR1 deficiency should be considered in individuals of Polynesian ancestry with severe viral illnesses.

Droplet digital PCR for identifying copy number variations in patients with primary immunodeficiency disorders

Primary immunodeficiency disorders comprise a rare group of mostly monogenic disorders caused by inborn errors of immunity. The majority can be identified by either Sanger sequencing or next generation sequencing. Some disorders result from large insertions or deletions leading to copy number variations (CNVs). Sanger sequencing may not identify these mutations. Here we present droplet digital PCR as an alternative cost-effective diagnostic method to identify CNV in these genes. The data from patients with large deletions of NFKB1, SERPING1, and SH2D1A are presented.

Severe COVID-19 is a T cell immune dysregulatory disorder triggered by SARS-CoV-2

INTRODUCTION

COVID-19 has had a calamitous impact on the global community. Apart from at least 6M deaths, hundreds of millions have been infected and a much greater number have been plunged into poverty. Vaccines have been effective but financial and logistical challenges have hampered their rapid global deployment. Vaccine disparities have allowed the emergence of new SARS-CoV-2 variants including delta and omicron, perpetuating the pandemic.

AREAS COVERED

The immunological response to SARS-CoV-2 has been the subject of intense study and is now better understood. Many of the clinical manifestations of severe disease are a consequence of immune dysregulation triggered by the virus. This may explain the lack of efficacy of antiviral treatments such as convalescent plasma infusions, given later in the disease.

EXPERT OPINION

T cells play a crucial role in both the outcome of COVID-19 as well as the protective response to vaccines. Vaccines do not prevent infection but reduce the risk of a chaotic and destructive cellular immune response to the virus. Severe COVID-19 should be considered a virus-induced secondary immune dysregulatory disorder of cellular immunity, with broad host susceptibility. This perspective of COVID-19 will lead to better diagnostic tests, vaccines and therapeutic strategies in the future.

Common Variable Immunodeficiency Disorders, T-Cell Responses to SARS-CoV-2 Vaccines, and the Risk of Chronic COVID-19

COVID-19 has had a calamitous effect on the global community. Despite intense study, the immunologic response to the infection is only partially understood. In addition to older age and ethnicity, patients with comorbidities including obesity, diabetes, hypertension, coronary artery disease, malignancy, renal, and pulmonary disease may experience severe outcomes. Some patients with primary immunodeficiency (PID) and secondary immunodeficiency also appear to be at increased risk from COVID-19. In addition to vulnerability to SARS-CoV-2, patients with PIDs often have chronic pulmonary disease and may not respond to vaccines, which exacerbates their long-term risk. Patients with common variable immunodeficiency disorders, the most frequent symptomatic PID in adults and children, have a spectrum of B- and T-cell defects. It may be possible to stratify their risk for severe COVID-19 based on age, ethnicity, the severity of the T-cell defect, and the presence of other comorbidities. Patients with common variable immunodeficiency disorders and other immunodeficiencies are at risk for Chronic COVID-19, a dangerous stalemate between a suboptimal immune response and SARS-CoV-2. Intra-host viral evolution could result in the rapid emergence of vaccine-resistant mutants and variants of high consequence; it is a public health emergency. Vaccination and prevention of Chronic COVID-19 in immunodeficient patients is therefore of the utmost priority. Having a reliable diagnostic assay for T-cell immunity to SARS-CoV-2 is critical for evaluating responses to vaccines in these patients. New treatments for SARS-CoV-2 such as NZACE2-Pātari are likely to be particularly beneficial for immunodeficient patients, especially those who fail to mount a robust T-cell response to COVID-19 vaccines.

Comparison of Diagnostic Criteria for Common Variable Immunodeficiency Disorders (CVID) in the New Zealand CVID Cohort Study

Common variable immunodeficiency disorders (CVID) are the most frequent symptomatic primary immune deficiencies in adults and children. In addition to recurrent and severe infections, patients with CVID are susceptible to autoimmune and inflammatory complications. The aetiologies of these uncommon conditions are, by definition, unknown. When the causes of complex disorders are uncertain, diagnostic criteria may offer valuable guidance to the management of patients. Over the last two decades, there have been four sets of diagnostic criteria for CVID in use. The original 1999 European Society for Immunodeficiencies and Pan-American Society for Immunodeficiency (ESID/PAGID) criteria are less commonly used than the three newer criteria: Ameratunga et al (Clin Exp Immunol 174:203-211, 2013), ESID (J Allergy Clin Immunol Pract, 2019) and ICON (J Allergy Clin Immunol Pract 4:38-59, 2016) criteria. The primary aim of the present study was to compare the utility of diagnostic criteria in a well-characterised cohort of CVID patients. The New Zealand CVID cohort study (NZCS) commenced in 2006 and currently comprises one hundred and thirteen patients, which represents approximately 70% of all known CVID patients in NZ. Many patients have been on subcutaneous or intravenous (SCIG/IVIG) immunoglobulin treatment for decades. Patients were given a clinical diagnosis of CVID as most were diagnosed before the advent of newer diagnostic criteria. Application of the three commonly used CVID diagnostic criteria to the NZCS showed relative sensitivities as follows: Ameratunga et al (Clin Exp Immunol 174:203-211, 2013), possible and probable CVID, 88.7%; ESID (J Allergy Clin Immunol Pract, 2019), 48.3%; and ICON (J Allergy Clin Immunol Pract 4:38-59, 2016), 47.1%. These differences were mostly due to the low rates of diagnostic vaccination challenges in patients prior to commencing SCIG/IVIG treatment and mirror similar findings in CVID cohorts from Denmark and Finland. Application of the Ameratunga et al (Clin Exp Immunol 174:203-211, 2013) CVID diagnostic criteria to patients on SCIG/IVIG may obviate the need to stop treatment for vaccine studies, to confirm the diagnosis.

Perspective: the nose and the stomach play a critical role in the NZACE2-Pātari* (modified ACE2) drug treatment project of SARS-CoV-2 infection

Background: COVID-19 has caused calamitous health, economic and societal consequences globally. Currently, there is no effective treatment for the infection. Areas covered: We have recently described the NZACE2-Pātari project, which seeks to administer modified Angiotensin Converting Enzyme 2 (ACE2) molecules early in the infection to intercept and block SARS-CoV-2 binding to the pulmonary epithelium. Expert opinion: Since the nasopharyngeal mucosa is infected in the first asymptomatic phase of the infection, treatment of the nose is likely to be safe and potentially effective. The intercepted virus will be swallowed and destroyed in the stomach. There is however a limited window of opportunity to alter the trajectory of the infection in an individual patient, which requires access to rapid testing for SARS-CoV-2. The proposed strategy is analogous to passive immunization of viral infections such as measles and may be of particular benefit to immunodeficient and unvaccinated individuals.

Perspective: diagnostic laboratories should urgently develop T cell assays for SARS-CoV-2 infection

Introduction: Diagnostic tests play a critical role in the management of Sars-CoV-2, the virus responsible for COVID-19. There are two groups of tests, which are in widespread use to identify patients who have contracted the virus. The commonly used reverse transcriptase quantitative polymerase chain reaction (RT-qPCR) test becomes negative once viral shedding ceases by approximately 2-3weeks. Antibody tests directed to viral antigens become positive after the second week of infection. IgG antibody responses to the virus are muted in children, pregnant females, and those with mild symptoms. IgA and IgM antibodies rapidly wane, although IgG antibodies directed to the receptor-binding domain (RBD) of the spike (S) glycoprotein are more durable. Current data show variability in the sensitivity of commercial and in-house antibody tests to SARS-CoV-2.Areas covered: The role of T cells in acute illness is uncertain, but long-term protection against the virus may rely on memory T cell responses. Measuring memory T cell responses is important for retrospective confirmation of cases, who may have been infected early in the pandemic before reliable RT-qPCR tests were available and whose SARS-CoV-2 antibodies may have become undetectable. Relevant peer-reviewed published references from PubMed are included up to 15 March 2021.Expert opinion: After surveying the literature, the authors present the case for urgent development of diagnostic T cell assays for SARS-CoV-2 by accredited laboratories.