Adaptation of the ultrasensitive HIV-1 p24 antigen assay to dried blood spot testing

Unravelling the Molecular Basis of High Affinity Nanobodies against HIV p24: In Vitro Functional, Structural, and in Silico Insights

Preventing the spread of infectious diseases remains an urgent priority worldwide, and this is driving the development of advanced nanotechnology to diagnose infections at the point of care. Herein, we report the creation of a library of novel nanobody capture ligands to detect p24, one of the earliest markers of HIV infection. We demonstrate that these nanobodies, one tenth the size of conventional antibodies, exhibit high sensitivity and broad specificity to global HIV-1 subtypes. Biophysical characterization indicates strong 690 pM binding constants and fast kinetic on-rates, 1 to 2 orders of magnitude better than monoclonal antibody comparators. A crystal structure of the lead nanobody and p24 was obtained and used alongside molecular dynamics simulations to elucidate the molecular basis of these enhanced performance characteristics. They indicate that binding occurs at C-terminal helices 10 and 11 of p24, a negatively charged region of p24 complemented by the positive surface of the nanobody binding interface involving CDR1, CDR2, and CDR3 loops. Our findings have broad implications on the design of novel antibodies and a wide range of advanced biomedical applications.

Human Immunodeficiency Virus Testing Practices and Interest in Self-Testing Options Among Young, Black Men Who Have Sex With Men in North Carolina

BACKGROUND

Young, black men who have sex with men (YBMSM) experience disproportionately high human immunodeficiency virus (HIV) incidence in the United States. Relative to other at-risk populations, less is known about their HIV testing behaviors and preferences regarding self-testing.

METHODS

We used an online survey to investigate testing practices and interest in self-testing among HIV-uninfected, 18- to 30-year-old YBMSM in North Carolina.

RESULTS

From July 2014 to March 2015, 212 completed the survey; median age was 24 years. Among 175 (83%) who had ever been tested, 160 (91%) reported testing in the prior year, 124 (71%) tested at least every 6 months, and 71 (40%) tested at least quarterly. About three quarters (77%; n = 164) were aware of HIV self-testing; 35 (17%) had ever purchased rapid (n = 27) or dried blood spot-based (n = 14) kits. Participants aware of kits had greater intention to test in the next 6 months, were more likely to have income for basic necessities and to ask sex partners about HIV status, and were less likely to have a main sex partner or to have had transactional sex. Among 142 participants at least somewhat likely to self-test in the future, convenience (35%), privacy (23%), and rapid result delivery (18%) were the principal motivators.

CONCLUSIONS

Eight of every 10 YBMSM have ever been tested for HIV, but intertest intervals remain unacceptably long for many. Awareness of and interest in self-testing is substantial, but few have used this method. Expanded use of self-tests could help increase the frequency of HIV testing in this epidemiologically important population.

Detection of HIV-1 p24 antigen in patients with varying degrees of viremia using an ELISA with a photochemical signal amplification system

BACKGROUND

We describe a photochemical signal amplification method (PSAM) for increasing the sensitivity of enzyme-linked immunosorbent assays (ELISAs) for the detection of HIV-1 p24 antigen, and present a preliminary validation study on ELISA+PSAM technology for detection of HIV-1 p24 antigen in clinical samples.

METHODS

ELISA+PSAM is compatible with commercially available microtiter plate readers, employs an inexpensive illumination device and the amplification takes around 10 min.

RESULTS

The PSAM technology not only increases the analytical sensitivity for detection of HIV-1 p24 antigen by approximately 40 times, but also significantly increases the clinical sensitivity of the ELISA: in instances where viral RNA load is <3000 copies/ml, conventional heat mediated immune complex disruption ELISA (HM-ELISA) cannot detect any HIV positive samples whereas HM-ELISA+PSAM can detect HIV infection in approximately half of the samples (clinical sensitivity is 52.63%). For viral RNA loads between 3000 and 30,000 copies/ml, the clinical sensitivities of the HM-ELISA and HM-ELISA+PSAM are 32.6% and 91.3%, and for that >30,000 copies/ml, clinical sensitivities of HM-ELISA and HM-ELISA+PSAM are 52.3% and 100%, respectively.

CONCLUSIONS

The HM-ELISA+PSAM represents an advancement in monitoring HIV-1 disease progression and treatment in the global healthcare setting.

Increased Sensitivity of HIV-1 p24 ELISA Using a Photochemical Signal Amplification System

BACKGROUND

In this study we describe a photochemical signal amplification method (PSAM) for increasing of the sensitivity of enzyme-linked immunosorbent assay (ELISA) for determination of HIV-1 p24 antigen. The photochemical signal amplification method is based on an autocatalytic photochemical reaction of a horseradish peroxidase (HRP) substrate, orthophenylenediamine (OPD).

METHODS

To compare the performance of PSAM-boosted ELISA with a conventional colorimetric ELISA for determination of HIV-1 p24 antigen we employed a PerkinElmer HIV-1 p24 ELISA kit, using conventional ELISA alongside ELISA + PSAM.

RESULTS

In the present study, we show that PSAM technology allows one to increase the analytical sensitivity and dynamic range of a commercial HIV-1 p24 ELISA kit, with and without immune-complex disruption, by a factor of approximately 40-fold.

CONCLUSIONS

ELISA + PSAM is compatible with commercially available microtiter plate readers, requires only an inexpensive illumination device, and the PSAM amplification step takes no longer than 15 min. This method can be used for both commercially available and in-house ELISA tests, and has the advantage of being considerably simpler and less costly than alternative signal amplification methods. This method can be used for both commercially available and in-house ELISA tests, and has the advantage of being considerably simpler and less costly than alternative signal amplification methods.

An overview of the clinical use of filter paper in the diagnosis of tropical diseases

Tropical infectious diseases diagnosis and surveillance are often hampered by difficulties of sample collection and transportation. Filter paper potentially provides a useful medium to help overcome such problems. We reviewed the literature on the use of filter paper, focusing on the evaluation of nucleic acid and serological assays for diagnosis of infectious diseases using dried blood spots (DBS) compared with recognized gold standards. We reviewed 296 eligible studies and included 101 studies evaluating DBS and 192 studies on other aspects of filter paper use. We also discuss the use of filter paper with other body fluids and for tropical veterinary medicine. In general, DBS perform with sensitivities and specificities similar or only slightly inferior to gold standard sample types. However, important problems were revealed with the uncritical use of DBS, inappropriate statistical analysis, and lack of standardized methodology. DBS have great potential to empower healthcare workers by making laboratory-based diagnostic tests more readily accessible, but additional and more rigorous research is needed.

Rapid detection of HIV-1 proviral DNA for early infant diagnosis using recombinase polymerase amplification

Early diagnosis and treatment of human immunodeficiency virus type 1 (HIV-1) infection in infants can greatly reduce mortality rates. However, current infant HIV-1 diagnostics cannot reliably be performed at the point of care, often delaying treatment and compromising its efficacy. Recombinase polymerase amplification (RPA) is a novel technology that is ideal for an HIV-1 diagnostic, as it amplifies target DNA in <20 min at a constant temperature, without the need for complex thermocycling equipment. Here we tested 63 HIV-1-specific primer and probe combinations and identified two RPA assays that target distinct regions of the HIV-1 genome (long terminal repeat [LTR] and pol) and can reliably detect 3 copies of proviral DNA by the use of fluorescence detection and lateral-flow strip detection. These pol and LTR primers amplified 98.6% and 93%, respectively, of the diverse HIV-1 variants tested. This is the first example of an isothermal assay that consistently detects all of the major HIV-1 global subtypes.

p24 antigen detection on dried blood spots is a feasible and reliable test for infant HIV infection in rural Tanzania

The difficulty of diagnosing HIV in infants is a major obstacle to early antiretroviral therapy (ART) in resource-limited settings. As serological tests are unreliable during the first 18 months of life, and the cost and complexity of polymerase chain reaction (PCR)-based assays limit their access in resource-limited settings, p24 antigen detection has emerged as an alternative diagnostic tool. In this study, the performance of an ultrasensitive p24 antigen assay on dried blood spots was evaluated under field conditions in rural Tanzania. Specimens were stored and shipped at tropical room temperature, and analysed within six weeks. In total, 27 consecutive children aged <18 months and exposed to vertical HIV transmission were enrolled. Overall sensitivity and specificity was 100% (95% confidence interval [CI], 47.8-100) and 95.5% (95% CI, 77.2-99.9), respectively. Our findings suggest that detection of p24 antigen on dried blood spots can be a reliable and feasible diagnostic tool for infant HIV infection in rural resource-limited settings.

Early infant HIV-1 diagnosis programs in resource-limited settings: opportunities for improved outcomes and more cost-effective interventions

Early infant diagnosis (EID) of HIV-1 infection confers substantial benefits to HIV-infected and HIV-uninfected infants, to their families, and to programs providing prevention of mother-to-child transmission (PMTCT) services, but has been challenging to implement in resource-limited settings. In order to correctly inform parents/caregivers of infant infection status and link HIV-infected infants to care and treatment, a 'cascade' of events must successfully occur. A frequently cited barrier to expansion of EID programs is the cost of the required laboratory assays. However, substantial implementation barriers, as well as personnel and infrastructure requirements, exist at each step in the cascade. In this update, we review challenges to uptake at each step in the EID cascade, highlighting that even with the highest reported levels of uptake, nearly half of HIV-infected infants may not complete the cascade successfully. We next synthesize the available literature about the costs and cost effectiveness of EID programs; identify areas for future research; and place these findings within the context of the benefits and challenges to EID implementation in resource-limited settings.

Inadequate coordination of maternal and infant HIV services detrimentally affects early infant diagnosis outcomes in Lilongwe, Malawi

OBJECTIVE

To assess the continuity of care and outcome of pediatric HIV prevention, testing, and treatment services, focusing on early infant diagnosis with DNA polymerase chain reaction (PCR).

DESIGN

A retrospective observational cohort.

METHODS

Maternal HIV antibody, infant HIV DNA PCR test results, and outcome data from HIV-infected infants from the prevention of mother-to-child transmission, early infant diagnosis, and pediatric HIV treatment programs operating in Lilongwe, Malawi, between 2004 and 2008 were collected, merged, and analyzed.

RESULTS

Of the 14,669 pregnant women who tested HIV antibody positive, 7875 infants (53.7%) received HIV DNA PCR testing. One thousand eighty-four infants (13.8%) were HIV infected. Three hundred twenty (29.5%) children enrolled into pediatric HIV care, with 202 (63.1%) at the Baylor Center of Excellence. Among these, antiretroviral therapy was initiated on 110 infants (54.5%) whose median age was 9.1 months (interquartile range, 5.4-13.8) and a median of 2.5 months (interquartile range, 1.4-5.2) after HIV clinic registration. Sixty-nine HIV-infected infants (34.2%) died or were lost by December 2008. Initiation of antiretroviral therapy increased the likelihood of survival 7-fold (odds ratio, 7.1; 95% confidence interval, 3.68 to 13.70).

CONCLUSIONS

Separate programs for maternal and infant HIV prevention and care services demonstrated high attrition rates of HIV-exposed and HIV-infected infants, elevated levels of mother-to-child transmission, late infant diagnosis, delayed pediatric antiretroviral therapy initiation, and high HIV-infected infant mortality. Antiretroviral therapy increased HIV-infected infant survival, emphasizing the urgent need for improved service coordination and strategies that increase access to infant HIV diagnosis, improve patient retention, and reduce antiretroviral therapy initiation delays.

Analysis of the optimal cut-point for HIV-p24 antigen testing to diagnose HIV infection in HIV-exposed children from resource-constrained settings

BACKGROUND

Nucleic-acid-testing (NAT) to diagnose HIV infection in children under age 18 months provides a barrier to HIV-testing in exposed children from resource-constrained settings. The ultrasensitive HIV-p24-antigen (Up24) assay is cheaper and easier to perform and is sensitive (84-98%) and specific (98-100%). The cut-point optical density (OD) selected for discriminating between positive and negative samples may need assessment due to regional differences in mother-to-child HIV-transmission rates.

OBJECTIVES

We used receiver operator characteristics (ROC) curves and logistic regression analyses to assess the effect of various cut-points on the diagnostic performance of Up24 for HIV-infection status among HIV-exposed children. Positive and negative predictive values at different rates of disease prevalence were also estimated.

STUDY DESIGN

A study of Up24 testing on dried blood spot (DBS) samples collected from 278 HIV-exposed Haitian children, 3-24-months of age, in whom HIV-infection status was determined by NAT on the same DBS card.

RESULTS

The sensitivity and specificity of Up24 varied by the cut-point-OD value selected. At a cut-point-OD of 8-fold the standard deviation of the negative control (NCSD), sensitivity and specificity of Up24 were maximized [87.8% (95% CI, 83.9-91.6) and 92% (95% CI, 88.8-95.2), respectively]. In lower prevalence settings (5%), positive and negative predictive values of Up24 were maximal (75.9% and 98.8%, respectively) at a cut-point-OD that was 15-fold the NCSD.

CONCLUSIONS

In low prevalence settings, a high degree of specificity can be achieved with Up24 testing of HIV-exposed children when a higher cut-point OD is used; a feature that may facilitate more frequent use of Up24 antigen testing for HIV-exposed children.

Using a simplified human immunodeficiency virus type 1 p24 antigen assay to diagnose pediatric HIV-infection in Malawi

BACKGROUND

There is a worldwide need for a pediatric HIV-1 diagnostic test that has a high diagnostic accuracy, is technically simple and cost efficient. The Up24 HIV-1 assay, which requires both the HIV-1 p24 ELISA and the ELAST signal amplification kit, has previously been shown to be a robust tool to diagnose pediatric HIV-1 from dried whole blood spots (DBS) (Cachafeiro et al., JCM 2009;47:459-62(13)). In order to make the assay more accessible to a resource-limited clinical setting, we eliminated the ELAST system, which simplified the Up24 assay, reduced its cost, and tested the accuracy of the modified assay in a rural Malawian hospital.

OBJECTIVES

In this proof of concept study, we tested the ability of a simplified Up24 antigen assay, without ELAST, to detect HIV-1 on DBS obtained via heel prick from 6-week-old Malawian infants.

STUDY DESIGN

A case-control study of DBS collected from 113 HIV-infected and 109 HIV-negative infants, using the HIV-1 DNA PCR assay as the reference standard.

RESULTS

The simplified HIV-1 Up24 assay had a sensitivity and specificity of 84% and 98%, respectively. When HIV-1 prevalence is 15%, the positive- and negative-predictive values are 89% and 97%, respectively.

CONCLUSION

The simplified Up24 assay has a good positive- and a robust negative-predictive values, is easier to perform and has a reduced cost compared to both HIV DNA PCR and Up24 assays. With additional testing, the simplified Up24 assay has the potential to increase global access to pediatric HIV-1 diagnostics.

Research needs and challenges in the development of HIV diagnostic and treatment monitoring tests for use in resource-limited settings

PURPOSE OF REVIEW

The aim of this article is to review research priorities for current and new technologies to diagnose HIV and to monitor treatment response, including technologies to enumerate CD4 cell counts and quantify plasma viral load, in resource-limited settings.

RECENT FINDINGS

Numerous challenges remain before HIV diagnostic and treatment monitoring technologies can be broadly implemented, especially in rural areas. New technologies that are less costly and complex to use are in development and may be better suited than current technologies for use in resource-limited settings. Investment into research activities is needed for development, evaluation and validation of new technologies. The lack of clarity in the process for evaluation and validation for these technologies affects country and program-level decisions on the appropriateness of technologies for individual settings. Implementation research is needed to assess how best to use CD4 and viral load to guide initiation and management of antiretroviral treatment, as well as how best to scale up diagnosis of HIV serostatus in infants. Studies also need to be conducted to determine if the same CD4 cutoffs can be used in resource-limited settings for initiating antiretroviral therapy and prophylaxis against opportunistic infections due to potential regional differences and the impact of other common co-morbidities on CD4 cell counts.

SUMMARY

Increased availability of antiretroviral therapy in resource-limited settings increases the need for reliable, less costly and simpler to use HIV diagnostic and treatment monitoring technologies. Global leadership is needed to coordinate the research and development necessary to ensure that HIV diagnostic and treatment monitoring technologies are properly evaluated in the setting where they will be used.

Measure of viral load by using the Abbott Real-Time HIV-1 assay on dried blood and plasma spot specimens collected in 2 rural dispensaries in Cameroon

BACKGROUND

This study aimed to evaluate the use of dried blood spots (DBSs) and dried plasma spots (DPSs) locally collected in 2 rural dispensaries in Cameroon for the quantification of HIV-1 RNA.

METHODS

Forty-one subjects were sampled and spots of whole blood and plasma were deposited onto Whatman 903 cards and dried at ambient temperature under local conditions. Two sets of DBS and DPS cards were done per patient. The rest of the liquid plasma (LP) was frozen until use. LPs were tested at the "Chantal Biya" International Reference Centre (Yaoundé, Cameroon) by the Abbott Real-Time HIV-1 assay (Abbott Molecular Diagnostics, Wiesbaden, Germany). One series of DBS and DPS was transported and tested between 2 and 6 weeks later at the Virology Laboratory of Saint-Etienne (France). The second series was routed by mail and tested after up to 3 months of storage at ambient temperature.

RESULTS

From the first series, the correlation rate between viral loads obtained from LP and DBS, and from LP and DPS, was 0.98 and 0.99, respectively; specificity of DBS and DPS results was 100%. The results obtained from the second series indicate a great stability of DBS after long-term storage.

CONCLUSION

This study demonstrates that DBSs collected under local conditions in resource-limited settings are suitable for the differed quantification of HIV-1 RNA.

Dried-plasma transport using a novel matrix and collection system for human immunodeficiency virus and hepatitis C virus virologic testing

A novel method for the collection and transportation of dried-blood-plasma samples, SampleTanker (ST), was developed and compared to standard shipping protocols for frozen-plasma specimens containing human immunodeficiency virus type 1 (HIV-1) and/or hepatitis C virus (HCV). Matched frozen and dried 1-ml EDTA-containing plasma samples were collected and analyzed by several molecular-based virologic assays. After addition of 1.175 ml of reconstitution buffer, 1.035 ml of dried plasma was recovered. Mean intra-assay variances were 0.05, 0.05, and 0.06 log(10) copies/ml for the Versant, Amplicor, and NucliSens QT HIV-1 load assays, respectively (P, not significant). However, mean HIV-1 viral load was consistently reduced in dried samples by 0.32 to 0.51 log(10) copies/ml, depending on assay type (P < 0.05). Infectious HIV-1 was not recovered from dried ST plasma. There was no significant difference in HIV-1 viral load results obtained using ST after 8 weeks of storage at ambient temperature. Compared to frozen plasma, HIV-1 genotypic results were >99% concordant at the nucleotide and amino acid levels, as well as for resistance-associated mutations. We further demonstrated successful detection of multiple analytes, including HIV-1 viral load, HIV-1 antiretroviral resistance genotype, and HCV genotype, from a single ST unit. Dried plasma collected with ST yielded comparable results to frozen samples for multiple-analyte clinical testing. As such, ST could be a useful alternative for virologic tests and clinical trials worldwide by significantly diminishing transportation cost and the sample volume restrictions associated with dried-blood-spot technology.

Early HIV-1 diagnosis using in-house real-time PCR amplification on dried blood spots for infants in remote and resource-limited settings

BACKGROUND

In resource-limited settings, most perinatally HIV-1-infected infants do not receive timely antiretroviral therapy because early HIV-1 diagnosis is not available or affordable.

OBJECTIVE

To assess the performance of a low-cost in-house real-time polymerase chain reaction (PCR) assay to detect HIV-1 DNA in infant dried blood spots (DBS).

METHODS

One thousand three hundred nineteen DBS collected throughout Thailand from non-breast-fed infants born to HIV-1-infected mothers were shipped at room temperature to a central laboratory.In-house real-time DNA PCR results were compared with Roche Amplicor HIV-1 DNA test (Version 1.5) results. In addition, we verified the Roche test performance on DBS sampled from 1218 other infants using as reference HIV serology result at 18 months of age.

RESULTS

Real-time DNA PCR and Roche DNA PCR results were 100% concordant. Compared with HIV serology results, the Roche test sensitivity was 98.6% (95% confidence interval: 92.6% to 100.0%) and its specificity at 4 months of age was 99.7% (95% confidence interval: 99.2% to 99.9%).

CONCLUSIONS

In-house real-time PCR performed as well as the Roche test in detecting HIV-1 DNA on DBS in Thailand. Combined use of DBS and real-time PCR assays is a reliable and affordable tool to expand access to early HIV-1 diagnosis in remote and resource-limited settings, enabling timely treatment for HIV-1-infected infants.

Pediatric HIV infection: the state of antiretroviral therapy

Pediatric HIV/AIDS has become less of a problem in resource-rich countries as the number of perinatal infections has reduced dramatically since the advent of antiretrovirals, resulting in the effective prevention of mother-to-child transmission. In resource-limited settings, however, pediatric HIV infection remains a colossal problem; a separate review in this same issue of Expert Review of Anti-Infective Therapy examines the international aspects of pediatric HIV/AIDS. Treatment of HIV infection in children differs from that in adults in the use of immunologic markers and owing to drug pharmacokinetics and age-related adherence issues. This review, geared for the general pediatrician or family practitioner who may see the HIV-positive child in the clinic or the hospital, summarizes the most recent pediatric data and guidelines for the testing and treatment of HIV, including the US NIH guidelines released in February 2008. Treatment-experienced patients, who should be cared for by pediatric HIV specialists, are not addressed here specifically. Adolescents, infected either perinatally or sexually, with their own unique issues, deserve a separate review.

Evaluation of the ultrasensitive human immunodeficiency virus type 1 (HIV-1) p24 antigen assay performed on dried blood spots for diagnosis of HIV-1 infection in infants

The diagnostic accuracy of the modified p24 antigen assay performed on pediatric dried blood spots was evaluated. Samples analyzed within 6 weeks of collection yielded no false-positive results (specificity, 100%) and few false-negative results (sensitivity, 96.5% to 98.3%). Laboratory services with limited resources should assess this option for routine infant diagnosis.

Ultrasensitive p24 antigen assay for diagnosis of perinatal human immunodeficiency virus type 1 infection

We evaluated an ultrasensitive p24 antigen enzyme immunosorbent assay on 802 plasma specimens from 582 infants and children of 0 to 180 days of age. Overall sensitivity and specificity were 91.7% and 98.5%, respectively. After exclusion of infants of less than 7 days of age, the sensitivity and specificity were 93.7% and 98.3%, respectively.