Human Immunodeficiency Virus Type 1 Elite Neutralizers: Individuals with Broad and Potent Neutralizing Activity Identified by Using a High-Throughput Neutralization Assay together with an Analytical Selection Algorithm

Abstract

The development of a rapid and efficient system to identify human immunodeficiency virus type 1 (HIV-1)-infected individuals with broad and potent HIV-1-specific neutralizing antibody responses is an important step toward the discovery of critical neutralization targets for rational AIDS vaccine design. In this study, samples from HIV-1-infected volunteers from diverse epidemiological regions were screened for neutralization responses using pseudovirus panels composed of clades A, B, C, and D and circulating recombinant forms (CRFs). Initially, 463 serum and plasma samples from Australia, Rwanda, Uganda, the United Kingdom, and Zambia were screened to explore neutralization patterns and selection ranking algorithms. Samples were identified that neutralized representative isolates from at least four clade/CRF groups with titers above prespecified thresholds and ranked based on a weighted average of their log-transformed neutralization titers. Linear regression methods selected a five-pseudovirus subset, representing clades A, B, and C and one CRF01_AE, that could identify top-ranking samples with 50% inhibitory concentration (IC 50 ) neutralization titers of >100 to multiple isolates within at least four clade groups. This reduced panel was then used to screen 1,234 new samples from the Ivory Coast, Kenya, South Africa, Thailand, and the United States, and 1% were identified as elite neutralizers. Elite activity is defined as the ability to neutralize, on average, more than one pseudovirus at an IC 50 titer of 300 within a clade group and across at least four clade groups. These elite neutralizers provide promising starting material for the isolation of broadly neutralizing monoclonal antibodies to assist in HIV-1 vaccine design.

Identification and specificity of broadly neutralizing antibodies against HIV

“…This was first achieved by defining criteria to rank 1800 HIV‐positive serum samples from the IAVI Protocol G cohort for broad and potent activity against relatively neutralization‐resistant isolates to represent circulating viruses 8, 21. We selected and validated a six‐virus cross‐clade indicator panel and developed a scoring system wherein elite activity is defined as neutralization of at least one virus with an IC 50 value of more than 1:300 across a minimum of four different clades 8. Having identified HIV‐positive donors with broad and potent neutralizing activity, the next step was to isolate the monoclonal Abs (mAbs) giving rise to this phenotype.…”

“…However, given that the mechanism of viral protection and clearance by antibodies in vivo is so widespread, we, and others, have studied humoral responses in HIV‐infected donors for more than two decades to understand how to prevent and control HIV infection. This persistence has led to the identification of many broadly neutralizing antibodies (bnAbs),3, 4, 5, 6 which, although relatively rare in HIV‐infected individuals,7, 8 are nevertheless highly effective against most circulating strains and can prevent infection in robust animal models 9, 10, 11. Therefore, although HIV infection does not induce protective antibody‐mediated immunity, it is possible for the human immune system to produce antibodies that may, in principle, protect from HIV infection.…”

“…High‐throughput neutralization assays were a major factor in changing that situation. The ability to analyze mAb and serum activity against large panels of viruses was demonstrated20 and subsequently used to evaluate large numbers of HIV‐infected donors in the International AIDS Vaccine Initiative (IAVI) Protocol G and C studies to identify those with exceptionally potent and broad sera,8 map the specificities underlying these responses,7, 21 and then isolate bnAbs from these individuals 22, 23, 24, 25, 26, 27, 28. Independently, the standardization of the TZM‐bl neutralization assay and the definition of neutralization sensitivity tiers29, 30, 31 allowed much more rigorous serum analysis.…”

Enhanced HIV-1 neutralization by antibody heteroligation

“…Although antibodies that neutralize autologous viruses are common, only a fraction of the patients infected with HIV-1 develop broadly neutralizing serologic activity, and only 2 to 3 y after infection (3)(4)(5)(6)(7)(8)(9). Several broadly neutralizing antibodies (bNAbs) to HIV-1 gp160 have been isolated, including a group that binds to gp120 (10)(11)(12)(13)(14)(15)(16)(17)(18) and a group that is specific for gp41 (19)(20)(21).…”

Immune responses during spontaneous control of HIV and AIDS: what is the hope for a cure?

“…A blunted antibody response during HIV infection is associated with B cell dysfunction. Some individuals, elite neutralizers, can elicit broadly neutralizing antibodies that recognize conserved regions of the virus envelope protein [168]. The presence of these broadly neutralizing antibodies is not associated with a dramatic control of viraemia in vivo, but has been shown to strongly decrease viraemia when administered to SHIVinfected macaques [169].…”