Stephanie Rainwater

Neutralization Escape Variants of Human Immunodeficiency Virus Type 1 Are Transmitted from Mother to Infant

ABSTRACT Maternal passive immunity typically plays a critical role in protecting infants from new infections; however, the specific contribution of neutralizing antibodies in limiting mother-to-child transmission of human immunodeficiency virus type 1 is unclear. By examining cloned envelope variants from 12 transmission pairs, we found that vertically transmitted variants were more resistant to neutralization by maternal plasma than were maternal viral variants near the time of transmission. The vertically transmitted envelope variants were poorly neutralized by monoclonal antibodies biz, 2G12, 2F5, and 4E10 individually or in combination. Despite the fact that the infant viruses were among the most neutralization resistant in the mother, they had relatively few glycosylation sites. Moreover, the transmitted variants elicited de novo neutralizing antibodies in the infants, indicating that they were not inherently difficult to neutralize. The neutralization resistance of vertically transmitted viruses is in contrast to the relative neutralization sensitivity of viruses sexually transmitted within discordant couples, suggesting that the antigenic properties of viruses that are favored for transmission may differ depending upon mode of transmission.

Gender differences in HIV-1 diversity at time of infection

To develop an HIV-1 vaccine with global efficacy, it is important to identify and characterize the viruses that are transmitted, particularly to individuals living in areas of high incidence. Several studies have shown that virus from the blood of acutely infected adults was homogeneous, even when the virus population in the index case was genetically diverse. In contrast to those results with mainly male cohorts in America and Europe, in several cases a heterogeneous virus population has been found early in infection in women in Africa. Thus, we more closely compared the diversity of transmitted HIV-1 in men and women who became infected through heterosexual contact. We found that women from Kenya were often infected by multiple virus variants, whereas men from Kenya were not. Moreover, a heterogeneous virus was present in the women before their seroconversion, and in each woman it was derived from a single index case, indicating that diversity was most likely to be the result of transmission of multiple variants. Our data indicate that there are important differences in the transmitted virus populations in women and men, even when cohorts from the same geographic region who are infected with the same subtypes of HIV-1 are compared.

HIV type 1 variants transmitted to women in Kenya require the CCR5 coreceptor for entry, regardless of the genetic complexity of the infecting virus.

Although nearly half of the HIV-1-infected adults in the world are women, little is known about the virologic determinants of transmission to women. Studies suggest that women are frequently infected with multiple HIV-1 genotypes, whereas men are infected with a single genotype. In the current study, we assessed whether the diverse HIV-1 genomes present at the time of infection in women encode viruses that have diverse coreceptor specificities. For this purpose, we defined the coreceptor requirements of viruses found in recently infected Kenyan women, three of whom had multiple viral genotypes and the remaining two of whom had a single genotype. Full-length envelope clones were amplified directly from blood and the dominant genotypes were identified. Envelope clones derived from all five women were able to pseudotype infectious particles competent to infect cells expressing CCR5, but not cells expressing only CXCR4. Thus, regardless of viral complexity at the time of infection, the viruses present at early stages of HIV-1 infection in women use CCR5, suggesting that cells expressing CCR5 are important targets for heterosexual HIV-1 transmission to women.

Evidence for Frequent Reinfection with Human Immunodeficiency Virus Type 1 of a Different Subtype

ABSTRACT A major premise underlying current human immunodeficiency virus type 1 (HIV-1) vaccine approaches is that preexisting HIV-1-specific immunity will block or reduce infection. However, the recent identification of several cases of HIV-1 reinfection suggests that the specific immune response generated for chronic HIV-1 infection may not be adequate to protect against infection by a second HIV-1 strain. It has been unclear, though, whether these individuals are representative of the global epidemic or are rare cases. Here we show that in a population of high-risk women, HIV-1 reinfection occurs almost as commonly as first infections. The study was designed to detect cases of reinfection by HIV-1 of a different subtype and thus captured cases where there was considerable diversity between the first and second strain. In each case, the second virus emerged ∼1 year after the first infection, and in two cases, it emerged when viral levels were high, suggesting that a well-established HIV-1 infection may provide little benefit in terms of immunizing against reinfection, at least by more-divergent HIV-1 variants. Our findings indicate an urgent need for studies of larger cohorts to determine the incidence and timing of both intersubtype and intrasubtype reinfection.

Subtype C Is Associated with Increased Vaginal Shedding of HIV-1

The prevalence of human immunodeficiency virus (HIV)-1-infected cells and HIV-1 RNA levels in genital secretions and breast milk and the risk of mother-to-child transmission of HIV-1 were compared among subtypes A, C, and D in a Kenyan cohort. Pregnant women infected with subtype C were significantly more likely to shed HIV-1-infected vaginal cells than were those infected with subtype A or D (odds ratio [OR], 3.6 [95% confidence interval {CI}, 1.4-8.8]; P = .006). This relationship held after adjusting for age, CD4 cell count, and plasma HIV-1 RNA load (OR, 3.1 [95% CI, 1.1-8.6]; P = .03). These observations suggest that HIV-1 subtype influences mucosal shedding of HIV-1.

Cross-Subtype Neutralization Sensitivity despite Monoclonal Antibody Resistance among Early Subtype A, C, and D Envelope Variants of Human Immunodeficiency Virus Type 1

ABSTRACT The human immunodeficiency virus type 1 (HIV-1) variants that are transmitted to newly infected individuals are the primary targets of interventions, such as vaccines and microbicides, aimed at preventing new infections. Newly acquired subtype A, B, and C variants have been the focus of neutralization studies, although many of these viruses, particularly of subtypes A and B, represent viruses circulating more than a decade ago. In order to better represent the global diversity of transmitted HIV-1 variants, an additional 31 sexually transmitted Kenyan HIV-1 env genes, representing several recent infections with subtype A, as well as subtypes A/D, C, and D, were cloned, and their neutralization profiles were characterized. Most env variants were resistant to neutralization by the monoclonal antibodies (MAbs) b12, 4E10, 2F5, and 2G12, suggesting that targeting the epitopes of these MAbs may not be effective against variants that are spreading in areas of endemicity. However, significant cross-subtype neutralization by plasma was observed, indicating that there may be other epitopes, not yet defined by the limited available MAbs, which could be recognized more broadly.

Cloning and characterization of functional subtype A HIV-1 envelope variants transmitted through breastfeeding.

Previous studies of HIV-1 variants transmitted from mother-to-infant have focused primarily on computational analyses of partial envelope gene sequences, rather than analyses of functional envelope variants. There are very few examples of well-characterized functional envelope clones from mother-infant pairs, especially from envelope variants representing the most prevalent subtypes worldwide. To address this, we amplified the envelope variants present in 4 mother-infant transmission pairs, all of whom were infected with subtype A and three of whom presumably transmitted HIV-1 during the breastfeeding period. Functional envelope clones were constructed, either encoding full-length envelope sequences from the mother and baby or by making chimeric envelope clones in a common backbone sequence. The infant envelope sequences were genetically homogeneous compared to the maternal viruses, and pseudoviruses bearing these envelopes all used CCR5 as a coreceptor. The infant viruses were generally resistant to neutralization by maternal antibodies present near the time of transmission. There were no notable differences in sensitivity of the mother and infant envelope variants to neutralization by heterologous plasma or monoclonal antibodies 2G12 and b12, or to inhibition by sCD4, PSC-RANTES or TAK779. This collection of viral envelopes, which can be used for making pseudotyped viruses, may be useful for examining the efficacy of interventions to block mother-infant transmission, including sera from vaccine candidates, purified antibodies under consideration for passive immunization and viral entry inhibitors.

Temporal analysis of HIV envelope sequence evolution and antibody escape in a subtype A-infected individual with a broad neutralizing antibody response.

The origin of broadly neutralizing HIV-specific antibodies and their relation to HIV evolution are not well defined. Here we examined virus evolution and neutralizing antibody escape in a subtype A infected individual with a broad, cross subtype, antibody response. The majority of envelope variants isolated over the first approximately 5 years after infection were poorly neutralized by contemporaneous plasma that neutralized variants from earlier in infection, consistent with a dynamic process of escape. The majority of variants could be neutralized by later plasma, suggesting these evolving variants may have contributed to the elicitation of new antibody responses. However, some variants from later in infection were recognized by plasma from earlier in infection, including one notably neutralization-sensitive variant that was sensitive due to a proline at position 199 in V2. These studies suggest a complex pattern of virus evolution in this individual with a broad NAb response, including persistence of neutralization-sensitive viruses.

HIV-specific CD4-induced Antibodies Mediate Broad and Potent Antibody-dependent Cellular Cytotoxicity Activity and are Commonly Detected in Plasma from HIV-infected Humans

HIV-specific antibodies (Abs) can reduce viral burden by blocking new rounds of infection or by destroying infected cells via activation of effector cells through Fc–FcR interaction. This latter process, referred to as antibody-dependent cellular cytotoxicity (ADCC), has been associated with viral control and improved clinical outcome following both HIV and SIV infections. Here we describe an HIV viral-like particle (VLP)-based sorting strategy that led to identification of HIV-specific memory B cells encoding Abs that mediate ADCC from a subtype A-infected Kenyan woman at 914 days post-infection. Using this strategy, 12 HIV-envelope-specific monoclonal antibodies (mAbs) were isolated and three mediated potent ADCC activity when compared to well-characterized ADCC mAbs. The ADCC-mediating Abs also mediated antibody-dependent cell-mediated virus inhibition (ADCVI), which provides a net measure of Fc receptor-triggered effects against replicating virus. Two of the three ADCC-mediating Abs targeted a CD4-induced (CD4i) epitope also bound by the mAb C11; the third antibody targeted the N-terminus of V3. Both CD4i Abs identified here demonstrated strong cross-clade breadth with activity against 10 of 11 envelopes tested, including those from clades A, B, C, A/D and C/D, whereas the V3-specific antibody showed more limited breadth. Variants of these CD4i, C11-like mAbs engineered to interrupt binding to FcγRs inhibited a measurable percentage of the donors ADCC activity starting as early as 189 days post-infection. C11-like antibodies also accounted for between 18–78% of ADCC activity in 9 chronically infected individuals from the same cohort study. Further, the two CD4i Abs originated from unique B cells, suggesting that antibodies targeting this epitope can be commonly produced. Taken together, these data provide strong evidence that CD4i, C11-like antibodies develop within the first 6 months of infection and they can arise from unique B-cell lineages in the same individual. Further, these mAbs mediate potent plasma IgG-specific ADCC breadth and potency and contribute to ADCC activity in other HIV-infected individuals.

Superinfection Drives HIV Neutralizing Antibody Responses from Several B Cell Lineages that Contribute to a Polyclonal Repertoire

SUMMARY Eliciting broad and potent HIV-specific neutralizing antibody responses represents the holy grail of HIV vaccine efforts. Data from singly infected individuals with broad and potent plasma neutralizing activity targeting one epitope have guided our understanding of how these responses develop. However, far less is known about responses developed by super-infected individuals who acquire two distinct HIV strains. Here, we isolated HIV-specific mAbs from a superinfected individual with a broad plasma response. In this superinfection case, neutralizing activity resulted from multiple distinct B cell lineages that arose in response to either the initial or the superinfecting virus, including an antibody that targets the N332 supersite. This nAb, QA013.2, was specific to the superinfecting virus and was associated with eventual reemergence of the initial infecting virus. The complex dynamic between viruses in superinfection may drive development of a unique collection of polyclonal nAbs that present a higher barrier to escape than monoclonal responses.