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In the large majority of cases, HIV infection is established by a single variant, and understanding the characteristics of successfully transmitted variants is relevant to prevention strategies. Few studies have investigated the viral determinants of mother-to-child transmission. To determine the impact of Gag-protease-driven viral replication capacity on mother-to-child transmission, the replication capacities of 148 recombinant viruses encoding plasma-derived Gag-protease from 53 nontransmitter mothers, 48 transmitter mothers, and 47 infected infants were assayed in an HIV-1-inducible green fluorescent protein reporter cell line. All study participants were infected with HIV-1 subtype C. There was no significant difference in replication capacities between the nontransmitter ( n = 53) and transmitter ( n = 44) mothers ( P = 0.48). Infant-derived Gag-protease NL4-3 recombinant viruses ( n = 41) were found to have a significantly lower Gag-protease-driven replication capacity than that of viruses derived from the mothers ( P < 0.0001 by a paired t test). High percent similarities to consensus subtype C Gag, p17, p24, and protease sequences were also found in the infants ( n = 28) in comparison to their mothers ( P = 0.07, P = 0.002, P = 0.03, and P = 0.02, respectively, as determined by a paired t test). These data suggest that of the viral quasispecies found in mothers, the HIV mother-to-child transmission bottleneck favors the transmission of consensus-like viruses with lower viral replication capacities. IMPORTANCE Understanding the characteristics of successfully transmitted HIV variants has important implications for preventative interventions. Little is known about the viral determinants of HIV mother-to-child transmission (MTCT). We addressed the role of viral replication capacity driven by Gag, a major structural protein that is a significant determinant of overall viral replicative ability and an important target of the host immune response, in the MTCT bottleneck. This study advances our understanding of the genetic bottleneck in MTCT by revealing that viruses transmitted to infants have a lower replicative ability as well as a higher similarity to the population consensus (in this case HIV subtype C) than those of their mothers. Furthermore, the observation that “consensus-like” virus sequences correspond to lower in vitro replication abilities yet appear to be preferentially transmitted suggests that viral characteristics favoring transmission are decoupled from those that enhance replicative capacity.

HIV-1 viremia has been shown to induce several phenotypic and functional abnormalities in natural killer (NK) cells. To assess immune defects associated with HIV viremia, we examined NK cell function, differentiation status, and phenotypic alterations based on expression of inhibitory and activating receptors on NK cells in HIV-1 subtype C chronically infected participants from Durban, South Africa. NK cell phenotypic profiles were characterized by assessing sialic acid-binding immunoglobulin-like lectin-7 (Siglec-7), NKG2A, and NKG2C markers on frozen peripheral blood mononuclear cells from viremic, antiretroviral therapy (ART)-naive HIV-1 chronically infected participants (n = 23), HIV-1 chronically infected participants who had been on combination antiretroviral therapy (cART) for at least 12 months (n = 23) compared with healthy donors (n = 23). NK cell differentiation was assessed by measurement of killer immunoglobulin receptor (KIR) and NKG2A expression; CD57 and CD107a measurements were carried out in HIV viremic and healthy donors. All phenotypic and functional assessments were analyzed by using multicolor flow cytometry. HIV-1-infected participants displayed greater frequencies of the CD56

A major obstacle to an HIV cure in adult infection is a viral reservoir largely composed of CTL escape mutants. Leitman et al. demonstrate that in children, but not adults, escape variant–specific CTLs are generated that can successfully “corner” the virus., Recent studies have suggested greater HIV cure potential among infected children than adults. A major obstacle to HIV eradication in adults is that the viral reservoir is largely comprised of HIV-specific cytotoxic T lymphocyte (CTL) escape variants. We here evaluate the potential for CTL in HIV-infected slow-progressor children to play an effective role in “shock-and-kill” cure strategies. Two distinct subgroups of children were identified on the basis of viral load. Unexpectedly, in both groups, as in adults, HIV-specific CTL drove the selection of escape variants across a range of epitopes within the first weeks of infection. However, in HIV-infected children, but not adults, de novo autologous variant-specific CTL responses were generated, enabling the pediatric immune system to “corner” the virus. Thus, even when escape variants are selected in early infection, the capacity in children to generate variant-specific anti-HIV CTL responses maintains the potential for CTL to contribute to effective shock-and-kill cure strategies in pediatric HIV infection.

The mechanisms of viral control and loss of viral control in chronically infected individuals with or without protective HLA class I alleles are not fully understood. We therefore characterized longitudinally the immunological and virological features that may explain divergence in disease outcome in 70 HIV-1 C-clade-infected antiretroviral therapy (ART)-naive South African adults, 35 of whom possessed protective HLA class I alleles. We demonstrate that, over 5 years of longitudinal study, 35% of individuals with protective HLA class I alleles lost viral control compared to none of the individuals without protective HLA class I alleles ( P = 0.06). Sustained HIV-1 control in patients with protective HLA class I alleles was characteristically related to the breadth of HIV-1 CD8 + T cell responses against Gag and enhanced ability of CD8 + T cells to suppress viral replication ex vivo . In some cases, loss of virological control was associated with reduction in the total breadth of CD8 + T cell responses in the absence of differences in HIV-1-specific CD8 + T cell polyfunctionality or proliferation. In contrast, viremic controllers without protective HLA class I alleles possessed reduced breadth of HIV-1-specific CD8 + T cell responses characterized by reduced ability to suppress viral replication ex vivo . These data suggest that the control of HIV-1 in individuals with protective HLA class I alleles may be driven by broad CD8 + T cell responses with potent viral inhibitory capacity while control among individuals without protective HLA class I alleles may be more durable and mediated by CD8 + T cell-independent mechanisms. IMPORTANCE Host mechanisms of natural HIV-1 control are not fully understood. In a longitudinal study of antiretroviral therapy (ART)-naive individuals, we show that those with protective HLA class I alleles subsequently experienced virologic failure compared to those without protective alleles. Among individuals with protective HLA class I alleles, viremic control was associated with broad CD8 + T cells that targeted the Gag protein, and CD8 + T cells from these individuals exhibited superior virus inhibition capacity. In individuals without protective HLA class I alleles, HIV-1-specific CD8 + T cell responses were narrow and poorly inhibited virus replication. These results suggest that broad, highly functional cytotoxic T cells (cytotoxic T lymphocytes [CTLs]) against the HIV-1 Gag protein are associated with control among those with protective HLA class I alleles and that loss of these responses eventually leads to viremia. A subset of individuals appears to have alternative, non-CTL mechanisms of viral control. These controllers may hold the key to an effective HIV vaccine.

The extreme polymorphism in the human leukocyte antigen (HLA) class I region of the human genome is suggested to provide an advantage in pathogen defence mediated by CD8+ T cells. HLA class I molecules present pathogen-derived peptides on the surface of infected cells for recognition by CD8+ T cells. However, the relative contributions of HLA-A and -B alleles have not been evaluated. We performed a comprehensive analysis of the class I restricted CD8+ T-cell responses against human immunodeficiency virus (HIV-1), immune control of which is dependent upon virus-specific CD8+ T-cell activity. In 375 HIV-1-infected study subjects from southern Africa, a significantly greater number of CD8+ T-cell responses are HLA-B-restricted, compared to HLA-A (2.5-fold; P = 0.0033). Here we show that variation in viral set-point, in absolute CD4 count and, by inference, in rate of disease progression in the cohort, is strongly associated with particular HLA-B but not HLA-A allele expression (P < 0.0001 and P = 0.91, respectively). Moreover, substantially greater selection pressure is imposed on HIV-1 by HLA-B alleles than by HLA-A (4.4-fold, P = 0.0003). These data indicate that the principal focus of HIV-specific activity is at the HLA-B locus. Furthermore, HLA-B gene frequencies in the population are those likely to be most influenced by HIV disease, consistent with the observation that B alleles evolve more rapidly than A alleles. The dominant involvement of HLA-B in influencing HIV disease outcome is of specific relevance to the direction of HIV research and to vaccine design.

Objectives: Infants infected with HIV-1 perinatally despite single-dose nevirapine progress rapidly. Data on treatment outcome in sub-Saharan African infants exposed to single-dose nevirapine are urgently required. This feasibility study addresses efficacy of infant antiretroviral therapy in this setting. Methods: HIV-infected infants in Durban, South Africa, received randomized immediate or deferred (when CD4 cell count reached

Mutational escape by human immunodeficiency virus (HIV) from cytotoxic T-lymphocyte (CTL) recognition is a major challenge for vaccine design. However, recent studies suggest that CTL escape may carry a sufficient cost to viral replicative capacity to facilitate subsequent immune control of a now attenuated virus. In order to examine how limitations can be imposed on viral escape, the epitope TSTLQEQIGW (TW10 [Gag residues 240 to 249]), presented by two HLA alleles associated with effective control of HIV, HLA-B*57 and -B*5801, was investigated. The in vitro experiments described here demonstrate that the dominant TW10 escape mutation, T242N, reduces viral replicative capacity. Structural analysis reveals that T242 plays a critical role in defining the start point and in stabilizing helix 6 within p24 Gag, ensuring that escape occurs at a significant cost. A very similar role is played by Thr-180, which is also an escape residue, but within a second p24 Gag epitope associated with immune control. Analysis of HIV type 1 gag in 206 B*57/5801-positive subjects reveals three principle alternative TW10-associated variants, and each is strongly linked to concomitant additional variants within p24 Gag, suggesting that functional constraints operate against their occurrence alone. The extreme conservation of p24 Gag and the predictable nature of escape variation resulting from these tight functional constraints indicate that p24 Gag may be a critical immunogen in vaccine design and suggest novel vaccination strategies to limit viral escape options from such epitopes.

HLA class I polymorphism has a major influence on adult HIV disease progression. An important mechanism mediating this effect is the impact on viral replicative capacity (VRC) of the escape mutations selected in response to HLA-restricted CD8+ T-cell responses. Factors that contribute to slow progression in pediatric HIV infection are less well understood. We here investigate the relationship between VRC and disease progression in pediatric infection, and the effect of HLA on VRC and on disease outcome in adult and pediatric infection. Studying a South African cohort of >350 ART-naïve, HIV-infected children and their mothers, we first observed that pediatric disease progression is significantly correlated with VRC. As expected, VRCs in mother-child pairs were strongly correlated (p = 0.004). The impact of the protective HLA alleles, HLA-B*57, HLA-B*58:01 and HLA-B*81:01, resulted in significantly lower VRCs in adults (p, Author Summary HLA plays a central role in determining disease outcome in adult HIV infection. A principal mechanism by which this HLA effect is mediated is via viral replicative capacity (VRC), protective HLA alleles such as HLA-B*57 driving the selection of viral escape mutants that reduce VRC. The factors contributing to the diverse disease progression rates observed in infected children, however, remain uncertain. We here address the role of HLA and VRC in pediatric disease progression in a large cohort in Kimberley, South Africa. The findings highlight the consistent and important role of VRC in both adult and pediatric progression. However, the impact of key HLA molecules in shaping disease outcome in adult infection is notably absent in pediatric infection. Further studies of pediatric infection therefore provide the potential to gain critical new insights into HLA-independent mechanisms of HIV disease non-progression that predominate in HIV-infected but healthy, ART-naive children. Understanding these mechanisms remains of direct relevance to the development of future interventions to minimize HIV disease.

Background Viruses can evade immune surveillance, but the underlying mechanisms are insufficiently understood. Here, we sought to understand the mechanisms by which natural killer (NK) cells recognize HIV-1-infected cells and how this virus can evade NK-cell-mediated immune pressure. Methods and Findings Two sequence mutations in p24 Gag associated with the presence of specific KIR/HLA combined genotypes were identified in HIV-1 clade C viruses from a large cohort of infected, untreated individuals in South Africa (n = 392), suggesting viral escape from KIR+ NK cells through sequence variations within HLA class I—presented epitopes. One sequence polymorphism at position 303 of p24 Gag (TGag303V), selected for in infected individuals with both KIR2DL3 and HLA-C*03:04, enabled significantly better binding of the inhibitory KIR2DL3 receptor to HLA-C*03:04-expressing cells presenting this variant epitope compared to the wild-type epitope (wild-type mean 18.01 ± 10.45 standard deviation [SD] and variant mean 44.67 ± 14.42 SD, p = 0.002). Furthermore, activation of primary KIR2DL3+ NK cells from healthy donors in response to HLA-C*03:04+ target cells presenting the variant epitope was significantly reduced in comparison to cells presenting the wild-type sequence (wild-type mean 0.78 ± 0.07 standard error of the mean [SEM] and variant mean 0.63 ± 0.07 SEM, p = 0.012). Structural modeling and surface plasmon resonance of KIR/peptide/HLA interactions in the context of the different viral sequence variants studied supported these results. Future studies will be needed to assess processing and antigen presentation of the investigated HIV-1 epitope in natural infection, and the consequences for viral control. Conclusions These data provide novel insights into how viruses can evade NK cell immunity through the selection of mutations in HLA-presented epitopes that enhance binding to inhibitory NK cell receptors. Better understanding of the mechanisms by which HIV-1 evades NK-cell-mediated immune pressure and the functional validation of a structural modeling approach will facilitate the development of novel targeted immune interventions to harness the antiviral activities of NK cells., An analysis from a cohort in South Africa reveals how the HIV virus may escape NK cell immunity by acquiring mutations in HLA-mediated epitopes, which affect binding to NK cell receptors., Editors' Summary Background Throughout life, our immune system—a complex network of cells, tissues, and organs—protects us from attack by viruses, bacteria, parasites, and fungi. The body’s first line of defense against these “pathogens” is the innate immune system, a collection of cells and proteins that is always ready to identify and kill a wide range of foreign invaders. As well as directly killing pathogens, the innate immune system activates the adaptive immune response, which recognizes and kills specific pathogens and is responsible for immunological memory. Most pathogens are dispatched quickly and effectively by the two arms of the immune system, but some infectious agents have found ways to evade the immune response. For example, infection with HIV-1, the virus that causes AIDS, results in prolonged, continuous viral replication even though the human body mounts a vigorous HIV-1-specific immune response. In large part, HIV-1’s evasion of the immune response reflects its ability to kill virus-specific CD4 lymphocytes, which are needed to help other immune system cells kill HIV-1-infected cells. In addition, the proteins on the surface of HIV-1 that are recognized by the human immune system (viral antigens) frequently acquire changes (mutations) that make it harder for the immune system to clear HIV-1 from the human body. Why Was This Study Done? Viruses evade immune surveillance in many ways, and if we understood the mechanisms underlying immune evasion better, it might be possible to develop targeted immune interventions to deal with viruses such as HIV-1. Here, the researchers investigate how natural killer (NK) cells, a type of lymphocyte that is an important component of the innate antiviral immune response, recognize HIV-infected cells and how HIV-1 evades NK-cell-mediated immune pressure. NK cell activation is determined by the integration of inhibitory and activating signals delivered to the cells by several different receptor families, including the family of killer-cell immunoglobulin-like receptors (KIRs). KIRs mainly bind to human leukocyte antigen (HLA) class I molecules (ligands) on their target cells. HLA class I proteins display fragments (epitopes; peptides recognized by the immune system) of pathogens present in infected cells on the cell surface so that the immune system knows that that cell needs destroying. The binding of distinct KIRs to HLA class I ligands depends on both the sequence of the HLA class I molecule and the sequence of the epitope presented by that HLA class I molecule. Thus, the researchers hypothesized that HIV-1 might evade NK-cell-mediated immune surveillance by acquiring mutations within epitopes presented by HLA class I molecules that enhance the engagement of inhibitory KIRs on NK cells, thereby inhibiting NK cell activity. What Did the Researchers Do and Find? To investigate this model, the researchers asked whether any polymorphisms (naturally occurring genetic variations) in the HIV-1 gene encoding the p24 Gag protein were selected on a population level in HIV-1-infected individuals expressing specific combinations of KIRs and HLA class I ligands. Using statistical methods to identify KIR/HLA combined genotypes in a large group of untreated HIV-1-infected individuals from South Africa, they showed that a specific sequence polymorphism in p24 Gag was selected for in individuals expressing both HLA-C*03:04 and KIR2DL3. Functional studies showed that the selection of this variant HIV-1 epitope resulted in better binding of KIR2DL3, an inhibitory KIR, to HLA-C*03:04 than the wild-type epitope. Moreover, the activation of KIR2DL3-positive NK cells from healthy donors in response to HLA-C*03:04-positive target cells presenting the variant epitope was significantly reduced compared to the activation of KIR2DL3-positive NK cells in response to target cells presenting the wild-type epitope. What Do These Findings Mean? Further studies are needed to assess the consequences of this and other viral sequence variants for viral fitness, the processing and presentation of the mutant epitope during natural infections, and the control of HIV-1 replication in patients. However, these findings provide new insights into how HIV-1 (and possibly other viruses that have a high mutation rate) might evade NK cell immunity through the selection of mutations in HLA-presented epitopes that enhance the binding of inhibitory KIRs to HLA class I/peptide complexes. A better understanding of this molecular mechanism for evasion of immune surveillance should facilitate the development of targeted immune interventions (for example, the use of KIR-blocking antibodies, some of which are already being clinically tested for the treatment of cancer) to maximize the antiviral activities of NK cells. Additional Information This list of resources contains links that can be accessed when viewing the PDF on a device or via the online version of the article at http://dx.doi.org/10.1371/journal.pmed.1001900. The US National Institute of Allergy and Infectious Diseases provides a simple description of the human immune system and information on all aspects of HIV infection and AIDS Information is available from Avert, an international AIDS charity, on many aspects of HIV/AIDS; Avert also provides personal stories about living with HIV/AIDS The British Society for Immunology provides short articles about various aspects of immunology, including general information about host–pathogen interactions and immune evasion and specific information about HIV and immune evasion Wikipedia has pages on natural killer cells, KIRs, and HLA molecules (note that Wikipedia is a free online encyclopedia that anyone can edit; available in several languages)

Natural killer (NK) cells play a critical role in the control of HIV-1 infection, and NK cells that respond to HIV-1 peptides have been recently described. However, the mechanisms by which NK cells recognize HIV-1 antigens are not fully understood. We investigated NK cell activation in response to HIV-1 peptides during early and chronic HIV-1 clade B infection using a whole-blood assay and multiparameter flow cytometry. Antibody-mediated NK cell activation in response to HIV-1 peptides was not detected in HIV-1-uninfected individuals. In contrast, 79% of individuals with chronic infection and 22% of individuals with early infection had detectable gamma interferon (IFN-γ) NK cell responses to HIV-1 antigens ( P < 0.00001). IFN-γ- and tumor necrosis factor alpha (TNF-α)-producing NK cells most frequently targeted Env gp120 (median of 4% and range of 0 to 31% of all NK cells). NK cells rarely targeted other HIV-1 proteins such as Gag, Pol, and Nef. Antibody-mediated NK cell responses to peptides mapped predominantly to Env protein, required the presence of plasma or plasma IgG, and resulted in lower CD16 expression on NK cells, suggesting an antibody-mediated activation of NK cells. Further studies are needed to assess the consequences of these antibody-mediated NK cell responses for HIV-1 disease progression and vaccine-induced protection from infection.

Pediatric HIV-1 infection is characterized by rapid disease progression and without antiretroviral therapy (ART), more than 50% of infected children die by the age of 2 years. However, a small subset of infected children progresses slowly to disease in the absence of ART. This study aimed to identify functional characteristics of HIV-1-specific T cell responses that distinguish children with rapid and slow disease progression. Fifteen perinatally HIV-infected children (eight rapid and seven slow progressors) were longitudinally studied to monitor T cell polyfunctionality. HIV-1-specific interferon (IFN)-γ(+) CD8(+) T cell responses gradually increased over time but did not differ between slow and rapid progressors. However, polyfunctional HIV-1-specific CD8(+) T cell responses, as assessed by the expression of four functions (IFN-γ, CD107a, TNF-α, MIP-1β), were higher in slow compared to rapid progressors (p=0.05) early in infection, and was associated with slower subsequent disease progression. These data suggest that the quality of the HIV-specific CD8(+) T cell response is associated with the control of disease in children as has been shown in adult infection.

Untreated human immunodeficiency virus (HIV)-infected infants progress more rapidly to AIDS and death than older children or adults (35). This is particularly the case in resource-limited settings, where mortality exceeds 50% by 2 years of age. Viral loads during infancy remain strikingly high, and the rapid reduction in viremia from peak levels characteristic of acute adult infection occurs only slowly over the first few years of life in pediatric infection. This late reduction in viremia, compared to the establishment of viral setpoint within a few weeks in adult infection, may coincide with the normal maturation of infant adaptive immune responses. There are several additional reasons for impaired virological control during infancy. First, HIV-induced T-cell depletion damages the developing immune system before an effective antiviral response can be mounted (13, 23). Second, HIV-infected infants are more likely to possess nonprotective HLA alleles, since at least 50% of the infant's HLA genotype is shared with the mother, and high maternal viremia is a risk factor for perinatal HIV transmission (35). Finally, the infecting virus may be adapted to maternally and paternally inherited HLA genes (19, 38). However, a minority of infants progress relatively slowly. The immune correlates of slow progression in pediatric HIV infection are still not well understood. In this context, the interactions between characteristics of the maternal virus transmitted but also the CD8+ T-cell responses generated by the child are likely to be important factors to HIV control in pediatric infection, as in adults (11, 28). In certain cases described in the literature, the biological properties of the virus have been determined as the primary reason for effective HIV control. Presence of attenuated HIV variants with low replicative capacity (RC) has been linked to nonprogressive disease (12, 36) and elite control (28) in HIV-infected adults. Moreover, transmission of certain HIV Gag CD8+ T-cell escape variants to a recipient lacking the same HLA molecules leads to reduced viral set point in acute adult infection and contributes to higher CD4 counts and lower viral load (6, 14). In other cases, control of viremia has been strongly associated with CD8+ T-cell responses mediated by “protective” HLA alleles such as HLA-B*57 or B*27 (16). In HIV-infected children, as in adults, there is evidence that CD8+ T-cell responses can contribute to viral containment and that the “protective” effect of certain HLA alleles identified in adult HIV infection may also operate in pediatric infection (42). In addition, HIV-infected infants lacking protective HLA alleles but whose mothers express protective HLA alleles such as HLA-B*57, B*5801, or B*8101 tend to progress more slowly, for reasons hypothesized to relate to transmission of virus that has been attenuated by the selection of CD8+ T-cell escape mutants in the mother (41). We therefore undertook the present study in perinatally HIV-infected infants in Durban, South Africa, the epicenter of the pediatric epidemic, to investigate the potential role of the viral RC of mother-to-child transmitted virus on pediatric HIV disease progression. We studied eight infants with clade C HIV infection: three defined as progressors (P) and five as slow progressors (SP). To characterize in detail biological properties of the virus, viral variants were isolated from plasma samples in both groups. The RC of viral isolates was measured in vitro in primary cells. In addition, viral tropism was determined for these isolates, together with the presence of polymorphisms in Nef, and of HLA-B*57/5801-associated Gag escape mutants, since these have been additional factors previously linked to viral attenuation and disease outcome.

A broad Gag-specific CD8 + T-cell response is associated with effective control of adult human immunodeficiency virus (HIV) infection. The association of certain HLA class I molecules, such as HLA-B*57, -B*5801, and -B*8101, with immune control is linked to mutations within Gag epitopes presented by these alleles that allow HIV to evade the immune response but that also reduce viral replicative capacity. Transmission of such viruses containing mutations within Gag epitopes results in lower viral loads in adult recipients. In this study of pediatric infection, we tested the hypothesis that children may tend to progress relatively slowly if either they themselves possess one of the protective HLA-B alleles or the mother possesses one of these alleles, thereby transmitting a low-fitness virus to the child. We analyzed HLA type, CD8 + T-cell responses, and viral sequence changes for 61 mother-child pairs from Durban, South Africa, who were monitored from birth. Slow progression was significantly associated with the mother or child possessing one of the protective HLA-B alleles, and more significantly so when the protective allele was not shared by mother and child ( P = 0.007). Slow progressors tended to make CD8 + T-cell responses to Gag epitopes presented by the protective HLA-B alleles, in contrast to progressors expressing the same alleles ( P = 0.07; Fisher's exact test). Mothers expressing the protective alleles were significantly more likely to transmit escape variants within the Gag epitopes presented by those alleles than mothers not expressing those alleles (75% versus 21%; P = 0.001). Reversion of transmitted escape mutations was observed in all slow-progressing children whose mothers possessed protective HLA-B alleles. These data show that HLA class I alleles influence disease progression in pediatric as well as adult infection, both as a result of the CD8 + T-cell responses generated in the child and through the transmission of low-fitness viruses by the mother.

Multiple HIV-1-specific cytokine and proliferative responses by CD4(+) T cells have not been studied in acutely infected infants. Using an intracellular cytokine staining assay, 34 untreated clade C HIV-1-infected infants (2-102 days old) were assessed for IFN-gamma, 28/34 for IL-2, and 26/34 for TNF-alpha responses to all HIV-1 proteins. Responses were detected in 29%, 36%, and 15% of infants, respectively. Twelve of the original 34 infants were then studied longitudinally for 14 months to determine the effect of viral load on IFN-gamma Gag-specific responses: seven infants were treated for 1 year, stopped treatment, and resumed when CD4% was < 20 and five infants were treated only when the CD4% was

In HIV-infected persons, certain HLA class I alleles are associated with effective control of viremia, while others are associated with rapid disease progression. Among the most divergent clinical outcomes are the relatively good prognosis in HLA-B*5801 expressing persons and poor prognosis with HLA-B*5802. These two alleles differ by only three amino acids in regions involved in HLA-peptide recognition. This study evaluated a cohort of over 1000 persons with chronic HIV clade C virus infection to determine whether clinical outcome differences associated with B*5801 (n = 93) and B*5802 ( n = 259) expression are associated with differences in HIV-1-specific CD8 (+) T cell responses. The overall breadth and magnitude of HIV-1-specific CD8(+) T cell responses were lower in persons expressing B*5802, and epitope presentation by B*5802 contributed significantly less to the overall response as compared to B*5801-restricted CD8 (+) T cells. Moreover, viral load in B*5802-positive persons was higher and CD4 cell counts lower when this allele contributed to the overall CD8 (+) T cell response, which was detected exclusively through a single epitope in Env. In addition, persons heterozygous for B*5802 compared to persons homozygous for other HLA-B alleles had significantly higher viral loads. Viral sequencing revealed strong selection pressure mediated through B*5801-restricted responses but not through B*5802. These data indicate that minor differences in HLA sequence can have a major impact on epitope recognition, and that selective targeting of Env through HLA-B*5802 is at least ineffectual if not actively adverse in the containment of viremia. These results provide experimental evidence that not all epitope-specific responses contribute to immune containment, a better understanding of which is essential to shed light on mechanisms involved in HIV disease progression.

OBJECTIVES: To determine the natural history of HIV infection following peripartum single-dose nevirapine (sd-NVP) prophylaxis in a resource-limited country, and to assess implications for antiretroviral therapy (ART) roll-out programmes. METHODS: Infants of HIV-infected mothers in KwaZulu-Natal, South Africa, were tested on days 1 and 28 to detect intrauterine (IU) and intrapartum (IP) infection. Infant follow-up included monthly viral load and CD4 cell measurement. ART was initiated at infant CD4 cell% < or = 20%. RESULTS: In 740 infants born to 719 HIV-infected women, mother-to-child transmission (MTCT) was 10.3% (69% IU, 31% IP). Median viral load was higher in mothers of infants infected IP than IU (279 000 versus 86 600 copies/ml; P = 0.039) and lower in mothers of uninfected infants (median 26 750 copies/ml; P < 0.001). Peak viraemia was higher in infants infected IP than IU (5 160 000 versus 984 000 copies/ml; P < 0.001). Median viral load at birth in IU-infected infants (155 000 copies/ml) fell 1.4 log to 6510 copies/ml by day 5 and was beneath the detection limit using dried blood spot analysis in 38% of infants. CD4 cell% declined rapidly, to < or = 20% in 70% and < or = 25% in 85% [current World Health Organization (WHO) criteria for initiating ART] of infants by 6 months. CONCLUSIONS: MTCT was reduced by sd-NVP through an effect on IP transmission. Where MTCT occurred despite NVP, two-thirds of transmissions arose IU; IP-infected babies were born to mothers with very high viral load. Disease progression was particularly rapid, 85% infants meeting WHO criteria for ART within 6 months. These findings argue for more effective MTCT-prevention programmes in resource-limited countries.

Human immunodeficiency virus (HIV)-1 amino acid sequence polymorphisms associated with expression of specific human histocompatibility leukocyte antigen (HLA) class I alleles suggest sites of cytotoxic T lymphocyte (CTL)-mediated selection pressure and immune escape. The associations most frequently observed are between expression of an HLA class I molecule and variation from the consensus sequence. However, a substantial number of sites have been identified in which particular HLA class I allele expression is associated with preservation of the consensus sequence. The mechanism behind this is so far unexplained. The current studies, focusing on two examples of “negatively associated” or apparently preserved epitopes, suggest an explanation for this phenomenon: negative associations can arise as a result of positive selection of an escape mutation, which is stable on transmission and therefore accumulates in the population to the point at which it defines the consensus sequence. Such negative associations may only be in evidence transiently, because the statistical power to detect them diminishes as the mutations accumulate. If an escape variant reaches fixation in the population, the epitope will be lost as a potential target to the immune system. These data help to explain how HIV is evolving at a population level. Understanding the direction of HIV evolution has important implications for vaccine development.

BACKGROUND: A dominance of Gag-specific CD8+ T cell responses is significantly associated with a lower viral load in individuals with chronic, untreated clade C human immunodeficiency virus type 1 (HIV-1) infection. This association has not been investigated in terms of Gag-specific CD4+ T cell responses, nor have clade C HIV-1-specific CD4+ T cell epitopes, likely a vital component of an effective global HIV-1 vaccine, been identified. METHODOLOGY/PRINCIPAL FINDINGS: Intracellular cytokine staining was conducted on 373 subjects with chronic, untreated clade C infection to assess interferon-gamma (IFN-gamma) responses by CD4+ T cells to pooled Gag peptides and to determine their association with viral load and CD4 count. Gag-specific IFN-gamma-producing CD4+ T cell responses were detected in 261/373 (70%) subjects, with the Gag responders having a significantly lower viral load and higher CD4 count than those with no detectable Gag response (p

HIV-1 specific HLA-B-restricted CD8+ T cell responses differ from HLA-C-restricted responses in antiviral effectiveness. To investigate possible reasons for these differences, we characterized the frequency and polyfunctionality of immmunodominant HLA-B*57/B5801- and HLA-Cw*07-restricted CD8+ T cells occurring concurrently in nine study subjects assessing IFN-gamma, TNF-alpha, IL-2, MIP-1beta, and CD107a by flow cytometry and analyzed sequence variation in targeted epitopes. HLA-B*57/5801 and HLA-Cw*07 restricted CD8+ T cells did not differ significantly in polyfunctionality (p=0.84). Possession of three or more functions correlated positively with CD4+ T cell counts (r=0.85; p=0.006) and monofunctional CD8+ T cells inversely correlated with CD4 cell counts (r=-0.79; p=0.05). There were no differences in polyfunctionality of CD8+ T cells specific to wildtype versus mutated epitopes. These results suggest that loss of polyfunctionality and increase in monofunctional HIV-1-specific CD8+ T cells are associated with disease progression independent of restricting HLA allele. Furthermore, sequence variation does not appear to significantly impact CD8+ T cell polyfunctionality in chronic HIV-1 infection.