Multiple Origins of Virus Persistence during Natural Control of HIV Infection.

Targeted HIV cure strategies require definition of the mechanisms that maintain the virus. Here, we tracked HIV replication and the persistence of infected CD4 T cells in individuals with natural virologic control by sequencing viruses, T cell receptor genes, HIV integration sites, and cellular transcriptomes. Our results revealed three mechanisms of HIV persistence operating within distinct anatomic and functional compartments. In lymph node, we detected viruses with genetic and transcriptional attributes of active replication in both T follicular helper (TFH) cells and non-TFH memory cells. In blood, we detected inducible proviruses of archival origin among highly differentiated, clonally expanded cells. Linking the lymph node and blood was a small population of circulating cells harboring inducible proviruses of recent origin. Thus, HIV replication in lymphoid tissue, clonal expansion of infected cells, and recirculation of recently infected cells act together to maintain the virus in HIV controllers despite effective antiviral immunity.

Success and failure of the cellular immune response against HIV-1.

The cellular immune response to HIV-1 has now been studied in extraordinary detail. A very large body of data provides the most likely reasons that the HIV-specific cellular immune response succeeds in a small number of people but fails in most. Understanding the success and failure of the HIV-specific cellular immune response has implications that extend not only to immunotherapies and vaccines for HIV-1 but also to the cellular immune response in other disease states. This Review focuses on the mechanisms that are most likely responsible for durable and potent immunologic control of HIV-1. Although we now have a detailed picture of the cellular immune responses to HIV-1, important questions remain regarding the nature of these responses and how they arise.

Class II-Restricted CD8s: New Lessons Violate Old Paradigms.

CD8+ T cells that recognize peptides presented by MHC class II molecules have been observed in a macaque SIV vaccine model. A new study by Ranasinghe et al. (2016) shows that virus-specific class-II-restricted CD8+ T cells can be found in some HIV-infected patients.

Identification of a CD4-Binding-Site Antibody to HIV that Evolved Near-Pan Neutralization Breadth.

Detailed studies of the broadly neutralizing antibodies (bNAbs) that underlie the best available examples of the humoral immune response to HIV are providing important information for the development of therapies and prophylaxis for HIV-1 infection. Here, we report a CD4-binding site (CD4bs) antibody, named N6, that potently neutralized 98% of HIV-1 isolates, including 16 of 20 that were resistant to other members of its class. N6 evolved a mode of recognition such that its binding was not impacted by the loss of individual contacts across the immunoglobulin heavy chain. In addition, structural analysis revealed that the orientation of N6 permitted it to avoid steric clashes with glycans, which is a common mechanism of resistance. Thus, an HIV-1-specific bNAb can achieve potent, near-pan neutralization of HIV-1, making it an attractive candidate for use in therapy and prophylaxis.

Evaluating a New Class of AKT/mTOR Activators for HIV Latency Reversing Activity Ex Vivo and In Vivo.

An ability to activate latent HIV-1 expression could benefit many HIV cure strategies, but the first generation of latency reversing agents (LRAs) has proven disappointing. We evaluated AKT/mTOR activators as a potential new class of LRAs. Two glycogen synthase kinase-3 inhibitors (GSK-3i's), SB-216763 and tideglusib (the latter already in phase II clinical trials) that activate AKT/mTOR signaling were tested. These GSK-3i's reactivated latent HIV-1 present in blood samples from aviremic individuals on antiretroviral therapy (ART) in the absence of T cell activation, release of inflammatory cytokines, cell toxicity, or impaired effector function of cytotoxic T lymphocytes or NK cells. However, when administered in vivo to SIV-infected rhesus macaques on suppressive ART, tideglusib exhibited poor pharmacodynamic properties and resulted in no clear evidence of significant SIV latency reversal. Whether alternative pharmacological formulations or combinations of this drug with other classes of LRAs will lead to an effective in vivo latency-reversing strategy remains to be determined.IMPORTANCE If combined with immune therapeutics, latency reversing agents (LRAs) have the potential to reduce the size of the reservoir sufficiently that an engineered immune response can control the virus in the absence of antiretroviral therapy. We have identified a new class of LRAs that do not induce T-cell activation and that are able to potentiate, rather than inhibit, CD8+ T and NK cell cytotoxic effector functions. This new class of LRAs corresponds to inhibitors of glycogen synthase kinase-3. In this work, we have also studied the effects of one member of this drug class, tideglusib, in SIV-infected rhesus monkeys. When tested in vivo, however, tideglusib showed unfavorable pharmacokinetic properties, which resulted in lack of SIV latency reversal. The disconnect between our ex vivo and in vivo results highlights the importance of developing next generation LRAs with pharmacological properties that allow systemic drug delivery in relevant anatomical compartments harboring latent reservoirs.

Lost in Translation: Lack of CD4 Expression due to a Novel Genetic Defect.

CD4 expression identifies a subset of mature T cells primarily assisting the germinal center reaction and contributing to CD8+ T-cell and B-cell activation, functions, and longevity. Herein, we present a family in which a novel variant disrupting the translation-initiation codon of the CD4 gene resulted in complete loss of membrane and plasma soluble CD4 in peripheral blood, lymph node, bone marrow, skin, and ileum of a homozygous proband. This inherited CD4 knockout disease illustrates the clinical and immunological features of a complete deficiency of any functional component of CD4 and its similarities and differences with other clinical models of primary or acquired loss of CD4+ T cells. The first inherited loss of any functional component of CD4, including soluble CD4, is clinically distinct from any other congenital or acquired CD4 T-cell defect and characterized by compensatory changes in T-cell subsets and functional impairment of B cells, monocytes, and natural killer cells.

Antigenic Restimulation of Virus-Specific Memory CD8+ T Cells Requires Days of Lytic Protein Accumulation for Maximal Cytotoxic Capacity.

In various infections or vaccinations of mice or humans, reports of the persistence and the requirements for restimulation of the cytotoxic mediators granzyme B (GrB) and perforin (PRF) in CD8+ T cells have yielded disparate results. In this study, we examined the kinetics of PRF and GrB mRNA and protein expression after stimulation and associated changes in cytotoxic capacity in virus-specific memory cells in detail. In patients with controlled HIV or cleared respiratory syncytial virus (RSV) or influenza virus infections, all virus-specific CD8+ T cells expressed low PRF levels without restimulation. Following stimulation, they displayed similarly delayed kinetics for lytic protein expression, with significant increases occurring by days 1 to 3 before peaking on days 4 to 6. These increases were strongly correlated with, but were not dependent upon, proliferation. Incremental changes in PRF and GrB percent expression and mean fluorescence intensity (MFI) were highly correlated with increases in HIV-specific cytotoxicity. mRNA levels in HIV-specific CD8+ T-cells exhibited delayed kinetics after stimulation as with protein expression, peaking on day 5. In contrast to GrB, PRF mRNA transcripts were little changed over 5 days of stimulation (94-fold versus 2.8-fold, respectively), consistent with posttranscriptional regulation. Changes in expression of some microRNAs, including miR-17, miR-150, and miR-155, suggested that microRNAs might play a significant role in regulation of PRF expression. Therefore, under conditions of extremely low or absent antigen levels, memory virus-specific CD8+ T cells require prolonged stimulation over days to achieve maximal lytic protein expression and cytotoxic capacity.IMPORTANCE Antigen-specific CD8+ T cells play a major role in controlling most virus infections, primarily by perforin (PRF)- and granzyme B (GrB)-mediated apoptosis. There is considerable controversy regarding whether PRF is constitutively expressed, rapidly increased similarly to a cytokine, or delayed in its expression with more prolonged stimulation in virus-specific memory CD8+ T cells. In this study, the degree of cytotoxic capacity of virus-specific memory CD8+ T cells was directly proportional to the content of lytic molecules, which required antigenic stimulation over several days for maximal levels. This appeared to be modulated by increases in GrB transcription and microRNA-mediated posttranscriptional regulation of PRF expression. Clarifying the requirements for maximal cytotoxic capacity is critical to understanding how viral clearance might be mediated by memory cells and what functions should be induced by vaccines and immunotherapies.

Small molecules and big killers: the challenge of eliminating the latent HIV reservoir.

In this issue of Immunity, Shan et al. (2012) explore the elimination of cells latently infected with HIV and the potential implications for strategies to eradicate the virus from infected patients.

Broad and potent HIV-1 neutralization by a human antibody that binds the gp41-gp120 interface.

The isolation of human monoclonal antibodies is providing important insights into the specificities that underlie broad neutralization of HIV-1 (reviewed in ref. 1). Here we report a broad and extremely potent HIV-specific monoclonal antibody, termed 35O22, which binds a novel HIV-1 envelope glycoprotein (Env) epitope. 35O22 neutralized 62% of 181 pseudoviruses with a half-maximum inhibitory concentration (IC50) <50 µg ml(-1). The median IC50 of neutralized viruses was 0.033 µg ml(-1), among the most potent thus far described. 35O22 did not bind monomeric forms of Env tested, but did bind the trimeric BG505 SOSIP.664. Mutagenesis and a reconstruction by negative-stain electron microscopy of the Fab in complex with trimer revealed that it bound to a conserved epitope, which stretched across gp120 and gp41. The specificity of 35O22 represents a novel site of vulnerability on HIV Env, which serum analysis indicates to be commonly elicited by natural infection. Binding to this new site of vulnerability may thus be an important complement to current monoclonal-antibody-based approaches to immunotherapies, prophylaxis and vaccine design.

IL-12-Dependent Cytomegalovirus-Specific CD4+ T Cell Proliferation, T-bet Induction, and Effector Multifunction during Primary Infection Are Key Determinants for Early Immune Control.

CMV remains an important opportunistic pathogen in solid organ and hematopoietic cell transplantation, particularly in lung transplant recipients (LTRs). LTRs mismatched for CMV (donor(+)/recipient(-); D(+)R(-)) are at high risk for active CMV infection and increased mortality; however, the immune correlates of viral control remain incompletely understood. We prospectively studied 27 D(+)R(-) LTRs during primary CMV infection to determine whether acute CD4(+) T cell parameters differentiated the capacity for viral control during early chronic infection. Unexpectedly, the T-box transcription factor, T-bet, was expressed at low levels in CD4(+) compared with CD8(+) T cells during acute primary infection. However, the capacity for in vitro CMV phosphoprotein 65-specific proliferation and CD4(+)T-bet(+) induction differentiated LTR controllers from early viremic relapsers, correlating with granzyme B loading and effector multifunction. Furthermore, impaired CMV-specific proliferative responses from relapsers, along with T-bet, and effector function could be significantly rescued, most effectively with phosphoprotein 65 Ag and combined exogenous IL-2 and IL-12. Acute CD4(+) T cell CMV-specific proliferative and effector responses were highly IL-12-dependent in blocking studies. In addition, we generated monocyte-derived dendritic cells using PBMC obtained during primary infection from relapsers and observed impaired monocyte-derived dendritic cell differentiation, a reduced capacity for IL-12 production, but increased IL-10 production compared with controls, suggesting an APC defect during acute CMV viremia. Taken together, these data show an important role for CMV-specific CD4(+) effector responses in differentiating the capacity of high-risk LTRs to establish durable immune control during early chronic infection and provide evidence for IL-12 as a key factor driving these responses.

Broad and potent neutralization of HIV-1 by a gp41-specific human antibody.

Characterization of human monoclonal antibodies is providing considerable insight into mechanisms of broad HIV-1 neutralization. Here we report an HIV-1 gp41 membrane-proximal external region (MPER)-specific antibody, named 10E8, which neutralizes ∼98% of tested viruses. An analysis of sera from 78 healthy HIV-1-infected donors demonstrated that 27% contained MPER-specific antibodies and 8% contained 10E8-like specificities. In contrast to other neutralizing MPER antibodies, 10E8 did not bind phospholipids, was not autoreactive, and bound cell-surface envelope. The structure of 10E8 in complex with the complete MPER revealed a site of vulnerability comprising a narrow stretch of highly conserved gp41-hydrophobic residues and a critical arginine or lysine just before the transmembrane region. Analysis of resistant HIV-1 variants confirmed the importance of these residues for neutralization. The highly conserved MPER is a target of potent, non-self-reactive neutralizing antibodies, suggesting that HIV-1 vaccines should aim to induce antibodies to this region of HIV-1 envelope glycoprotein.

Monitoring Integration over Time Supports a Role for Cytotoxic T Lymphocytes and Ongoing Replication as Determinants of Reservoir Size.

The dynamics of HIV reservoir accumulation off antiretroviral therapy (ART) is underexplored. Levels of integrated HIV DNA in peripheral blood mononuclear cells (PBMCs) were longitudinally monitored before and after antiviral therapy. HIV integration increased over time in both elite controllers (ECs; n = 8) and noncontrollers (NCs; n = 6) before ART, whereas integration remained stable in patients on ART (n = 4). The median annual fold change was higher in NCs than in ECs and negatively correlated with CD4/CD8 T-cell ratio. Cytotoxic T lymphocyte (CTL) function as assessed by infected CD4 T-cell elimination (ICE) and granzyme B activity did not significantly change over time in ECs, suggesting that the gradual increase in integrated HIV DNA observed in ECs was not a result of progressive loss of immune-mediated control. Also, acutely infected (n = 7) but not chronically infected (n = 6) patients exhibited a significant drop in integrated HIV DNA 12 months after ART initiation. In conclusion, in the absence of ART, integrated HIV accumulates over time both in NCs and in ECs, at variable individual rates. Starting ART early in infection leads to a greater drop in integrated HIV DNA than does initiating treatment after years of infection. The increase in integrated HIV DNA over time suggests that early treatment may be of benefit in limiting HIV reservoirs. IMPORTANCE: The establishment of a latent reservoir represents a barrier to cure among HIV-infected individuals. The dynamics of HIV reservoir accumulation over time in patients before antiviral therapy is underexplored, in large part because it is difficult to accurately and reproducibly measure the size of HIV reservoir in this setting. In our study, we compared the dynamics of integrated HIV DNA over time in ECs and NCs before and after ART was initiated. We found that integrated HIV DNA levels progressively increase over time in the absence of ART, but with a higher, albeit variable, rate in NCs compared to ECs. In addition, integrated HIV DNA declines more dramatically when ART is initiated in acute rather than chronic HIV infection, suggesting important differences between acute and chronic infection. Our study highlights the role of HIV replication and CTL control in reservoir accumulation in sanctuary sites and why ART appears to be more effective in acute infection.

Lytic granule loading of CD8+ T cells is required for HIV-infected cell elimination associated with immune control.

Virus-specific CD8+ T cells probably mediate control over HIV replication in rare individuals, termed long-term nonprogressors (LTNPs) or elite controllers. Despite extensive investigation, the mechanisms responsible for this control remain incompletely understood. We observed that HIV-specific CD8+ T cells of LTNPs persisted at higher frequencies than those of treated progressors with equally low amounts of HIV. Measured on a per-cell basis, HIV-specific CD8+ T cells of LTNPs efficiently eliminated primary autologous HIV-infected CD4+ T cells. This function required lytic granule loading of effectors and delivery of granzyme B to target cells. Defective cytotoxicity of progressor effectors could be restored after treatment with phorbol ester and calcium ionophore. These results establish an effector function and mechanism that clearly segregate with immunologic control of HIV. They also demonstrate that lytic granule contents of memory cells are a critical determinant of cytotoxicity that must be induced for maximal per-cell killing capacity.

A Subset of CD4/CD8 Double-Negative T Cells Expresses HIV Proteins in Patients on Antiretroviral Therapy.

UNLABELLED: A major goal in HIV eradication research is characterizing the reservoir cells that harbor HIV in the presence of antiretroviral therapy (ART), which reseed viremia after treatment is stopped. In general, it is assumed that the reservoir consists of CD4(+) T cells that express no viral proteins. However, recent findings suggest that this may be an overly simplistic view and that the cells that contribute to the reservoir may be a diverse population that includes both CD4(+) and CD4(-) cells. In this study, we directly infected resting CD4(+) T cells and used fluorescence-activated cell sorting (FACS) and fiber-optic array scanning technology (FAST) to identify and image cells expressing HIV Gag. We found that Gag expression from integrated proviruses occurred in resting cells that lacked surface CD4, likely resulting from Nef- and Env-mediated receptor internalization. We also extended our approach to detect cells expressing HIV proteins in patients suppressed on ART. We found evidence that rare Gag(+) cells persist during ART and that these cells are often negative for CD4. We propose that these double-negative α/ß T cells that express HIV protein may be a component of the long-lived reservoir. IMPORTANCE: A reservoir of infected cells persists in HIV-infected patients during antiretroviral therapy (ART) that leads to rebound of virus if treatment is stopped. In this study, we used flow cytometry and cell imaging to characterize protein expression in HIV-infected resting cells. HIV Gag protein can be directly detected in infected resting cells and occurs with simultaneous loss of CD4, consistent with the expression of additional viral proteins, such as Env and Nef. Gag(+) CD4(-) cells can also be detected in suppressed patients, suggesting that a subset of infected cells express proteins during ART. Understanding the regulation of viral protein expression during ART will be key to designing effective strategies to eradicate HIV reservoirs.

Increased sequence coverage through combined targeting of variant and conserved epitopes correlates with control of HIV replication.

A major challenge in the development of an HIV vaccine is that of contending with the extensive sequence variability found in circulating viruses. Induction of HIV-specific T-cell responses targeting conserved regions and induction of HIV-specific T-cell responses recognizing a high number of epitope variants have both been proposed as strategies to overcome this challenge. We addressed the ability of cytotoxic T lymphocytes from 30 untreated HIV-infected subjects with and without control of virus replication to recognize all clade B Gag sequence variants encoded by at least 5% of the sequences in the Los Alamos National Laboratory HIV database (1,300 peptides) using gamma interferon and interleukin-2 (IFN-γ/IL-2) FluoroSpot analysis. While targeting of conserved regions was similar in the two groups (P = 0.47), we found that subjects with control of virus replication demonstrated marginally lower recognition of Gag epitope variants than subjects with normal progression (P = 0.05). In viremic controllers and progressors, we found variant recognition to be associated with viral load (r = 0.62, P = 0.001). Interestingly, we show that increased overall sequence coverage, defined as the overall proportion of HIV database sequences targeted through the Gag-specific repertoire, is inversely associated with viral load (r = -0.38, P = 0.03). Furthermore, we found that sequence coverage, but not variant recognition, correlated with increased recognition of a panel of clade B HIV founder viruses (r = 0.50, P = 0.004). We propose sequence coverage by HIV Gag-specific immune responses as a possible correlate of protection that may contribute to control of virus replication. Additionally, sequence coverage serves as a valuable measure by which to evaluate the protective potential of future vaccination strategies.

CD4+ memory stem cells are infected by HIV-1 in a manner regulated in part by SAMHD1 expression.

UNLABELLED: CD4(+) and CD8(+) memory T cells with stem cell-like properties (T(SCM) cells) have been identified in mice, humans, and nonhuman primates and are being investigated for antitumor and antiviral vaccines and immunotherapies. Whether CD4(+) T(SCM) cells are infected by human immunodeficiency virus (HIV) was investigated by using a combination HIV reporter virus system in vitro and by direct staining for HIV p24 antigen ex vivo. A proportion of T(SCM) cells were found to express the HIV coreceptors CCR5 and CXCR4 and were infected by HIV both in vitro and in vivo. Analysis of viral outcome following fusion using the combination reporter virus system revealed that T(SCM) cells can become productively or latently infected, although the vast majority of T(SCM) cells are abortively infected. Knockdown of the HIV restriction factor SAMHD1 using Vpx-containing simian immunodeficiency virus (SIV) virion-like particles enhanced the productive infection of T(SCM) cells, indicating that SAMHD1 contributes to abortive infection in these cells. These results demonstrate that CD4(+) T(SCM) cells are targets for HIV infection, that they become productively or latently infected at low levels, and that SAMHD1 expression promotes abortive infection of this important memory cell subset. IMPORTANCE: Here we demonstrate the susceptibility of CD4(+) memory stem cells (T(SCM) cells) to infection by HIV in vitro and in vivo, provide an in-depth analysis of coreceptor expression, demonstrate the infection of naïve and memory CD4(+) T cell subsets with both CCR5- and CXCR4-tropic HIV, and also perform outcome analysis to calculate the percentage of cells that are productively, latently, or abortively infected. Through these outcome studies, we determined that the vast majority of T(SCM) cells are abortively infected by HIV, and we demonstrate that knockdown of SAMHD1 significantly increases the frequency of infection of this CD4(+) T cell subset, indicating that SAMHD1 is an active restriction factor in T(SCM) cells.

Cytotoxic capacity of SIV-specific CD8(+) T cells against primary autologous targets correlates with immune control in SIV-infected rhesus macaques.

Although the study of non-human primates has resulted in important advances for understanding HIV-specific immunity, a clear correlate of immune control over simian immunodeficiency virus (SIV) replication has not been found to date. In this study, CD8(+) T-cell cytotoxic capacity was examined to determine whether this function is a correlate of immune control in the rhesus macaque (RM) SIV infection model as has been suggested in chronic HIV infection. SIVmac251-infected human reverse transcriptase (hTERT)-transduced CD4(+) T-cell clone targets were co-incubated with autologous macaque effector cells to measure infected CD4(+) T-cell elimination (ICE). Twenty-three SIV-infected rhesus macaques with widely varying plasma viral RNA levels were evaluated in a blinded fashion. Nineteen of 23 subjects (83%) were correctly classified as long-term nonprogressor/elite controller (LTNP/EC), slow progressor, progressor or SIV-negative rhesus macaques based on measurements of ICE (weighted Kappa 0.75). LTNP/EC had higher median ICE than progressors (67.3% [22.0-91.7%] vs. 23.7% [0.0-58.0%], p = 0.002). In addition, significant correlations between ICE and viral load (r = -0.57, p = 0.01), and between granzyme B delivery and ICE (r = 0.89, p<0.001) were observed. Furthermore, the CD8(+) T cells of LTNP/EC exhibited higher per-cell cytotoxic capacity than those of progressors (p = 0.004). These findings support that greater lytic granule loading of virus-specific CD8(+) T cells and efficient delivery of active granzyme B to SIV-infected targets are associated with superior control of SIV infection in rhesus macaques, consistent with observations of HIV infection in humans. Therefore, such measurements appear to represent a correlate of control of viral replication in chronic SIV infection and their role as predictors of immunologic control in the vaccine setting should be evaluated.

Evidence for innate immune system activation in HIV type 1-infected elite controllers.

BACKGROUND: Elite controllers maintain high CD4(+) T-cell counts and suppress plasma human immunodeficiency virus (HIV) viremia in the absence of antiretroviral therapy (ART). It is unclear whether levels of biomarkers associated with coagulation, monocyte activation, and inflammation, which are linked to HIV-associated mortality, differ among elite controllers, ART recipients with suppressed viremia (plasma HIV type 1 RNA load, <50 copies/mL), and HIV-negative controls. METHODS: A total of 68 elite controllers, 68 ART recipients with suppressed viremia, and 35 HIV-negative participants were evaluated. Levels of biomarkers in cryopreserved plasma were measured by enzyme-linked immunosorbent assay and electrochemiluminescence-based assay. Cryopreserved peripheral blood mononuclear cells were used to assess monocyte phenotype and function and interferon-inducible gene expression (IFIG). Nonparametric testing was used to compare median values among groups. RESULTS: CD4(+) T-cell counts were similar between elite controllers and HIV-negative controls but significantly lower in ART recipients with suppressed viremia. Levels of C-reactive protein and interleukin 6 were higher and IFIG upregulated in both HIV-positive groups, compared with HIV-negative controls. D-dimer and soluble tissue factor levels were significantly elevated in elite controllers, compared with those in ART recipients with suppressed viremia and HIV-negative controls (P < .01). Monocytes from elite controllers (and ART recipients with suppressed viremia) expressed lower CCR2 and higher CX3CR1 levels than monocytes from HIV-negative controls. In addition, elite controllers had a significantly higher proportion of CD14(++)CD16(+) monocytes, compared with HIV-negative controls. CONCLUSION: Elite controllers maintain control of plasma HIV viremia and have evidence of an activated innate immune response.

Comprehensive analysis of unique cases with extraordinary control over HIV replication.

True long-term nonprogressors (LTNPs)/elite controllers (ECs) maintain durable control over HIV replication without antiretroviral therapy. Herein we describe 4 unique persons who were distinct from conventional LTNPs/ECs in that they had extraordinarily low HIV burdens and comparatively weak immune responses. As a group, typical LTNPs/ECs have unequivocally reactive HIV-1 Western blots, viral loads below the lower threshold of clinical assays, low levels of persistent viral reservoirs, an over-representation of protective HLA alleles, and robust HIV-specific CD8(+) T-cell responses. The 4 unique cases were distinguished from typical LTNPs/ECs based on weakly reactive Western blots, undetectable plasma viremia by a single copy assay, extremely low to undetectable HIV DNA levels, and difficult to isolate replication-competent virus. All 4 had at least one protective HLA allele and CD8(+) T-cell responses that were disproportionately high for the low antigen levels but comparatively lower than those of typical LTNPs/ECs. These unique persons exhibit extraordinary suppression over HIV replication, therefore, higher-level control than has been demonstrated in previous studies of LTNPs/ECs. Additional insight into the full spectrum of immune-mediated suppression over HIV replication may enhance our understanding of the associated mechanisms, which should inform the design of efficacious HIV vaccines and immunotherapies.

Broad HIV-1 neutralization mediated by CD4-binding site antibodies.

We have identified several patient sera showing potent and broad HIV-1 neutralization. Using antibody adsorption and elution from selected gp120 variants, the neutralizing specificities of the two most broadly reactive sera were mapped to the primary receptor CD4-binding region of HIV-1 gp120. Novel antibodies to the CD4-binding site are elicited in some HIV-1-infected individuals, and new approaches to present this conserved region of gp120 to the immune system may result in improved vaccine immunogens.