HIV This Week

Human erythrocytes selectively bind and enrich infectious HIV-1 virions.

Beck Z, Brown BK, Wieczorek L, Peachman KK, Matyas GR, Polonis VR, Rao M, Alving CR. PLoS One.2009.4:e8297.

Although CD4(+) cells represent the major target for HIV infection in blood, claims of complement-independent binding of HIV-1 to erythrocytes and the possible role of Duffy blood group antigen, have generated controversy . To examine the question of binding to erythrocytes, HIV-1 was incubated in vitro with erythrocytes from 30 healthy leukapheresis donors, and binding was determined by p24 analysis and adsorption of HIV-1 with reduction of infectivity for CD4(+) target cells. All of the cells, regardless of blood group type, bound HIV-1 p24. A typical preparation of erythrocytes bound <2.4% of the added p24, but erythrocytes selectively removed essentially all of the viral infectivity as determined by decreased infection of CD4(+) target cells; however, cell-associated HIV-1 was approximately 100-fold more efficient, via trans infection, than unadsorbed virus for infection of CD4(+) cells. All of the bound HIV-1 p24 was released by treatment of the cells with EDTA, and binding was optimized by adding Ca(2+) and Mg(2+) during the washing of erythrocytes containing bound HIV-1. Although the small number of contaminating leukocytes in the erythrocyte preparation also bound HIV-1 p24, there was no significant binding to CD4, and it thus appears that the binding occurred on leukocytes at non-CD4 sites. Furthermore, binding occurred to erythrocyte ghosts from which contaminating leukocytes had been previously removed. The results demonstrate that erythrocytes incubated in vitro with HIV-1 differentially adsorb all of the infectious HIV-1 virions (as opposed to non-infectious or degraded virions) in the absence of complement and independent of blood group, and binding is dependent on divalent cations. By analogy with HIV-1 bound to DC-SIGN on dendritic cells, erythrocyte-bound HIV-1 might comprise an important surface reservoir for trans-infection of permissive cells.

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Editors’ note : Although the exact mechanism of binding of HIV-1 to erythrocytes remains unknown, there is likely more than one mechanism. This study demonstrates that in the absence of complement which HIV-1 usually activates so that it can bind to complement receptors on cells, HIV-1 binds to erythrocytes, regardless of whether they display Duffy blood group antigen or not. The binding occurs only on the cell surface, permitting erythrocytes with HIV-1 on their surface to present it to CD4+ cells which are not in plentiful supply compared to other cell types. Thus, erythrocytes in the blood may be acting like dendritic cells in tissue to carry and offer HIV-1 to the very target cells that HIV-1 uses for replication, in a process called trans infection. This appears likely to be a far more frequent infecting mechanism than direct infection of CD4+ cells by circulating free virus.

Adenovirus vector vaccination induces expansion of memory CD4 T cells with a mucosal homing phenotype that are readily susceptible to HIV-1.

Benlahrech A, Harris J, Meiser A, Papagatsias T, Hornig J, Hayes P, Lieber A, Athanasopoulos T, Bachy V, Csomor E, Daniels R, Fisher K, Gotch F, Seymour L, Logan K, Barbagallo R, Klavinskis L, Dickson G, Patterson S. Proc Natl Acad Sci U S A. 2009;106:19940-5. Epub 2009 Nov 16.

In the recently halted HIV type 1 (HIV-1) vaccine STEP trial, individuals that were seropositive for adenovirus serotype 5 (Ad5) showed increased rates of HIV-1 infection on vaccination with an Ad5 vaccine. The authors propose that this was due to activation and expansion of Ad5-specific mucosal-homing memory CD4 T cells. To test this hypothesis, Ad5 and Ad11 antibody titres were measured in 20 healthy volunteers. Dendritic cells (DCs) from these individuals were pulsed with replication defective Ad5 or Ad11 and co-cultured with autologous lymphocytes. Cytokine profiles, proliferative capacity, mucosal migration potential, and susceptibility to HIV infection of the adenovirus-stimulated memory CD4 T cells were measured. Stimulation of T cells from healthy Ad5-seropositive but Ad11-seronegative individuals with Ad5, or serologically distinct Ad11 vectors induced preferential expansion of adenovirus memory CD4 T cells expressing alpha(4)beta(7) integrins and CCR9, indicating a mucosal-homing phenotype. CD4 T-cell proliferation and IFN-gamma production in response to Ad stimulation correlated with Ad5 antibody titres. However, Ad5 serostatus did not correlate with total cytokine production upon challenge with Ad5 or Ad11. Expanded Ad5 and Ad11 memory CD4 T cells showed an increase in CCR5 expression and higher susceptibility to infection by R5 tropic HIV-1. This suggests that adenoviral-based vaccination against HIV-1 in individuals with pre-existing immunity against Ad5 results in preferential expansion of HIV-susceptible activated CD4 T cells that home to mucosal tissues, increases the number of virus targets, and leads to a higher susceptibility to HIV acquisition.

Abstract: 1 

Editors’ note: After the STEP vaccine trial was halted in 2007 for futility when the vaccine was declared ineffective, subgroup analyses revealed that people with high levels of antibodies to the vaccine delivery system (Adenovirus serotype 5 or Ad5) were more vulnerable to acquiring HIV infection if they received the vaccine rather than the placebo. This study of their immune responses found that the vaccine vector increased the number of CD4 T cells homing to mucosa to mount defences. Once there, they were sitting ducks for HIV to infect and replicate. Whether adenovirus vectors can be used in HIV vaccine trials remains in dispute and the current HVTN 505 trial is recruiting only individuals with low Ad5 titres to avoid increasing subjects’ susceptibility to HIV.

Orally exposed uninfected individuals have systemic anti-HIV responses associating with partners’ viral load.

Hasselrot K, Bratt G, Hirbod T, Säberg P, Ehnlund M, Lopalco L, Sandström E, Broliden K. AIDS; 2010 24:35-43.

The aim of this study was determine whether oral HIV-1 exposure incites a persistent systemic anti-HIV-1 response in exposed uninfected individuals of discordant couples of men who have sex with men, and whether this response associates with HIV-1 exposure measured by viral load in the HIV-positive partners. Plasma samples were collected from exposed uninfected individuals (n = 25), HIV-positive partners (n = 25) and low-risk controls (n = 22). A peripheral blood mononuclear cells-based neutralization assay was used to test these samples against three primary HIV-1 isolates. Self-reported questionnaires described routes of HIV-1-exposure, and clinical records documented viral loads in HIV-positive partners. At enrolment, plasma samples from seven of 25 exposed uninfected individuals neutralized at least two of the three HIV-1 isolates. No samples from the 22 controls neutralized any HIV-1 isolate (P = 0.01). Of these seven exposed uninfected individuals, six retained neutralization capacity during follow-up. Neutralization capacity among exposed uninfected individuals associated with the highest measured viral load of their respective partners (P = 0.01) and also time since highest viral load (P = 0.02). Purified plasma immunoglobulin (Ig) A1-mediated neutralization was observed in six of the seven samples, whereas none of the IgA1-depleted plasma samples neutralized HIV-1. The neutralizing IgA1 was not HIV envelope specific as detected by ELISA and western blot. Orally exposed uninfected men who have sex with men can mount neutralizing anti HIV-1 activity in plasma, mediated primarily by non-HIV envelope-specific IgA1. Neutralization was associated with previous measured highest viral load in the HIV-positive partner, as well as time elapsed since the peak viral load. Neutralization also persisted over time in spite of a continuous low viral exposure.

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Editors’ note: In this intriguing study of discordant couples of men who have sex with men, oral mucosal exposure to HIV (measured as the highest observed level of HIV-RNA in each subject’s infected partner) was correlated with the development of a functional anti-HIV response in the plasma. Looking for explanations, the researchers checked for the CCR5 delta 32 deletion that confers protection if both genes are affected but only one individual was homoyzygous. One of the seven men that had anti-HIV responses subsequently became infected, but with a different clade than the one his partner had. This suggests that the antibodies that were generated, if protective, are not likely to be broadly neutralizing. In any case, the findings of this study have implications for vaccine research because they suggest that low-level mucosal exposure may induce acquired immunity.

Polyclonal B cell differentiation and loss of gastrointestinal tract germinal centers in the earliest stages of HIV-1 infection.

Levesque MC, Moody MA, Hwang KK, Marshall DJ, Whitesides JF, Amos JD, Gurley TC, Allgood S, Haynes BB, Vandergrift NA, Plonk S, Parker DC, Cohen MS, Tomaras GD, Goepfert PA, Shaw GM, Schmitz JE, Eron JJ, Shaheen NJ, Hicks CB, Liao HX, Markowitz M, Kelsoe G, Margolis DM, Haynes BF. PLoS Med. 2009; 6(7):e1000107.

The antibody response to HIV-1 does not appear in the plasma until approximately 2-5 weeks after transmission, and neutralizing antibodies to autologous HIV-1 generally do not become detectable until 12 weeks or more after transmission. Moreover, levels of HIV-1-specific antibodies decline on antiretroviral treatment. The mechanisms of this delay in the appearance of anti-HIV-1 antibodies and of their subsequent rapid decline are not known. While the effect of HIV-1 on depletion of gut CD4(+) T cells in acute HIV-1 infection is well described, the authors studied blood and tissue B cells soon after infection to determine the effect of early HIV-1 on these cells. In human participants, they analyzed B cells in blood as early as 17 days after HIV-1 infection, and in terminal ileum inductive and effector microenvironments beginning at 47 days after infection. They found that HIV-1 infection rapidly induced polyclonal activation and terminal differentiation of B cells in blood and in gut-associated lymphoid tissue (GALT) B cells. The specificities of antibodies produced by GALT memory B cells in acute HIV-1 infection (AHI) included not only HIV-1-specific antibodies, but also influenza-specific and autoreactive antibodies, indicating very early onset of HIV-1-induced polyclonal B cell activation. Follicular damage or germinal centre loss in terminal ileum Peyer’s patches was seen with 88% of follicles exhibiting B or T cell apoptosis and follicular lysis. Early induction of polyclonal B cell differentiation, coupled with follicular damage and germinal centre loss soon after HIV-1 infection, may explain both the high rate of decline in HIV-1-induced antibody responses and the delay in plasma antibody responses to HIV-1.

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Editors’ note: B lymphocytes are born and mature in the bone marrow before they enter the blood stream looking for interesting antigens. Once activated, they change into antibody-secreting cells and memory B lymphocytes that respond quickly to that antigen. The death of infected and uninfected CD4 T cells in the gut in acute infection is well known but less is understood about what happens to B cells and why the antibody response to HIV is so slow. This study demonstrates that Peyer’s patch B cells in the gut die massively, with significant germinal centre destruction. How this happens is unclear but we really need to understand how HIV subverts our initial humoral responses in order to know how quickly neutralising antibodies that are pre-primed by a vaccine would have to appear in order to be effective against HIV.

 Multiple-infection and recombination in HIV-1 within a longitudinal cohort of women.

Templeton AR, Kramer MG, Jarvis J, Kowalski J, Gange S, Schneider MF, Shao Q, Zhang GW, Yeh MF, Tsai HL, Zhang H, Markham RB. Retrovirology. 2009; 6:54.

Recombination between strains of HIV-1 only occurs in individuals with multiple infections, and the incidence of recombinant forms implies that multiple infection is common. Most direct studies indicate that multiple infection is rare. Templeton and colleagues set out to determine the rate of multiple infection in a longitudinal study of 58 HIV-1 positive participants from The Women’s Interagency HIV Study with a richer sampling design than previous direct studies, and they investigated the role of recombination and sampling design on estimating the multiple infection rate. 40% of their sample had multiple HIV-1 infections. This rate of multiple infection is statistically consistent with previous studies once differences in sampling design are taken into account. Injection drug use significantly increased the incidence of multiple infections. In general there was rapid elimination of secondary strains to undetectable levels, but in 3 cases a superinfecting strain displaced the initial infecting strain and in two cases the strains coexisted throughout the study. All but one secondary strain was detected as an inter- and/or intra-genic recombinant. Injection drug use significantly increased the rate of observed recombinants. The study’s multiple infection rate is consistent with rates estimated from the frequency of recombinant forms of HIV-1. The fact that the results are also consistent with previous direct studies that had reported a much lower rate illustrates the critical role of sampling design in estimating this rate. Multiple infection and recombination significantly add to the genetic diversity of HIV-1 and its evolutionary potential, and injection drug use significantly increases both.

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Editors’ note: Multiple infection may mean co-infection, where the host is infected by two or more strains of HIV, or superinfection, where the initial infection is followed by a later secondary infection. In this detailed genetic study of 23 women with multiple infections, 10 were detected as potentially co-infected at the first study visit and 13 were definitely superinfected during the study. All of them experienced recombination between pol and env genes, with most eventually losing the recombinant strain. Among the 13 superinfected women, the original strain was replaced by the second strain in 3 cases. This suggests that most of the time selection works to eliminate recombinants and superinfecting strains unless they have very superior fitness and competitive ability. However, the bottom line is that initial HIV infection does not protect against superinfection, underscoring the personal benefits of positive prevention for people living with HIV. 

Chomont N, El-Far M, Ancuta P, Trautmann L, Procopio FA, Yassine-Diab B, Boucher G, Boulassel MR, Ghattas G, Brenchley JM, Schacker TW, Hill BJ, Douek DC, Routy JP, Haddad EK, Sékaly RP. HIV reservoir size and persistence are driven by T cell survival and homeostatic proliferation. Nat Med. 2009;15:893-900.

HIV persists in a reservoir of latently infected CD4(+) T cells in individuals treated with highly active antiretroviral therapy (HAART). Here Chomont and colleagues identify central memory (T(CM)) and transitional memory (T(TM)) CD4(+) T cells as the major cellular reservoirs for HIV and find that viral persistence is ensured by two different mechanisms. HIV primarily persists in T(CM) cells in subjects showing reconstitution of the CD4(+) compartment upon HAART. This T-cell central memory reservoir is maintained through T cell survival and low-level antigen-driven proliferation and is slowly depleted with time. In contrast, proviral DNA is preferentially detected in transitional memory t-cells from aviremic individuals with low CD4(+) counts and higher amounts of interleukin-7-mediated homeostatic proliferation, a mechanism that ensures the persistence of these cells. The authors conclude that their results suggest that viral eradication might be achieved through the combined use of strategic interventions targeting viral replication and, as in cancer, drugs that interfere with the self renewal and persistence of proliferating memory T cells.

Editor’s note: Early initiation of antiretroviral therapy is often associated with a reduced size of the HIV reservoir. Conversely, CD4 T-cell depletion associated with high levels of immune activation and increased proliferation tends to increase the size of the reservoir. The mechanisms underlying this have perplexed basic scientists for years. Chomont and colleagues have shed light on this by showing that there are two distinct HIV reservoirs. One is a long-lasting genetically stable reservoir found in immune responders to antiretroviral therapy that decays slowly and is regulated by antigen-driven proliferation. The second reservoir is genetically variable, predominates in people with low CD4 counts and persistent immune activation, and is regulated by homeostatic proliferation. The size of this second reservoir is reduced in individuals treated early in infection, supporting the concept of early initiation of antiretroviral treatment. The findings suggest that, beyond antiretroviral treatment, eradication of HIV in people with undetectable viral loads will require new therapies that target pathways downstream of proliferation such as those developed for treatment of leukaemia and cancer.

Grabar S, Selinger-Leneman H, Abgrall S, Pialoux G, Weiss L, Costagliola D. Prevalence and comparative characteristics of long-term nonprogressors and HIV controller patients in the French Hospital Database on HIV. AIDS. 2009;23(9):1163-9.

Grabar and colleagues set out to estimate the prevalence and characteristics of long-term nonprogressor and HIV controller patients in a very large French cohort of HIV 1-infected patients. In the French Hospital Database on HIV [FHDH, Agence Nationale de Recherches sur le SIDA et les hépatites virales (ANRS) CO4], they selected patients who had been seen in 2005, who had been infected for more than 8 years, who were treatment-naive, and who remained asymptomatic. Patients with these characteristics then categorized as follows: long-term nonprogressor (> or =8 years of HIV infection and CD4 cell nadir > or =500/microl), elite long-term nonprogressor (> or =8 years of HIV infection, CD4 cell nadir > or =600/microl, and a positive CD4 slope), HIV controllers (>10 years of HIV infection with 90% of plasma viral load values < or =500 copies/ml), and elite controllers (same as HIV controllers, but with last plasma viral load value < or =50 copies/ml in 2005). Among the 46 880 HIV-1-infected patients followed in 2005 in the French Hospital Database on HIV, 0.4% (N = 202) were long-term nonprogressor, 0.05% (N = 25) were elite long-term nonprogressor, 0.22% (N = 101) were HIV controllers, and 0.15% (N = 69) were elite controllers. Ten elite long-term nonprogressor patients (40% of 25) were also HIV controllers, eight (32%) were elite controllers, and 60% had detectable plasma viral load (>50 copies/ml). Among the elite controllers, 32 (46%) were long-term nonprogressor, eight (12%) were elite long-term nonprogressor, and one-quarter had a last CD4 cell count less than 500/microl. Long-term nonprogressor, elite LTNP, HIV controller, and elite controller patients are rare phenotypes. Elite long-term nonprogressor patients are less frequent than HIV controllers. There is little overlap among the four subgroups of patients.

Editors’ note: With the advent of viral load assays in clinical care, new groups of patients with slow disease progression joined the patients known as long-term nonprogressors. Defined by virologic parameters, they are called the HIV controllers, some of whom are elite controllers. Although the definitions of these various groups vary in the literature and there is some overlap, they are of intense interest because the mechanisms by which they have some natural protection against HIV may provide insights for the development of preventive and therapeutic vaccines. Both viral factors and host genetic factors, such as HLA-B27 and HLA-B57, may play a role. This study of more than 110,000 patients confirms the very low prevalence (less than 0.5%) of these valuable patients. Some are viraemic with high CD4 counts while others control viraemia but have CD4 depletion and yet others appear to have both viral control and stable CD4 cell counts.

Lassen KG, Lobritz MA, Bailey JR, Johnston S, Nguyen S, Lee B, Chou T, Siliciano RF, Markowitz M, Arts EJ.  Elite suppressor-derived HIV-1 envelope glycoproteins exhibit reduced entry efficiency and kinetics. PLoS Pathog. 2009;5(4):e1000377.

Elite suppressors are a rare subset of HIV-1-infected individuals who are able to maintain HIV-1 viral loads below the limit of detection by ultra-sensitive clinical assays in the absence of antiretroviral therapy.  Mechanism(s) responsible for this elite control are poorly understood but likely involve both host and viral factors. This study assesses elite suppressors plasma-derived envelope glycoprotein (env) fitness as a function of entry efficiency as a possible contributor to viral suppression. Fitness of virus entry was first evaluated using a novel inducible cell line with controlled surface expression levels of CD4 (receptor) and CCR5 (co-receptor). In the context of physiologic CCR5 and CD4 surface densities, elite supressors envs exhibited significantly decreased entry efficiency relative to chronically infected viremic progressors. Elite suppressors envs also demonstrated slow entry kinetics indicating the presence of virus with reduced entry fitness. Overall, elite suppressors env clones were less efficient at mediating entry than chronic progressor envs. Interestingly, acute infection envs exhibited an intermediate phenotypic pattern not distinctly different from elite suppressors or chronic progressor envs. These results imply that lower env fitness may be established early and may directly contribute to viral suppression in elite suppressors individuals.

Editors’ note: This study is the first to provide direct evidence that the envelope glycoprotein, the coat protein of HIV, in elite suppressors is less efficient in supporting HIV entry into host cells that that of HIV found in people with disease progression. In acute infection, there are HIV variants with a wide range of efficiencies, suggesting that elite suppressors may be selecting relatively lower fitness env variants right at the start. How they would do this remains a mystery, as no data exist on the natural history of acute infection in elite suppressors.

Scheid JF, Mouquet H, Feldhahn N, Seaman MS, Velinzon K, Pietzsch J, Ott RG, Anthony RM, Zebroski H, Hurley A, Phogat A, Chakrabarti B, Li Y, Connors M, Pereyra F, Walker BD, Wardemann H, Ho D, Wyatt RT, Mascola JR, Ravetch JV, Nussenzweig MC. Broad diversity of neutralizing antibodies isolated from memory B cells in HIV-infected individuals. Nature. 2009;458(7238):636-40.

Antibodies to conserved epitopes on the human immunodeficiency virus (HIV) surface protein gp140 can protect against infection in non-human primates, and some infected individuals show high titres of broadly neutralizing immunoglobulin (Ig)G antibodies in their serum. However, little is known about the specificity and activity of these antibodies. To characterize the memory antibody responses to HIV, Scheid and colleagues cloned 502 antibodies from HIV envelope-binding memory B cells from six HIV-infected patients with broadly neutralizing antibodies and low to intermediate viral loads. They show that in these patients, the B-cell memory response to gp140 is composed of up to 50 independent clones expressing high affinity neutralizing antibodies to the gp120 variable loops, the CD4-binding site, the co-receptor-binding site, and to a new neutralizing epitope that is in the same region of gp120 as the CD4-binding site. Thus, the IgG memory B-cell compartment in the selected group of patients with broad serum neutralizing activity to HIV is comprised of multiple clonal responses with neutralizing activity directed against several epitopes on gp120.

Editors’ note: Although the possibility exists that a single highly effective antibody may produce broadly neutralizing activity in serum, to date it has not been possible to isolate such an antibody from patients or induce it by immunisation in experimental animals. These findings from a study of 6 ‘elite controller’ patients suggest, however, that a vaccine that could copy the natural anti-HIV immune response seen in patients with broadly neutralising serological activity and elicit a combination of antibodies might also be an effective means of protection against a large number of HIV strains.

Cao W, Jamieson BD, Hultin LE, Hultin PM, Effros RB, Detels R. Premature Aging of T cells is Associated With Faster HIV-1 Disease Progression. J Acquir Immune Defic Syndr. 2009;50(2):137-47.

Cao and colleagues aimed to determine if untreated HIV-1 infection and progression is associated with premature aging of memory CD8 and CD4 T cells and naive CD4 T cells. Twenty HIV-1-infected fast progressors and 40 slow progressors were included in the study, using risk set sampling. The expression of cell surface markers reflecting the differentiation stages of lymphocytes was measured using flow cytometry analyses performed on cryopreserved peripheral blood mononuclear cells. The authors found that HIV-1 disease progression is associated with a decreased CD28 median florescence intensity on CD4 and CD8 T cells; an increased proportion of intermediate- and late-differentiated CD8 T cells and a decreased CD31 median florescence intensity on naive CD4 T cells of recent thymic origin. A selective depletion of peripherally expanded naive CD4 T cells was found to be associated with HIV-1 infection but not with HIV-1 disease progression. The overall change during HIV-1 infection and progression is associated with a shift in the T-cell population toward an aged conformation, which may be further compromised by impaired renewal of the less-differentiated CD4 T-cell population. Their results suggest that HIV-1 infection induces an accelerated aging of T lymphocytes, which is associated with the clinical progression to AIDS and death.

Editors’ note: This study comparing 20 fast progressors with 40 slow progressors found that HIV-1 infection itself induces premature aging of both memory T-cells and naïve CD4+ T cells. Fast progressors experience accelerated aging of lymphocytes, which display reduced replicative capacity and shortened telomeres. This overall structural change to more aged memory T-cells may be due to accelerated differentiation driven by chronic antigenic stimulation and immune activation. Possible therapeutic approaches could include physically removing aged T cells to make room for more functional earlier subsets and using drugs to enhance telomerase activity to slow the shortening of telomere length.

Kawashima Y, Pfafferott K, Frater J, Matthews P, Payne R, Addo M, Gatanaga H, Fujiwara M, Hachiya A, Koizumi H, Kuse N, Oka S, Duda A, Prendergast A, Crawford H, Leslie A, Brumme Z, Brumme C, Allen T, Brander C, Kaslow R, Tang J, Hunter E, Allen S, Mulenga J, Branch S, Roach T, John M, Mallal S, Ogwu A, Shapiro R, Prado JG, Fidler S, Weber J, Pybus OG, Klenerman P, Ndung’u T, Phillips R, Heckerman D, Harrigan PR, Walker BD, Takiguchi M, Goulder P. Adaptation of HIV-1 to human leukocyte antigen class I.  Nature. 2009. [Epub ahead of print]

The rapid and extensive spread of the human immunodeficiency virus (HIV) epidemic provides a rare opportunity to witness host-pathogen co-evolution involving humans. A focal point is the interaction between genes encoding human leukocyte antigen (HLA) and those encoding HIV proteins. HLA molecules present fragments (epitopes) of HIV proteins on the surface of infected cells to enable immune recognition and killing by CD8(+) T cells; particular HLA molecules, such as HLA-B*57, HLA-B*27 and HLA-B*51, are more likely to mediate successful control of HIV infection. Mutation within these epitopes can allow viral escape from CD8(+) T-cell recognition. Here Kawashima and colleagues analysed viral sequences and HLA alleles from >2,800 subjects, drawn from 9 distinct study cohorts spanning 5 continents. Initial analysis of the HLA-B*51-restricted epitope, TAFTIPSI (reverse transcriptase residues 128-135), showed a strong correlation between the frequency of the escape mutation I135X and HLA-B*51 prevalence in the 9 study cohorts (P = 0.0001). Extending these analyses to incorporate other well-defined CD8(+) T-cell epitopes, including those restricted by HLA-B*57 and HLA-B*27, showed that the frequency of these epitope variants (n = 14) was consistently correlated with the prevalence of the restricting HLA allele in the different cohorts (together, P < 0.0001), demonstrating strong evidence of HIV adaptation to HLA at a population level. This process of viral adaptation may dismantle the well-established HLA associations with control of HIV infection that are linked to the availability of key epitopes, and highlights the challenge for a vaccine to keep pace with the changing immunological landscape presented by HIV.

Editors’ note: The finding that HIV has been evolving at the population level over the past couple of decades to neutralise the slower disease progression advantage conferred by certain protective HLA genetic profiles is disturbing. Escape mutations that do not revert but rather persist stably after HIV transmission appear to accumulate at the population level over time, changing the dynamics of immune control and disease progression. If more effective immune responses now come into play that would be good news but, for now, these findings underscore yet another challenge for vaccine development – keeping up with the moving target of HIV as it worms its way around human immune responses.

Although combination therapy for HIV infection represents a triumph for modern medicine, chronic suppressive therapy is required to contain persistent infection in reservoirs such as latently infected CD4+ lymphocytes and cells of the macrophage-monocyte lineage. Despite its success, chronic suppressive therapy is limited by its cost, the requirement of lifelong adherence, and the unknown effects of long-term treatment. This review discusses current understanding of suppressive antiretroviral therapy, the latent viral reservoir, and the needs for and challenges of attacking this reservoir to achieve a cure.

Editors’ note: Ongoing viraemia detected at the level of 1 to 50 copies/ml in the majority of patients is thought to result from episodic production of HIV by long-lived cells rather than ongoing rounds of replication. Exploring how the mechanisms that drive this latency can be therapeutically exploited, this review paper argues that drug-free remission should now be the new goal of HIV therapeutics. It proposes a public-private joint research venture, called the HIV Latency Collaboratory, which would see government contributing funding, regulatory oversight, and coordination; industry contributing funding, drug discovery, technology, and expertise; and academia contributing ideas and investigative capacity.

Biloglav and colleagues assessed the frequency of 32 base pair deletion in CCR5 (CCR5Delta32), which has been shown to confer resistance to HIV infection in a homozygous form, in 10 isolated island communities of Dalmatia, Croatia, with different histories of exposure to epidemics during and since the medieval period. In 2002, DNA analysis of 100 randomly selected individuals from each of the 10 isolated communities of 5 Croatian islands (Susak, Rab, Vis, Lastovo, and Mljet) showed high levels of 3-generational endogamy, indicating limited gene flow. Five of the communities were decimated by epidemics of unknown cause between 1449-1456, while the other 5 villages remained unaffected. Genotyping of the CCR5 gene was performed using the polymerase chain reaction method with primers flanking the region containing 32-bp deletion. The frequency of CCR5Delta32 in the 5 villages affected by the epidemic was 6.1-10.0%, and 1.0-3.8% in the 5 unaffected villages. The Delta32 mutation was found in 71 of 916 alleles among the individuals from the affected villages (7.5%), and in 24 of 968 alleles in unaffected villages (2.5%, chi(2)=27.3, P<10-6). A previous study in 303 random Croatian blood donors showed the frequency of the CCR5 Delta32 of 7.1% in the general population. The difference remained significant after correcting for population structure using both STRAT and STRUCTURE software and the genomic control test, to ensure results do not arise from the background genetic differences. The authors concluded that their results and historical evidence, suggest that the mid-15 th century epidemic could have acted as a selection pressure for the CCR5Delta32 mutation.

Editors’ note: This fascinating article enters the ongoing debate on the genetic and epidemiological ‘archaeology’ of the CCR5Delta32 mutation which provides almost complete resistance to HIV in homozygous form (both gene alleles) and partial resistance/slower progression to AIDS in heterozygous form. The average frequency of this mutation in European populations is 10% but it is almost absent in African, American Indian, and East Asian populations. Based on this analysis of historical and genetic information obtained for 10 isolated communities in Croatia, this research programme (entitled ’10,001 Dalmations’) concludes that two exceedingly lethal viral epidemics characterised by peak incidence in the summer months, a long incubation period (about 1 month), 70% cumulative mortality, and person-to-person transmission, were most likely a hemorrhagic fever rather than bubonic plague or smallpox. The disease, thought to have arrived from northern Europe through the ‘route of Amber’ to Venice, caused the fall of Croatian Benedictine monasteries where the ill sought treatment. These epidemics could have created selection pressure upon an already widespread but rare CCR5Delta32 mutation resulting in the unusually high frequencies now observed across Europe today.

Li Q, Estes JD, Schlievert PM, Duan L, Brosnahan AJ, Southern PJ, Reilly CS, Peterson ML, Schultz-Darken N, Brunner KG, Nephew KR, Pambuccian S, Lifson JD, Carlis JV & Haase AT. Glycerol monolaurate prevents mucosal SIV transmission. Nature 2009 [Epub ahead of print] doi:10.1038/nature07831

Although there has been great progress in treating human immunodeficiency virus 1 (HIV-1) infection, preventing transmission has thus far proven an elusive goal. Indeed, recent trials of a candidate vaccine and microbicide have been disappointing, both for want of efficacy and concerns about increased rates of transmission. Nonetheless, studies of vaginal transmission in the simian immunodeficiency virus (SIV)–rhesus macaque (Macacca mulatta) model point to opportunities at the earliest stages of infection in which a vaccine or microbicide might be protective, by limiting the expansion of infected founder populations at the portal of entry. Here Li and colleagues show in this SIV–macaque model, that an outside-in endocervical mucosal signalling system, involving MIP-3 (also known as CCL20), plasmacytoid dendritic cells and CCR5 cell-attracting chemokines produced by these cells, in combination with the innate immune and inflammatory responses to infection in both cervix and vagina, recruits CD4 1 T cells to fuel this obligate expansion . They then show that glycerol monolaurate—a widely used antimicrobial compound with inhibitory activity against the production of MIP-3a and other proinflammatory cytokines— can inhibit mucosal signalling and the innate and inflammatory response to HIV-1 and SIV in vitro, and in vivo it can protect rhesus macaques from acute infection despite repeated intra-vaginal exposure to high doses of SIV. This new approach, plausibly linked to interfering with innate host responses that recruit the target cells necessary to establish systemic infection, opens a promising new avenue for the development of effective interventions to block HIV-1 mucosal transmission.

Editors’ note: This study reveals that the endocervix, the inner surface of the cervix linking the vagina with the uterus or womb, is the predominant site for initial infected cell clusters. There are not enough target cells there for SIV infection to take hold but the inflammatory response of the innate mucosal immune system calls more target cells to this site, expanding the infected founder cell population which then allows establishment of self-propagating infection in lymph tissues. In this encouraging report, inexpensive and safe glycerol monolaurate brakes this vicious cycle of signalling and inflammatory response to prevent acute SIV infection in several repeatedly exposed animals. Longer-term and well-powered studies with larger numbers of animals are clearly warranted.

Hütter G, Nowak D, Mossner M, Ganepola S, Müssig A, Allers K, Schneider T, Hofmann J, Kücherer C, Blau O, Blau IW, Hofmann WK, Thiel E. Long-term control of HIV by CCR5 Delta32/Delta32 stem-cell transplantation. N Engl J Med. 2009;360(7):692-8.

Infection with the human immunodeficiency virus type 1 (HIV-1) requires the presence of a CD4 receptor and a chemokine receptor, principally chemokine receptor 5 (CCR5). Homozygosity for a 32-bp deletion in the CCR5 allele provides resistance against HIV-1 acquisition. Hütter and colleagues transplanted stem cells from a donor who was homozygous for CCR5 delta32 in a patient with acute myeloid leukemia and HIV-1 infection. The patient remained without viral rebound 20 months after transplantation and discontinuation of antiretroviral therapy. This outcome demonstrates the critical role CCR5 plays in maintaining HIV-1 infection.

Editors’ note: After 20 months, this patient’s CD4+ counts are in the normal range; HIV-1 is not detectable in blood, bone marrow, or rectal mucosa; and the disappearance of the effector T-cells that normally fight HIV suggests that HIV is not around to provoke them. The patient could still be harbouring a CXCR4 type of HIV; many people die from bone marrow transplantation procedures, and people lacking CCR5 may be more susceptible to serious effects from certain infections. Nonetheless, this case will continue to be followed with interest and will no doubt open the door to further innovations in HIV treatment.

Behringer RR, Gonzalez G, Shpall EJ, Gathe J. Cord blood stem cell therapy for acquired immune deficiency syndrome. Stem Cells Dev. 2008. [Epub ahead of print]

Cord blood stem cell transplantation is routinely used to treat hematopoietic diseases. Individuals who are homozygous for the Delta32 polymorphism of the CCR5 locus, encoding a co-receptor for HIV-1, are normal and resistant to HIV infection. Here Behringer and colleagues suggest that public cord blood repositories are likely to contain CCR5 homozygous units that could be used as a therapy for HIV infected individuals.

Editors’ note: Cord blood stem cells, collected non-invasively from the placenta and umbilical cord after separation from a newborn, are less mature and would require less matching between donor and recipient than is the case for a bone marrow transplant. Homozygosity of the CCR5 delta 32 allele (meaning both chromosomes have the same 32 base pair deletion) occurs in 1 to 3% of current cord bank specimens in western populations that have high allele frequencies. The idea of cord stem cells for HIV treatment has yet to be explored but may have some merit.

Blish CA, Dogan OC, Derby NR, Nguyen MA, Chohan B, Richardson BA, Overbaugh J. HIV-1 Superinfection Occurs Despite Relatively Robust Neutralizing Antibody Responses. J Virol. 2008;82(24):12094-103.

Superinfection by a second HIV-1 strain indicates that gaps in protective immunity occur during natural infection. To define the role of HIV-1-specific neutralizing antibodies in this setting, Blish and colleagues examined neutralizing antibody responses in 6 women who became superinfected between approximately 1-5 years following initial infection compared to 18 women with similar risk factors who did not. Although superinfected individuals had less neutralizing antibody breadth than did matched controls at approximately 1 year post-infection, no significant differences in the breadth or potency of neutralizing antibody responses were observed just prior to the second infection. In fact, four of the six subjects had relatively broad and potent neutralizing antibody responses prior to infection by the second strain. To more specifically examine the specificity of the neutralizing antibodies against the superinfecting virus, these variants were cloned from five of the six individuals. The superinfecting variants did not appear to be inherently neutralization resistant, as measured against a pool of plasma from unrelated HIV-infected individuals. Moreover, the superinfected individuals were able to mount autologous neutralizing antibody responses to these variants following re-infection. In addition, most superinfected individuals had neutralizing antibodies that could neutralize their second viral strains prior to their re-infection, suggesting that the level of neutralizing antibodies elicited during natural infection was not sufficient to block infection. These data indicate that preventing infection by vaccination will likely require broader and more potent neutralizing antibody responses than those found in HIV-1 infected individuals.

Editors’ note: Superinfection can occur in the first year following initial infection when immune responses to HIV may not be fully mature or during chronic infection when they should be fully developed. It is unknown whether individuals who acquire a second HIV infection are a subset of people with particularly poor immune responses or whether normal immune responses to HIV are inadequate to prevent superinfection. This small study suggests the latter, i.e. the levels of neutralizing antibodies to susceptible virus were inadequate to prevent superinfection. As is the case for hepatitis B and human papilloma virus, it appears that an HIV-1 vaccine will need to elicit more robust neutralising antibody responses than those found during natural infection.

Willberg CB, McConnell JJ, Eriksson EM, Bragg LA, York VA, Liegler TJ, Hecht FM, Grant RM, Nixon DF. Immunity to HIV-1 is influenced by continued natural exposure to exogenous virus. PLoS Pathog. 2008;4(10):e1000185.

Unprotected sexual intercourse between individuals who are both infected with HIV-1 can lead to exposure to their partner’s virus, and potentially to super-infection. However, the immunological consequences of continued exposure to HIV-1 by individuals already infected, has to our knowledge never been reported. Willberg and colleagues measured T cell responses in 49 HIV-1 infected individuals who were on antiretroviral therapy with suppressed viral loads. All the individuals were in a long-term sexual partnership with another HIV-1 infected individual, who was either also on HAART and suppressing their viral loads, or viraemic (>9000 copies/ml). T cell responses to HIV-1 epitopes were measured directly ex-vivo by the Interferon-gamma enzyme linked immuno-spot assay and by cytokine flow cytometry. Sexual exposure data was generated from questionnaires given to both individuals within each partnership. Individuals who continued to have regular sexual contact with a HIV-1 infected viraemic partner had significantly higher frequencies of HIV-1-specific T cell responses, compared to individuals with aviraemic partners. Strikingly, the magnitude of the HIV-1-specific T cell response correlated strongly with the level and route of exposure. Responses consisted of both CD4(+) and CD8(+) T cell subsets. Longitudinally, decreases in exposure were mirrored by a lower T cell response. However, no evidence for systemic super-infection was found in any of the individuals. Continued sexual exposure to exogenous HIV-1 was associated with increased HIV-1-specific T cell responses, in the absence of systemic super-infection, and correlated with the level and type of exposure.

Editors’ note: When one already has HIV infection and is on antiretroviral therapy, another person’s HIV can act as a natural immune stimulus with unknown benefits or disadvantages. In this study of 49 seroconcordant couples in which one person was virally suppressed and the other either was either suppressed or viraemic, exposure to the partner’s virus appeared to boost T-cell specific responses to HIV with little effect on general immune activation. The authors speculate that this may represent limited superinfection within rectal tissues.

Kuller LH, Tracy R, Belloso W, De Wit S, Drummond F, Lane HC, Ledergerber B, Lundgren J, Neuhaus J, Nixon D, Paton NI, Neaton JD; INSIGHT SMART Study Group Inflammatory and coagulation biomarkers and mortality in patients with HIV infection.. PLoS Med. 2008;5(10):e203.

In the Strategies for Management of Anti-Retroviral Therapy trial, all-cause mortality was higher for participants randomized to intermittent, CD4-guided antiretroviral treatment (drug conservation [DC]) than continuous antiretroviral treatment (viral suppression [VS]). Kuller et al hypothesized that increased HIV-RNA levels following antiretroviral treatment interruption induced activation of tissue factor pathways, thrombosis, and fibrinolysis. Stored samples were used to measure six biomarkers: high sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6), amyloid A, amyloid P, D-dimer, and prothrombin fragment 1+2. Two studies were conducted: (1) a nested case-control study for studying biomarker associations with mortality, and (2) a study to compare participants in the drug conservation and viral suppression trial arms for biomarker changes. For (1), markers were determined at study entry and before death (latest level) for 85 deaths and for two controls (n = 170) matched on country, age, sex, and date of randomization. Odds ratios (ORs) were estimated with logistic regression. For each biomarker, each of the three upper quartiles was compared to the lowest quartile. For (2), the biomarkers were assessed for 249 drug conservation and 250 viral suppression participants at study entry and 1 month following randomization. Higher levels of high sensitivity C-reactive protein (hsCRP), interleukin-6 (IL-6), and D-dimer at study entry were significantly associated with an increased risk of all-cause mortality. Unadjusted ORs (highest versus lowest quartile) were 2.0 (95% confidence interval [CI], 1.0-4.1; p = 0.05), 8.3 (95% CI, 3.3-20.8; p < 0.0001), and 12.4 (95% CI, 4.2-37.0; p < 0.0001), respectively. Associations were significant after adjustment, when the drug conservation and viral suppression groups were analyzed separately, and when latest levels were assessed. IL-6 and D-dimer increased at 1 month by 30% and 16% in the drug conservation group and by 0% and 5% in the viral suppression group (p < 0.0001 for treatment difference for both biomarkers); increases in the drug conservation group were related to HIV-RNA levels at 1 month (p < 0.0001). In an expanded case-control analysis (four controls per case), the odds ratio (drug conservation/viral suppression) for mortality was reduced from 1.8 (95% CI, 1.1-3.1; p = 0.02) to 1.5 (95% CI, 0.8-2.8) and 1.4 (95% CI, 0.8-2.5) after adjustment for latest levels of IL-6 and D-dimer, respectively. The authors conclude that IL-6 and D-dimer were strongly related to all-cause mortality. Interrupting ART may further increase the risk of death by raising IL-6 and D-dimer levels. Therapies that reduce the inflammatory response to HIV and decrease IL-6 and D-dimer levels may warrant investigation.

Editors’ note: Confidence intervals for the odd ratios in this analysis are wide, due to the low number of deaths in the SMART study which enrolled relatively health people living with HIV, and they lose statistical significance in the expanded case-control analysis. In any case most deaths were not HIV-related. Increases in inflammatory markers from the first study visit to the study preceding death appear to be associated with increased risk of death and several were more commonly found in people in the treatment interruption arm. HIV induces activation of inflammatory and coagulation pathways and it is these inflammatory changes that may be associated with premature mortality in people living with HIV. It should be recalled however that biomarker levels just before death may reflect reverse causality – they may be the result of an already present disease process rather than causing it. More research is needed.

Cadogan M, Dalgleish AG. HIV immunopathogenesis and strategies for intervention. Lancet Infect Dis. 2008;8(11):675-84

Therapeutic options aimed at tackling the HIV pandemic face many obstacles. The lack of readily accessible and affordable therapies means that most of those affected go untreated. The array of escape mechanisms used by HIV has undermined the efficiency of many antiviral products and continually represents a barrier to the development of an effective vaccine. Recent developments have seen a shift away from a cytopathic viral model of HIV pathogenesis towards the crucial role of immunopathogenic features-notably generalised immune activation-in the development of AIDS. As conventional vaccine strategies have sought to promote viral neutralisation and suppressive cellular responses, novel strategies that aim to address HIV immunopathogenesis should be sought. We review current opinion on HIV-induced pathogenic immune activation and strategies aimed at eliminating HIV, including a potential role for non-neutralising antibodies as part of a therapeutic vaccine option.

Editors’ note: Current HIV treatment focuses on interrupting the viral life-cycle using long-term reduction of viral load as a measure of success. Despite complete viral suppression, chronic generalised immune activation can persist with resultant progression to AIDS. Although HIV is well adapted to humans, taking advantage of cellular machinery for replication and transmission while using a number of immune evasion strategies, it provokes immune activation. This inadvertently benefits HIV because activated lymphocytes are its preferential targets. After reading this review, which has good tables and coloured graphics of virus-lymphocyte interactions, you will be hard pressed not to be convinced that more effort should be devoted to understanding and minimising HIV immunopathogenesis.