HIV This Week

Weijing He, Stuart Neil, Hemant Kulkarni, Edward Wright, Brian K. Agan, Vincent C. Marconi, Matthew J. Dolan, Robin A. Weiss, and Sunil K. Ahuja. Duffy Antigen Receptor for Chemokines Mediates trans-Infection of HIV-1 from Red Blood Cells to Target Cells and Affects HIV-AIDS Susceptibility. Cell Host & Microbe. 2008;4:52–62.

Photo credit: BOEHRINGER INGELHEIM

Sarker MS, Rahman M, Yirrell D, Campbell E, Rahman AS, Islam LN, Azim T. Molecular evidence for polyphyletic origin of human immunodeficiency virus type 1 subtype C in Bangladesh. Virus Res. 2008;135(1):89-94

HIV-1 positive blood samples were collected between 1999 and 2005 from population groups most at risk of HIV infection in Bangladesh through the national surveillance, from clients of the Voluntary Counselling and Testing (VCT) Unit for HIV at the International Centre for Diarrhoeal Diseases Research, Bangladesh, and a from survey of HIV in patients with tuberculosis. Partial sequences of the gag gene were used for subtyping the HIV strains by nested polymerase chain reaction using selective primers. Of the 198 HIV strains tested, subtype C (41.4%) was the commonest strain identified. Phylogenetic analysis of Bangladeshi subtype C strains showed that they clustered in polyphyletic branches representing HIV strains from different parts of the world. Most of the strains from injecting drug users clustered together and were similar to Indian strains. The VCT strains however were very heterogeneous and clustered with strains from India, Myanmar, Ethiopia and Zimbabwe. Data suggest that there have been few introductions into the injecting drug user population where the epidemic is driven by indigenous transmission. On the other hand there have been many and regular introductions of subtype C viruses through migrant workers in the VCT group. Very little overlap was observed in the strains obtained from injecting drug users and those from other population groups.

Editors´note: Injecting drug use transmission of subtype C virus in Bangladesh appears to be confined primarily to the community of people who inject drugs, with the strains being very similar. The majority of strains from the VCT clients were not subtype C and those that were subtype C were a very heterogeneous population, suggesting transmission from a variety of different geographical sources. None of the strains from the VCT clients clustered with isolates from the injecting drug users, suggesting little interaction between these two populations that could lead to HIV transmission. Studying HIV subtypes can provide a window on the dynamics of a country’s epidemic.

Hirbod T, Kaul R, Reichard C, Kimani J, Ngugi E, Bwayo JJ, Nagelkerke N, Hasselrot K, Li B, Moses S; Kibera HIV Study Group, MacDonald KS, Broliden K. Collaborators: Keli F, Kamunyo G, Wanguru R, Mwakisha R, Waithira G, Nganga D, Nyambogo C, Ombette J, Njeri J, Onyango I, Malonza I, Mwangi F, Fonck K, Temmerman M, Ronald AR, Luscher M. HIV-neutralizing immunoglobulin A and HIV-specific proliferation are independently associated with reduced HIV acquisition in Kenyan sex workers. AIDS. 2008;22(6):727-35.

HIV-neutralizing immunoglobulin A (IgA) and HIV-specific cellular immunity have been described in highly exposed, persistently seronegative individuals, but well controlled studies have not been performed. Hirbod and colleagues performed a prospective, nested case-control study to examine the association of genital IgA and systemic cellular immune responses with subsequent HIV acquisition in high-risk Kenyan female sex workers. A randomized trial of monthly antibiotic prophylaxis to prevent sexually transmitted disease/HIV infection was performed from 1998 to 2002 in HIV-uninfected Kenyan female sex workers. After the completion of trial, female sex workers who had acquired HIV (cases) were matched 1: 4 with persistently uninfected controls based on study arm, duration of HIV-seronegative follow-up, and time of cohort enrolment. Blinded investigators assayed the ability at enrolment of genital IgA to neutralize primary HIV isolates as well as systemic HIV-specific cellular IFN-gamma-modified enzyme-linked immunospot and proliferative responses. The study cohort comprised 113 female sex workers: 24 cases who acquired HIV and 89 matched controls. Genital HIV-neutralizing IgA was associated with reduced HIV acquisition (P = 0.003), as was HIV-specific proliferation (P = 0.002), and these associations were additive.  HIV-specific IFN-gamma production did not differ between case and control groups.  In multivariable analysis, HIV-neutralizing IgA and HIV-specific proliferation each remained independently associated with lack of HIV acquisition. Genital herpes (HSV2) was associated with increased HIV risk and with reduced detection of HIV-neutralizing IgA. Genital HIV-neutralizing IgA and systemic HIV-specific proliferative responses, assayed by blinded investigators, were prospectively associated with HIV nonacquisition. The induction of these immune responses may be an important goal for HIV vaccines.

Editors´note: Much is to be learned from the careful study of the immune responses of high exposed, persistently seronegative individuals, whether they are sex workers or seronegative people in long-term discordant partnerships. In this study, two independent factors were prospectively associated with reduced sexual acquisition: HIV-neutralizing immunoglobulin A (IgA) and HIV-specific proliferation in cervicovaginal lavage specimens. Herpes simplex-2 infection interfered with this partial protection by reducing HIV-neutralizing IgA in the genital tract. How to induce such protective humoral immune responses in the genital tract, whether they are associated with specific host genetics, and how they might combine with strong cellular responses are questions waiting to be answered.

Phillips EJ, Mallal SA. Pharmacogenetics and the potential for the individualization of antiretroviral therapy. Curr Opin Infect Dis. 2008;21(1):16-24.

Genetic associations highlighting differences in the response to HIV infection and treatment have significantly furthered our understanding of the pathogenesis, pharmacokinetics and pharmacodynamics of antiretroviral drug action and toxicities and HIV disease itself. This review focuses on the current knowledge of associations between polymorphisms and treatment outcomes in HIV with particular emphasis on clinically relevant relationships likely to lead to the individualization of antiretroviral therapy. Our understanding of the immunogenetic basis of drug toxicity has been furthered by human leukocyte antigen associations with hypersensitivities for the antiretroviral drugs abacavir and nevirapine. For abacavir in particular, the use of HLA-B*5701 as a screening test appears to be generalizable across racially diverse populations and has been supported by both observational, and blinded randomized controlled trials. Differences in HIV acquisition and progression as well as antiretroviral efficacy and toxicity will continue to provide the basis for research to define the genetic basis of such diversity. Despite the plethora of research in this area, numerous barriers exist to the successful operationalization of genetic testing to the clinic. HLA-B*5701 screening to prevent abacavir hypersensitivity is currently the most relevant to clinical practice and highlights that the promise of cost-effective testing can be facilitated by robust laboratory methodology and quality assurance programs that can be applied to diverse treatment settings.

Editors´note: Drug hypersensitivity syndromes are not directly related to the dose of a drug but are thought to be related to a combination of factors and associated with specific human leukocyte antigen (HLA) alleles within the major histocompatibility complex. In the case of patients starting nevirapine, 16% develop rash, 5% have hypersensitivity reactions with fever and hepatitis, and 0.3% can have severe skin syndromes. Knowledge of HIV pharmacogenetics is growing but unfortunately it will be some time before antiretroviral treatment in the real world can be tailored to patient genetics to avoid hypersensitivity reactions.

During the evolution, the immune system has developed several strategies to fight viral infections. Apoptosis, autophagy and necrosis are different types of cell death that play a main role in the interactions between infective agents and the host, since they are often important defence mechanisms that have to avoid the spreading of the infection. In turn, viruses have evolved numerous ways to evade the host immune system by influencing the behaviour and functionality of several components. HIV infects and kills CD4+ T helper lymphocytes, preferentially those that are antigen-specific, but also encodes proteins with apoptotic capacities, including gp120, gp160, Tat, Nef, Vpr, Vpu, Vif and, last but not least, the viral protease. This latter protein can kill infected and uninfected lymphocytes through the action of several host molecules, mainly members of the tumour necrosis factor family, or via the mitochondrial apoptotic pathway. The proinflammatory state that is characteristic of both the acute and chronic phase of HIV infection facilitates cell death, and is an additional cause of immune damage. Potent antiretroviral drugs that are largely used in therapy can reduce apoptosis by different mechanisms, that not only include the diminished production of the virus by infected cells and the subsequent reduction of inflammation, but also a direct action on the viral protease. The role of the host genetic background is finally crucial in understanding the process of cell death in HIV infection.

Editors´note: Programmed cell death or apoptosis is one of our most ancestral and potent cell defence mechanisms. HIV manipulates the apoptotic machinery to its advantage. For example, some viral proteins cause down- regulation of CD4 preventing gp120-CD4-mediated cell death. If HIV caused massive cell death, it couldn’t survive itself. On our side, we trigger activation of non-infected cells to help cope with the virus but then these innocent bystanders are induced to die by the virus. Research on immunogenetics can provide insights into why some people control HIV better, which may help with the design of antiretroviral therapy for immune reconstitution.

Streeck H, Brumme ZL, Anastario M, Cohen KW, Jolin JS, Meier A, Brumme CJ, Rosenberg ES, Alter G, Allen TM, Walker BD, Altfeld M. Antigen load and viral sequence diversification determine the functional profile of HIV-1-specific CD8+ T cells. PLoS Med. 2008;5(5):e100.

Virus-specific CD8(+) T lymphocytes play a key role in the initial reduction of peak viremia during acute viral infections, but display signs of increasing dysfunction and exhaustion under conditions of chronic antigen persistence. It has been suggested that virus-specific CD8(+) T cells with a “polyfunctional” profile, defined by the capacity to secrete multiple cytokines or chemokines, are most competent in controlling viral replication in chronic HIV-1 infection. Streeck and colleagues used HIV-1 infection as a model of chronic persistent viral infection to investigate the process of exhaustion and dysfunction of virus-specific CD8(+) T cell responses on the single-epitope level over time, starting in primary HIV-1 infection. They longitudinally analyzed the polyfunctional epitope-specific CD8(+) T cell responses of 18 patients during primary HIV-1 infection before and after therapy initiation or sequence variation in the targeted epitope. Epitope-specific CD8(+) T cells responded with multiple effector functions to antigenic stimulation during primary HIV-1 infection, but lost their polyfunctional capacity in response to antigen and up-regulated programmed death 1 (PD-1) expression with persistent viremic infection. This exhausted phenotype significantly decreased upon removal of stimulation by antigen, either in response to antiretroviral therapy or by reduction of epitope-specific antigen load in the presence of ongoing viral replication, as a consequence of in vivo selection of cytotoxic T lymphocyte escape mutations in the respective epitopes. Monofunctionality increased in CD8(+) T cell responses directed against conserved epitopes from 49% (95% confidence interval 27%-72%) to 76% (56%-95%) (standard deviation [SD] of the effect size 0.71), while monofunctionality remained stable or slightly decreased for responses directed against escaped epitopes from 61% (47%-75%) to 56% (42%-70%) (SD of the effect size 0.18 ) (p < 0.05). In conclusion, the data suggest that persistence of antigen can be the cause, rather than the consequence, of the functional impairment of virus-specific T cell responses observed during chronic HIV-1 infection, and underscore the importance of evaluating autologous viral sequences in studies aimed at investigating the relationship between virus-specific immunity and associated pathogenesis.

Editors´note: Polyfunctional CD8 + T cells that release multiple cytokines in response to antigen are essential to effective immune responses. This study found that these cells lose their polyfunctionality and are exhausted in the face of persistent viral infection. Antiretroviral treatment reduces the amount of antigen in patients and reverses the T-cell exhaustion. The Short Pulse Antiretroviral Therapy at HIV Seroconversion (SPARTAC) international trial is assessing whether early treatment can be beneficial and there are hopes that eventually therapeutic vaccination can lead to restoration of a broad and fully functional cytotoxic lymphocyte immune response.

Jlizi A, Edouard J, Fadhlaoui-Zid K, Frigi S, Debré P, Slim A, Theodorou I, El Gaaied AB, Carpentier W. Identification of the CCR5-Delta32 HIV resistance allele and new mutations of the CCR5 gene in different Tunisian populations. Hum Immunol. 2007 ;68(12):993-1000.

Polymorphisms in some chemokine receptor genes are associated with susceptibility to and progression of human immunodeficiency virus-1 (HIV-1) infection . Most mutations detected in the CC-chemokine receptor 5 (CCR5) gene are specific to different populations. In this study, Jlizi and colleagues focused on polymorphisms of the CCR5 coding region in three healthy populations from Tunisia, corresponding to a cosmopolitan population from Tunis, and two isolated Berber populations. In addition to the CCR5-Delta32 deletion, eleven single nucleotide polymorphisms were detected. Some of these point mutations were associated with the same genotype and even the same haplotype. The (L55Q-C101X), I124, V131F, T143N, A159V, I237, T239A and G301R alleles have not been described previously, whereas the CCR5-Delta32, L55Q, A335V and Y339F variants have already been reported in the literature. The distribution and frequency of these variants were different among the three groups studied, a result in agreement with the mosaic genetic structure of the Tunisian population. To determine whether these alleles affect HIV-1 transmission, the authors compared allele frequencies between healthy and HIV-1 infected individuals from Tunis. The frequency of the CCR5-Delta32 variant was significantly different between the two groups, leading us to conclude that this mutation might confer protection against HIV infection in Tunisian populations.

Editors’ note: CCR5-Delta32 produces a truncated protein affecting CCR5 gene expression and function and is associated with resistance to HIV infection and slower disease progression. In this study, CCR5-Delta32 was the most frequent variant found in healthy individuals (frequency 0.034) but not found at all in infected individuals. Furthermore, the CCR5-Delta32 mutant was present in the Tunisian population at its highest frequency among Arab countries. The authors speculate that even this low frequency of genetic difference may combine with male circumcision, religious customs, and social norms to explain the low incidence of HIV infection in Tunisia. Additional studies are needed to confirm this interesting hypothesis.

Transmission of HIV-1 via intercellular connections has been estimated as 100-1000 times more efficient than a cell-free process, perhaps in part explaining persistent viral spread in the presence of neutralizing antibodies. Such effective intercellular transfer of HIV-1 could occur through virological synapses or target-cell filopodia connected to infected cells. Here Sowinski and colleagues report that membrane nanotubes, formed when T cells make contact and subsequently part, provide a new route for HIV-1 transmission. Membrane nanotubes are known to connect various cell types, including neuronal and immune cells, and allow calcium-mediated signals to spread between connected myeloid cells. However, T-cell nanotubes are distinct from open-ended membranous tethers between other cell types, as a dynamic junction persists within T-cell nanotubes or at their contact with cell bodies. The authors also report that an extracellular matrix scaffold allows T-cell nanotubes to adopt variably shaped contours. HIV-1 transfers to uninfected T cells through nanotubes in a receptor-dependent manner. These data lead us to propose that HIV-1 can spread using nanotubular connections formed by short-term intercellular unions in which T cells specialize.

Editors’ note: Transfer of HIV-1 via nanotubes that create physical connections between T cells minimize exposure of the virus to extracellular antibodies, permitting it to escape an important immune defence. This may help explain the virulence and pathogenicity of HIV-1; it also suggests a new avenue for drug targets.

Bernstein A. AIDS and the next 25 years. Science. 2008 ; 320(5877):717.

Since HIV was discovered as the cause of AIDS a quarter century ago, over 60 million people have been infected with the virus and over 25 million people have died. These numbers make the result of two “proof of concept” vaccine efficacy trials—the STEP and Phambili trials—extremely disappointing. These results reflect our still-limited knowledge of HIV, its interactions with the human immune system, and the formidable, unprecedented challenges that it poses. But evidence of immunological protection in certain experimental models of HIV in nonhuman primates, and the intriguing observation that a small proportion of HIV-infected individuals (“elite controllers”) can completely suppress the virus for years, suggest that a vaccine may be achievable. More, not less, basic and early-stage clinical research is needed. We need to understand the role of both the innate and adaptive immune responses during HIV infection. We need to make it much more attractive for young researchers, including those from other fields, to enter the HIV vaccine field. And the continued engagement of industry is essential if we are ever to have a vaccine. We know from experience with other pathogens that a vaccine is the best way to stop a virus. The only end for a journey that began 25 years ago should be the development of a safe and effective HIV vaccine.

Editors’ Notes: Disappointment can lead to sober reflection and taking stock of what should remain a firm foundation and what can and should be challenged and changed. HIV has a high degree of sequence diversity and is a phenomenal foe, striking the very cells needed for an effective immune response. The stakes are high- this is not the time to walk away.

A quarter century of scientific discovery has been applied to developing an AIDS vaccine, yet this goal remains elusive. Specific characteristics of the virus, including the extreme genetic variability in circulating viral isolates worldwide, biological properties of HIV that impede immune attack, and a high mutation rate that allows for rapid escape from adaptive immune responses, render this a huge challenge. However, evidence of protection against AIDS viruses in animal models and control of HIV in humans under certain circumstances, together with scientific advances in understanding disease pathogenesis, provide a strong rationale and objective paths to continue the pursuit of an effective AIDS vaccine to stem the global epidemic.

Editors’ Notes: This review explains how the vaccines that work do so, before address ing the unique challenges for the development of an HIV vaccine. These include failure thus far to generate an immunogen to elicit effective neutralising antibodies and to identify the nature of T cell responses that could best contribute to vaccine protection against HIV. Nine critical issues and recommendations for immediate attention are laid out along with a call to pursue an HIV vaccine with greater passion than ever.

Highly active antiretroviral therapy prolongs the life of HIV-infected individuals, but it requires lifelong treatment and results in cumulative toxicities and viral-escape mutants. Gene therapy offers the promise of preventing progressive HIV infection by sustained interference with viral replication in the absence of chronic chemotherapy. Gene-targeting strategies are being developed with RNA-based agents, such as ribozymes, antisense, RNA aptamers and small interfering RNA, and protein-based agents, such as the mutant HIV Rev protein M10, fusion inhibitors and zinc-finger nucleases. Recent advances in T-cell-based strategies include gene-modified HIV-resistant T cells, lentiviral gene delivery, CD8(+) T cells, T bodies and engineered T-cell receptors. HIV-resistant hematopoietic stem cells have the potential to protect all cell types susceptible to HIV infection. The emergence of viral resistance can be addressed by therapies that use combinations of genetic agents and that inhibit both viral and host targets. Many of these strategies are being tested in ongoing and planned clinical trials.

Editors’ note: The plot thickens! Gene therapy could be a stand-alone approach or an adjuvant to drug regimens. However, most people living with HIV today are in settings with insufficient infrastructure to support such technology and viral escape will confound even gene therapy approaches. Several clinical trials testing gene transfer strategies are underway, but don’t hold your breath- this will take some time.

Hauser KF, El-Hage N, Buch S, Nath A, Tyor WR, Bruce-Keller AJ, Knapp PE. Impact of opiate-HIV-1 interactions on neurotoxic signaling. J Neuroimmune Pharmacol. 2006; 1(1):98-105.

Opiate drug abuse exacerbates the pathogenesis of human immunodeficiency virus-1 (HIV-1) in the central nervous system through direct actions on glia and neurons. Opiate abuse causes widespread disruption of astroglial and microglial function, and significant increases in astroglial-derived proinflammatory cytokines and chemokines, which likely contributes to neuronal dysfunction, death, and HIV encephalitis. Neurons are also directly affected by opiate-HIV-1 interactions. HIV-1 and the viral proteins gp120 and Tat activate multiple caspase-dependent and caspase-independent proapoptotic pathways in neurons involving phosphatidylinositol 3-kinase (PI3 kinase)/Akt, as well as p38, c-Jun N-terminal kinase (JNK) and/or other mitogen-activated protein kinases (MAPKs). Opiates appear to decrease the threshold for HIV-1-mediated neurotoxicity by sending convergent signals that exacerbate proapoptotic events induced by viral and cellular toxic products. The synergistic proinflammatory and neurotoxic effects of opiate drugs on glia and neurons are largely mediated through mu opioid receptors, which are expressed by subpopulations of astroglia, microglia, and neurons. Opiate abuse intrinsically modifies the host response to HIV-1. Identification of how this occurs is providing considerable insight toward understanding the mechanisms underlying HIV-1-associated dementia.

Editors’ note: HIV can cause neurotoxicity leading to symptoms and signs of dementia in some individuals and not others. Substances may exist that can counter this HIV-induced neurotoxicity but opiates are certainly not among them. Opiates appear to confuse neural communications and increase inflammation, undermining natural defences.

Human immunodeficiency virus type 1 (HIV-1) protease plays an essential role in the life cycle of the virus. Consequently, its inhibition can control acquired immunodeficiency syndrome. Any pharmacological treatment targeting the active site of the protease is known to generate escape mutants. On the other hand, if a drug targets a site crucial for the correct folding of the protease, mutations affecting this region would denaturate the protein and thus will not be expressed. Broglia and colleagues review the progress in our understanding of the folding of the protease, which has been instrumental in the design of a (non-conventional) folding inhibitor. The transferability of these results to other proteins testify to the universality of the folding-inhibition scenario for the design of leads of drugs which are unlikely to generate resistance.

Editors’ note: A drug that could incapacitate HIV’s protease by inhibiting it from folding into an action position, without producing an escape mutant, would be an important step forward.

Desquilbet L, Jacobson LP, Fried LP, Phair JP, Jamieson BD, Holloway M, Margolick JB: Multicenter AIDS Cohort Study. HIV-1 infection is associated with an earlier occurrence of a phenotype related to frailty J Gerontol A Biol Sci Med Sci. 2007;62(11):1279-86

Older healthy and adults living with HIV exhibit physiological similarities. Frailty is a clinical syndrome associated with aging that identifies a subset of older adults at high risk of mortality and other outcomes. Desquilbet and colleagues investigated whether HIV infection increases the prevalence of a frailty-related phenotype that approximates a clinical definition of frailty. The authors first defined the frailty-related phenotype and assessed its prevalence among HIV-uninfected men followed in the Multicenter AIDS Cohort Study (MACS) between 1994 and 2004. Using repeated measurements logistic regression models, they then assessed the association between frailty-related phenotype and HIV infection before the era of highly active antiretroviral therapies, adjusting for covariates among HIV-uninfected (N = 1905) and incident HIV infections (N = 245). HIV infection was strongly associated with frailty-related phenotype prevalence. Compared to men without HIV of similar age, ethnicity and education, men with HIV were more likely to have the frailty-related phenotype for all durations of infection: for < or =4 years, the adjusted odds ratio (OR) was 3.38, with 95% confidence interval (CI), 1.25-9.11, and for 4.01-8 years and 8.01-12 years the corresponding figures were ( OR = 12.95, 95% CI, 6.60-25.40) and ( OR = 14.68, 95% CI, 7.60-28.35), respectively. The frailty-related phenotype prevalence for 55-year-old men infected with HIV for < or =4 years (3.4%; 95% CI, 1.3-8.6) was similar to that of uninfected men > or =65 years old (3.4%; 95% CI, 1.5-7.6). The authors conclude that in this cohort, HIV infection was associated with an earlier occurrence of a phenotype that resembles the phenotype of frailty in older adults without HIV infection. Studies of frailty in the setting of HIV infection may help to clarify the biological mechanism of frailty.

Editors’ note: Aging is associated with both increased risk of certain diseases and frailty involving enhanced vulnerability to stressors and impairments of immunological and inflammatory regulation. Similar mechanisms seem to be operation in HIV infection. This long-term cohort study found that the duration of HIV infection, low CD4 count, and high viral load were associated with a higher likelihood of frailty-like manifestations, suggesting that earlier treatment could potentially slow down the aging-like effects of HIV infection.

Chun TW, Nickle DC, Justement JS, Meyers JH, Roby G, Hallahan CW, Kottilil S, Moir S, Mican JM, Mullins JI, Ward DJ, Kovacs JA, Mannon PJ, Fauci AS. Persistence of HIV in Gut-Associated Lymphoid Tissue despite Long-Term Antiretroviral Therapy. J Infect Dis. 2008;197: 714-20.

Human immunodeficiency virus (HIV) persists in peripheral blood mononuclear cells despite sustained, undetectable plasma viremia resulting from long-term antiretroviral therapy. However, the source of persistent HIV in such infected individuals remains unclear. Given recent data suggesting high levels of viral replication and profound depletion of CD4(+) T cells in gut-associated lymphoid tissue of animals infected with simian immunodeficiency virus and HIV-infected humans, Chun and colleagues sought to determine the level of CD4(+) T cell depletion as well as the degree and extent of HIV persistence in the gut-associated lymphoid tissue of infected individuals who had been receiving effective antiviral therapy for prolonged periods of time. The authors demonstrate incomplete recoveries of CD4(+) T cells in the gut-associated lymphoid tissue of aviremic, HIV-infected individuals who had received up to 9.9 years of effective antiretroviral therapy. In addition, the authors demonstrate higher frequencies of HIV infection in gut-associated lymphoid tissue, compared with peripheral blood mononuclear cells, in these aviremic individuals and provide evidence for cross-infection between these 2 cellular compartments. Together, these data provide a possible mechanism for the maintenance of viral reservoirs revolving around the gut-associated lymphoid tissue of HIV-infected individuals despite long-term viral suppression and suggest that the gut-associated lymphoid tissue may play a major role in the persistence of HIV in such individuals.

Editors’ note: Gut-associated lymphoid tissue is the largest component of the human lymphoid system and contains the highest number of CD4+ T cells. This study reveals that persistent depletion of CD4+ T cells in the gut, indicating a lack of mucosal immune reconstitution, is due to ongoing HIV replication despite undetectable plasma viral loads achieved through existing drug regimens. New drugs are needed to stop HIV seeding from the gut into the bloodstream if this important viral reservoir is to be controlled.

Most human immunodeficiency virus (HIV) is acquired during sex, across a mucosal membrane. Despite many advances in our understanding of HIV pathogenesis, the initial events during mucosal transmission have been poorly characterized, and a better understanding of these events will probably be a key to the development of successful microbicide(s) and/or a preventative HIV vaccine. While a vast majority of mucosal HIV exposures do not result in productive infection, implying that innate mucosal immune defenses are highly protective, failure of these mucosal defenses resulted in over 3 million new HIV infections in 2006. Iqbal and colleagues review recent findings regarding HIV mucosal immunopathogenesis, emphasizing the importance of innate immunity in natural protection from infection, and examine how natural or induced perturbations in the mucosal innate system may underpin HIV transmission. Given the great challenges to the development of HIV microbicides and vaccines, identification and enhancement of ‘natural’ innate immune defenses present attractive avenues for development of safe, non-toxic microbicides.

Editors’ note: At stake is how to translate natural HIV protection into HIV prevention. On the genetic side, discovery in highly exposed persistently seronegative people of the CCR5- r 32 mutation that confers near complete resistance to sexual HIV acquisition led to a new class of CCR5 inhibitor antiretroviral drugs. On the innate (inborn) immunity side, the challenge is to turn key innate proteins that have low toxicity and demonstrated real life efficacy into effective microbicides, pumping up what we already have.

Kaul M, Lipton SA. Mechanisms of neuroimmunity and neurodegeneration associated with HIV-1 infection and AIDS. J Neuroimmune Pharmacol. 2006 Jun;1(2):138-51.

Infection with the human immunodeficiency virus-1 (HIV-1) the virus causing acquired immunodeficiency syndrome (AIDS), is a persistent health problem worldwide. HIV-1 seems to enter the brain very soon after peripheral infection and can induce severe and debilitating neurological problems that include behavioural abnormalities, motor dysfunction, and frank dementia. Infected peripheral immune-competent cells, in particular macrophages, appear to infiltrate the CNS and provoke a neuropathological response involving all cell types in the brain. The course of HIV-1 disease is strongly influenced by viral and host factors, such as the viral strain and the response of the host’s immune system. In addition, HIV-1-dependent disease processes in the periphery have a substantial effect on the pathological changes in the central nervous system (CNS), although the brain eventually harbours a distinctive viral population of its own. In the CNS, HIV-1 also incites activation of chemokine receptors, inflammatory mediators, extracellular matrix-degrading enzymes, and glutamate receptor-mediated excitotoxicity, all of which can initiate numerous downstream signalling pathways and disturb neuronal and glial function. Although there have been many major improvements in the control of viral infection in the periphery, an effective therapy for HIV-1-associated dementia (HAD) is still not available. This article addresses recently uncovered pathologic neuroimmune and degenerative mechanisms contributing to neuronal damage induced by HIV-1 and discusses experimental and potentially future therapeutic approaches.

Editors’ note: This review provides an overview of how HIV in the brain stimulates immune system reactions, including inflammatory cytokines that are highly toxic to cells of the central nervous system. Prior to combination antiretroviral treatment, the majority of patients with HIV associated dementia would deteriorate rapidly over several months. Now it appears that virological improvement of patients with dementia who are on antiretroviral treatment correlates with neurological improvement, leading to a more favourable prognosis. Differences in the abilities of specific antiretroviral drugs to penetrate the central nervous system may explain why some people with dementia and not others respond well.

Intranasal drug administration is a noninvasive method of bypassing the blood-brain barrier to deliver neurotrophins and other therapeutic agents to the brain and spinal cord. This method allows drugs that do not cross the blood-brain barrier to be delivered to the central nervous system (CNS) and eliminates the need for systemic delivery, thereby reducing unwanted systemic side effects. Delivery from the nose to the CNS occurs within minutes along both the olfactory and trigeminal neural pathways. Intranasal delivery occurs by an extracellular route and does not require that drugs bind to any receptor or undergo axonal transport. Intranasal delivery also targets the nasal associated lymphatic tissues and deep cervical lymph nodes. In addition, intranasally administered therapeutics are observed at high levels in the blood vessel walls and perivascular spaces of the cerebrovasculature. Using this intranasal method in animal models, researchers have successfully reduced stroke damage, reversed Alzheimer’s neurodegeneration, reduced anxiety, improved memory, stimulated cerebral neurogenesis, and treated brain tumors. In humans, intranasal insulin has been shown to improve memory in normal adults and patients with Alzheimer’s disease. Intranasal delivery strategies that can be employed to treat and prevent NeuroAIDS include: (1) target antiretrovirals to reach HIV that harbors in the CNS; (2) target therapeutics to protect neurons in the CNS; (3) modulate the neuroimmune function of monocyte/macrophages by targeting the lymphatics, perivascular spaces of the cerebrovasculature, and the CNS; and (4) improve memory and cognitive function by targeting therapeutics to the CNS.

Editors’ note: The blood – brain barrier serves to protect the brain and spinal cord from a variety of pathogens and toxic substances, but it is also a barrier to treatment of central nervous system disorders, including those caused by HIV infection. Intranasal drug delivery, which patients can do themselves, targets therapeutic agents directly to the brain, by-passing the blood-brain barrier and reducing systemic exposure. It can be used to treat neuroAIDS by targeting antiretroviral drugs, including neuroimmune modulators, to reach HIV that harbours in the central nervous system (CNS), to protect neurons in the CNS, and to improve memory and cognitive function. Intranasal insulin anyone?

Kiwanuka N, Laeyendecker O, Robb M, Kigozi G, Arroyo M, McCutchan F, Eller LA, Eller M, Makumbi F, Birx D, Wabwire-Mangen F, Serwadda D, Sewankambo NK, Quinn TC, Wawer M, Gray R. Effect of Human Immunodeficiency Virus Type 1 (HIV-1) Subtype on Disease Progression in Persons from Rakai, Uganda, with Incident HIV-1 Infection. J Infect Dis. 2008 Feb 11 [Epub ahead of print].

Human immunodeficiency virus type 1 (HIV-1) subtypes differ in biological characteristics that may affect pathogenicity. Kiwanuka and colleagues determined the HIV-1 subtype-specific rates of disease progression among 350 HIV-1 seroconverters. Subtype, viral load, and CD4(+) cell count were determined. Cox proportional hazards regression modelling was used to estimate adjusted hazard ratios (HRs) of progression to acquired immunodeficiency syndrome (AIDS) (defined as a CD4(+) cell count of </=250 cells/mm(3)) and to AIDS-associated death. A total of 59.1% of study subjects had subtype D strains, 15.1% had subtype A, 21.1% had intersubtype recombinant subtypes, 4.3% had multiple subtypes, and 0.3% had subtype C. Of the 350 subjects, 129 (37%) progressed to AIDS, and 68 (19.5%) died of AIDS. The median time to AIDS onset was shorter for persons with subtype D (6.5 years), recombinant subtypes (5.6 years), or multiple subtypes (5.8 years), compared with persons with subtype A (8.0 years). Relative to subtype A, adjusted hazard rations of progression to AIDS were 2.13 [95% confidence interval {CI}, 1.10-4.11] for subtype D, 2.16 [95% CI, 1.05-4.45] for recombinant subtypes, and 4.40 [95% CI, 1.71-11.3] for multiple subtypes. The risk of progression to death was significantly higher for subtype D (adjusted HR, 5.65; 95% CI, 1.37-23.4), recombinant subtypes (adjusted HR, 6.70; 95% CI, 1.56-28.8), and multiple subtypes (adjusted HR, 7.67; 95% CI, 1.27-46.3), compared with subtype A. HIV disease progression is affected by HIV-1 subtype. This finding may affect decisions on when to initiate antiretroviral therapy and may have implications for future trials of HIV-1 vaccines aimed at slowing disease progression.

Editors’ note: Subtype does matter ― subtype D has a higher frequency of syncytium formation and of the CXCR4 receptor use which is associated with more rapid decreases in CD4 cell count. Infection with multiple subtypes also was associated with faster disease progression compared to infection with a single subtype, emphasising the importance of positive prevention to avoid super-infection. Future therapeutic HIV vaccine trials should assess subtype specific responses; however, current treatment programmes, with subtype analysis remaining a research and surveillance tool, will have to continue to initiate antiretroviral treatment using standard thresholds for everyone, regardless of subtype.

Pereyra F, Addo MM, Kaufmann DE, Liu Y, Miura T, Rathod A, Baker B, Trocha A, Rosenberg R, Mackey E, Ueda P, Lu Z, Cohen D, Wrin T, Petropoulos CJ, Rosenberg ES, Walker BD. Genetic and Immunologic Heterogeneity among Persons Who Control HIV Infection in the Absence of Therapy. J Infect Dis. 2008 Feb 15;197(4):563-571.

Spontaneous control of human immunodeficiency virus (HIV) infection has been documented in a minority of HIV-infected individuals. The mechanisms behind this outcome remain largely unknown, and a better understanding of them will likely influence future vaccine strategies. HIV-specific T cell and antibody responses as well as host genetics were examined in untreated HIV-infected patients who maintain comparatively low plasma HIV RNA levels (hereafter, controllers), including those with levels of < 50 RNA copies/mL (elite controllers), those with levels of 50-2000  copies/mL (viremic controllers). Pereyra and colleagues also examined HIV-specific T cell and antibody responses as well as host genetics for patients with levels of >10,000 copies/mL (chronic progressors). CD8+ T cells from both controller groups preferentially target Gag over other proteins in the context of diverse HLA class I alleles, whereas responses are more broadly distributed in persons with progressive infection. Elite controllers represent a distinct group of individuals who have significantly more CD4 and CD8 T cells that secrete interferon-gamma and interleukin-2 and lower levels of HIV-neutralizing antibodies. Individual responses were quite heterogeneous, and none of the parameters evaluated was uniquely associated with the ability to control viremia. Elite controllers are a distinct group, even when compared to persons with low level viremia, but they exhibit marked genetic and immunologic heterogeneity. Even low-level viremia among HIV controllers was associated with measurable T cell dysfunction, which has implications for current prophylactic vaccine strategies.

Editors’ note: The CD8 T cells of elite controllers appear to have enhanced ability to inhibit virus replication in vitro. Elite controllers have the highest ratio of functional CD4 to CD8 T cells (chronic progressors have the lowest). Whether this association between T cell function and HIV is cause or effect is unclear. The lower neutralising antibody activity seen in elite controllers suggests that neutralising antibodies do not play a major role in maintaining viral suppression in people who spontaneously control viral replication.

Weiser B, Philpott S, Klimkait T, Burger H, Kitchen C, Burgisser P, Gorgievsk M, Perrin L, Piffaretti JC, Ledergerber B, the Swiss HIV Cohort Study. HIV-1 coreceptor usage and CXCR4-specific viral load predict clinical disease progression during combination antiretroviral therapy. AIDS 2008; 22(4):469-479.

Although combination antiretroviral therapy dramatically reduces rates of AIDS and death, a minority of patients experience clinical disease progression during treatment. Weiser and colleagues aimed to investigate whether detection of CXCR4(X4)-specific strains or quantification of X4-specific HIV-1 load predict clinical outcome. From the Swiss HIV Cohort Study, 96 participants who initiated combination antiretroviral therapy yet subsequently progressed to AIDS or death were compared with 84 contemporaneous, treated nonprogressors. A sensitive heteroduplex tracking assay was developed to quantify plasma X4 and CCR5 variants and resolve HIV-1 load into coreceptor-specific components. Measurements were analyzed as cofactors of progression in multivariable Cox models adjusted for concurrent CD4 cell count and total viral load, applying inverse probability weights to adjust for sampling bias. Patients with X4 variants at baseline displayed reduced CD4 cell responses compared with those without X4 strains (40 versus 82 cells/[mu]l; P = 0.012). The adjusted multivariable hazard ratio (HR) for clinical progression was 4.8 [95% confidence interval (CI) 2.3-10.0] for those demonstrating X4 strains at baseline. The X4-specific HIV-1 load was a similarly independent predictor, with HR values of 3.7 (95% CI, 1.2-11.3) and 5.9 (95% CI, 2.2-15.0) for baseline loads of 2.2-4.3 and > 4.3 log10 copies/ml, respectively, compared with < 2.2 log10 copies/ml. In conclusion, HIV-1 coreceptor usage and X4-specific viral loads strongly predicted disease progression during combination antiretroviral therapy, independent of and in addition to CD4 cell count or total viral load. Detection and quantification of X4 strains promise to be clinically useful biomarkers to guide patient management and study HIV-1 pathogenesis.

Editors’ note: HIV-1 requires two receptors to infect cells: CD4 is the primary receptor, with chemokine receptors CCR5 and CXCR4 serving as co-receptors. CCR5 using viruses (called R5 viruses) are those most commonly transmitted between people but after years of infection CXCR4-using strains (X4 viruses) are detected in half of people living with HIV and often predict CD4 cell depletion and accelerated disease progression. This study suggests that an assay detecting a high fraction of viruses using the X4 coreceptor early in the course of infection could be clinically useful; clinical trials are now needed to evaluate whether early treatment of asymptomatic people with CD4 counts above 350 cells/µl who harbor X4 strains can reduce HIV-1 levels and slow disease progression.

Vitezica, Zulma G; Milpied, Brigitte; Lonjou, Christine; Borot, Nicolas; Ledger, Terence Niel; Lefebvre, Anne; Hovnanian, Alain. HLA-DRB1*01 associated with cutaneous hypersensitivity induced by nevirapine and efavirenz. AIDS 2008;22(4):540-541.

HLA typing, demographic and immunological risk factors for nevirapine and efavirenz reactions were studied in a French cohort of HIV patients. Cases with isolated rash were significantly associated with HLA-DRB1*01 allele. No liver toxicity was observed and no association was detected with the percentage of CD4 T-cells. This study suggests that HLA-DRB1*01 allele plays an important role in susceptibility to cutaneous reactions associated with nevirapine and efavirenz in HIV patients.

Editors’ note: Being able to detect which patients are more likely to develop rashes with the first line non-nucleoside reverse transcriptase inhibitor (NNRTI) drugs nevirapine (NVP) and efavirenz (EFV) would be very useful clinically. Between 20-35% of patients on nevirapine and 32% of patients on efavirenz develop cutaneous hypersensitivity reactions within 6 weeks of treatment initiation and need to be switched to other drugs. This small study of 21 patients should be confirmed and, although its findings are promising, there is a way to go before genetic screening of human leukocyte antigen (HLA) markers to detect such susceptibility can be turned into a diagnostic test which would help decrease or eliminate this problem.

Boberg A, Isaguliants M Vaccination against drug resistance in HIV infection. Expert Rev Vaccines. 2008;7(1):131-45.

HIV-1 resistance to currently employed antiretroviral drugs and drug-associated adverse reactions and toxicity point to a need for additional measures to control HIV-1 replication in HIV-infected patients. The immune system of HIV-infected individuals mount an immune response against the regions harboring drug-resistance mutations, sometimes stronger than that against the parental wild-type sequences. A potent cross-reactive immune response against drug-resistant pol proteins can suppress the replication of drug-escaping HIV. This suggests the possibility for a vaccination against existing and anticipated drug-resistant HIV variants. If successful, therapeutic vaccines against drug resistance would ease the therapeutic modalities and limit the spread of drug-resistant HIV. A better understanding of the complex interactions between patterns of drug-resistance mutations, immune responses against these mutations and their antigen presentation by particular human lymphocyte antigen alleles could help to tailor these vaccines after new drugs/new mutations. In this review, we describe the developments in the field of immunization against mutations conferring drug resistance and evaluate their prospects for human vaccination.

Editors’ note: None of the therapeutic vaccine concepts and vaccination strategies tested thus far (subunit protein and DNA vaccines, live-vectored recombinant vaccines and various prime-boost vaccine combinations) have targeted drug-resistant HIV variants. Such a strategy would aim to induce immune pressure which would act synergistically with antiretroviral drugs. Ideally such a therapeutic vaccine would stimulate a strong cross-reactive immune response against both the wild-type and drug-escape HIV variants. Pie in the sky? Boberg and Isaguliants think this is feasible.

Bernard EJ, Azad Y, Vandamme AM, Weait M, Geretti AM. HIV forensics: pitfalls and acceptable standards in the use of phylogenetic analysis as evidence in criminal investigations of HIV transmission. HIV Med 2007;8:382-7.

Phylogenetic analysis - the study of the genetic relatedness between HIV strains - has recently been used in criminal prosecutions as evidence of responsibility for HIV transmission. In these trials, the expert opinion of virologists has been of critical importance. Pitfalls of phylogenetic analysis of HIV gene sequences relate to its complexity and its findings which do not achieve the levels of certainty obtained with the forensic analysis of human DNA. Although two individuals may carry HIV strains that are closely related, these will not necessarily be unique to the two parties and could extend to other persons within the same transmission network. For forensic purposes, phylogenetic analysis of acceptable standard should be conducted under strictly controlled conditions by laboratories with relevant expertise applying rigorous methods. It is vitally important to include the right controls, which should be epidemiologically and temporally relevant to the parties under investigation. Use of inappropriate controls can exaggerate any relatedness between the virus strains of the complainant and defendant as being strikingly unique. It will be often difficult to obtain the relevant controls. If convenient but less appropriate controls are used, interpretation of the findings should be tempered accordingly. Phylogenetic analysis cannot prove that HIV transmission occurred directly between two individuals. However, it can exonerate individuals by demonstrating that the defendant carries a virus strain unrelated to that of the complainant. Expert witnesses should acknowledge the limitations of the inferences that might be made and choose the correct language in both written and verbal testimony.

Editors’ note: In trying to determine in a court of law whether an HIV transmission has been intentional/purposeful transmission or reckless transmission or negligent transmission it is important first of all to establish whether transmission has occurred. Phylogenetic analysis can rule it out but is less likely to be able to rule it in with any certainty.

Brass AL, Dykxhoorn DM, Benita Y, Yan N, Engelman A, Xavier RJ, Lieberman J, Elledge SJ. Identification of Host Proteins Required for HIV Infection Through a Functional Genomic Screen. Science. 2008 Jan 10 [Epub ahead of print]

Photo credit: Boehringer-Ingelheim

HIV-1 exploits multiple host proteins during infection. Brass and colleagues performed a large-scale small interfering RNA (siRNA) screen to identify host factors required by HIV-1 and identified over 250 HIV-dependency factors (HDFs). These proteins participate in  a broad array of cellular functions and implicate new pathways in the viral life  cycle. Further analysis revealed previously unknown roles for retrograde Golgi transport proteins (Rab6 and Vps53) in viral entry, a karyopherin (TNPO3) in viral integration, and the Mediator complex (Med28) in viral transcription. Transcriptional analysis revealed that HDF genes were enriched for high expression in immune cells suggesting that viruses evolve in host cells that optimally perform the functions required for their life cycle. This effort illustrates the power with which RNA interference and forward genetics can be used to expose the dependencies of human pathogens such as HIV, and in so doing identify potential targets for therapy.

Editors’ note: A small virus, HIV-1 has nine genes that code only 15 proteins and yet has a complex life cycle. This elegant research began with the premise that HIV-1 must depend on host factors and found that 273 human proteins help HIV to infect cells, enter the nucleus, integrate into the human chromosome, and make copies of itself. These host-dependency factors could make excellent targets for drugs in much the same way that CCR5 inhibitors prevent viral docking for cell entry. However, we humans need these proteins too, so determining which ones we can get by without is the challenging path of research inquiry this work has opened up.