HIV-neutralizing immunoglobulin A and HIV-specific proliferation are independently associated with reduced HIV acquisition in Kenyan sex workers

Strong HIV-specific CD4+ and CD8+ T-lymphocyte proliferative responses in healthy individuals immunized with an HIV-1 DNA vaccine and boosted with recombinant modified vaccinia virus ankara expressing HIV-1 genes

We investigated HIV-1 vaccine-induced lymphoproliferative responses in healthy volunteers immunized intradermally or intramuscularly (with or without adjuvant granulocyte-macrophage colony-stimulating factor [GM-CSF] protein) with DNA expressing HIV-1 gag, env, rev, and rt at months 0, 1, and 3 using a Biojector and boosted at 9 months with modified vaccinia virus Ankara (MVA) expressing heterologous HIV-1 gag, env, and pol (HIV-MVA). Lymphoproliferative responses to aldrithiol-2 (AT-2)-inactivated-HIV-1 antigen were tested by a [(3)H]thymidine uptake assay and a flow-cytometric assay of specific cell-mediated immune response in activated whole blood (FASCIA-WB) 2 weeks after the HIV-MVA boost (n = 38). A FASCIA using peripheral blood mononuclear cells (FASCIA-PBMC) was also employed (n = 14). Thirty-five of 38 (92%) vaccinees were reactive by the [(3)H]thymidine uptake assay. Thirty-two of 38 (84%) vaccinees were reactive by the CD4(+) T-cell FASCIA-WB, and 7 of 38 (18%) also exhibited CD8(+) T-cell responses. There was strong correlation between the proliferative responses measured by the [(3)H]thymidine uptake assay and CD4(+) T-cell FASCIA-WB (r = 0.68; P < 0.01). Fourteen vaccinees were analyzed using all three assays. Ten of 14 (71%) and 11/14 (79%) demonstrated CD4(+) T-cell responses in FASCIA-WB and FASCIA-PBMC, respectively. CD8(+) T-cell reactivity was observed in 3/14 (21%) and 7/14 (50%) using the FASCIA-WB and FASCIA-PBMC, respectively. All 14 were reactive by the [(3)H]thymidine uptake assay. The overall HIV-specific T-cell proliferative response in the vaccinees employing any of the assays was 100% (38/38). A standardized FASCIA-PBMC, which allows simultaneous phenotyping, may be an option to the [(3)H]thymidine uptake assay for assessment of vaccine-induced T-cell proliferation, especially in isotope-restricted settings.

HIV viral set point and host immune control in individuals with HIV-specific CD8+ T-cell responses prior to HIV acquisition

OBJECTIVE

Vaccine-induced CD8(+) T-cell responses in primates have been associated with a reduced simian immunodeficiency virus plasma viral load and enhanced T-cell responses, but cellular vaccines have shown limited success in human trials. We previously described HIV-specific T-cell responses in two groups of highly exposed, persistently seronegative Kenyan female sex workers, and a subset of these participants have subsequently acquired HIV. We examined the impact of pre-existing CD8(+) T-cell responses on post-acquisition outcomes.

DESIGN AND METHODS

HIV-specific CD8(+) T-cell responses had been examined in highly exposed, persistently seronegative participants from the Pumwani and Kibera cohorts, using a combination of virus-specific lysis, proliferation, interferon-gamma production, or all. Plasma viral load set point and HIV-specific T-cell proliferation and cytokine production were now examined post hoc by blinded investigators in the subset of participants who acquired HIV.

RESULTS

Pre-acquisition cellular immune assays and post-infection viral load were available for 46 participants, and HIV-specific CD8(+) T-cell responses had been detected in 25 of 46 (54%) participants. Pre-acquisition CD8(+) T-cell responses were associated with a lower post-acquisition HIV viral load set point in both cohorts (pooled analysis, 3.1 vs. 4.1 log(10) RNA copies/ml; P=0.0002) and with enhanced post-acquisition HIV-specific CD8(+) T-cell proliferation (3.8 vs. 1.0%, P=0.03), but with a trend to reduced post-acquisition CD8(+) T-cell interferon-gamma responses.

CONCLUSION

HIV-specific CD8(+) T-cell responses prior to HIV acquisition were associated with a lower HIV viral load and an altered functional profile of post-acquisition CD8(+) T-cell responses.

HIV-1-specific antibody responses during acute and chronic HIV-1 infection

PURPOSE OF REVIEW

The humoral immune response to HIV-1 throughout infection is comprised of complex mixtures of antibody isotypes with numerous HIV-1 specificities. However, unlike antibody responses to most infections, protective antibody responses are delayed and do not arise until long after HIV-1 latency is established. We review recent data on HIV-1-specific antibody isotypes induced following HIV-1 transmission: to understand the effects of HIV-1 on B cell and T cell effector responses, to understand the timing of the rise and fall of different anti-HIV-1 antibodies and to understand how antibodies could contribute to protective immunity if they were either pre-existing or elicited immediately after HIV-1 transmission.

RECENT FINDINGS

Studies of the earliest events following infection by the transmitted/founder virus have recently revealed that early destruction of B cell generative microenvironments may be responsible for delay of potentially protective anti-HIV-1 antibody responses. Unlike the initial CD8 T cell response to HIV-1, the initial induced antibody response is usually ineffective in controlling virus replication during acute HIV-1 infection.

SUMMARY

The antibody isotypes and specificities elicited during HIV-1 infection can provide a window into deciphering the detrimental effects of HIV-1 on B cell and T cell responses. Additionally, further characterization of the virus inhibitory capabilities of anti-HIV-1 antibody isotypes can define the spectrum of potential protective HIV-1 antibodies that could be readily elicited by experimental vaccines and adjuvants.

Immune responses to HIV and SIV in mucosal tissues: 'location, location, location'

PURPOSE OF REVIEW

This review summarizes research literature regarding mucosal immunity to HIV and simian immunodeficiency virus (SIV), with an emphasis on work published within the past 18 months.

RECENT FINDINGS

Notable recent studies have focused on the pivotal events occurring within mucosal tissues during acute HIV/SIV infection that serve to establish a balance between detrimental immune activation and beneficial adaptive responses. In cervicovaginal mucosa, an early inflammatory response leads to recruitment of susceptible target cells. At this acute stage, the in-vivo ratio between CD8 effector cells and infected CD4 T-cells may be critical for limiting viral dissemination. Acute infection is also accompanied by loss of germinal center architecture and T/B cell apoptosis in Peyer's patches of the gastrointestinal tract. During chronic infection, mucosal CD8 T-cells may play a role in immune control, as suggested by studies of elite controllers.

SUMMARY

Mucosal tissues serve as the major portal of entry for HIV, and house a majority of the body's lymphocytes, including CD4 T-cells that are targets for infection. Recent studies have focused renewed attention on events occurring immediately after transmission, and underscore the concept that the balance between inflammation and protective immunity is established by host responses in mucosal tissues.

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

OBJECTIVES

To 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.

METHODS

Plasma 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.

RESULTS

At enrollment, 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.

CONCLUSION

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.

HIV Infection and Gut Mucosal Immune Function: Updates on Pathogenesis with Implications for Management and Intervention

HIV is primarily a sexually transmitted infection. However, given that the gastrointestinal tract (GIT) houses most of the body's lymphocytes, including activated memory CD4(+) T cells that are preferential targets for HIV, recent research has focused on the role of the GIT in transmission and pathogenesis. In health, the GIT maintains a balance between immune tolerance and rapid responsiveness. A complex network of innate and adaptive responses maintains this balance, which is severely perturbed in HIV infection. Recent studies have focused on mechanisms of GIT CD4(+) T-cell depletion and epithelial disruption in HIV infection, the role of inflammation in accelerating viral dissemination, the kinetics of the adaptive response following transmission, and the extent of T-cell reconstitution following antiretroviral therapy. This review summarizes the results of recent investigations that may have important implications for the development of vaccines, microbicides, and therapeutic interventions for HIV and other mucosal pathogens.

Antibody-Mediated Fcγ Receptor-Based Mechanisms of HIV Inhibition: Recent Findings and New Vaccination Strategies

The HIV/AIDS pandemic is one of the most devastating pandemics worldwide. Today, the major route of infection by HIV is sexual transmission. One of the most promising strategies for vaccination against HIV sexual infection is the development of a mucosal vaccine, which should be able to induce strong local and systemic protective immunity. It is believed that both humoral and cellular immune responses are needed for inducing a sterilizing protection against HIV. Recently, passive administration of monoclonal neutralizing antibodies in macaques infected by vaginal challenge demonstrated a crucial role of FcγRs in the protection afforded by these antibodies. This questioned about the role of innate and adaptive immune functions, including ADCC, ADCVI, phagocytosis of opsonized HIV particles and the production of inflammatory cytokines and chemokines, in the mechanism of HIV inhibition in vivo. Other monoclonal antibodies - non-neutralizing inhibitory antibodies - which recognize immunogenic epitopes, have been shown to display potent FcγRs-dependent inhibition of HIV replication in vitro. The potential role of these antibodies in protection against sexual transmission of HIV and their biological relevance for the development of an HIV vaccine therefore need to be determined. This review highlights the potential role of FcγRs-mediated innate and adaptive immune functions in the mechanism of HIV protection.

Female genital tract secretions inhibit herpes simplex virus infection: correlation with soluble mucosal immune mediators and impact of hormonal contraception

PROBLEM

Female genital tract secretions inhibit herpes simplex virus (HSV) infection, however, the intra- and inter-subject variability, contribution of specific mediators, and impact of reproductive hormones have not been defined.

METHOD

of study Cervicovaginal lavage (CVL) (n = 89) obtained from nine cyclers and seven women on hormonal contraception (HC), who completed between three and eight weekly visits, were examined for anti-herpes simplex virus activity and concentrations of mediators.

RESULTS

The CVL inhibited HSV infection by a mean value of approximately 57% during the follicular or luteal phase, but only by 36% in hormonal contraceptive users. Human neutrophil peptides 1-3 (HNP1-3) (P = 0.03), IL-8 (P = 0.003), lactoferrin (P = 0.005), lysozyme (P = 0.003), IgA (P = 0.002), and IgG (P = 0.02) correlated with antiviral activity. Intra-subject and inter-subject variability was observed, suggesting that factors other than hormones contribute to innate defense.

CONCLUSION

Endogenous antimicrobial activity may provide a biomarker of healthy mucosal immunity and may be reduced in the setting of HC. However, larger prospective studies are needed.

HIV-1 gp41-specific monoclonal mucosal IgAs derived from highly exposed but IgG-seronegative individuals block HIV-1 epithelial transcytosis and neutralize CD4(+) cell infection: an IgA gene and functional analysis

AIDS is mainly a sexually transmitted disease, and accordingly, mucosal tissues are the primary sites of natural human immunodeficiency virus type-1 (HIV-1) transmission. Mucosal immunoglobulin A (IgA) antibody specific for HIV-1 envelope gp41 subunit is one correlate of protection in individuals who are highly sexually exposed to HIV-1 but remain persistently IgG seronegative (HEPS). Understanding these peculiar IgAs at the gene and functional level is possible only with monoclonal IgAs. We have constructed a mucosal Fab IgA library from HEPS and have characterized a series of HIV-1 IgAs specific for gp41 that, in vitro, are transcytosis-blocking and infection-neutralizing. Characterization of their IgA genes shows that Fab specific for the gp41 membrane-proximal region harbors a long heavy-chain CDR3 loop (CDRH3) similar to the two broadly neutralizing IgG monoclonal antibodies, 2F5 and 4E10. Furthermore, the selected Fab IgA shows extensive somatic mutations that cluster in the CDR regions, indicating that affinity maturation due to an antigen-driven process had occurred in HEPS individuals, presumably upon multiple exposures to HIV. This analysis of HEPS monoclonal IgA gives a unique opportunity to correlate an antibody function (resistance to a pathogen in vivo) with an antibody gene. Such neutralizing monoclonal IgAs could be used in microbicide formulation.

Elevated elafin/trappin-2 in the female genital tract is associated with protection against HIV acquisition

OBJECTIVES

Globally, heterosexual intercourse is the primary route of HIV-1 (HIV) transmission. It follows that mechanisms that protect against HIV infection are likely operative at the genital mucosa. In HIV-resistant Kenyan sex workers who are highly exposed to HIV infection yet remain uninfected, protection correlates with HIV-specific immune responses and genetic factors. However, these factors do not entirely explain this model of natural immunity to HIV. We hypothesized that protection may be mediated by innate immune proteins in the genital tract of HIV-resistant sex workers.

DESIGN AND METHODS

The genital proteome of mucosal secretions from HIV-resistant women was examined using surface-enhanced laser desorption/ionization time-of-flight mass spectrometry. Cervical lavage samples were collected from 315 HIV-resistant, HIV-uninfected and HIV-infected commercial sex workers.

RESULTS

Univariate analysis identified a 6 kDa biomarker of HIV resistance in genital secretions from these women. This protein was identified by tandem mass spectrometry as elafin and was found to be overexpressed in HIV-resistant women compared with HIV-uninfected (P = 0.001) and infected (P = 0.002) women. The elevated levels of elafin/trappin-2 in HIV-resistant women were confirmed using ELISA. The prospective association of elevated cervicovaginal elafin/trappin-2 levels with protection from HIV acquisition was then confirmed in an independent cohort of high-risk female sex workers.

CONCLUSION

Using a unique proteomics approach in a large scale, cross-sectional cohort study, we identified elafin/trappin-2 as a novel innate immune factor, which is highly associated with resistance. This association was confirmed within an independent, prospective cohort study. Genital tract elafin/trappin-2 levels constitute a natural correlate of HIV protection in humans.

Obstacles to the successful development of an efficacious T cell-inducing HIV-1 vaccine

An efficacious vaccine to HIV-1 is direly needed to stem the global pandemic. Immunogens that elicit broadly cross-neutralizing antibodies to HIV-1 remain elusive, and thus, most HIV-1 vaccine efforts are focusing on induction of T cells. The notion that T cells can mediate protection against HIV-1 has been called into question by the failure of the STEP trial, which was designed to test this concept by the use of an E1-deleted Ad vaccine carrier. Lack of efficacy of the STEP trial vaccine underscores our limited knowledge about correlates of immune protection against HIV-1 and stresses the need for an enhanced commitment to basic research, including preclinical and clinical vaccine studies. In this review, we discuss known correlates of protection against HIV-1 and different vaccine strategies that have been or are being explored to induce such correlates, focusing on T cell-inducing vaccines and particularly on Ad vectors.

Early detection of human immunodeficiency virus type 1-specific B-lymphocyte-derived antibodies in a high-risk population

Diagnosis of acute human immunodeficiency virus (HIV) infection, a key driver of the HIV epidemic, remains a public health challenge. The PlasmAcute technology offers an opportunity to detect early anti-HIV antibody responses. B lymphocytes (B cells) were isolated from the blood of seronegative miners in South Africa by using the PlasmAcute method. B-cell lysates and paired sera were tested for anti-HIV-1 antibodies by two different enzyme-linked immunosorbent assays; immunoreactivity was confirmed by Western blotting. All volunteers were tested for HIV type 1 (HIV-1) viral load, p24 antigen, and CD4 count. Sera from HIV-seronegative men who had positive viral loads and were positive for p24 antigen were retested for anti-HIV antibodies after immune complex dissociation. Anti-HIV antibodies were detected in lysates from 16/259 subjects without immunoreactivity in paired sera. Four subjects, one of whom had a positive viral load initially, subsequently seroconverted. Six subjects showed transient anti-HIV-1 antibodies in the lysates and tested negative for all markers at the follow-up. Five subjects without follow-up data initially had lysate-positive/serum-negative samples, and these cases were classified as inconclusive. One subject had lysate antibodies and a detectable viral load but was seronegative at follow-up. In conclusion, lysate-derived anti-HIV-1 B-cell antibodies can be detected prior to seroconversion and earlier than or contemporary with HIV-1 RNA detection.

Live attenuated measles vaccine expressing HIV-1 Gag virus like particles covered with gp160DeltaV1V2 is strongly immunogenic

Although a live attenuated HIV vaccine is not currently considered for safety reasons, a strategy inducing both T cells and neutralizing antibodies to native assembled HIV-1 particles expressed by a replicating virus might mimic the advantageous characteristics of live attenuated vaccine. To this aim, we generated a live attenuated recombinant measles vaccine expressing HIV-1 Gag virus-like particles (VLPs) covered with gp160DeltaV1V2 Env protein. The measles-HIV virus replicated efficiently in cell culture and induced the intense budding of HIV particles covered with Env. In mice sensitive to MV infection, this recombinant vaccine stimulated high levels of cellular and humoral immunity to both MV and HIV with neutralizing activity. The measles-HIV virus infected human professional antigen-presenting cells, such as dendritic cells and B cells, and induced efficient presentation of HIV-1 epitopes and subsequent activation of human HIV-1 Gag-specific T cell clones. This candidate vaccine will be next tested in non-human primates. As a pediatric vaccine, it might protect children and adolescents simultaneously from measles and HIV.

Sang Froid in a time of trouble: is a vaccine against HIV possible?

Since the announcement of the STEP trial results in the past months, we have heard many sober pronouncements on the possibility of an HIV vaccine. On the other hand, optimistic quotations have been liberally used, from Shakespeare's Henry V's "Once more unto the breach, dear friends" to Winston Churchill's definition of success as "going from one failure to another with no loss of enthusiasm". I will forgo optimistic quotations for the phrase "Sang Froid", which translates literally from the French as "cold blood"; what it really means is to avoid panic when things look bad, to step back and coolly evaluate the situation. This is not to counsel easy optimism or to fly in face of the facts, but I believe that while the situation is serious, it is not desperate.I should stipulate at the outset that I am neither an immunologist nor an expert in HIV, but someone who has spent his life in vaccine development. What I will try to do is to provide a point of view from that experience.There is no doubt that the results of STEP were disappointing: not only did the vaccine fail to control viral load, but may have adversely affected susceptibility to infection. But HIV is not the only vaccine to experience difficulties; what lessons can we glean from prior vaccine development?

Oral HIV-exposure elicits mucosal HIV-neutralizing antibodies in uninfected men who have sex with men

OBJECTIVE

To determine whether oral sexual exposure to HIV-1 (HIV) results in HIV-neutralizing activity in saliva of uninfected men who have sex with infected men?

DESIGN

Saliva samples were collected from HIV IgG seronegative men (n = 25) whose male partners were HIV infected and from low-risk healthy controls (n = 22) and analyzed for HIV-neutralizing capacity.

METHODS

The presence of neutralizing activity in saliva was tested in a peripheral blood mononuclear cell-based assay using primary HIV isolates. Self-reporting questionnaires described the individuals' sexual behaviors and routes of possible HIV exposure.

RESULTS

Of 25 exposed, uninfected individuals (EUI), 21 reported receptive unprotected oral intercourse, whereas three of the 25 reported unprotected anal receptive intercourse. Whole saliva from both EUI and low-risk healthy controls contained HIV-neutralizing activity. However, a significant difference was seen when analyzing the salivary IgA1 fraction: 13 of 25 EUI neutralized HIV, whereas none of the 22 controls had this capacity. The neutralizing capacity of the EUI males persisted during 2 years of follow-up.

CONCLUSION

Unprotected oral sex evokes a salivary IgA1-mediated HIV-neutralizing response that persists over time during continuous exposure in uninfected male partners of infected men.

Levels of innate immune factors in genital fluids: association of alpha defensins and LL-37 with genital infections and increased HIV acquisition

BACKGROUND

Several mucosal innate immune proteins exhibit HIV inhibitory activity and their analogues are potential microbicide candidates. However, their clinical associations and in-vivo role in cervicovaginal host defense against HIV acquisition are poorly defined.

METHODS

Cervicovaginal secretions (CVSs) were collected from HIV uninfected Kenyan sex workers at enrolment into an HIV prevention trial. After trial completion, CVS from participants acquiring HIV (cases) and matched controls were assessed for levels of innate immune factors and HIV neutralizing capacity, by blinded investigators. Cross-sectional and prospective associations of innate immune factors were examined.

RESULTS

CVS contained high levels of defensins (human neutrophil peptide-1-3 and human beta defensin-2-3), LL-37 and secretory leukocyte protease inhibitor. Regulated upon activation normal T-cell expressed and secreted levels were lower, and IFNalpha was undetectable. CVS from 20% of participants neutralized a clade A primary HIV isolate, and 12% neutralized both clade A and C isolates. HIV neutralization was correlated with human neutrophil peptide-1-3 (alpha-defensins) and LL-37 levels. However, alpha-defensin and LL-37 levels were increased in participants with bacterial sexually transmitted infections and were independently associated with increased HIV acquisition in multivariate analysis.

CONCLUSIONS

Despite significant HIV inhibitory activity, cervicovaginal levels of alpha-defensins and LL-37 were associated with increased HIV acquisition, perhaps due to their association with bacterial sexually transmitted infections.

Cervical HIV-specific IgA in a population of commercial sex workers correlates with repeated exposure but not resistance to HIV

We conducted a comprehensive cross-sectional analysis of total and HIV-specific cervical antibody levels in HIV-1-resistant, uninfected, and infected women in order to examine the role of HIV-specific antibody responses in the female genital tract and examine the effect on antibody levels of various epidemiologic factors in this population. Cervical lavages were collected from 272 subjects of the Pumwani commercial sex worker cohort. Total and HIV-specific genital tract IgA and IgG levels were measured using an ELISA and correlated with behavioral and demographic factors. No significant difference was seen between cervical HIV-specific IgA levels in infected, uninfected, and resistant individuals, nor were any correlations between cervical HIV-specific IgA and neutralization capacity or viral shedding seen. We did, however, note increased HIV-specific IgA in HIV-negative women with four or more clients per day, and decreased HIV-specific IgA in both long-term nonprogressors and long-term survivors. These results show that there is not a strong cohort-wide correlation between HIV-specific cervical IgA levels and resistance to infection by HIV-1 as previously believed, but there is a correlation between exposure to HIV and HIV-specific cervical IgA. Our findings do not preclude the possibility that functional differences in the cervical IgA of HEPS women may play a role in resistance, but argue that HIV-specific responses may not be a universal protective factor. They also indicate that resistance to HIV is a complex condition related to more factors than exposure. Further studies of correlates of immune protection in these individuals would be beneficial to the field.

Mucosal immunity and protection against HIV/SIV infection: strategies and challenges for vaccine design

To date, most HIV vaccine strategies have focused on parenteral immunization and systemic immunity. These approaches have not yielded the efficacious HIV vaccine urgently needed to control the AIDS pandemic. As HIV is primarily mucosally transmitted, efforts are being re-focused on mucosal vaccine strategies, in spite of complexities of immune response induction and evaluation. Here, we outline issues in mucosal vaccine design and illustrate strategies with examples from the recent literature. Development of a successful HIV vaccine will require in-depth understanding of the mucosal immune system, knowledge that ultimately will benefit vaccine design for all mucosally transmitted infectious agents.

Prevention of the sexual transmission of HIV-1: preparing for success

There are four opportunities for HIV prevention: before exposure, at the moment of exposure, immediately after exposure, and as secondary prevention focused on infected subjects. Until recently, most resources have been directed toward behavioral strategies aimed at preventing exposure entirely. Recognizing that these strategies are not enough to contain the epidemic, investigators are turning their attention to post-exposure prevention opportunities. There is increasing focus on the use of ART–either systemic or topical (microbicides)–to prevent infection at the moment of exposure. Likewise, there is growing evidence that ART treatment of infected people could serve as prevention as well. A number of ongoing clinical trials will shed some light on the potential of these approaches. Above all, prevention of HIV requires decision-makers to focus resources on strategies that are most effective. Finally, treatment of HIV and prevention of HIV must be considered and deployed together.

Mucosal immunity to HIV: a review of recent literature

PURPOSE OF REVIEW

This review summarizes recent literature in the field of mucosal immunology as it applies to HIV transmission and pathogenesis.

RECENT FINDINGS

Pertinent recent findings include elucidation of the role of mucosal antigen-presenting cells and retinoic acid in imprinting a gut-homing phenotype on antigen-specific T and B cells, and the identification of Th17 and T regulatory cells as key modulators of the balance between tolerance and inflammation in mucosal tissues.

SUMMARY

Mucosal surfaces of the body serve as the major portal of entry for HIV. These tissues also house a majority of the body's lymphocytes, including the CD4 T-cells that are the major cellular target for HIV infection. Elucidating mucosal immune responses is critical to our understanding of the host-pathogen relationship for two reasons: first, mucosal barriers are defended by a range of innate and adaptive defenses that might be exploited to develop effective vaccines or microbicides; second, adaptive immune responses in mucosal lymphoid tissues might serve to limit viral replication, decreasing the host's viral burden as well as reducing the likelihood of sexual transmission to a naïve host.