Effect of humoral immune responses on controlling viremia during primary infection of rhesus monkeys with simian immunodeficiency virus

Assessment of anti-CD20 antibody pre-treatment for augmentation of CAR-T cell therapy in SIV-infected rhesus macaques

During chronic HIV and SIV infections, the majority of viral replication occurs within lymphoid follicles. In a pilot study, infusion of SIV-specific CD4-MBL-CAR-T cells expressing the follicular homing receptor, CXCR5, led to follicular localization of the cells and a reduction in SIV viral loads in rhesus macaques. However, the CAR-T cells failed to persist. We hypothesized that temporary disruption of follicles would create space for CAR-T cell engraftment and lead to increased abundance and persistence of CAR-T cells. In this study we treated SIV-infected rhesus macaques with CAR-T cells and preconditioned one set with anti-CD20 antibody to disrupt the follicles. We evaluated CAR-T cell abundance and persistence in four groups of SIVmac239-infected and ART-suppressed animals: untreated, CAR-T cell treated, CD20 depleted, and CD20 depleted/CAR-T cell treated. In the depletion study, anti-CD20 was infused one week prior to CAR-T infusion and cessation of ART. Anti-CD20 antibody treatment led to temporary depletion of CD20+ cells in blood and partial depletion in lymph nodes. In this dose escalation study, there was no impact of CAR-T cell infusion on SIV viral load. However, in both the depleted and non-depleted animals, CAR-T cells accumulated in and around lymphoid follicles and were Ki67+. CAR-T cells increased in number in follicles from 2 to 6 days post-treatment, with a median 15.2-fold increase in follicular CAR-T cell numbers in depleted/CAR-T treated animals compared to an 8.1-fold increase in non-depleted CAR-T treated animals. The increase in CAR T cells in depleted animals was associated with a prolonged elevation of serum IL-6 levels and a rapid loss of detectable CAR-T cells. Taken together, these data suggest that CAR-T cells likely expanded to a greater extent in depleted/CAR-T cell treated animals. Further studies are needed to elucidate mechanisms mediating the rapid loss of CAR-T cells and to evaluate strategies to improve engraftment and persistence of HIV-specific CAR-T cells. The potential for an inflammatory cytokine response appears to be enhanced with anti-CD20 antibody treatment and future studies may require CRS control strategies. These studies provide important insights into cellular immunotherapy and suggest future studies for improved outcomes.

Anti-viral efficacy of a next-generation CD4-binding site bNAb in SHIV-infected animals in the absence of anti-drug antibody responses

Broadly neutralizing antibodies (bNAbs) against HIV-1 are promising immunotherapeutic agents for treatment of HIV-1 infection. bNAbs can be administered to SHIV-infected rhesus macaques to assess their anti-viral efficacy; however, their delivery into macaques often leads to rapid formation of anti-drug antibody (ADA) responses limiting such assessment. Here, we depleted B cells in five SHIV-infected rhesus macaques by pretreatment with a depleting anti-CD20 antibody prior to bNAb infusions to reduce ADA. Peripheral B cells were depleted following anti-CD20 infusions and remained depleted for at least 9 weeks after the 1^st anti-CD20 infusion. Plasma viremia dropped by more than 100-fold in viremic animals after the initial bNAb treatment. No significant humoral ADA responses were detected for as long as B cells remained depleted. Our results indicate that transient B cell depletion successfully inhibited emergence of ADA and improved the assessment of anti-viral efficacy of a bNAb in a SHIV-infected rhesus macaque model.

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Highly potent CD4bs bNAb reduces viremia up to 4 log₁₀ in SHIV-infected animals

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Sustained B cell depletion prevents development of ADA responses

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Lack of ADA enables multiple bNAb infusions over 12 weeks

Immunization by exposure to live virus (SIVmne/HIV-2287) during antiretroviral drug prophylaxis may reduce risk of subsequent viral challenge

Rationale/Study design

A major challenge in the development of HIV vaccines is finding immunogens that elicit protection against a broad range of viral strains. Immunity to a narrow range of viral strains may protect infants of HIV-infected women or partners discordant for HIV. We hypothesized that immunization to the relevant viral variants could be achieved by exposure to infectious virus during prophylaxis with antiretroviral drugs. To explore this approach in an animal model, macaques were exposed to live virus (SIV_mne or HIV-2₂₈₇) during prophylaxis with parenteral tenofovir and humoral and cellular immune responses were quantified. Subsequently, experimental animals were challenged with homologous virus to evaluate protection from infection, and if infection occurred, the course of disease was compared to control animals. Experimental animals uninfected with SIV_mne were challenged with heterologous HIV-2₂₈₇ to assess resistance to retroviral infection.

Methodology/Principal findings

Juvenile female Macaca nemestrina (N = 8) were given ten weekly intravaginal exposures with either moderately (SIV_mne) or highly (HIV-2₂₈₇) pathogenic virus during tenofovir prophylaxis. Tenofovir protected all 8 experimental animals from infection, while all untreated control animals became infected. Specific non-neutralizing antibodies were elicited in blood and vaginal secretions of experimental animals, but no ELISPOT responses were detected. Six weeks following the cessation of tenofovir, intravaginal challenge with homologous virus infected 2/4 (50%) of the SIV_mne-immunized animals and 4/4 (100%) of the HIV-2₂₈₇-immunized animals. The two SIV_mne-infected and 3 (75%) HIV-2₂₈₇-infected had attenuated disease, suggesting partial protection.

Conclusions/Significance

Repeated exposure to SIV_mne or HIV-2₂₈₇, during antiretroviral prophylaxis that blocked infection, induced binding antibodies in the blood and mucosa, but not neutralizing antibodies or specific cellular immune responses. Studies to determine whether antibodies are similarly induced in breastfeeding infants and sexual partners discordant for HIV infection and receiving pre-exposure antiretroviral prophylaxis are warranted, including whether these antibodies appear to confer partial or complete protection from infection.

CD8+ T cells in HIV control, cure and prevention

HIV infection can be effectively treated by lifelong administration of combination antiretroviral therapy, but an effective vaccine will likely be required to end the HIV epidemic. Although the majority of current vaccine strategies focus on the induction of neutralizing antibodies, there is substantial evidence that cellular immunity mediated by CD8⁺ T cells can sustain long-term disease-free and transmission-free HIV control and may be harnessed to induce both therapeutic and preventive antiviral effects. In this Review, we discuss the increasing evidence derived from individuals who spontaneously control infection without antiretroviral therapy as well as preclinical immunization studies that provide a clear rationale for renewed efforts to develop a CD8⁺ T cell-based HIV vaccine in conjunction with B cell vaccine efforts. Further, we outline the remaining challenges in translating these findings into viable HIV prevention, treatment and cure strategies.

Recently, antibody-mediated control of HIV infection has received considerable attention. Here, the authors discuss the importance of CD8⁺ T cells in HIV infection and suggest that efforts to develop vaccines that target these cells in conjunction with B cells should be renewed.

Analysis of HIV-1 envelope evolution suggests antibody-mediated selection of common epitopes among Chinese former plasma donors from a narrow-source outbreak

The HIV-1 envelope mutates rapidly to evade recognition and killing, and is a major target of humoral immune responses and vaccine development. Identification of common epitopes for vaccine development have been complicated by genetic variation on both virus and host levels. We studied HIV-1 envelope gp120 evolution in 12 Chinese former plasma donors infected with a purportedly single founder virus, with the aim of identifying common antibody epitopes under immune selection. We found five amino acid sites under significant positive selection in ≥50% of the study participants, and 22 sites consistent with antibody-mediated selection. Despite strong selection pressure, some sites housed a limited repertoire of amino acids. Structural modelling revealed that most of the variable amino acid sites were located on the exposed distal edge of the Gp120 trimer, whilst invariant sites clustered within the centre of the protein complex. Two sites, flanking the V3 hypervariable loop, represent novel antibody sites. Analysis of HIV-1 evolution in hosts infected with a narrow-source virus may provide insight and novel understanding of common epitopes under antibody-mediated selection. If verified in functional studies, such epitopes could be suitable as targets in vaccine development.

Pathogenic Correlates of Simian Immunodeficiency Virus-Associated B Cell Dysfunction

We compared and contrasted pathogenic (in pig-tailed macaques [PTMs]) and nonpathogenic (in African green monkeys [AGMs]) SIVsab infections to assess the significance of the B cell dysfunction observed in simian (SIV) and human immunodeficiency virus (HIV) infections. We report that the loss of B cells is specifically associated with the pathogenic SIV infection, while in the natural hosts, in which SIV is nonpathogenic, B cells rapidly increase in both lymph nodes (LNs) and intestine. SIV-associated B cell dysfunction associated with the pathogenic SIV infection is characterized by loss of naive B cells, loss of resting memory B cells due to their redistribution to the gut, increases of the activated B cells and circulating tissue-like memory B cells, and expansion of the B regulatory cells (Bregs). While circulating B cells are virtually restored to preinfection levels during the chronic pathogenic SIV infection, restoration is mainly due to an expansion of the "exhausted," virus-specific B cells, i.e., activated memory cells and tissue-like memory B cells. Despite of the B cell dysfunction, SIV-specific antibody (Ab) production was higher in the PTMs than in AGMs, with the caveat that rapid disease progression in PTMs was strongly associated with lack of anti-SIV Ab. Neutralization titers and the avidity and maturation of immune responses did not differ between pathogenic and nonpathogenic infections, with the exception of the conformational epitope recognition, which evolved from low to high conformations in the natural host. The patterns of humoral immune responses in the natural host are therefore more similar to those observed in HIV-infected subjects, suggesting that natural hosts may be more appropriate for modeling the immunization strategies aimed at preventing HIV disease progression. The numerous differences between the pathogenic and nonpathogenic infections with regard to dynamics of the memory B cell subsets point to their role in the pathogenesis of HIV/SIV infections and suggest that monitoring B cells may be a reliable approach for assessing disease progression.IMPORTANCE We report here that the HIV/SIV-associated B cell dysfunction (defined by loss of total and memory B cells, increased B regulatory cell [Breg] counts, and B cell activation and apoptosis) is specifically associated with pathogenic SIV infection and absent during the course of nonpathogenic SIV infection in natural nonhuman primate hosts. Alterations of the B cell population are not correlated with production of neutralizing antibodies, the levels of which are similar in the two species. Rapid progressive infections are associated with a severe impairment in SIV-specific antibody production. While we did not find major differences in avidity and maturation between the pathogenic and nonpathogenic SIV infections, we identified a major difference in conformational epitope recognition, with the nonpathogenic infection being characterized by an evolution from low to high conformations. B cell dysfunction should be considered in designing immunization strategies aimed at preventing HIV disease progression.

T-bet-expressing B cells during HIV and HCV infections

T-bet-expressing B cells, first identified as perpetuators of autoimmunity, were recently shown to be critical for murine antiviral responses. While their role in human viral infections remains unclear, B cells expressing T-bet or demonstrating a related phenotype have been described in individuals chronically infected with HIV or HCV, suggesting these cells represent a component of human antiviral responses. In this review, we discuss the induction of T-bet in B cells following both HIV and HCV infections, the factors driving T-bet⁺ B cell expansions, T-bet's relationship to atypical memory B cells, and the consequences of T-bet induction. We propose potential antiviral roles for T-bet⁺ B cells and discuss whether this population poses any utility to the HIV and HCV immune responses.

Divergent Expression of CXCR5 and CCR5 on CD4+ T Cells and the Paradoxical Accumulation of T Follicular Helper Cells during HIV Infection

Viral infection sets in motion a cascade of immune responses, including both CXCR5⁺CD4⁺ T follicular helper (Tfh) cells that regulate humoral immunity and CCR5⁺CD4⁺ T cells that mediate cell-mediated immunity. In peripheral blood mononuclear cells, the majority of memory CD4⁺ T cells appear to fall into either of these two lineages, CCR5⁻CXCR5⁺ or CCR5⁺CXCR5⁻. Very high titers of anti-HIV IgG antibodies are a hallmark of infection, strongly suggesting that there is significant HIV-specific CD4⁺ T cell help to HIV-specific B cells. We now know that characteristic increases in germinal centers (GC) in lymphoid tissue (LT) during SIV and HIV-1 infections are associated with an increase in CXCR5⁺PD-1^high Tfh, which expand to a large proportion of memory CD4⁺ T cells in LT, and are presumably specific for SIV or HIV epitopes. Macaque Tfh normally express very little CCR5, yet are infected by CCR5-using SIV, which may occur mainly through infection of a subset of PD-1^intermediateCCR5⁺Bcl-6⁺ pre-Tfh cells. In contrast, in human LT, a subset of PD-1^high Tfh appears to express low levels of CCR5, as measured by flow cytometry, and this may also contribute to the high rate of infection of Tfh. Also, we have found, by assessing fine-needle biopsies of LT, that increases in Tfh and GC B cells in HIV infection are not completely normalized by antiretroviral therapy (ART), suggesting a possible long-lasting reservoir of infected Tfh. In contrast to the increase of CXCR5⁺ Tfh, there is no accumulation of proliferating CCR5⁺ CD4 T HIV Gag-specific cells in peripheral blood that make IFN-γ. Altogether, CXCR5⁺CCR5⁻ CD4 T cells that regulate humoral immunity are allowed greater freedom to operate and expand during HIV-1 infection, but at the same time can contain HIV DNA at levels at least as high as in other CD4 subsets. We argue that early ART including a CCR5 blocker may directly reduce the infected Tfh reservoir in LT and also interrupt cycles of antibody pressure driving virus mutation and additional GC responses to resulting neoantigens.

T-bet+ B cells are induced by human viral infections and dominate the HIV gp140 response

Humoral immunity is critical for viral control, but the identity and mechanisms regulating human antiviral B cells are unclear. Here, we characterized human B cells expressing T-bet and analyzed their dynamics during viral infections. T-bet+ B cells demonstrated an activated phenotype, a distinct transcriptional profile, and were enriched for expression of the antiviral immunoglobulin isotypes IgG1 and IgG3. T-bet+ B cells expanded following yellow fever virus and vaccinia virus vaccinations and also during early acute HIV infection. Viremic HIV-infected individuals maintained a large T-bet+ B cell population during chronic infection that was associated with increased serum and cell-associated IgG1 and IgG3 expression. The HIV gp140-specific B cell response was dominated by T-bet-expressing memory B cells, and we observed a concomitant biasing of gp140-specific serum immunoglobulin to the IgG1 isotype. These findings suggest that T-bet induction promotes antiviral immunoglobulin isotype switching and development of a distinct T-bet+ B cell subset that is maintained by viremia and coordinates the HIV Env-specific humoral response.

The HIV-1 transmission bottleneck

It is well established that most new systemic infections of HIV-1 can be traced back to one or a limited number of founder viruses. Usually, these founders are more closely related to minor HIV-1 populations in the blood of the presumed donor than to more abundant lineages. This has led to the widely accepted idea that transmission selects for viral characteristics that facilitate crossing the mucosal barrier of the recipient’s genital tract, although the specific selective forces or advantages are not completely defined. However, there are other steps along the way to becoming a founder virus at which selection may occur. These steps include the transition from the donor’s general circulation to the genital tract compartment, survival within the transmission fluid, and establishment of a nascent stable local infection in the recipient’s genital tract. Finally, there is the possibility that important narrowing events may also occur during establishment of systemic infection. This is suggested by the surprising observation that the number of founder viruses detected after transmission in intravenous drug users is also limited. Although some of these steps may be heavily selective, others may result mostly in a stochastic narrowing of the available founder pool. Collectively, they shape the initial infection in each recipient.

Effects of neutralizing antibodies on escape from CD8+ T-cell responses in HIV-1 infection

Despite substantial advances in our knowledge of immune responses against HIV-1 and of its evolution within the host, it remains unclear why control of the virus eventually breaks down. Here, we present a new theoretical framework for the infection dynamics of HIV-1 that combines antibody and CD8⁺ T-cell responses, notably taking into account their different lifespans. Several apparent paradoxes in HIV pathogenesis and genetics of host susceptibility can be reconciled within this framework by assigning a crucial role to antibody responses in the control of viraemia. We argue that, although escape from or progressive loss of quality of CD8⁺ T-cell responses can accelerate disease progression, the underlying cause of the breakdown of virus control is the loss of antibody induction due to depletion of CD4⁺ T cells. Furthermore, strong antibody responses can prevent CD8⁺ T-cell escape from occurring for an extended period, even in the presence of highly efficacious CD8⁺ T-cell responses.

Faster Adaptation in Smaller Populations: Counterintuitive Evolution of HIV during Childhood Infection

Analysis of HIV-1 gene sequences sampled longitudinally from infected individuals can reveal the evolutionary dynamics that underlie associations between disease outcome and viral genetic diversity and divergence. Here we extend a statistical framework to estimate rates of viral molecular adaptation by considering sampling error when computing nucleotide site-frequencies. This is particularly beneficial when analyzing viral sequences from within-host viral infections if the number of sequences per time point is limited. To demonstrate the utility of this approach, we apply our method to a cohort of 24 patients infected with HIV-1 at birth. Our approach finds that viral adaptation arising from recurrent positive natural selection is associated with the rate of HIV-1 disease progression, in contrast to previous analyses of these data that found no significant association. Most surprisingly, we discover a strong negative correlation between viral population size and the rate of viral adaptation, the opposite of that predicted by standard molecular evolutionary theory. We argue that this observation is most likely due to the existence of a confounding third variable, namely variation in selective pressure among hosts. A conceptual non-linear model of virus adaptation that incorporates the two opposing effects of host immunity on the virus population can explain this counterintuitive result.

Since some common approaches to the study of molecular adaptation may not be optimal for answering questions regarding within-host virus evolution, we have developed an alternative approach that estimates an absolute rate of molecular adaptation from serially-sampled viral populations. Here, we extend this framework to include sampling error when estimating the rate of adaptation, which is an important addition when analyzing historical data sets obtained in the pre-HAART era, for which the number of sequences per time point is often limited. We applied this extended method to a cohort of 24 pediatric HIV-1 patients and discovered that viral adaptation is strongly associated with the rate of disease progression, which is in contrast to previous analyses of these data that did not find a significant association. Strikingly, this results in a negative relationship between the rate of viral adaptation and viral population size, which is unexpected under standard micro-evolutionary models since larger populations are predicted to fix more mutations per unit time than smaller populations. Our findings indicate that the negative correlation is unlikely to be driven by relaxation of selective constraint, but instead by significant variation in host immune responses. Consequently, this supports a previously proposed non-linear model of viral adaptation in which host immunity imposes counteracting effects on population size and selection.

Fully human anti-BAFF inhibitory monoclonal antibody tabalumab does not adversely affect T-dependent antibody responses in cynomolgus monkey (Macaca fasicularis): A summary of three pre-clinical immunotoxicology evaluations

The potential immunotoxicity of tabalumab was assessed as a component of standard pre-clinical toxicology studies in cynomolgus monkeys. To evaluate potential tabalumab-associated immunosuppression after antigen challenge, cynomolgus monkeys were administered placebo control or tabalumab in three immunotoxicological safety studies. Study 1, a 4-week pilot study, evaluated biweekly intravenous (IV) control, and 0.3, 1.0, 5.0, and 15.0 mg/kg tabalumab doses. Study 2 evaluated IV control, and 0.1, 1.0, and 30.0 mg/kg tabalumab doses biweekly for 6 weeks. Study 3 evaluated IV control and 0.1, 1.0, 30.0 mg/kg, and subcutaneous (SC) 30.0 mg/kg tabalumab biweekly for 6 months, with recovery (16 weeks) to monitor standard immunotoxicity endpoints. T-cell dependent primary and secondary antibody responses to tetanus toxoid antigen challenge (4-week and 6-week studies) or keyhole limpet hemocyanin (KLH; 6-week and 6-month studies) were evaluated as a measure of immunocompetence, together with quantitation of T- and B-cell subsets. In addition, anti-tabalumab antibody formation (6-week and 6-month studies) was assessed. The results indicated that, despite expected decreases in circulating B-cell populations, no changes in follicle histopathology or organ weights, except decreases in spleen weight (after 6-months of 30 mg/kg IV/SC treatment only), were attributed to tabalumab. Non-adverse microscopic decreases in size or number of germinal centers in spleen, mesenteric, and mandibular lymph nodes occurred, but without an effect on antibody responses to KLH or tetanus. At 16-weeks recovery, microscopic compound-related changes observed after 6 months of treatment were completely reversed (0.1 mg/kg group) and partially reversed (1.0 and 30.0 mg/kg groups), while peripheral blood B cells remained 66-72% reduced from baseline. Despite reduced germinal centres in lymphoid organs, and reductions in circulating B cells, T-cell-dependent humoral immunity was maintained following tabalumab administration in three safety studies in cynomolgus monkeys.

An investigation of the breadth of neutralizing antibody response in cats naturally infected with feline immunodeficiency virus

Neutralizing antibodies (NAbs) are believed to comprise an essential component of the protective immune response induced by vaccines against feline immunodeficiency virus (FIV) and human immunodeficiency virus (HIV) infections. However, relatively little is known about the role of NAbs in controlling FIV infection and subsequent disease progression. Here, we present studies where we examined the neutralization of HIV-luciferase pseudotypes bearing homologous and heterologous FIV envelope proteins (n = 278) by sequential plasma samples collected at 6 month intervals from naturally infected cats (n = 38) over a period of 18 months. We evaluated the breadth of the NAb response against non-recombinant homologous and heterologous clade A and clade B viral variants, as well as recombinants, and assessed the results, testing for evidence of an association between the potency of the NAb response and the duration of infection, CD4⁺ T lymphocyte numbers, health status and survival times of the infected cats. Neutralization profiles varied significantly between FIV-infected cats and strong autologous neutralization, assessed using luciferase-based in vitro assays, did not correlate with the clinical outcome. No association was observed between strong NAb responses and either improved health status or increased survival time of infected animals, implying that other protective mechanisms were likely to be involved. Similarly, no correlation was observed between the development of autologous NAbs and the duration of infection. Furthermore, cross-neutralizing antibodies were evident in only a small proportion (13 %) of cats.

Enhanced HIV-1 immunotherapy by commonly arising antibodies that target virus escape variants

Antibody-mediated immunotherapy is effective in humanized mice when combinations of broadly neutralizing antibodies (bNAbs) are used that target nonoverlapping sites on the human immunodeficiency virus type 1 (HIV-1) envelope. In contrast, single bNAbs can control simian-human immunodeficiency virus (SHIV) infection in immune-competent macaques, suggesting that the host immune response might also contribute to the control of viremia. Here, we investigate how the autologous antibody response in intact hosts can contribute to the success of immunotherapy. We find that frequently arising antibodies that normally fail to control HIV-1 infection can synergize with passively administered bNAbs by preventing the emergence of bNAb viral escape variants.

Functional characterization of two scFv-Fc antibodies from an HIV controller selected on soluble HIV-1 Env complexes: a neutralizing V3- and a trimer-specific gp41 antibody

HIV neutralizing antibodies (nAbs) represent an important tool in view of prophylactic and therapeutic applications for HIV-1 infection. Patients chronically infected by HIV-1 represent a valuable source for nAbs. HIV controllers, including long-term non-progressors (LTNP) and elite controllers (EC), represent an interesting subgroup in this regard, as here nAbs can develop over time in a rather healthy immune system and in the absence of any therapeutic selection pressure. In this study, we characterized two particular antibodies that were selected as scFv antibody fragments from a phage immune library generated from an LTNP with HIV neutralizing antibodies in his plasma. The phage library was screened on recombinant soluble gp140 envelope (Env) proteins. Sequencing the selected peptide inserts revealed two major classes of antibody sequences. Binding analysis of the corresponding scFv-Fc derivatives to various trimeric and monomeric Env constructs as well as to peptide arrays showed that one class, represented by monoclonal antibody (mAb) A2, specifically recognizes an epitope localized in the pocket binding domain of the C heptad repeat (CHR) in the ectodomain of gp41, but only in the trimeric context. Thus, this antibody represents an interesting tool for trimer identification. MAb A7, representing the second class, binds to structural elements of the third variable loop V3 and neutralizes tier 1 and tier 2 HIV-1 isolates of different subtypes with matching critical amino acids in the linear epitope sequence. In conclusion, HIV controllers are a valuable source for the selection of functionally interesting antibodies that can be selected on soluble gp140 proteins with properties from the native envelope spike.

Role of Fc-mediated antibody function in protective immunity against HIV-1

The importance of Fc-mediated effector function in protective immunity to HIV-1 (hereafter referred to simply as HIV) is becoming increasingly apparent. A large of number of studies in natural infection cohorts, spanning the last 26 years, have associated Fc-mediated effector function, particularly antibody-dependent cellular cytotoxicity, with a favourable clinical course. These studies strongly suggest a role for Fc-mediated effector function in the post-infection control of viraemia. More recently, studies in both humans and non-human primates (NHPs) also implicate Fc-mediated effector function in blocking HIV acquisition. Accordingly, this review will discuss the results supporting a role of Fc-mediated effector function in both blocking acquisition and post-infection control of viraemia. Parallel studies in NHPs and humans will be compared for common themes. Context for this discussion will be provided by summarizing the temporal emergence of key host and virological events over the course of an untreated HIV infection framing where, when and how Fc-mediated effector function might be protective. A hypothesis that Fc-mediated effector function protects primarily in the early stages of both acquisition and post-infection control of viraemia will be developed.

Effect of MHC haplotype on immune response upon experimental SHIVSF162P4cy infection of Mauritian cynomolgus macaques

Little is known about the effects of Major Histocompatibility Complex (MHC) haplotypes on immunity to primate lentiviruses involving both acquired and innate immune responses. We present statistical evidence of the influence of MHC polymorphism on antiviral immunity of Mauritian cynomolgus macaques (MCM) following simian/human immunodeficiency virus SHIV_SF162P4cy infection, involving the production of pro- and anti-inflammatory cytokines and α-defensins, which may modulate acquired immune responses. During the acute phase of infection, IL-10 correlated positively with viral load and negatively with CD4+T cell counts. Furthermore, α-defensins production was directly correlated with plasma viral RNA, particularly at peak of viral load. When the effects of the MHC were analyzed, a significant association between lower anti-Env binding and neutralizing antibody levels with class IB M4 haplotype and with class IA, IB M4 haplotype, respectively, was observed in the post-acute phase. Lower antibody responses may have resulted into a poor control of infection thus explaining the previously reported lower CD4 T cell counts in these monkeys. Class II M3 haplotype displayed significantly lower acute and post-acute IL-10 levels. In addition, significantly lower levels of α-defensins were detected in class IA M3 haplotype monkeys than in non-M3 macaques, in the post-acute phase of infection. These data indicate that the MHC could contribute to the delicate balance of pro-inflammatory mechanisms, particularly with regard to the association between IL-10 and α-defensins in lentivirus infection. Our results show that host genetic background, virological and immunological parameters should be considered for the design and interpretation of HIV-1 vaccine efficacy studies.

Immune response to HIV

PURPOSE OF REVIEW

Major advances have been made in the delineation of HIV-specific immune response and in the mechanisms of virus escape. The kinetics of the immunological and virological events occurring during primary HIV infection indicate that the establishment of the latent HIV reservoir, the major obstacle to HIV eradication likely occurs during the very early stages of primary infection, that is, the 'eclipse phase', prior to the development of the HIV-specific immune response which has limited efficacy in the control of the early events of infection. Therefore, the window of opportunity to develop effective interventions either to clear HIV during primary infection or to prevent rebound of HIV in patients successfully treated who stop antiretroviral therapy is very narrow.

RECENT FINDINGS

Genetic factors most strongly associated with nonprogressive infection are human leukocyte antigen (HLA) class I alleles and particularly HLA-B5701. CD4 and CD8 T-cell responses with polyfunctional profile are associated with nonprogressive infection. Broader neutralizing antibodies are detected 3-4 years after infection, generated only in 20% of individuals but show no efficacy in the control of HIV replication.

SUMMARY

In the present review, we shall discuss the different components of the HIV-specific immune response elicited by the infection, the kinetics of these responses during primary infection and the changes following transition to the chronic phase of infection, and the functional profile of 'effective' versus 'noneffective' HIV-specific immune responses.

Investigational treatment suspension and enhanced cell-mediated immunity at rebound followed by drug-free remission of simian AIDS

Background

HIV infection persists despite antiretroviral treatment (ART) and is reignited as soon as therapies are suspended. This vicious cycle is fueled by the persistence of viral reservoirs that are invulnerable to standard ART protocols, and thus therapeutic agents able to target these reservoirs are needed. One such agent, auranofin, has recently been shown to decrease the memory T-cell reservoir in chronically SIVmac251-infected macaques. Moreover, auranofin could synergize with a fully suppressive ART protocol and induce a drug-free post-therapy containment of viremia.

Results

We administered buthionine sulfoximine (BSO), an inhibitor of glutathione synthesis currently in clinical trials for cancer, in combination with auranofin to chronically SIVmac251-infected macaques under highly-intensified ART (H-iART). The ART/auranofin/BSO therapeutic protocol was followed, after therapy suspension, by a significant decrease of viral RNA and DNA in peripheral blood as compared to pre-therapy levels. Drug-free post-therapy control of the infection was achieved in animals with pre-therapy viral loads ranging from values comparable to average human set points to levels largely higher. This control was dependent on the presence CD8⁺ cells and associated with enhanced levels of cell-mediated immune responses.

Conclusions

The level of post-therapy viral set point reduction achieved in this study is the largest reported so far in chronically SIVmac251-infected macaques and may represent a promising strategy to improve over the current “ART for life” plight.

CD4+ T cells support production of simian immunodeficiency virus Env antibodies that enforce CD4-dependent entry and shape tropism in vivo

CD4(+) T cells rather than macrophages are the principal cells infected by human immunodeficiency virus type 1 (HIV-1) and simian immunodeficiency virus (SIV) in vivo. Macrophage tropism has been linked to the ability to enter cells through CCR5 in conjunction with limiting CD4 levels, which are much lower on macrophages than on T cells. We recently reported that rhesus macaques (RM) experimentally depleted of CD4(+) T cells before SIV infection exhibit extensive macrophage infection as well as high chronic viral loads and rapid progression to AIDS. Here we show that early-time-point and control Envs were strictly CD4 dependent but that, by day 42 postinfection, plasma virus of CD4(+) T cell-depleted RM was dominated by Envs that mediate efficient infection using RM CCR5 independently of CD4. Early-time-point and control RM Envs were resistant to neutralization by SIV-positive (SIV(+)) plasma but became sensitive if preincubated with sCD4. In contrast, CD4-independent Envs were highly sensitive to SIV(+) plasma neutralization. However, plasma from SIV-infected CD4(+) T cell-depleted animals lacked this CD4-inducible neutralizing activity and failed to neutralize any Envs regardless of sCD4 pre-exposure status. Enhanced sensitivity of CD4-independent Envs from day 42 CD4(+) T cell-depleted RM was also seen with monoclonal antibodies that target both known CD4-inducible and other Env epitopes. CD4 independence and neutralization sensitivity were both conferred by Env amino acid changes E84K and D470N that arose independently in multiple animals, with the latter introducing a potential N-linked glycosylation site within a predicted CD4-binding pocket of gp120. Thus, the absence of CD4 T cells results in failure to produce antibodies that neutralize CD4-independent Envs and CD4-pretriggered control Envs. In the absence of this constraint and with a relative paucity of CD4(+) target cells, widespread macrophage infection occurs in vivo accompanied by emergence of variants carrying structural changes that enable entry independently of CD4.

The Antibody Response against HIV-1

Neutralizing antibodies (NAbs) typically play a key role in controlling viral infections and contribute to the protective effect of many successful vaccines. In the case of HIV-1 infection, there is compelling data in experimental animal models that NAbs can prevent HIV-1 acquisition, although there is no similar data in humans and their role in controlling established infection in humans is also limited. It is clear HIV-specific NAbs drive the evolution of the HIV-1 envelope glycoprotein within an infected individual. The virus's ability to evade immune selection may be the main reason HIV-1 NAbs exert limited control during infection. The extraordinary antigenic diversity of HIV-1 also presents formidable challenges to defining NAbs that could provide broad protection against diverse circulating HIV-1 strains. Several new potent monoclonal antibodies (MAbs) have been identified, and are beginning to yield important clues into the epitopes common to diverse HIV-1 strains. In addition, antibodies can also act in concert with effector cells to kill HIV-infected cells; this could provide another mechanism for antibody-mediated control of HIV-1 replication. Understanding the impact of antibodies on HIV-1 transmission and pathogenesis is critical to helping move forward with rational HIV-1 vaccine design.

Generation of lineage-related, mucosally transmissible subtype C R5 simian-human immunodeficiency viruses capable of AIDS development, induction of neurological disease, and coreceptor switching in rhesus macaques

Most human immunodeficiency virus (HIV) transmissions are initiated with CCR5 (R5)-using viruses across mucosal surfaces, with the majority in regions where HIV type 1 (HIV-1) clade C predominates. Mucosally transmissible, highly replication competent, pathogenic R5 simian-human immunodeficiency viruses (SHIVs) encoding biologically relevant clade C envelopes are therefore needed as challenge viruses in vaccine efficacy studies with nonhuman primates. Here we describe the generation of three lineage-related subtype C SHIVs through four successive rapid transfers in rhesus macaques of SHIVC109F.PB4, a molecular clone expressing the soluble-CD4 (sCD4)-sensitive CCR5-tropic clade C envelope of a recently infected subject in Zambia. The viruses differed in their monkey passage histories and neutralization sensitivities but remained R5 tropic. SHIVC109P3 and SHIVC109P3N were recovered from a passage-3 rapid-progressor animal during chronic infection (24 weeks postinfection [wpi]) and at end-stage disease (34 wpi), respectively, and are classified as tier 1B strains, whereas SHIVC109P4 was recovered from a passage-4 normal-progressor macaque at 22 wpi and is a tier 2 virus, more difficult to neutralize. All three viruses were transmitted efficiently via intrarectal inoculation, reaching peak viral loads of 10(7) to 10(9) RNA copies/ml plasma and establishing viremia at various set points. Notably, one of seven (GC98) and two of six (CL31, FI08) SHIVC109P3- and SHIVC109P3N-infected macaques, respectively, progressed to AIDS, with neuropathologies observed in GC98 and FI08, as well as coreceptor switching in the latter. These findings support the use of these new SHIVC109F.PB4-derived viruses to study the immunopathology of HIV-1 clade C infection and to evaluate envelope-based AIDS vaccines in nonhuman primates.

Structural and immunological characterization of sulphatides: relevance of sulphate moieties in Trypanosoma cruzi glycoconjugates

Sulphoglycosphingolipids, present on the surface of diverse cells, participate in the regulation of various cellular events. However, little is known about the structure and the role of sulphoglycosphingolipids in trypanosomatids. Herein, sulphated dihexosylceramide structures - composed mainly of sphingosine as the long chain base acylated with stearic acid - have been determined for the first time in Trypanosoma cruzi epimastigotes by UV-MALDI-TOF-MS analysis. Interestingly, inhibition ELISA assays using cruzipain as antigen and polyclonal rabbit antibodies specific for cruzipain, the major cysteine proteinase of T. cruzi, or for its C-terminal domain, have demonstrated (i) that sulphate epitopes are shared between cruzipain and sulphatides of T. cruzi, (ii) that cross-reactivity maps to the C-terminal domain and (iii) the existence of other antigenic determinants in the glycolipidic structures. These features provide evidence that sulphate groups are antigenic in sulphate-containing parasite glycoconjugates. Furthermore, IgG2 antibody levels inversely correlate with disease severity in chronic Chagas disease patients, suggesting that IgG2 antibodies specific for sulphated epitopes might be associated with protective immunity and might be considered as potential surrogates of the course of chronic Chagas disease.

B-lymphocyte dysfunction in chronic HIV-1 infection does not prevent cross-clade neutralization breadth

Aberrant expression of regulatory receptors programmed death-1 (PD-1) and B- and T-lymphocyte attenuator (BTLA) is linked with dysregulation and exhaustion of T lymphocytes during chronic human immunodeficiency virus type 1 (HIV-1) infection; however, less is known about whether a similar process impacts B-lymphocyte function during HIV-1 infection. We reasoned that disruption of the peripheral B cell compartment might be associated with decreased neutralizing antibody activity. Expression of markers that indicate dysregulation (BTLA and PD-1), immune activation (CD95), and proliferation (Ki-67) was evaluated in B cells from HIV-1-infected viremic and aviremic subjects and healthy subjects, in conjunction with immunoglobulin production and CD4 T cell count. Viral load and cross-clade neutralizing activity in plasma from viremic subjects were also assessed. Dysregulation of B lymphocytes was indicated by a marked disruption of peripheral B cell subsets, increased levels of PD-1 expression, and decreased levels of BTLA expression in viremic subjects compared to aviremic subjects and healthy controls. PD-1 and BTLA were correlated in a divergent fashion with immune activation, CD4 T cell count, and the total plasma IgG level, a functional correlate of B cell dysfunction. Within viremic subjects, the total IgG level correlated directly with cross-clade neutralizing activity in plasma. The findings demonstrate that even in chronically infected subjects in which B lymphocytes display multiple indications of dysfunction, antibodies that mediate cross-clade neutralization breadth continue to circulate in plasma.

Sequential evolution and escape from neutralization of simian immunodeficiency virus SIVsmE660 clones in rhesus macaques

Simian immunodeficiency virus (SIV) infection of rhesus macaques has become an important surrogate model for evaluating HIV vaccine strategies. The extreme resistance to neutralizing antibody (NAb) of many commonly used strains, such as SIVmac251/239 and SIVsmE543-3, limits their potential relevance for evaluating the role of NAb in vaccine protection. In contrast, SIVsmE660 is an uncloned virus that appears to be more sensitive to neutralizing antibody. To evaluate the role of NAb in this model, we generated full-length neutralization-sensitive molecular clones of SIVsmE660 and evaluated two of these by intravenous inoculation of rhesus macaques. All animals became infected and maintained persistent viremia that was accompanied by a decline in memory CD4(+) T cells in blood and bronchoalveolar lavage fluid. High titers of autologous NAb developed by 4 weeks postinoculation but were not associated with control of viremia, and neutralization escape variants were detected concurrently with the generation of NAb. Neutralization escape was associated with substitutions and insertion/deletion polymorphisms in the V1 and V4 domains of envelope. Analysis of representative variants revealed that escape variants also induced NAbs within a few weeks of their appearance in plasma, in a pattern that is reminiscent of the escape of human immunodeficiency virus type 1 (HIV-1) isolates in humans. Although early variants maintained a neutralization-sensitive phenotype, viruses obtained later in infection were significantly less sensitive to neutralization than the parental viruses. These results indicate that NAbs exert selective pressure that drives the evolution of the SIV envelope and that this model will be useful for evaluating the role of NAb in vaccine-mediated protection.

Use of praziquantel as an adjuvant enhances protection and Tc-17 responses to killed H5N1 virus vaccine in mice

Background

H5N1 is a highly pathogenic influenza A virus, which can cause severe illness or even death in humans. Although the widely used killed vaccines are able to provide some protection against infection via neutralizing antibodies, cytotoxic T-lymphocyte responses that are thought to eradicate viral infections are lacking.

Methodology/Principal Findings

Aiming to promote cytotoxic responses against H5N1 infection, we extended our previous finding that praziquantel (PZQ) can act as an adjuvant to induce IL-17-producing CD8⁺ T cells (Tc17). We found that a single immunization of 57BL/6 mice with killed viral vaccine plus PZQ induced antigen-specific Tc17 cells, some of which also secreted IFN-γ. The induced Tc17 had cytolytic activities. Induction of these cells was impaired in CD8 knockout (KO) or IFN-γ KO mice, and was even lower in IL-17 KO mice. Importantly, the inoculation of killed vaccine with PZQ significantly reduced virus loads in the lung tissues and prolonged survival. Protection against H5N1 virus infection was obtained by adoptively transferring PZQ-primed wild type CD8⁺ T cells and this was more effective than transfer of activated IFN-γ KO or IL-17 KO CD8⁺ T cells.

Conclusions/Significance

Our results demonstrated that adding PZQ to killed H5N1 vaccine could promote broad Tc17-mediated cytotoxic T lymphocyte activity, resulting in improved control of highly pathogenic avian influenza virus infection.

The use of nonhuman primate models of HIV infection for the evaluation of antiviral strategies

Several nonhuman primate models are used in HIV/AIDS research. In contrast to natural host models, infection of macaques with virulent simian immunodeficiency virus (SIV) isolates results in a disease (simian AIDS) that closely resembles HIV infection and AIDS. Although there is no perfect animal model, and each of the available models has its limitations, a carefully designed study allows experimental approaches that are not feasible in humans, but that can provide better insights in disease pathogenesis and proof-of-concept of novel intervention strategies. In the early years of the HIV pandemic, nonhuman primate models played a minor role in the development of antiviral strategies. Since then, a better understanding of the disease and the development of better compounds and assays to monitor antiviral effects have increased the usefulness and relevance of these animal models in the preclinical development of HIV vaccines, microbicides, and antiretroviral drugs. Several strategies that were first discovered to have efficacy in nonhuman primate models are now increasingly used in humans. Recent trends include the use of nonhuman primate models to explore strategies that could reduce viral reservoirs and, ultimately, attempt to cure infection. Ongoing comparison of results obtained in nonhuman primate models with those observed in human studies will lead to further validation and improvement of these animal models so they can continue to advance our scientific knowledge and guide clinical trials.

Simian immunodeficiency virus infection in rhesus macaques induces selective tissue specific B cell defects in double positive CD21+CD27+ memory B cells

B cell dysfunction represents a central feature in HIV infection and pathogenesis. Our recent studies have shown that peripheral and lymphoid double positive CD21+CD27+ B cells were able to become activated and proliferate at higher rates than other B cell subpopulations. Increased proliferation of tonsillar memory B cells was identified compared to other tissues examined. Here, we demonstrate the decreased proliferation of tonsillar memory (CD21+CD27+) B cells during acute SIV infection also suggests that these cells may play an important role in SIV pathogenesis. Our findings demonstrate that SIV infection may induce selective defective responses in specific tissues, by suppressing memory B cell proliferation in tissues.

Memory B cells and CD8⁺ lymphocytes do not control seasonal influenza A virus replication after homologous re-challenge of rhesus macaques

This study sought to define the role of memory lymphocytes in the protection from homologous influenza A virus re-challenge in rhesus macaques. Depleting monoclonal antibodies (mAb) were administered to the animals prior to their second experimental inoculation with a human seasonal influenza A virus strain. Treatment with either anti-CD8α or anti-CD20 mAbs prior to re-challenge had minimal effect on influenza A virus replication. Thus, in non-human primates with pre-existing anti-influenza A antibodies, memory B cells and CD8α⁺ T cells do not contribute to the control of virus replication after re-challenge with a homologous strain of influenza A virus.

Immunodeficiency lentiviral infections in natural and non-natural hosts

The host immune system is profoundly affected during the acute phase of progressive immunodeficiency lentiviral infections. Studies of these alterations have been quite restricted in humans because of the limited availability of samples from acutely HIV-infected persons. Therefore, numerous studies have turned attention to nonhuman primate models. Specifically, SIV-infected rhesus macaques (RMs) have been informative for understanding the pathogenesis of HIV infection in humans. Indeed, advantages of the nonhuman primate model include the ability to study the very early events after infection and the ability to retrieve copious amounts of tissues. In addition, nonhuman primates allow for comparative studies between non-natural and natural hosts for SIV, in which SIV infection results in progression, or not, to AIDS, respectively. Although SIV infection of RM is the best model for HIV infection, the immunologic and/or virologic phenomena in SIV-infected RM do not always reflect those seen in HIV-infected humans. Here virologic and immunologic aspects of acute HIV infection of humans and SIV infection of Asian and African nonhuman primates are discussed and compared in relation to how these aspects relate to disease progression.

Effect of B-cell depletion on coreceptor switching in R5 simian-human immunodeficiency virus infection of rhesus macaques

We recently described a coreceptor switch in rapid progressor (RP) R5 simian-human immunodeficiency virus SF162P3N (SHIV(SF162P3N))-infected rhesus macaques that had high virus replication and undetectable or weak and transient antiviral antibody response (S. H. Ho et al., J. Virol. 81:8621-8633, 2007; S. H. Ho, N. Trunova, A. Gettie, J. Blanchard, and C. Cheng-Mayer, J. Virol. 82:5653-5656, 2008; and W. Ren et al., J. Virol. 84:340-351, 2010). The lack of antibody selective pressure, together with the observation that the emerging X4 variants were neutralization sensitive, suggested that the absence or weakening of the virus-specific humoral immune response could be an environmental factor fostering coreceptor switching in vivo. To test this possibility, we treated four macaques with 50 mg/kg of body weight of the anti-CD20 antibody rituximab every 2 to 3 weeks starting from the week prior to intravenous infection with SHIV(SF162P3N) for a total of six infusions. Rituximab treatment successfully depleted peripheral and lymphoid CD20(+) cells for up to 25 weeks according to flow cytometry and immunohistochemical staining, with partial to full recovery in two of the four treated monkeys thereafter. Three of the four treated macaques failed to mount a detectable anti-SHIV antibody response, while the response was delayed in the remaining animal. The three seronegative macaques progressed to disease, but in none of them could the presence of X4 variants be demonstrated by V3 sequence and tropism analyses. Furthermore, viruses did not evolve early in these diseased macaques to be more soluble CD4 sensitive. These results demonstrate that the absence or diminution of humoral immune responses by itself is insufficient to drive the R5-to-X4 switch and the neutralization susceptibility of the evolving viruses.

B-cell depletion reveals a role for antibodies in the control of chronic HIV-1 infection

HIV can be partially contained by host immunity and understanding the basis of this may inform vaccine design. The importance of B-cell function in long-term control is poorly understood. One method of investigating this is in vivo cellular depletion. In this study, we take advantage of a unique opportunity to investigate the role of B cells in an HIV-infected patient. The HIV-1(+) patient studied here was not taking antiretroviral drugs and was treated for pre-existing low-grade lymphoplasmacytoid lymphoma by depletion of CD20+ B cells using rituximab. We demonstrate that B-cell depletion results in a decline in autologous neutralizing antibody (NAb) responses and a 1.7 log(10) rise in HIV-1 plasma viral load (pVL). The recovery of NAbs results in a decline in pVL. The HIV-1 sequences diversify and NAb-resistant mutants are subsequently selected. These data suggest that B-cell function can contribute to the long-term control of pVL, and that NAbs may be more important in controlling chronic HIV-1 infection than previously suspected.

A tonsillar PolyICLC/AT-2 SIV therapeutic vaccine maintains low viremia following antiretroviral therapy cessation

BACKGROUND

HIV-infected individuals rely on antiretroviral therapy (ART) to control viral replication. Despite abundant demonstrable benefits, the multiple limitations of ART point to the potential advantages of therapeutic vaccination approaches that could provide sustained host control of viral replication after discontinuation of ART. We provide evidence from a non-human primate model that a therapeutic vaccine applied to the tonsils can maintain low viral loads after cessation of ART.

METHODOLOGY/PRINCIPAL FINDINGS

Animals received 40 weeks of ART initiated 9 weeks after rectal SIVmac239 infection. During ART, animals were vaccinated (or not) with AT-2 inactivated SIVmac239 using CpG-C ISS-ODN (C274) or polyICLC as adjuvants. PolyICLC/AT-2 SIV vaccinated animals maintained viral loads <3×10(3) copies/ml for up to 16 weeks post-ART, whereas the C274/AT-2 SIV vaccinated and non-vaccinated animals' viremia ranged between 1×10(4)-4×10(5) copies/ml (p<0.03). Neutralizing Ab activity in plasma was increased by polyICLC/AT-2 tonsillar vaccination under ART, compared to controls (p<0.03). Subsequent vaccination of all animals with polyICLC/AT-2 SIV in the absence of ART did not alter viral loads. Other immune parameters measured in blood and tissues were comparable between groups.

CONCLUSIONS/SIGNIFICANCE

These results provide support for the potential benefit of mucosally delivered vaccines in therapeutic immunization strategies for control of AIDS virus infection.

Innovative approaches to develop prophylactic and therapeutic vaccines against HIV/AIDS

The acquired immunodeficiency syndrome (AIDS) emerged in the human population in the summer of 1981. According to the latest United Nations estimates, worldwide over 33 million people are infected with human immunodeficiency virus (HIV) and the prevalence rates continue to rise globally. To control the alarming spread of HIV, an urgent need exists for developing a safe and effective vaccine that prevents individuals from becoming infected or progressing to disease. To be effective, an HIV/AIDS vaccine should induce broad and long-lasting humoral and cellular immune responses, at both mucosal and systemic level. However, the nature of protective immune responses remains largely elusive and this represents one of the major roadblocks preventing the development of an effective vaccine. Here we summarize our present understanding of the factors responsible for resistance to infection or control of progression to disease in human and monkey that may be relevant to vaccine development and briefly review recent approaches which are currently being tested in clinical trials. Finally, the rationale and the current status of novel strategies based on nonstructural HIV-1 proteins, such as Tat, Nef and Rev, used alone or in combination with modified structural HIV-1 Env proteins are discussed.

Neutralizing antibodies in SIV control: co-impact with T cells

Human immunodeficiency virus type 1 (HIV-1) and pathogenic simian immunodeficiency virus (SIV)-infected naïve hosts experience a characteristic absence of early and potent virus-specific neutralizing antibody (NAb) responses preceding establishment of persistent infection. Yet conversely, we have recently shown that NAbs passively immunized in rhesus macaques at early post-SIV challenge are capable of playing a critical role in non-sterile viremia control with implications of antibody-enhanced antigen presentation. In a current follow-up study we have further reported that NAbs mediate rapid elicitation of polyfunctional virus-specific CD4+ T-cells in vivo. The NAb-immunized macaques mounting these responses exhibited sustained viremia control for over 1 year, accompanied with robust anti-SIV cellular immunity. Perspectives obtained from the results are discussed.

The role of antibodies in HIV vaccines

Licensed vaccines against viral diseases generate antibodies that neutralize the infecting virus and protect against infection or disease. Similarly, an effective vaccine against HIV-1 will likely need to induce antibodies that prevent initial infection of host cells or that limit early events of viral dissemination. Such antibodies must target the surface envelope glycoproteins of HIV-1, which are highly variable in sequence and structure. The first subunit vaccines to enter clinical trails were safe and immunogenic but unable to elicit antibodies that neutralized most circulating strains of HIV-1. However, potent virus neutralizing antibodies (NAbs) can develop during the course of HIV-1 infection, and this is the type of antibody response that researchers seek to generate with a vaccine. Thus, current vaccine design efforts have focused on a more detailed understanding of these broadly neutralizing antibodies and their epitopes to inform the design of improved vaccines.

[Theory for prophylactic AIDS vaccine development]

In the natural courses of human immunodeficiency virus (HIV) infections, host immune responses fail to contain the virus and allow persistent HIV replication, leading to AIDS progression. For development of an effective vaccine against those viral infections which do not show spontaneous remission, it is important to elucidate which immune responses to be induced for viral control. This review focuses on antibodies and cytotoxic T lymphocytes, key adaptive immune effectors, and discusses possible mechanisms for HIV control by vaccine-induced antibody, memory B lymphocyte, and (effector and central) memory T lymphocyte responses. Finally, we mention the ongoing international project for a clinical trial of our Sendai virus vector-based AIDS vaccine.

Immunization responses in rheumatoid arthritis patients treated with rituximab: results from a controlled clinical trial

OBJECTIVE

To examine immunization responses in patients with rheumatoid arthritis (RA) treated with rituximab and to investigate the effects of rituximab-induced CD20+ B cell depletion on immune responses to tetanus toxoid (T cell-dependent antigen), pneumococcal polysaccharide (T cell-independent antigen), and keyhole limpet hemocyanin (KLH) (neoantigen) and on delayed-type hypersensitivity (DTH).

METHODS

In a controlled trial, we enrolled 103 patients with active RA receiving a stable dose of methotrexate (MTX). Tetanus toxoid, pneumococcal polysaccharide, and KLH vaccines as well as a Candida albicans skin test were administered to 1 group of patients receiving rituximab plus MTX (called rituximab-treated patients) for 36 weeks and to 1 group of patients receiving MTX alone for 12 weeks. The primary end point was the proportion of patients with a >or=4-fold rise in antitetanus IgG levels. Antitetanus, antipneumococcal, and anti-KLH serum IgG levels were measured prior to and 4 weeks following vaccine administration. The DTH response to C albicans was measured 2-3 days following placement.

RESULTS

Responses to tetanus toxoid vaccine (>or=4-fold rise) were similar in both groups (39.1% of rituximab-treated patients and 42.3% of patients treated with MTX alone). The ability to maintain a positive DTH response to the C albicans skin test was comparable in both groups (77.4% of rituximab-treated patients and 70% of patients treated with MTX alone), showing no effect of rituximab treatment. Rituximab-treated patients had decreased responses to pneumococcal polysaccharide vaccine (57% of patients had a 2-fold rise in titer in response to >or=1 serotype, compared with 82% of patients treated with MTX alone) and to KLH vaccine (47% of patients had detectable anti-KLH IgG, compared with 93% of patients treated with MTX alone).

CONCLUSION

Recall responses to the T cell-dependent protein antigen tetanus toxoid as well as DTH responses were preserved in rituximab-treated RA patients 24 weeks after treatment. Responses to neoantigen (KLH) and T cell-independent responses to pneumococcal vaccine were decreased, but many patients were able to mount responses. These data suggest that polysaccharide and primary immunizations should be administered prior to rituximab infusions to maximize responses.

Suppression of adaptive immune responses during primary SIV infection of sabaeus African green monkeys delays partial containment of viremia but does not induce disease

One of the most puzzling observations in HIV research is the lack of pathogenicity in most nonhuman primate species that are natural hosts of simian immunodeficiency virus (SIV) infection. Despite this, natural hosts experience a level of viremia similar to humans infected with HIV or macaques infected with SIV. To determine the role of adaptive immune responses in viral containment and lack of disease, we delayed the generation of cellular and humoral immune responses by administering anti-CD8- and anti-CD20 lymphocyte-depleting antibodies to sabaeus African green monkeys (Chlorocebus sabaeus) before challenge with SIV(sab9315BR). In vivo lymphocyte depletion during primary infection resulted in a brief elevation of viremia but not in disease. Based on the magnitude and timing of SIV-specific CD8(+) T-cell responses in the lymphocyte-depleted animals, CD8(+) T-cell responses appear to contribute to viral containment in natural hosts. We found no evidence for a contribution of humoral immune responses in viral containment. These studies indicate that natural hosts have developed mechanisms in addition to classic adaptive immune responses to cope with this lentiviral infection. Thus, adaptive immune responses in natural hosts appear to be less critical for viral containment than in HIV infection.

In vivo CD8+ T-cell suppression of siv viremia is not mediated by CTL clearance of productively infected cells

The CD8+ T-cell is a key mediator of antiviral immunity, potentially contributing to control of pathogenic lentiviral infection through both innate and adaptive mechanisms. We studied viral dynamics during antiretroviral treatment of simian immunodeficiency virus (SIV) infected rhesus macaques following CD8+ T-cell depletion to test the importance of adaptive cytotoxic effects in clearance of cells productively infected with SIV. As previously described, plasma viral load (VL) increased following CD8+ T-cell depletion and was proportional to the magnitude of CD8+ T-cell depletion in the GALT, confirming a direct relationship between CD8+ T-cell loss and viral replication. Surprisingly, first phase plasma virus decay following administration of antiretroviral drugs was not slower in CD8+ T-cell depleted animals compared with controls indicating that the short lifespan of the average productively infected cell is not a reflection of cytotoxic T-lymphocyte (CTL) killing. Our findings support a dominant role for non-cytotoxic effects of CD8+ T-cells on control of pathogenic lentiviral infection and suggest that cytotoxic effects, if present, are limited to early, pre-productive stages of the viral life cycle. These observations have important implications for future strategies to augment immune control of HIV.

The recognition and elimination of infected host cells by CD8+ T-lymphocytes is held to be a key component of the immune response against viral pathogens. However, this basic tenet of viral immunology may not hold true for HIV and the related SIV. In the current work, we eliminated CD8+ T-cells by treating simian immunodeficiency virus (SIV) infected macaques with a CD8-depleting monoclonal antibody then treated the animals with antiretroviral drugs and measured virus levels. Viral levels fell just as fast for the animals with or without CD8+ T-cells, implying that survival of infected cells producing SIV was not impacted by the presence or absence of CD8+ T-cells. Virus obtained after CD8+ T-cell depletion showed changes in the types of sequences in a viral protein (Nef) that is expressed early after infection of a cell but not in a viral protein (Gag) that is expressed later. These findings suggest CD8+ T-cells have a limited ability to kill cells already expressing SIV but instead may be restricted to non-killing mechanisms or to targeting cells during earlier stages of infection before virus production begins. Understanding and overcoming the factors that prevent CD8+ T-cells from effectively eliminating infected cells producing virus could advance HIV vaccine efforts.

Influence of disulfide-stabilized structure on the specificity of helper T-cell and antibody responses to HIV envelope glycoprotein gp120

CD4(+) helper T cells specific for human immunodeficiency virus type 1 (HIV-1) are associated with control of viremia. Nevertheless, vaccines have had limited effectiveness thus far, in part because sequence variability and other structural features of the HIV envelope glycoprotein deflect the immune response. Previous studies indicated that CD4(+) T-cell epitope dominance is controlled by antigen three-dimensional structure through its influence on antigen processing and presentation. In this work, three disulfide bonds in the outer domain of gp120 were individually deleted in order to destabilize the local three-dimensional structure and enhance the presentation of nearby weakly immunogenic epitopes. However, upon immunization of groups of BALB/c mice, the CD4(+) T-cell response was broadly reduced for all three variants, and distinct epitope profiles emerged. For one variant, antibody titers were sharply increased, and the antibody exhibited significant CD4-blocking activity.

Alcohol's role in HIV transmission and disease progression

Alcohol use has negative effects on HIV disease progression through several mechanisms, including transmission, viral replication, host immunity, and treatment efficacy. Research with animal models has explored the effect of alcohol intake on several aspects of simian immunodeficiency virus (SIV) disease progression. Data suggest that the increased SIV levels observed in alcohol-consuming animals may represent an increase in virus production as opposed to a decrease in host defense. Results also suggest that changes in nutritional balance and metabolism, as a possible consequence of a proinflammatory state, together with increased virus production in animals consuming alcohol, accelerate SIV and possibly HIV disease progression. Further studies using the animal model are necessary.

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.

Breadth of neutralizing antibody response to human immunodeficiency virus type 1 is affected by factors early in infection but does not influence disease progression

The determinants of a broad neutralizing antibody (NAb) response and its effect on human immunodeficiency virus type 1 (HIV-1) disease progression are not well defined, partly because most prior studies of a broad NAb response were cross-sectional. We examined correlates of NAb response breadth among 70 HIV-infected, antiretroviral-naïve Kenyan women from a longitudinal seroincident cohort. NAb response breadth was measured 5 years after infection against five subtype A viruses and one subtype B virus. Greater NAb response breadth was associated with a higher viral load set point and greater HIV-1 env diversity early in infection. However, greater NAb response breadth was not associated with a delayed time to a CD4(+) T-cell count of <200, antiretroviral therapy, or death. Thus, a broad NAb response results from a high level of antigenic stimulation early in infection, which likely accounts for prior observations that greater NAb response breadth is associated with a higher viral load later in infection.