Boosting of HIV-1 neutralizing antibody responses by a distally related retroviral envelope protein.

Our knowledge of the binding sites for neutralizing Abs (NAb) that recognize a broad range of HIV-1 strains (bNAb) has substantially increased in recent years. However, gaps remain in our understanding of how to focus B cell responses to vulnerable conserved sites within the HIV-1 envelope glycoprotein (Env). In this article, we report an immunization strategy composed of a trivalent HIV-1 (clade B envs) DNA prime, followed by a SIVmac239 gp140 Env protein boost that aimed to focus the immune response to structurally conserved parts of the HIV-1 and simian immunodeficiency virus (SIV) Envs. Heterologous NAb titers, primarily to tier 1 HIV-1 isolates, elicited during the trivalent HIV-1 env prime, were significantly increased by the SIVmac239 gp140 protein boost in rabbits. Epitope mapping of Ab-binding reactivity revealed preferential recognition of the C1, C2, V2, V3, and V5 regions. These results provide a proof of concept that a distally related retroviral SIV Env protein boost can increase pre-existing NAb responses against HIV-1.

Evolution of human immunodeficiency virus type 1 in a patient with cross-reactive neutralizing activity in serum.

Analysis of longitudinally obtained HIV-1 env sequences from an individual with reported cross-reactive neutralizing activity revealed that the majority of viral variants obtained from serum between 4 and 7 years after seroconversion were unable to persist in peripheral blood. Here we show that these viral variants were more sensitive to autologous serum neutralization, had shorter envelopes with fewer potential N-linked glycosylation sites, and showed lower replication kinetics than successfully evolving HIV-1 variants. These data reflect the host selection pressures on phenotypic characteristics of HIV-1 and illustrate in detail the dynamic interaction between HIV-1 and its host's humoral immune responses.

Generation of neutralizing antibodies and divergence of SIVmac239 in cynomolgus macaques following short-term early antiretroviral therapy.

Neutralizing antibodies (NAb) able to react to heterologous viruses are generated during natural HIV-1 infection in some individuals. Further knowledge is required in order to understand the factors contributing to induction of cross-reactive NAb responses. Here a well-established model of experimental pathogenic infection in cynomolgus macaques, which reproduces long-lasting HIV-1 infection, was used to study the NAb response as well as the viral evolution of the highly neutralization-resistant SIVmac239. Twelve animals were infected intravenously with SIVmac239. Antiretroviral therapy (ART) was initiated ten days post-inoculation and administered daily for four months. Viral load, CD4(+) T-cell counts, total IgG levels, and breadth as well as strength of NAb in plasma were compared simultaneously over 14 months. In addition, envs from plasma samples were sequenced at three time points in all animals in order to assess viral evolution. We report here that seven of the 12 animals controlled viremia to below 10(4) copies/ml of plasma after discontinuation of ART and that this control was associated with a low level of evolutionary divergence. Macaques that controlled viral load developed broader NAb responses early on. Furthermore, escape mutations, such as V67M and R751G, were identified in virus sequenced from all animals with uncontrolled viremia. Bayesian estimation of ancestral population genetic diversity (PGD) showed an increase in this value in non-controlling or transient-controlling animals during the first 5.5 months of infection, in contrast to virus-controlling animals. Similarly, non- or transient controllers displayed more positively-selected amino-acid substitutions. An early increase in PGD, resulting in the generation of positively-selected amino-acid substitutions, greater divergence and relative high viral load after ART withdrawal, may have contributed to the generation of potent NAb in several animals after SIVmac239 infection. However, early broad NAb responses correlated with relatively preserved CD4(+) T-cell numbers, low viral load and limited viral divergence.

Mitochondrial DNA transmission and transcription after somatic cell fusion to one or more cytoplasts.

Following fertilization, mitochondrial DNA is inherited from the oocyte and transmitted homoplasmically. However, following nuclear transfer, mitochondrial DNA can be transmitted from both the donor cell and recipient oocyte, resulting in a state of heteroplasmy. To determine whether the genetic diversity between donor cell and recipient cytoplast mitochondrial DNA influences development, we generated bovine embryos by fusing a donor cell to one or more enucleated cytoplasts. Analysis of mitochondrial DNA from embryos, fetal tissues, and blood samples from offspring revealed that early preimplantation embryos from two or three cytoplasts had significantly more mitochondrial DNA variants than fetal tissues. Phylogenic analysis of embryos generated using single cytoplasts divided the mitochondrial DNA sequence variants into three separate groups with various amounts of genetic divergence from the donor cell line. In heteroplasmic tissue and blood samples, the predominant mitochondrial DNA population was significantly more divergent from the donor cell than the less frequent allele. Furthermore, analysis of the mitochondrially encoded cytochrome B gene showed that two heteroplasmic alleles encoded for different amino acids, and the ratios of mitochondrial DNA/mRNA for each allele differed significantly between tissues. The degree of evolutionary distance between the donor cell and the cytoplast and the variability in heteroplasmy between tissues may have an impact on more divergent intergeneric nuclear transfer and the use of this approach for the generation of embryonic stem cells.

Contrasting effects of in vitro fertilization and nuclear transfer on the expression of mtDNA replication factors.

Mitochondrial DNA (mtDNA) is normally only inherited through the oocyte. However, nuclear transfer (NT), the fusion of a donor cell with an enucleated oocyte, can transmit both donor cell and recipient oocyte mtDNA. mtDNA replication is under the control of nuclear-encoded replication factors, such as polymerase gamma (POLG) and mitochondrial transcription factor A (TFAM). These are first expressed during late preimplantation embryo development. To account for the persistence of donor cell mtDNA, even when introduced at residual levels (mtDNA(R)), we hypothesized that POLG and TFAM would be upregulated in intra- and interspecific (ovine-ovine) and intergeneric (caprine-ovine) NT embryos when compared to in vitro fertilized (IVF) embryos. For the intra- and interspecific crosses, PolGA (catalytic subunit), PolGB (accessory subunit), and TFAM mRNA were expressed at the 2-cell stage in both nondepleted (mtDNA(+)) and mtDNA(R) embryos with protein being expressed up to the 16-cell stage for POLGA and TFAM. However, at the 16-cell stage, there was significantly more PolGA expression in the mtDNA(R) embryos compared to their mtDNA(+) counterparts. Expression for all three genes first matched IVF embryos at the blastocyst stage. In the intergeneric model, POLG was upregulated during preimplantation development. Although these embryos did not persist further than the 16+-cell stage, significantly more mtDNA(R) embryos reached this stage. However, the vast majority of these embryos were homoplasmic for recipient oocyte mtDNA. The upreglation in mtDNA replication factors was most likely due to the donor cells still expressing these factors prior to NT.

Aberrant nucleo-cytoplasmic cross-talk results in donor cell mtDNA persistence in cloned embryos.

Mitochondrial DNA is an extranuclear genome normally maternally inherited through the oocyte. However, the use of nuclear transfer can result in both donor cell and recipient oocyte mitochondrial DNA persisting through to blastocyst and being transmitted to the offspring. The degree of donor mitochondrial DNA transmission appears to be random and currently no evidence exists to explain this phenomenon. To determine whether this is a dilution factor or directly related to the transcriptional status of the donor cell in respect of mitochondrial DNA transcription factors, we have generated sheep nuclear transfer embryos using donor cells: (1) possessing their full mitochondrial DNA complement, (2) those partially depleted, and (3) those depleted but containing residual levels. For each donor type, donor mitochondrial DNA persisted in some blastocysts. It is evident from the donor cells used that nuclear-encoded mitochondrial DNA transcription and replication factors persist even after mitochondrial DNA depletion, as do transcripts for some of the mitochondrial-encoded genes. These cells are therefore still programmed to drive mitochondrial DNA replication and transcription. In nuclear transfer-derived embryos, we have observed the persistence of these nuclear-encoded mitochondrial DNA transcription and replication factors but not in those embryos generated through in vitro fertilization. Consequently, nucleo-mitochondrial interaction following nuclear transfer is out of sequence as the onset of mitochondrial replication is a postimplantation event.

The analysis of mitochondria and mitochondrial DNA in human embryonic stem cells.

As human embryonic stem cells (hESCs) undergo differentiation, they express genes characteristic of the lineage for which they are destined. However, fully differentiated individual cell types can be characterized by the number of mitochondria they possess and the copies of the mitochondrial genome per mitochondrion. These characteristics are indicative of a specific cell's requirement for adenosine triphosphate (ATP) and therefore cellular viability and function. Consequently, failure for an ESC to possess the full complement of mitochondria and mitochondrial DNA (mtDNA) could limit its final commitment to a particular fate. We describe a series of protocols that analyze the process of cellular mitochondrial and mtDNA differentiation during hESC differentiation. In addition, mtDNA transcription and replication are key events in cellular differentiation that require interaction between the nucleus and the mitochondrion. To this extent, we describe a series of protocols that analyze the initiation of these key events as hESCs progress from their undifferentiated state to the fully committed cell. Last, we describe real-time polymerase chain reaction protocols that allow both the identification of mtDNA copy number and determine whether mtDNA copy is uniform (homoplasmy) in its transmission or heterogeneous (heteroplasmy).

Humoral responses to HIVconsv induced by heterologous vaccine modalities in rhesus macaques.

Vaccines delivering T cell immunogen HIVconsv vectored by plasmid DNA, non-replicating simian adenovirus and non-replicating modified vaccinia virus Ankara (MVA) are under clinical evaluation in phase I/IIa trials in UK, Europe, and Africa. While these vaccines aim to induce effector T cell responses specific for HIV-1, we here characterized the humoral responses induced by HIVconsv administration to macaques using six different vaccine modalities: plasmid DNA, human adenovirus serotype 5, simian adenovirus serotype 63, MVA, Semliki Forest virus replicons, and adjuvanted overlapping synthetic long peptides (SLP). We found that only the SLP formulation, but none of the genetic vaccine platforms induced antibodies recognizing linear HIVconsv epitopes, median 32/46 SLP.HIVconsv peptides. These antibodies bound to 15-mer and SLP peptides, recombinant gp120 and trimeric gp140 of HIV-1 Bal, YU2, JRFL, and UG037, but failed to react with HIV-1 Bal and IIIB virions and HIV-1 Bal- and IIIB-infected human cells, and consequently failed to induce neutralizing antibodies. The HIVconsv immunogen contains conserved regions derived from Gag, Pol, Vif, and Env proteins of HIV-1, and antibodies induced by the SLP.HIVconsv vaccination resulted in positive signals in routine HIV-1 tests. Thus, only HIVconsv delivered by SLP resulted in seroconversion, an observation that provides important guidance for recruiting volunteers into future clinical trials. Furthermore, our data confirms that vaccine delivery by SLP induces humoral as well as cellular immune responses and could be considered for inclusion in future vaccine regimens where this is required.

Cerebral aneurysm and aneurysmal subarachnoid haemorrhage.

A cerebral aneurysm is a weak or thin spot on a blood vessel in the brain that swells and fills with blood. Rupture of a cerebral aneurysm, known as aneurysmal subarachnoid haemorrhage, is a medical emergency and is associated with increased mortality. This article explores the anatomy and physiology of the brain and blood vessels. Current research and guidelines are used to highlight risk factors for cerebral aneurysms and their rupture and to discuss best practice for treating both. The article provides information on the management and complications of the condition, alongside nursing considerations, long-term care, discharge and rehabilitation.

Low level of HIV-1 evolution after transmission from mother to child.

Mother-to-child HIV-1 transmission pairs represent a good opportunity to study the dynamics of CTL escape and reversion after transmission in the light of shared and non-shared HLA-alleles. Mothers share half of their HLA alleles with their children, while the other half is inherited from the father and is generally discordant between mother and child. This implies that HIV-1 transmitted from mother to child enters a host environment to which it has already partially adapted. Here, we studied viral evolution and the dynamics of CTL escape mutations and reversion of these mutations after transmission in the context of shared and non-shared HLA alleles in viral variants obtained from five mother-to-child transmission pairs. Only limited HIV-1 evolution was observed in the children after mother-to-child transmission. Viral evolution was mainly driven by forward mutations located inside CTL epitopes restricted by HLA alleles inherited from the father, which may be indicative of CTL pressure.

Comparison of neutralizing antibody responses elicited from highly diverse polyvalent heterotrimeric HIV-1 gp140 cocktail immunogens versus a monovalent counterpart in rhesus macaques.

Eliciting neutralizing antibodies capable of inactivating a broad spectrum of HIV-1 strains is a major goal of HIV-1 vaccine design. The challenge is that envelopes (Envs) of circulating viruses are almost certainly different from any Env used in a vaccine. A novel immunogen composed of a highly diverse set of gp140 Envs including subtypes A, B, C, D and F was developed to stimulate a more cross-neutralizing antibody response. Env heterotrimers composed of up to 54 different gp140s were produced with the aim of focusing the response to the conserved regions of Env while reducing the dominance of any individual hypervariable region. Heterotrimeric gp140 Envs of inter- and intra-subtype combinations were shown to bind CD4 and a panel of neutralizing monoclonal antibodies with similar affinity to monovalent UG37 gp140. Macaques immunized with six groups of heterotrimer mixtures showed slightly more potent neutralizing antibody responses in TZM-BL tier 1 and A3R5 tier 2 pseudovirus assays than macaques immunized with monovalent Env gp140, and exhibited a marginally greater focus on the CD4-binding site. Carbopol enhanced neutralization when used as an adjuvant instead of RIBI in combination with UG37 gp140. These data indicate that cross-subtype heterotrimeric gp140 Envs may elicit some improvement of the neutralizing antibody response in macaques compared to monovalent gp140 Env.

Selected HIV-1 Env trimeric formulations act as potent immunogens in a rabbit vaccination model.

BACKGROUND: Ten to 30% of HIV-1 infected subjects develop broadly neutralizing antibodies (bNAbs) during chronic infection. We hypothesized that immunizing rabbits with viral envelope glycoproteins (Envs) from these patients may induce bNAbs, when formulated as a trimeric protein and in the presence of an adjuvant. METHODS: Based on in vitro neutralizing activity in serum, patients with bNAbs were selected for cloning of their HIV-1 Env. Seven stable soluble trimeric gp140 proteins were generated from sequences derived from four adults and two children infected with either clade A or B HIV-1. From one of the clade A Envs both the monomeric and trimeric Env were produced for comparison. Rabbits were immunized with soluble gp120 or trimeric gp140 proteins in combination with the adjuvant dimethyl dioctadecyl ammonium/trehalose dibehenate (CAF01). Env binding in rabbit immune serum was determined using ELISAs based on gp120-IIIB protein. Neutralizing activity of IgG purified from rabbit immune sera was measured with the pseudovirus-TZMbl assay and a PBMC-based neutralization assay for selected experiments. RESULTS: It was initially established that gp140 trimers induce better antibody responses over gp120 monomers and that the adjuvant CAF01 was necessary for such strong responses. Gp140 trimers, based on HIV-1 variants from patients with bNAbs, were able to elicit both gp120IIIB specific IgG and NAbs to Tier 1 viruses of different subtypes. Potency of NAbs closely correlated with titers, and an gp120-binding IgG titer above a threshold of 100,000 was predictive of neutralization capability. Finally, peptide inhibition experiments showed that a large fraction of the neutralizing IgG was directed against the gp120 V3 region. CONCLUSIONS: Our results indicate that the strategy of reverse immunology based on selected Env sequences is promising when immunogens are delivered as stabilized trimers in CAF01 adjuvant and that the rabbit is a valuable model for HIV vaccine studies.

Optimization of HIV-1 Envelope DNA Vaccine Candidates within Three Different Animal Models, Guinea Pigs, Rabbits and Cynomolgus Macaques.

HIV-1 DNA vaccines have many advantageous features. Evaluation of HIV-1 vaccine candidates often starts in small animal models before macaque and human trials. Here, we selected and optimized DNA vaccine candidates through systematic testing in rabbits for the induction of broadly neutralizing antibodies (bNAb). We compared three different animal models: guinea pigs, rabbits and cynomolgus macaques. Envelope genes from the prototype isolate HIV-1 Bx08 and two elite neutralizers were included. Codon-optimized genes, encoded secreted gp140 or membrane bound gp150, were modified for expression of stabilized soluble trimer gene products, and delivered individually or mixed. Specific IgG after repeated i.d. inoculations with electroporation confirmed in vivo expression and immunogenicity. Evaluations of rabbits and guinea pigs displayed similar results. The superior DNA construct in rabbits was a trivalent mix of non-modified codon-optimized gp140 envelope genes. Despite NAb responses with some potency and breadth in guinea pigs and rabbits, the DNA vaccinated macaques displayed less bNAb activity. It was concluded that a trivalent mix of non-modified gp140 genes from rationally selected clinical isolates was, in this study, the best option to induce high and broad NAb in the rabbit model, but this optimization does not directly translate into similar responses in cynomolgus macaques.

Generation of mtDNA homoplasmic cloned lambs.

Generally in mammals, individual animals contain only maternally inherited mitochondrial DNA (mtDNA), as paternal (sperm)-derived mitochondria are usually eliminated during early development. Somatic cell nuclear transfer (SCNT) bypasses the normal routes of mtDNA inheritance and introduces not only a different nuclear genome into the recipient cytoplast (in general an enucleated oocyte) but also somatic mitochondria. Differences in mtDNA genotype between recipient oocytes and potential mtDNA heteroplasmy due to persistence and replication of somatic mtDNA means that offspring generated by SCNT are not true clones. However, more importantly, the consequences of the presence of somatic mtDNA, mtDNA heteroplasmy, or possible incompatibility between nuclear and mtDNA genotypes on subsequent development and function of the embryo, fetus and offspring are unknown. Following sexual reproduction, mitochondrial function requires the biparental control of maternally inherited mtDNA, whereas following SCNT incompatibility between the recipient cell mitochondrial and transplanted nuclear genomes, or mtDNA heteroplasmy, may result in energy imbalance and initiate the onset of mtDNA-type disease, or disruption of normal developmental events. To remove the potentially adverse effects of somatic mtDNA following SCNT we have previously produced embryos using donor cells depleted to residual levels of mtDNA (mtDNA). We now report that these cells support development to term and produced live lambs in which no donor somatic mtDNA was detected, the lambs being homoplasmic for recipient oocyte DNA.

Genetic composition of replication competent clonal HIV-1 variants isolated from peripheral blood mononuclear cells (PBMC), HIV-1 proviral DNA from PBMC and HIV-1 RNA in serum in the course of HIV-1 infection.

The HIV-1 quasispecies in peripheral blood mononuclear cells (PBMC) is considered to be a mix of actively replicating, latent, and archived viruses and may be genetically distinct from HIV-1 variants in plasma that are considered to be recently produced. Here we analyzed the genetic relationship between gp160 env sequences from replication competent clonal HIV-1 variants that were isolated from PBMC and from contemporaneous HIV-1 RNA in serum and HIV-1 proviral DNA in PBMC of four longitudinally studied therapy naïve HIV-1 infected individuals. Replication competent clonal HIV-1 variants, HIV-1 RNA from serum, and HIV-1 proviral DNA from PBMC formed a single virus population at most time points analyzed. However, an under-representation in serum of HIV-1 sequences with predicted CXCR4 usage was sometimes observed implying that the analysis of viral sequences from different sources may provide a more complete assessment of the viral quasispecies in peripheral blood in vivo.

Sperm mitochondria and fertilisation.

Human mitochondrial DNA (mtDNA) is an extranuclear genome that encodes 13 of the polypeptides associated with the process of oxidative phosphorylation (OXPHOS). The role and importance of OXPHOS in sperm motility and function has been debated over the last few years. Here, we argue that sperm OXPHOS is important to sperm function in the light of clinical based evidence in the human where pathogenic mutations have also been described in sperm and are associated with varying degrees of male subfertility. We also discuss the importance of maintaining maternal inheritance of mtDNA and how sperm mtDNA might be eliminated during early embryogenesis in a manner similar to the process which decreases oocyte mtDNA to extremely low levels once it reaches the blastocyst stage of preimplantation development. Finally, we discuss the role of sperm mtDNA replication and why it may be prudent to considerably reduce sperm mtDNA numbers during the transition from spermatogenesis to spermiogenesis.

Nuclear transfer: preservation of a nuclear genome at the expense of its associated mtDNA genome(s).

Nuclear transfer technology has uses across theoretical and applied applications, but advances are restricted by continued poor success rates and health problems associated with live offspring. Development of reconstructed embryos is dependent upon numerous interlinking factors relating both to the donor cell and the recipient oocyte. For example, abnormalities in gene expression following somatic cell nuclear transfer (SCNT) have been linked with an inability of the oocyte cytoplasm to sufficiently epigenetically reprogram the nucleus. Furthermore, influences on the propagation of mitochondria and mitochondrial DNA (mtDNA) could be of great importance in determining the early developmental potential of NT embryos and contributing to their genetic identity. mtDNA encodes some of the subunits of the electron transfer chain, responsible for cellular ATP production. The remaining subunits and those factors required for mtDNA replication, transcription and translation are encoded by the nucleus, necessitating precise intergenomic communication. Additionally, regulation of mtDNA copy number, via the processes of mtDNA transcription and replication, is essential for normal preimplantation embryo development and differentiation. Unimaternal transmission following natural fertilization usually results in the presence of a single identical population of mtDNA, homoplasmy. Heteroplasmy can result if mixed populations of mtDNA genomes co-exist. Many abnormalities observed in NT embryos, fetuses, and offspring may be caused by deficiencies in OXPHOS, perhaps resulting in part from heteroplasmic mtDNA populations. Additionally, incompatibilities between the somatic nucleus and the cytoplast may be exacerbated by increased genetic divergence between the two genomes. It is important to ensure that the nucleus is capable of sufficiently regulating mtDNA, requiring a level of compatibility between the two genomes, which may be a function of evolutionary distance. We suggest that abnormal expression of factors such as TFAM and POLG in NT embryos will prematurely drive mtDNA replication, hence impacting on early development.

The consequences of nuclear transfer for mammalian foetal development and offspring survival. A mitochondrial DNA perspective.

The introduction of nuclear transfer (NT) and other technologies that involve embryo reconstruction require us to reinvestigate patterns of mitochondrial DNA (mtDNA) transmission, transcription and replication. MtDNA is a 16.6 kb genome located within each mitochondrion. The number of mitochondria and mtDNA copies per organelle is specific to each cell type. MtDNA is normally transmitted through the oocyte to the offspring. However, reconstructed oocytes often transmit both recipient oocyte mtDNA and mtDNA associated with the donor nucleus. We argue that the transmission of two populations of mtDNA may have implications for offspring survival as only one allele might be actively transcribed. This could result in the offspring phenotypically exhibiting mtDNA depletion-type syndromes. A similar occurrence could arise when nucleo-cytoplasmic interactions fail to regulate mtDNA transcription and replication, especially as the initiation of mtDNA replication post-implantation is a key developmental event. Furthermore, failure of the donor somatic nucleus to be reprogrammed could result in the early initiation of replication and the loss of cellular mtDNA specificity. We suggest investigations should be conducted to enhance our understanding of nucleo-cytoplasmic interactions in order to improve NT efficiency.