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T Leitner

Publications and source records attributed to T Leitner.

30 records · Page 2Linked to original sources
PubMed1996

Heterogeneity of papillomaviruses.

The classification of the papillomaviral sequence into types is satisfactory for many purposes, but the resulting catalog does not accurately depict the extent of diversification of this family of viruses. Phylogenetic and mutational analyses reveal that some viral forms are much more ancient than other forms. Episodic evolutionary events and zoonotic transmission may have contributed to the overall pattern. Convergent evolution appears to be the best explanation for the scattered occurrence across the family tree of viruses with high oncogenic risk. We look for the determinants of this risk among the less conserved residues of the viral E6 and E7 transforming proteins.

Amino Acid Sequence↗
PubMed1996

Interplay of HIV-1 phenotype and neutralizing antibody response in pathogenesis of AIDS.

A majority of human immunodeficiency virus type 1 (HIV-1) infected individuals display a rapid loss of CD4+ lymphocytes with fast progression towards overt acquired immunodeficiency syndrome (AIDS). However, a small proportion of individuals infected by HIV-1 remain immunologically intact for many years. In order to identify factors that might influence the pathogenesis of HIV-1 infection, 21 Italian mothers and 11 Swedish homosexual men were studied for the presence of autologous neutralizing antibodies in serum, biological phenotype of virus isolates and envelope variable region 3 (V3) sequences. The results were compared to the risk of mother-to-child transmission and progression of the disease. The presence of a neutralizing antibody response to the autologous virus as well as a virus with slow replicative capacity were linked both to low risk of mother-to-child transmission and non-progression of the disease. Patients whose peripheral blood mononuclear cells contained a mutation in the tip of the V3 loop (Arg318 to serine, lysine or leucine) significantly more often had neutralizing antibodies to autologous virus isolates containing arginine at this position. Thus, it appears that the interplay and balance between neutralizing antibody response of the host and the biological phenotype of HIV-1 strongly influence pathogenesis.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Phylogeny of the Mycoplasma mycoides cluster as determined by sequence analysis of the 16S rRNA genes from the two rRNA operons.

The so-called Mycoplasma mycoides cluster consists of six species or subspecies of mycoplasmas (Mollicutes). These species are pathogenic for ruminants and some of them are of great concern in veterinary medicine. The members of the M. mycoides cluster have two rRNA operons (rrnA and rrnB). The nucleotide sequences of the 16S rRNA genes of 10 strains, representing all of the known species and subspecies of the M. mycoides cluster, were determined by direct automated solid-phase DNA sequencing. The sequences of both rRNA operons were determined by a novel strategy involving in vitro amplification by PCR with one operon-specific primer pair and one general primer pair. Interestingly, sequence differences (polymorphisms) between the two operons were observed for all strains. Two strains of M. capricolum subsp. capripneumoniae were sequenced, and 15 polymorphisms were found in the type strain (F38) and 17 polymorphisms were found in the other strain (4/2LC). Eight polymorphisms were found in the 16S rRNA genes of the M. mycoides subsp. mycoides small-colony type, and sequence length variations in a poly(A) region were observed in the 16S rRNA genes of the two operons of this species. Secondary-structure analysis showed that polymorphisms were present in both stem and loop regions. The nucleotide substitutions in the polymorphic sites of the stem regions often resulted in a change from a canonical to a noncanonical base pairing or vice versa. A compensatory mutation was never observed in the other nucleotide of the base pair. Phylogenetic analysis based on the 16S rRNA sequences indicated that Mycoplasma sp. strain PG50 should be included in the M. capricolum species group. Furthermore, the 16S rRNA sequences of M. mycoides subsp. capri and the M. mycoides subsp. mycoides large-colony type were 99.9% identical. We therefore suggest that these species be reclassified in a common species group (for instance, "Mycoplasma capri") distinct from the M. mycoides subsp. mycoides small-colony type, which formed an intermediate branch between the M. capricolum species group and the M. capri species group.

Base Sequence↗
PubMed1995

Biological and molecular characterization of subtype D, G, and A/D recombinant HIV-1 transmissions in Sweden.

HIV-1 can be subdivided into at least nine genetic subtypes (A through H and O), but in Europe and the United States there is an almost complete dominance of subtype B. In this study three Swedish HIV-1 transmission chains of subtypes other than subtype B have been biologically and molecularly characterized. The three index cases were African men. The p17 gag and env V3 regions of the HIV-1 genome were directly sequenced from uncultured lymphocytes. Phylogenetic analyses showed that the HIV-1 variants with each transmission group were genetically closely related, supporting the epidemiological information. The individuals in transmission groups I (n = 3) and II (n = 2) carried subtype G and D virus, respectively. Interestingly, all four individuals in transmission group III displayed a recombinant genotype with subtype D p17 gag sequence and subtype A V3 sequence. The biological phenotype of virus isolates (rapid/high, syncytium-inducing; or slow/low, non-syncytium-inducing) correlated with the clinical stage of the infected individual. The study also suggested that the correlation between biological phenotype and V3 genotype that has been established for subtype B HIV-1 variants may be valid also for other subtypes. This study demonstrates that HIV-1 variants of subtypes other than B, including a subtype A/D recombinant, are being transmitted in Europe.

Adult↗
PubMed1995

Reverse transcriptase sequence of paired isolates of cerebrospinal fluid and blood from patients infected with human immunodeficiency virus type 1 during zidovudine treatment.

Human immunodeficiency virus type 1 (HIV-1) isolates obtained from the blood of patients undergoing treatment with 3'-azido-3'-deoxythymidine (zidovudine [AZT]) show a decreased sensitivity to the drug in vitro. The aim of the present study was to determine if HIV-1 variants resistant to AZT are present also in the brain compartment. We selected sequential HIV-1 isolates from the blood and the cerebrospinal fluid (CSF) of six patients with HIV-1 infection undergoing AZT therapy for a time varying between 1 and 3 years. The isolates were used to infect peripheral blood mononuclear cell cultures which were used to prepare viral DNA. The viral DNA was amplified by PCR and then directly sequenced. Analysis of the reverse transcriptase (RT) sequence of the isolates from the CSF during therapy demonstrated that CSF-resistant isolates are characterized by the same mutations documented in resistant isolates from the blood compartment. Isolates obtained from one patient (patient 3) showed the same two mutations (codons 70 and 215) in blood and CSF, whereas isolates obtained from an additional four patients presented a different pattern of mutations in the two compartments. We also analyzed the degree of amino acid homology between RT sequences from blood and CSF isolates in patients before and during AZT treatment. The percentages of amino acid variations were approximately equal when isolates from the same or different compartments were considered. Excluding the codons involved in AZT resistance, the time point of sampling did not affect RT variations during therapy significantly. In conclusion, our studies show that AZT-resistant HIV-1 can be found in the CSF of patients undergoing treatment. The mutations linked to AZT resistance in the CSF isolates are the same as those identified in AZT-resistant isolates from blood.

AIDS Dementia Complex↗
PubMed1994

Analysis of a rape case by direct sequencing of the human immunodeficiency virus type 1 pol and gag genes.

Transmission of human immunodeficiency virus type 1 (HIV-1) from a male accused of rape and deliberate transmission of HIV-1 was investigated by sequencing of the HIV-1 pol and gag genes from virus obtained from the male and from the female victim. Parts of the reverse transcriptase and p17gag genes were amplified and directly sequenced from uncultured peripheral blood mononuclear cells. The sequences were compared with sequences from 21 unrelated HIV-1-infected controls from the same geographic area (Stockholm, Sweden). Bootstrap analysis of phylogenetic trees demonstrated that the sequences from the female were significantly more closely related to the sequences from the male than to sequences from the controls. Furthermore, we found that the male and female shared two distinct genetic variants of HIV-1. In p17gag the major variant had an unusual, out-of-frame deletion of 3 nucleotides which the minor variant lacked. These results indicated that the male had transmitted more than one infectious unit to the female. From this study we concluded that it was highly likely that the HIV-1 strains carried by the male and female were closely epidemiologically linked.

Base Sequence↗
PubMed1993

Comparison of variable region 3 sequences of human immunodeficiency virus type 1 from infected children with the RNA and DNA sequences of the virus populations of their mothers.

We have compared the variable region 3 sequences from 10 human immunodeficiency virus type 1 (HIV-1)-infected infants to virus sequences from the corresponding mothers. The sequences were derived from DNA of uncultured peripheral blood mononuclear cells (PBMC), DNA of cultured PBMC, and RNA from serum collected at or shortly after delivery. The infected infants, in contrast to the mothers, harbored homogeneous virus populations. Comparison of sequences from the children and clones derived from DNA of the corresponding mothers showed that the transmitted virus represented either a minor or a major virus population of the mother. In contrast to an earlier study, we found no evidence of selection of minor virus variants during transmission. Furthermore, the transmitted virus variant did not show any characteristic molecular features. In some cases the transmitted virus was more related to the virus RNA population of the mother and in other cases it was more related to the virus DNA population. This suggests that either cell-free or cell-associated virus may be transmitted. These data will help AIDS researchers to understand the mechanism of transmission and to plan strategies for prevention of transmission.

Amino Acid Sequence↗
PubMed1993

Neutralizing antibodies and viral characteristics in mother-to-child transmission of HIV-1.

OBJECTIVE: To determine viral characteristics and the protective effect of virus neutralizing antibodies in mother-to-child transmission of HIV-1. MOLECULAR STUDIES: Ten HIV-1-infected mother-child pairs were sampled within 4 months of delivery. Variable region 3 of the viral envelope was amplified by nested polymerase chain reaction and sequenced, directly and/or after cloning, by solid-phase DNA sequencing. The amino acid sequence of variable region 3 from all 10 children was homogeneous, whereas the mothers showed varying degrees of heterogeneity. Apparently, selection of an HIV-1 variant occurs either at transmission or during initial virus replication in the infected child. No characteristic molecular features of the transmitted virus were identified. BIOLOGICAL STUDIES: Virus isolates from 13 mother-child pairs were characterized for replicative capacity in a variety of cell lines. Eight mothers from whom a virus with a slow/low replicative pattern was isolated transmitted the slow/low virus to their children, whereas mothers with a rapid/high virus transmitted either a rapid/high or a slow/low virus (two cases each). This indicates that viruses with rapid/high replicative capacity do not have a selective advantage during transmission. VIRUS NEUTRALIZING: Sera from 20 mothers were characterized for the ability to neutralize their own virus (autologous neutralization) and virus from other mothers (heterologous neutralization). The results showed that non-transmitting mothers had neutralizing antibodies against autologous virus more frequently than transmitting mothers. In addition, all mothers with autologous neutralizing antibodies also neutralized at least two heterologous primary isolates. This indicates that a broad neutralizing antibody response may be linked to a lower risk of mother-to-child transmission. CONCLUSION: On the basis of the variable region 3 loop sequence, HIV-1-infected infants harbour homogenous virus populations. Despite this, no molecular or biological markers for selective transmission could be identified. A maternal neutralizing antibody response with broad specificity may protect the child from HIV-1 infection.

Amino Acid Sequence↗
PubMed1993

Analysis of heterogeneous viral populations by direct DNA sequencing.

The ability of direct PCR sequencing to detect and quantify sequence polymorphisms was investigated using samples containing mixed populations of HIV-1. A part of the genome encoding the polymorphic variable region 3 of the envelope was directly sequenced to yield a consensus sequence of the virus population. The results were compared with sequences obtained by analysis of multiple clones derived from the same clinical samples. The results of five patients suggested that the direct-sequencing method can be used as a rapid tool to analyze and quantify heterogeneous viral populations. Reconstitution experiments using cloned material demonstrated that it was possible to detect and quantify minor sequence variants present in as little as 10% of the total virus population. The use of the method for molecular diagnosis is discussed.

Acquired Immunodeficiency Syndrome↗