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Biomedical subjects

Philip R Johnson

Publications and source records attributed to Philip R Johnson.

7 recordsLinked to original sources
PubMed2005

Novel adeno-associated virus vector vaccine restricts replication of simian immunodeficiency virus in macaques.

Gene transfer vectors based on recombinant adeno-associated virus (rAAV) are simple, versatile, and safe. While the conventional applications for rAAV vectors have focused on delivery of therapeutic genes, we have developed the system for delivery of vaccine antigens. In particular, we are interested in generating rAAV vectors for use as a prophylactic human immunodeficiency virus type 1 (HIV-1) vaccine. To that end, we constructed vaccine vectors that expressed genes from the simian immunodeficiency virus (SIV) for evaluation in the monkey SIV model. After a single intramuscular dose, rAAV/SIV vaccines elicited SIV-specific T cells and antibodies in macaques. Furthermore, immunized animals were able to significantly restrict replication of a live, virulent SIV challenge. These data suggest that rAAV vaccine vectors induced biologically relevant immune responses, and thus, warrant continued development as a viable HIV-1 vaccine candidate.

Animals↗
PubMed2004

Passive immunotherapy in simian immunodeficiency virus-infected macaques accelerates the development of neutralizing antibodies.

Passively transferred neutralizing antibodies can block lentivirus infection, but their role in postexposure prophylaxis is poorly understood. In this nonhuman-primate study, the effects of short-term antibody therapy on 5-year disease progression, virus load, and host immunity were explored. We reported previously that postinfection passive treatment with polyclonal immune globulin with high neutralizing titers against SIVsmE660 (SIVIG) significantly improved the 67-week health of SIVsmE660-infected Macaca mulatta macaques. Four of six treated macaques maintained low or undetectable levels of virus in plasma, compared with one of ten controls, while two rapid progressors controlled viremia only as long as the SIVIG was present. SIVIG treatment delayed the de novo production of envelope (Env)-specific antibodies by 8 weeks (13). We show here that differences in disease progression were also significant at 5 years postinfection, excluding rapid progressors (P = 0.05). Macaques that maintained </=10(3) virus particles per ml of plasma and </=30 infectious virus particles per 10(6) mononuclear cells from peripheral blood and lymph nodes had delayed disease onset. All macaques that survived beyond 18 months had measurable Gag-specific CD8(+) cytotoxic T cells, regardless of treatment. Humoral immunity in survivors beyond 20 weeks was strikingly different in the SIVIG and control groups. Despite a delay in Env-specific binding antibodies, de novo production of neutralizing antibodies was significantly accelerated in SIVIG-treated macaques. Titers of de novo neutralizing antibodies at week 12 were comparable to levels achieved in controls only by week 32 or later. Acceleration of de novo simian immunodeficiency virus immunity in the presence of passively transferred neutralizing antibodies is a novel finding with implications for postexposure prophylaxis and vaccines.

Animals↗
PubMed2004

Correlation between env V1/V2 region diversification and neutralizing antibodies during primary infection by simian immunodeficiency virus sm in rhesus macaques.

Evolution of the domain encoding the V1/V2 variable region of the simian immunodeficiency virus sm (SIVsm) envelope (env) gene was analyzed in relation to route of virus challenge, virus load, and neutralizing antibody (NAb) titers during primary infection of rhesus macaques with the pathogenic SIVsmE660 isolate. In this model system animals are initially infected with multiple viruses as evidenced by the presence of multiple V1/V2 genotypic variants that could be resolved by using a heteroduplex tracking assay (HTA). Overlapping subsets of the multiple variants were established in each animal. There was no selection for the establishment of specific variants in comparing intravenous- and intrarectal-challenged macaques at week 2 postinfection, suggesting that no genotypic selection occurred at the mucosal surface. There was an initial period of significant stability of the V1/V2 variants. Macaques challenged intravenously displayed subsequent V1/V2 diversification significantly earlier than macaques challenged intrarectally and well past the initial resolution of viremia. The time when SIVsmE660-specific NAbs reached a threshold titer of 100 was significantly correlated with the timing of V1/V2 diversification, even though antibodies to the Env protein could be detected much earlier. The time when NAbs reached a titer of 400 was significantly correlated with virus load late in infection. These results show that the route of infection affects the timing of V1/V2 diversification and that this diversification is correlated with the maturation of a specific NAb response. However, prior immunization capable of priming an anamnestic Env antibody response did not accelerate V1/V2 diversification. This result suggests that diversification of the SIV env V1/V2 region is the result of a type-specific antibody response.

Amino Acid Sequence↗
PubMed2003

Quantum logic gates for coupled superconducting phase qubits.

Based on a quantum analysis of two capacitively coupled current-biased Josephson junctions, we propose two fundamental two-qubit quantum logic gates. Each of these gates, when supplemented by single-qubit operations, is sufficient for universal quantum computation. Numerical solutions of the time-dependent Schrödinger equation demonstrate that these operations can be performed with good fidelity.

Journal Article↗
PubMed2003

Genetic fate of recombinant adeno-associated virus vector genomes in muscle.

Recombinant adeno-associated virus (rAAV) vectors are promising human gene transfer vectors, because they mediate long-term gene expression in vivo. The vector DNA form responsible for sustained gene expression has not been clearly defined, but it has been presumed that the vector integrates to some degree and persists in this manner. Using two independent methods, we were unable to identify rAAV integrants in mouse muscle. In the first approach, we were unable to recover host cell-vector DNA junctions from a lambda phage library generated using transduced mouse muscle DNA that contained a high vector copy number. Following this result, we devised a PCR assay based on the principle that integrated rAAV vector sequences could be amplified using primers specific for mouse interspersed repetitive sequences (B1 elements). Using this assay, we analyzed transduced mouse muscle DNA isolated from 6 to 57 weeks after injection and did not detect amplification above background levels. Based on the demonstrated sensitivity of the assay, these results suggested that >99.5% of vector DNA was not integrated. Additional analyses using a novel DNA exonuclease showed that the majority of the rAAV vector DNA in muscle persisted over time as transcriptionally active monomeric and concatameric episomes.

Animals↗
PubMed2002

Generation of neutralizing activity against human immunodeficiency virus type 1 in serum by antibody gene transfer.

Although several human immunodeficiency virus (HIV) vaccine approaches have elicited meaningful antigen-specific T-cell responses in animal models, no single vaccine candidate has engendered antibodies that broadly neutralize primary isolates of HIV type 1 (HIV-1). Thus, there remains a significant gap in the design of HIV vaccines. To address this issue, we exploited the existence of rare human monoclonal antibodies that have been isolated from HIV-infected individuals. Such antibodies neutralize a wide array of HIV-1 field isolates and have been shown to be effective in vivo. However, practical considerations preclude the use of antibody preparations as a prophylactic passive immunization strategy in large populations. Our concept calls for an antibody gene of choice to be transferred to muscle where the antibody molecule is synthesized and distributed to the circulatory system. In these experiments, we used a recombinant adeno-associated virus (rAAV) vector to deliver the gene for the human antibody IgG1b12 to mouse muscle. Significant levels of HIV-neutralizing activity were found in the sera of mice for over 6 months after a single intramuscular administration of the rAAV vector. This approach allows for predetermination of antibody affinity and specificity prior to "immunization" and avoids the need for an active humoral immune response against the HIV envelope protein.

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