- Infectious Disease
Assistant Director, Stanford Medical Scientist Training Program (MSTP) (2014 - Present)
Honors & Awards
NIH Director's New Innovator Award, NIH (2013)
Clinical Scientist Development Award, Doris Duke Charitable Foundation (2013)
Faculty Scholar, Donald E. and Delia B. Baxter Foundation (2013)
Outstanding Faculty Mentor Award, Stanford Immunology (2012)
McCormick Faculty Award, Stanford University School of Medicine, Office of Diversity and Leadership (2012)
Young Investigator Award, Arnold and Mabel Beckman Foundation (2012)
ICAAC Young Investigator Award, American Society for Microbiology (2010)
Young and Early Career Investigator, Enterprise-OCTAVE Workshop on Correlates of Vaccine Protection to HIV (2010)
New Investigator Award, University of Washington Center for AIDS Research (2009)
Young Investigator Award, AIDS Vaccine, Seattle, WA (2007)
Outstanding Consultant, Infectious Diseases, MedCon (2003)
Boards, Advisory Committees, Professional Organizations
Member, Infectious Diseases Society of America (2013 - Present)
Member, American Association of Immunologists (2012 - Present)
Member, American Society for Microbiology (2009 - Present)
Residency:University of Washington Medical Center (2003) WA
University of Washington School of Medicine (1999) WA
Medical Education:University of Washington School of Medicine (2001) WA
Fellowship:University of Washington Infectious Disease Program (2007) WA
Board Certification: Infectious Disease, American Board of Internal Medicine (2006)
Board Certification: Internal Medicine, American Board of Internal Medicine (2004)
PhD, University of Washington, Immunology (1999)
BS, University of California, Davis, Biochemistry (1993)
Current Research and Scholarly Interests
Our goal is to develop new methods to prevent and control infectious diseases through better understanding of human immunology. We have several major areas of ongoing investigation.
Understanding the diversity and biology of human natural killer (NK) cells.
Our interest in NK cells stems from their ability to directly lyse infected and tumor cells and to mediate antibody-dependent cellular cytotoxicity, acting as a bridge between innate and adaptive immune responses. Our recent study demonstrated that human NK cells are much more diverse than previously appreciated, with both genetic and environmental determinants. We are currently examining how this diversity is regulated and its implications for viral immunity in both healthy and diseased states.
Defining the role of NK cells in viral immunity.
Vaccination is one of the most effective methods to prevent morbidity and mortality related to infectious diseases, yet there are many viral infections for which durable, broadly cross-protective vaccines remain desperately needed. Recent data indicating that NK cells may be capable of immunologic memory raises the possibility that we could harness NK cells to fight viruses. Current projects in the laboratory are focused on better understanding how human NK cells recognize and control infection with HIV-1, influenza, West Nile Virus, and Epstein Barr Virus.
Immune signatures of human pregnancy.
Pregnant women are at increased risk of contracting viruses including HIV and influenza, and are more susceptible to severe complications once infected. A major focus of the laboratory is to define the immune mechanisms that contribute to viral susceptibility in pregnant women. These investigations focus broadly on T cell, antibody, and NK cell responses to viruses during pregnancy, and use infection and vaccination as models. In addition, we are also studying the role of immunity in preterm birth.
Independent Studies (13)
- Biomedical Informatics Teaching Methods
BIOMEDIN 290 (Aut, Win, Spr)
- Directed Reading and Research
BIOMEDIN 299 (Aut, Win, Spr, Sum)
- Directed Reading in Immunology
IMMUNOL 299 (Aut)
- Directed Reading in Medicine
MED 299 (Aut)
- Early Clinical Experience in Immunology
IMMUNOL 280 (Aut)
- Early Clinical Experience in Medicine
MED 280 (Win)
- Graduate Research
IMMUNOL 399 (Aut, Win, Spr, Sum)
- Graduate Research
MED 399 (Aut)
- Medical Scholars Research
BIOMEDIN 370 (Aut, Win, Spr, Sum)
- Medical Scholars Research
MED 370 (Aut, Spr)
- Teaching in Immunology
IMMUNOL 290 (Aut)
- Undergraduate Research
IMMUNOL 199 (Aut)
- Undergraduate Research
MED 199 (Aut)
- Biomedical Informatics Teaching Methods
- Coordinated Regulation of NK Receptor Expression in the Maturing Human Immune System JOURNAL OF IMMUNOLOGY 2014; 193 (10): 4871-4879
Enhanced natural killer-cell and T-cell responses to influenza A virus during pregnancy.
Proceedings of the National Academy of Sciences of the United States of America
Pregnant women experience increased morbidity and mortality after influenza infection, for reasons that are not understood. Although some data suggest that natural killer (NK)- and T-cell responses are suppressed during pregnancy, influenza-specific responses have not been previously evaluated. Thus, we analyzed the responses of women that were pregnant (n = 21) versus those that were not (n = 29) immediately before inactivated influenza vaccination (IIV), 7 d after vaccination, and 6 wk postpartum. Expression of CD107a (a marker of cytolysis) and production of IFN-γ and macrophage inflammatory protein (MIP) 1β were assessed by flow cytometry. Pregnant women had a significantly increased percentage of NK cells producing a MIP-1β response to pH1N1 virus compared with nonpregnant women pre-IIV [median, 6.66 vs. 0.90% (P = 0.0149)] and 7 d post-IIV [median, 11.23 vs. 2.81% (P = 0.004)], indicating a heightened chemokine response in pregnant women that was further enhanced by the vaccination. Pregnant women also exhibited significantly increased T-cell production of MIP-1β and polyfunctionality in NK and T cells to pH1N1 virus pre- and post-IIV. NK- and T-cell polyfunctionality was also enhanced in pregnant women in response to the H3N2 viral strain. In contrast, pregnant women had significantly reduced NK- and T-cell responses to phorbol 12-myristate 13-acetate and ionomycin. This type of stimulation led to the conclusion that NK- and T-cell responses during pregnancy are suppressed, but clearly this conclusion is not correct relative to the more biologically relevant assays described here. Robust cellular immune responses to influenza during pregnancy could drive pulmonary inflammation, explaining increased morbidity and mortality.
View details for DOI 10.1073/pnas.1416569111
View details for PubMedID 25246558
Genetic and Environmental Determinants of Human NK Cell Diversity Revealed by Mass Cytometry
SCIENCE TRANSLATIONAL MEDICINE
2013; 5 (208)
View details for Web of Science ID 000326090200006
- Delayed BCG vaccination--time to take a shot. journal of infectious diseases 2015; 211 (3): 335-337
Association between Latent Proviral Characteristics and Immune Activation in Antiretrovirus-Treated Human Immunodeficiency Virus Type 1-Infected Adults.
Journal of virology
2014; 88 (15): 8629-8639
Generalized immune activation during HIV infection is associated with an increased risk of cardiovascular disease, neurocognitive disease, osteoporosis, metabolic disorders, and physical frailty. The mechanisms driving this immune activation are poorly understood, particularly in individuals effectively treated with antiretroviral medications. We hypothesized that viral characteristics such as sequence diversity may play a role in driving HIV-associated immune activation. We therefore sequenced proviral DNA isolated from peripheral blood mononuclear cells from HIV-infected individuals on fully suppressive antiretroviral therapy. We performed phylogenetic analyses, calculated viral diversity and divergence in the env and pol genes, and determined coreceptor tropism and the frequency of drug resistance mutations. Comprehensive immune profiling included quantification of immune cell subsets, plasma cytokine levels, and intracellular signaling responses in T cells, B cells, and monocytes. These antiretroviral-treated HIV-infected individuals exhibited a wide range of diversity and divergence in both env and pol genes. However, proviral diversity and divergence in env and pol, coreceptor tropism, and the level of drug resistance did not significantly correlate with markers of immune activation. A clinical history of virologic failure was also not significantly associated with levels of immune activation, indicating that a past history of virologic failure does not inexorably lead to increased immune activation as long as suppressive antiretroviral medications are provided. Overall, this study demonstrates that latent viral diversity is unlikely to be a major driver of persistent HIV-associated immune activation.Chronic immune activation, which is associated with cardiovascular disease, neurologic disease, and early aging, is likely to be a major driver of morbidity and mortality in HIV-infected individuals. Although treatment of HIV with antiretroviral medications decreases the level of immune activation, levels do not return to normal. The factors driving this persistent immune activation, particularly during effective treatment, are poorly understood. In this study, we investigated whether characteristics of the latent, integrated HIV provirus that persists during treatment are associated with immune activation. We found no relationship between latent viral characteristics and immune activation in treated individuals, indicating that qualities of the provirus are unlikely to be a major driver of persistent inflammation. We also found that individuals who had previously failed treatment, but were currently effectively treated, did not have significantly increased levels of immune activation, providing hope that past treatment failures do not have a lifelong "legacy" impact.
View details for DOI 10.1128/JVI.01257-14
View details for PubMedID 24850730
Systemic Cytokine Levels Show Limited Correlation With Risk of HIV-1 Acquisition
JAIDS-JOURNAL OF ACQUIRED IMMUNE DEFICIENCY SYNDROMES
2014; 66 (2): 135-139
It has been hypothesized that immune activation and inflammation may increase HIV-1 susceptibility and that cytokines may be useful biomarkers for risk. Within a prospective cohort, we conducted a nested case-control analysis of plasma cytokine levels among women who acquired HIV-1 <3 months after sampling, compared to three different control groups. We observed associations between lower IL-6 and IL-10 and higher IL-7 levels with HIV-1 acquisition, however these associations were inconsistent when comparing to different control groups. Inconsistent results within our study and among prior studies suggest that reproducible findings are needed before cytokines are useful biomarkers for HIV-1 susceptibility.
View details for DOI 10.1097/QAI.0000000000000104
View details for Web of Science ID 000337685800014
View details for PubMedID 24413043
Association between Cellular Immune Activation, Target Cell Frequency, and Risk of Human Immunodeficiency Virus Type 1 Superinfection
JOURNAL OF VIROLOGY
2014; 88 (10): 5894-5899
We performed a case-control study of women at risk of HIV-1 superinfection to understand the relationship between immune activation and HIV-1 acquisition. An increase in the frequency of HIV-1 target cells, but not in other markers of T cell activation, was associated with a 1.7-fold increase in the odds of superinfection. This suggests that HIV-1 acquisition risk is influenced more by the frequency of target cells than by the generalized level of immune activation.
View details for DOI 10.1128/JVI.00187-14
View details for Web of Science ID 000335446400062
View details for PubMedID 24623424
Antibody-dependent cell-mediated virus inhibition antibody activity does not correlate with risk of HIV-1 superinfection.
Journal of acquired immune deficiency syndromes
2013; 63 (1): 31-33
Previous studies of HIV-infected women with high-risk behavior have indicated that neither neutralizing antibody nor cellular immunity elicited by an initial HIV-1 infection is associated with protection against superinfection with a different HIV-1 strain. Here, we measured antibody-dependent cell-mediated virus inhibition (ADCVI) antibody activity in the plasma of 12 superinfected cases and 36 singly infected matched controls against 2 heterologous viruses. We found no association between plasma ADCVI activity and superinfection status. ADCVI antibody activity against heterologous virus elicited by the original infection may not contribute to preventing a superinfecting HIV-1.
View details for DOI 10.1097/QAI.0b013e3182874d41
View details for PubMedID 23344546
Genital Inflammation Predicts HIV-1 Shedding Independent of Plasma Viral Load and Systemic Inflammation
JAIDS-JOURNAL OF ACQUIRED IMMUNE DEFICIENCY SYNDROMES
2012; 61 (4): 436-440
In women, genital HIV-1 RNA levels predict the risk of HIV-1 transmission independent of plasma viral load. To better understand the factors that contribute to genital HIV-1 shedding, we evaluated the relationships between genital and plasma cytokine concentrations and HIV-1 RNA levels. Vaginal, but not plasma, levels of interferon gamma-induced protein 10 (IP-10) were significantly associated with vaginal viral load, independent of plasma viral load. Thus, efforts to decrease HIV-1 transmission must take into account the role of local inflammation, which is not necessarily reflected in plasma measurements.
View details for DOI 10.1097/QAI.0b013e31826c2edd
View details for Web of Science ID 000311083200008
View details for PubMedID 22878424
- HIV-1 Transmission Goes Retro (Steps Back) JOURNAL OF INFECTIOUS DISEASES 2012; 206 (9): 1336-1338
Measurements of Immune Responses for Establishing Correlates of Vaccine Protection Against HIV
AIDS RESEARCH AND HUMAN RETROVIRUSES
2012; 28 (7): 641-648
Well-defined correlates of protective immunity are an essential component of rational vaccine development. Despite years of basic science and three HIV vaccine efficacy trials, correlates of immunological protection from HIV infection remain undefined. In December 2010, a meeting of scientists engaged in basic and translational work toward developing HIV-1 vaccines was convened. The goal of this meeting was to discuss current opportunities and optimal approaches for defining correlates of protection, both for ongoing and future HIV-1 vaccine candidates; specific efforts were made to engage young scientists. We discuss here the highlights from the meeting regarding the progress made and the way forward for a protective HIV-1 vaccine.
View details for DOI 10.1089/aid.2011.0239
View details for Web of Science ID 000305810900002
View details for PubMedID 21861777
Cellular immune responses and susceptibility to HIV-1 superinfection: a case-control study
2012; 26 (5): 643-646
A case-control study was performed to determine the effects of HIV-1-specific cellular immune responses on the odds of acquiring a second HIV-1 infection (superinfection). Changes in the frequency of cytokine-producing or cytolytic CD8+ or CD4+ T cells were not associated with significant alterations in the odds of superinfection, suggesting that HIV-1 specific cellular immune responses at the level induced by chronic infection do not appear to significantly contribute to protection from HIV-1 superinfection.
View details for DOI 10.1097/QAD.0b013e3283509a0b
View details for Web of Science ID 000301333000015
View details for PubMedID 22210637
The impact of HIV-1 infection and exposure on natural killer (NK) cell phenotype in Kenyan infants during the first year of life.
Frontiers in immunology
2012; 3: 399-?
Natural killer (NK) cells play an important role in the containment of HIV replication during primary infection, though their functions are impaired during chronic HIV infection. Infants experience more rapid HIV disease progression than adults, but contributions of infant NK cells to containing HIV infection are unknown. The aim of this study was to determine the impact of HIV infection on infant NK cell phenotype by evaluating samples and data from a cohort study of women and their infants, conducted in Nairobi, Kenya between 1999 and 2003. The percentage and phenotype of NK cells was evaluated longitudinally by multi-parameter flow cytometry over the first year of life in HIV-infected (HIV+, = 16), HIV-exposed uninfected (HIV-EU, n = 6), and healthy unexposed controls (HIV-, n = 4). At birth, NK subset distributions based on expression of CD56 and CD16 did not differ between HIV+, HIV-EU, or HIV- infants. However, HIV infection was associated with a subsequent decline in NK cells as a percentage of total lymphocytes (p < 0.001), and an expanding proportion of CD56-CD16+ NK cells (p < 0.001). Activated CD38(bright)CD69+ NK cells were more frequent in the HIV+ infants, followed by HIV-EU and HIV- infants, in both CD56(dim) (p = 0.005) and CD56(bright) compartments (p = 0.03). HIV infection and exposure was also associated with a significant decline in the percentage of perforin-expressing NK cells in the CD56(dim) compartment over the first year of life, with HIV+ infants losing approximately 2.5% (p < 0.001) and HIV-EU infants losing 3.0% (p = 0.01) of perforin+ cells per month. Thus, infant HIV infection is associated with alterations in NK cell subsets, activation, and cytolytic potential that could contribute to their poor control over HIV infection. Furthermore, exposure to HIV infection in infants who escaped infection is also associated with alterations in NK cells that may contribute to the reduced ability to fight infections that is observed in HIV-EU infants.
View details for DOI 10.3389/fimmu.2012.00399
View details for PubMedID 23293640
The role of amino acid changes in the human immunodeficiency virus type 1 transmembrane domain in antibody binding and neutralization
2011; 421 (2): 235-244
The detailed interactions between antibodies and the HIV-1 envelope protein that lead to neutralization are not well defined. Here, we show that several conservative substitutions in the envelope gp41 led to a ~100 fold increase in neutralization sensitivity to monoclonal antibodies (MAbs) that target gp41: 4E10 and 2F5. Substitution at position 675 alone did not impact neutralization susceptibility to MAbs that recognize more distal sites in gp120 (b12, VRC01, PG9). However, changes at position 675 in conjunction with Thr to Ala at position 569 increased the neutralization sensitivity to all gp41 and gp120 MAbs and plasma, in some cases by more than 1000-fold. Interestingly, the T569A change had a dramatic effect on b12 binding, but no effect on neutralization sensitivity. This finding suggests that antibody neutralization may occur through a multi-step pathway that includes distinct changes in envelope conformation that may affect binding but not neutralization susceptibility.
View details for DOI 10.1016/j.virol.2011.09.032
View details for Web of Science ID 000297183900017
View details for PubMedID 22029936
The Breadth and Potency of Passively Acquired Human Immunodeficiency Virus Type 1-Specific Neutralizing Antibodies Do Not Correlate with the Risk of Infant Infection
JOURNAL OF VIROLOGY
2011; 85 (11): 5252-5261
Although a major goal of human immunodeficiency virus type 1 (HIV-1) vaccine efforts is to elicit broad and potent neutralizing antibodies (NAbs), there are no data that directly demonstrate a role for such NAbs in protection from HIV-1 infection in exposed humans. The setting of mother-to-child transmission provides an opportunity to examine whether NAbs provide protection from HIV-1 infection because infants acquire passive antibodies from their mothers prior to exposure to HIV-1 through breastfeeding. We evaluated the characteristics of HIV-1-specific NAbs in 100 breast-fed infants of HIV-1-positive mothers who were HIV-1 negative at birth and monitored them until age 2. A panel of eight viruses that included variants representative of those in the study region as well as more diverse strains was used to determine the breadth of the infant NAbs. From their mothers, infants acquired broad and potent NAbs that were capable of recognizing heterologous circulating HIV-1 variants of diverse subtypes, but the presence of NAbs of broad HIV-1 specificity was not associated with transmission risk. There was also no correlation between responses to any particular virus tested, which included a range of diverse variants that demonstrated different neutralization profiles, including recognition by specific antibodies with known epitope targets. The eight viruses tested exhibited neutralization profiles to a variety of monoclonal antibodies (2F5, PG9, and VRC01) similar to those of viruses present in pregnant women in the cohort. These results suggest that the breadth and potency of the heterologous antibody response in exposed infants, measured against a virus panel comprised of variants typical of those circulating in the population, does not predict protection.
View details for DOI 10.1128/JVI.02216-10
View details for Web of Science ID 000290298700003
View details for PubMedID 21411521
Hormonal Contraception and HIV-1 Transmission
AMERICAN JOURNAL OF REPRODUCTIVE IMMUNOLOGY
2011; 65 (3): 302-307
Safe and effective contraceptive choices are essential for women with HIV-1 infection and at risk for HIV-1 infection. Epidemiological and laboratory-based studies suggest that hormonal contraception may influence HIV-1 transmission. Several large studies in high-risk populations indicate that hormonal contraceptive use may modestly increase the risk of HIV-1 acquisition. In addition, HIV-1-infected users of hormonal contraceptives may be more infectious to their uninfected partners, although no studies have directly measured HIV-1 transmission risk from women to men. However, several studies failed to demonstrate a link between contraceptive use and HIV-1 acquisition or transmission, and interpretation of many studies limited by methodological considerations, such as infrequent measurements of contraceptive exposure and HIV-1 status. As a result, many questions remain, and high-quality studies remain needed. It is clear that hormonal contraceptives are not protective against HIV-1 infection and that dual protection with condoms should be the goal for women using hormonal contraception.
View details for DOI 10.1111/j.1600-0897.2010.00930.x
View details for Web of Science ID 000287037200017
View details for PubMedID 21087338
Changes in Plasma Cytokines after Treatment of Ascaris lumbricoides Infection in Individuals with HIV-1 Infection
JOURNAL OF INFECTIOUS DISEASES
2010; 201 (12): 1816-1821
Albendazole treatment of individuals with human immunodeficiency virus type 1 (HIV-1) and Ascaris lumbricoides co-infection has led to significantly improved CD4(+) cell counts and a trend for lower plasma HIV-1 RNA levels in a previous randomized placebo-controlled trial. To define mechanisms by which deworming contributed to changes in markers of HIV-1 disease progression, plasma cytokine levels were evaluated. Albendazole treatment, compared with placebo, was associated with significantly decreased plasma interleukin (IL) 10 levels (P = .01)ot associated with significant changes in levels of IL-1beta, IL-2, IL-4, IL-5, IL-6, IL-7, IL-8, IL-12p70, IL-13, interferon gamma, tumor necrosis factor alpha, or thymic stromal lymphopoietin. Treatment of A. lumbricoides co-infection may delay HIV-1 disease progression by reducing helminth-induced, IL-10-mediated immunosuppression.
View details for DOI 10.1086/652784
View details for Web of Science ID 000277687900007
View details for PubMedID 20441516
Comparative Immunogenicity of Subtype A Human Immunodeficiency Virus Type 1 Envelope Exhibiting Differential Exposure of Conserved Neutralization Epitopes
JOURNAL OF VIROLOGY
2010; 84 (5): 2573-2584
Development of broadly cross-reactive neutralizing antibodies (NAbs) remains a major goal of HIV-1 vaccine development, but most candidate envelope immunogens have had limited ability to cross-neutralize heterologous strains. To evaluate the immunogenicity of subtype A variants of HIV-1, rabbits were immunized with pairs of closely related subtype A envelopes from the same individual. In each immunogen pair, one variant was readily neutralized by a variety of monoclonal antibodies and plasma antibodies, while the other was neutralization resistant, suggesting differences in the exposures of key epitopes. The breadth of the antibody response was evaluated against subtype A, B, C, and D variants of HIV-1. The specificity of the immunogen-derived neutralizing antibody response was also compared to that of the infected individuals from whom these variants were cloned. None of the immunogens produced broad neutralizing antibodies in immunized animals, and most of the neutralizing antibodies were directed to the variable loops, particularly the V3 loop. No detectable antibodies to either of the potentially exposed conserved epitopes, the membrane proximal external region, or the CD4 binding site were found with immunized rabbits. In contrast, relatively little of the neutralizing activity within the plasma samples of the infected individuals was directed to linear epitopes within the variable loops. These data indicate that immunogens designed to expose conserved regions did not enhance generation of broadly neutralizing antibodies in comparison with the immunogens that failed to expose those regions using this immunization approach.
View details for DOI 10.1128/JVI.01687-09
View details for Web of Science ID 000274330300035
View details for PubMedID 20015987
Breadth of Neutralizing Antibody Response to Human Immunodeficiency Virus Type 1 Is Affected by Factors Early in Infection but Does Not Influence Disease Progression
JOURNAL OF VIROLOGY
2009; 83 (19): 10269-10274
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.
View details for DOI 10.1128/JVI.01149-09
View details for Web of Science ID 000269614300059
View details for PubMedID 19640996
Cross-Subtype Neutralization Sensitivity despite Monoclonal Antibody Resistance among Early Subtype A, C, and D Envelope Variants of Human Immunodeficiency Virus Type 1
JOURNAL OF VIROLOGY
2009; 83 (15): 7783-7788
The human immunodeficiency virus type 1 (HIV-1) variants that are transmitted to newly infected individuals are the primary targets of interventions, such as vaccines and microbicides, aimed at preventing new infections. Newly acquired subtype A, B, and C variants have been the focus of neutralization studies, although many of these viruses, particularly of subtypes A and B, represent viruses circulating more than a decade ago. In order to better represent the global diversity of transmitted HIV-1 variants, an additional 31 sexually transmitted Kenyan HIV-1 env genes, representing several recent infections with subtype A, as well as subtypes A/D, C, and D, were cloned, and their neutralization profiles were characterized. Most env variants were resistant to neutralization by the monoclonal antibodies (MAbs) b12, 4E10, 2F5, and 2G12, suggesting that targeting the epitopes of these MAbs may not be effective against variants that are spreading in areas of endemicity. However, significant cross-subtype neutralization by plasma was observed, indicating that there may be other epitopes, not yet defined by the limited available MAbs, which could be recognized more broadly.
View details for DOI 10.1128/JVI.00673-09
View details for Web of Science ID 000267747400043
View details for PubMedID 19474105
Human Immunodeficiency Virus Type 1 Superinfection Occurs despite Relatively Robust Neutralizing Antibody Responses
JOURNAL OF VIROLOGY
2008; 82 (24): 12094-12103
Superinfection by a second human immunodeficiency virus type 1 (HIV-1) strain indicates that gaps in protective immunity occur during natural infection. To define the role of HIV-1-specific neutralizing antibodies (NAbs) in this setting, we examined NAb responses in 6 women who became superinfected between approximately 1 to 5 years following initial infection compared to 18 women with similar risk factors who did not. Although superinfected individuals had less NAb breadth than matched controls at approximately 1 year postinfection, no significant differences in the breadth or potency of NAb responses were observed just prior to the second infection. In fact, four of the six subjects had relatively broad and potent NAb responses prior to infection by the second strain. To more specifically examine the specificity of the NAbs against the superinfecting virus, these variants were cloned from five of the six individuals. The superinfecting variants did not appear to be inherently neutralization resistant, as measured against a pool of plasma from unrelated HIV-infected individuals. Moreover, the superinfected individuals were able to mount autologous NAb responses to these variants following reinfection. In addition, most superinfected individuals had NAbs that could neutralize their second viral strains prior to their reinfection, suggesting that the level of NAbs elicited during natural infection was not sufficient to block infection. These data indicate that preventing infection by vaccination will likely require broader and more potent NAb responses than those found in HIV-1-infected individuals.
View details for DOI 10.1128/JVI.01730-08
View details for Web of Science ID 000261164000011
View details for PubMedID 18842728
Enhancing exposure of HIV-1 neutralization epitopes through mutations in gp41
2008; 5 (1): 90-103
The generation of broadly neutralizing antibodies is a priority in the design of vaccines against HIV-1. Unfortunately, most antibodies to HIV-1 are narrow in their specificity, and a basic understanding of how to develop antibodies with broad neutralizing activity is needed. Designing methods to target antibodies to conserved HIV-1 epitopes may allow for the generation of broadly neutralizing antibodies and aid the global fight against AIDS by providing new approaches to block HIV-1 infection. Using a naturally occurring HIV-1 Envelope (Env) variant as a template, we sought to identify features of Env that would enhance exposure of conserved HIV-1 epitopes.Within a cohort study of high-risk women in Mombasa, Kenya, we previously identified a subtype A HIV-1 Env variant in one participant that was unusually sensitive to neutralization. Using site-directed mutagenesis, the unusual neutralization sensitivity of this variant was mapped to two amino acid mutations within conserved sites in the transmembrane subunit (gp41) of the HIV-1 Env protein. These two mutations, when introduced into a neutralization-resistant variant from the same participant, resulted in 3- to >360-fold enhanced neutralization by monoclonal antibodies specific for conserved regions of both gp41 and the Env surface subunit, gp120, >780-fold enhanced neutralization by soluble CD4, and >35-fold enhanced neutralization by the antibodies found within a pool of plasmas from unrelated individuals. Enhanced neutralization sensitivity was not explained by differences in Env infectivity, Env concentration, Env shedding, or apparent differences in fusion kinetics. Furthermore, introduction of these mutations into unrelated viral Env sequences, including those from both another subtype A variant and a subtype B variant, resulted in enhanced neutralization susceptibility to gp41- and gp120-specific antibodies, and to plasma antibodies. This enhanced neutralization sensitivity exceeded 1,000-fold in several cases.Two amino acid mutations within gp41 were identified that expose multiple discontinuous neutralization epitopes on diverse HIV-1 Env proteins. These exposed epitopes were shielded on the unmodified viral Env proteins, and several of the exposed epitopes encompass desired target regions for protective antibodies. Env proteins containing these modifications could act as a scaffold for presentation of such conserved domains, and may aid in developing methods to target antibodies to such regions.
View details for DOI 10.1371/journal.pmed.0050009
View details for Web of Science ID 000254928700017
View details for PubMedID 18177204
Transmission of HIV-1 in the face of neutralizing antibodies
CURRENT HIV RESEARCH
2007; 5 (6): 578-587
In most cases of HIV-1 transmission, only a subset of variants is transmitted from the index case to the newly infected individual. Understanding the characteristics of these transmitted variants may aid in developing new methods to halt the spread of HIV-1. Studies evaluating the genotypic and antigenic properties of transmitted variants have provided insights into how the selective pressures applied during different modes of transmission uniquely imprint the infecting viruses. In the setting of sexual transmission, variants with increased neutralization sensitivity appeared to be selected during transmission in discordant subtype C-infected couples, although transmitted variants from different risk groups and HIV-1 subtypes did not demonstrate increased neutralization sensitivity, suggesting this may not be a consistent feature of transmitted variants. Studies of both mother to child transmission (MTCT) and superinfection, where preexisting NAbs are present at the time of exposure, provide opportunities to analyze whether the breadth and potency of the NAb response influence the incidence of new infections. MTCT resulted in selection for variants that were resistant to maternal antibodies, suggesting that maternal antibodies can protect the baby from those variants that are susceptible to the antibodies present. There are some data to suggest that poor neutralizing antibody (NAb) responses are present in cases of superinfection, although these data are preliminary. Defining the characteristics of the viruses transmitted in the presence and absence of NAbs as well as defining the NAb responses that fail to protect from infection during MTCT and superinfection may provide critical insights into the antibody responses that are needed for effective vaccines and other prophylactic therapeutics.
View details for Web of Science ID 000253633600008
View details for PubMedID 18045114
HIV-1 subtype A envelope variants from early in infection have variable sensitivity to neutralization and to inhibitors of viral entry
2007; 21 (6): 693-702
An effective HIV-1 vaccine or microbicide must block the transmitted virus variants that initially establish a new infection; consequently, it is critical that such viruses be isolated and characterized.To evaluate HIV-1 envelope variants from early in infection from individuals infected heterosexually with subtype A HIV-1 for their sensitivity to antibody-mediated neutralization and to inhibitors of viral entry.Full-length subtype A HIV-1 envelope clones from 28-75 days postinfection were used to generate pseudoviruses for infection studies. The susceptibility of these pseudoviruses to neutralization by autologous and heterologous plasma and by monoclonal antibodies was examined. The sensitivity of these pseudoviruses to PSC-RANTES and TAK-779, inhibitors of CCR5, and to soluble CD4 (sCD4) was also evaluated.Pseudoviruses with subtype A HIV-1 envelopes from early in infection demonstrated a broad range of neutralization sensitivities to both autologous and heterologous plasma. However, neutralization by the monoclonal antibodies b12, 2G12, 4E10 and 2F5 was generally poor; notably, none of the 14 early virus variants were neutralized by 2G12 and only one was neutralized by b12. Viruses bearing these early CCR5-using envelopes were generally sensitive to the CCR5 inhibitors PSC-RANTES and TAK-779, but they demonstrated more variable sensitivity to sCD4.These subtype A HIV-1 variants, representing the viruses that must be blocked by antibody-based prevention strategies, vary in their susceptibility to neutralization. A subset of these HIV-1 variants from early in infection will be useful for screening candidate vaccines and microbicides.
View details for Web of Science ID 000245637500007
View details for PubMedID 17413690
Anergic CD8(+) T cells can persist and function in vivo
JOURNAL OF IMMUNOLOGY
1999; 163 (1): 155-164
Using a mouse model system, we demonstrate that anergic CD8+ T cells can persist and retain some functional capabilities in vivo, even after the induction of tolerance. In TCR Vbeta5 transgenic mice, mature CD8+Vbeta5+ T cells transit through a CD8lowVbeta5low deletional intermediate during tolerance induction. CD8low cells are characterized by an activated phenotype, are functionally compromised in vitro, and are slated for deletion in vivo. We now demonstrate that CD8low cells derive from a proliferative compartment, but do not divide in vivo. CD8low cells persist in vivo with a t1/2 of 3-5 days, in contrast to their in vitro t1/2 of 0.5-1 day. During this unexpectedly long in vivo life span, CD8low cells are capable of producing IFN-gamma in vivo despite their inability to proliferate or to kill target cells in vitro. CD8low cells also accumulate at sites of inflammation, where they produce IFN-gamma. Therefore, rather than withdrawing from the pool of functional CD8+ T cells, anergic CD8low cells retain a potential regulatory role despite losing their capacity to proliferate. The ability of anergic cells to persist and function in vivo adds another level of complexity to the process of tolerance induction in the lymphoid periphery.
View details for Web of Science ID 000080973700023
View details for PubMedID 10384112
Chronic modulation of the TCR repertoire in the lymphoid periphery
JOURNAL OF IMMUNOLOGY
1999; 162 (6): 3131-3140
Using TCR V beta 5 transgenic mice as a model system, we demonstrate that the induction of peripheral tolerance can mold the TCR repertoire throughout adult life. In these mice, three distinct populations of peripheral T cells are affected by chronic selective events in the lymphoid periphery. First, CD4+V beta 5+ T cells are deleted in the lymphoid periphery by superantigens encoded by mouse mammary tumor viruses-8 and -9 in an MHC class II-dependent manner. Second, mature CD8+V beta 5+ T cells transit through a CD8lowV beta 5low deletional intermediate during tolerance induction by a process that depends upon neither mouse mammary tumor virus-encoded superantigens nor MHC class II expression. Third, a population of CD4-CD8-V beta 5+ T cells arises in the lymphoid periphery in an age-dependent manner. We analyzed the TCR V alpha repertoire of each of these cellular compartments in both V beta 5 transgenic and nontransgenic C57BL/6 mice as a function of age. This analysis revealed age-related changes in the expression of V alpha families among different cellular compartments, highlighting the dynamic state of the peripheral immune repertoire. Our work indicates that the chronic processes maintaining peripheral T cell tolerance can dramatically shape the available TCR repertoire.
View details for Web of Science ID 000079105000004
View details for PubMedID 10092762
LOSS OF CELL-CYCLE CONTROLS IN APOPTOTIC LYMPHOBLASTS OF THE BURSA OF FABRICIUS
MOLECULAR BIOLOGY OF THE CELL
1994; 5 (7): 763-772
Lymphoblasts of the normal embryonic follicles of the chicken bursa of Fabricius undergo rapid apoptosis when exposed to gamma-radiation or when cell-cell contacts are disrupted by mechanical dispersion in short term culture. We have observed previously that overexpression of v-myc sensitizes preneoplastic bursal lymphoblasts to induction of cell death, whereas resistance to induced cell death is acquired during progression to neoplasia. In this study we observed extensive DNA degradation in the large majority of the lymphoblast population within the first hour after dispersion-induced apoptosis. Paradoxically these cells continued to progress into S-phase with the bulk of DNA cleavage and death occurring in S-phase cells (i.e., in cells with more than 2C and less than 4C DNA content). We confirmed the S phase status of apoptotic cells by determining that detection of nuclear cyclin A in individual cells also corresponded with detection of DNA breakage. Levels of cyclin E, cyclin E-dependent H1 histone kinase, and p53 proteins were maintained during dispersion-induced DNA cleavage. gamma-radiation failed either to inhibit cell cycle progression or to raise p53 levels in dispersed bursal lymphoblasts. In intact bursal follicles low doses of gamma-radiation induced p53 whereas higher, apoptosis-inducing doses failed to induce p53 or prevent G1 to S-phase progression. These results suggest that normal DNA damage-induced cell cycle checkpoint controls are lost or overridden when apoptosis is induced in bursal lymphoblasts.
View details for Web of Science ID A1994PC03800005
View details for PubMedID 7812045