Recent biological, structural, and technical advances are converging within the HIV-1 vaccine field to harness the power of antibodies for prevention and therapy. Numerous monoclonal antibodies with broad neutralizing activity against diverse HIV-1 isolates have now been identified, revealing at least five sites of vulnerability on the envelope (Env) glycoproteins. While there are practical and technological barriers blocking a clear path from broadly neutralizing antibodies (bNAb) to a protective vaccine, this is not a dead end. Scientists are revisiting old approaches with new technology, cutting new trails through unexplored territory, and paving new roads in the hopes of preventing HIV-1 infection. Other promising avenues to capitalize on the power of bNAbs are also being pursued, such as passive antibody immunotherapy and gene therapy approaches. Moreover, non-neutralizing antibodies have inhibitory activities that could have protective potential, alone or in combination with bNAbs. With a new generation of bNAbs, and a clinical trial that associated antibodies with reduced acquisition, the field is closer than ever to developing strategies to use antibodies against HIV-1.
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Rosangela Salerno-Goncalves;
Wilbur H Chen;
Mark Mulligan;
Sharon E Frey;
Jack T Stapleton;
Wendy A Keitel;
Jason Bailey;
Eli Sendra;
Hill Hill;
Robert A Johnson;
Marcelo B Sztein
Objectives: Francisella tularensis, the causative agent of tularaemia, is an exceptionally infectious bacterium, potentially fatal for humans if left untreated and with the potential to be developed as a bioweapon. Both natural infection and live-attenuated vaccine strain (LVS) confer good protection against tularaemia. LVS vaccination is traditionally administered by scarification, and the formation of a cutaneous reaction or take at the vaccination site is recognised as a clinical correlate of protection. Although previous studies have suggested that high antibody titres following vaccination might serve as a useful surrogate marker, the immunological correlates of protection remain unknown. Methods: We investigated the host T-cell-mediated immune (T-CMI) responses elicited following immunisation with LVS vaccine formulated by the DynPort Vaccine Company (DVC-LVS) or the United States Army Medical Research Institute of Infectious Diseases (USAMRIID-LVS). We compared T-CMI responses prompted by these vaccines and correlated them with take size. Results: We found that both LVS vaccines elicited similar T-CMI responses. Interestingly, take size associated with the T cells’ ability to proliferate, secrete IFN-γ and mobilise degranulation, suggesting that these responses play an essential role in tularaemia protection. Conclusions: These results renew the appreciation for vaccination through the scarification as a prime route of inoculation to target pathogens driving specific T-CMI responses and provide further evidence that T-CMI plays a role in protection from tularaemia.
Four Ebola patients received care at Emory University Hospital, presenting a unique opportunity to examine the cellular immune responses during acute Ebola virus infection. We found striking activation of both B and T cells in all four patients. Plasmablast frequencies were 10-50% of B cells, compared with less than 1% in healthy individuals. Many of these proliferating plasmablasts were IgG-positive, and this finding coincided with the presence of Ebola virus-specific IgG in the serum. Activated CD4 T cells ranged from 5 to 30%, compared with 1-2% in healthy controls. The most pronounced responses were seen in CD8 T cells, with over 50% of the CD8 T cells expressing markers of activation and proliferation. Taken together, these results suggest that all four patients developed robust immune responses during the acute phase of Ebola virus infection, a finding that would not have been predicted based on our current assumptions about the highly immunosuppressive nature of Ebola virus. Also, quite surprisingly, we found sustained immune activation after the virus was cleared from the plasma, observed most strikingly in the persistence of activated CD8 T cells, even 1 mo after the patients' discharge from the hospital. These results suggest continued antigen stimulation after resolution of the disease. From these convalescent time points, we identified CD4 and CD8 T-cell responses to several Ebola virus proteins, most notably the viral nucleoprotein. Knowledge of the viral proteins targeted by T cells during natural infection should be useful in designing vaccines against Ebola virus.
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Mauricio A. Martins;
Damien C. Tully;
Michael A. Cruz;
Karen A. Power;
Marlon G. Veloso de Santana;
David J. Bean;
Colin B. Ogilvie;
Rujuta Gadgil;
Noemia Lima;
Diogo M. Magnani;
Keisuke Ejima;
David B. Allison;
Michael Piatak, Jr.;
John Altman;
Christopher L. Parks;
Eva G. Rakasz;
Saverio Capuano, III;
Ricardo Galler;
Myrna C. Bonaldo;
Jeffrey D. Lifson;
Todd M. Allen;
David I. Watkins
Certain major histocompatibility complex class I (MHC-I) alleles (e.g., HLA-B*27) are enriched among human immunodeficiency virus type 1 (HIV-1)-infected individuals who suppress viremia without treatment (termed "elite controllers" [ECs]). Likewise, Mamu-B*08 expression also predisposes rhesus macaques to control simian immunodeficiency virus (SIV) replication. Given the similarities between Mamu-B*08 and HLA-B*27, SIV-infected Mamu-B*08(+) animals provide a model to investigate HLA-B*27-mediated elite control. We have recently shown that vaccination with three immunodominant Mamu-B*08-restricted epitopes (Vif RL8, Vif RL9, and Nef RL10) increased the incidence of elite control in Mamu-B*08(+) macaques after challenge with the pathogenic SIVmac239 clone. Furthermore, a correlate analysis revealed that CD8(+) T cells targeting Nef RL10 was correlated with improved outcome. Interestingly, this epitope is conserved between SIV and HIV-1 and exhibits a delayed and atypical escape pattern. These features led us to postulate that a monotypic vaccine-induced Nef RL10-specific CD8(+) T-cell response would facilitate the development of elite control in Mamu-B*08(+) animals following repeated intrarectal challenges with SIVmac239. To test this, we vaccinated Mamu-B*08(+) animals with nef inserts in which Nef RL10 was either left intact (group 1) or disrupted by mutations (group 2). Although monkeys in both groups mounted Nef-specific cellular responses, only those in group 1 developed Nef RL10-specific CD8(+) T cells. These vaccine-induced effector memory CD8(+) T cells did not prevent infection. Escape variants emerged rapidly in the group 1 vaccinees, and ultimately, the numbers of ECs were similar in groups 1 and 2. High-frequency vaccine-induced CD8(+) T cells focused on a single conserved epitope and therefore did not prevent infection or increase the incidence of elite control in Mamu-B*08(+) macaques.
IMPORTANCE: Since elite control of chronic-phase viremia is a classic example of an effective immune response against HIV/SIV, elucidating the basis of this phenomenon may provide useful insights into how to elicit such responses by vaccination. We have previously established that vaccine-induced CD8(+) T-cell responses against three immunodominant epitopes can increase the incidence of elite control in SIV-infected Mamu-B*08(+) rhesus macaques—a model of HLA-B*27-mediated elite control. Here, we investigated whether a monotypic vaccine-induced CD8(+) T-cell response targeting the conserved "late-escaping" Nef RL10 epitope can increase the incidence of elite control in Mamu-B*08(+) monkeys. Surprisingly, vaccine-induced Nef RL10-specific CD8(+) T cells selected for variants within days after infection and, ultimately, did not facilitate the development of elite control. Elite control is, therefore, likely to involve CD8(+) T-cell responses against more than one epitope. Together, these results underscore the complexity and multidimensional nature of virologic control of lentivirus infection.
Human respiratory syncytial virus (RSV) is an important pathogen causing acute lower respiratory tract disease in children. The RSV attachment glycoprotein (G) is not required for infection, as G-null RSV replicates efficiently in several cell lines. Our laboratory previously reported that the viral fusion (F) protein is a determinant of strain-dependent pathogenesis. Here, we hypothesized that virus dependence on G is determined by the strain specificity of F. We generated recombinant viruses expressing G and F, or null for G, from the laboratory A2 strain (Katushka RSV-A2GA2F [kRSV-A2GA2F] and kRSV-GstopA2F) or the clinical isolate A2001/2-20 (kRSV-2-20G2-20F and kRSV-Gstop2-20F). We quantified the virus cell binding, entry kinetics, infectivity, and growth kinetics of these four recombinant viruses in vitro. RSV expressing the 2-20 G protein exhibited the greatest binding activity. Compared to the parental viruses expressing G and F, removal of 2-20 G had more deleterious effects on binding, entry, infectivity, and growth than removal of A2 G. Overall, RSV expressing 2-20 F had a high dependence on G for binding, entry, and infection.
Although multiple restriction factors have been shown to inhibit HIV/SIV replication, little is known about their expression in vivo. Expression of 45 confirmed and putative HIV/SIV restriction factors was analyzed in CD4 + T cells from peripheral blood and the jejunum in rhesus macaques, revealing distinct expression patterns in naive and memory subsets. In both peripheral blood and the jejunum, memory CD4 + T cells expressed higher levels of multiple restriction factors compared to naive cells. However, relative to their expression in peripheral blood CD4 + T cells, jejunal CCR5 + CD4 + T cells exhibited significantly lower expression of multiple restriction factors, including APOBEC3G, MX2, and TRIM25, which may contribute to the exquisite susceptibility of these cells to SIV infection. In vitro stimulation with anti- CD3/CD28 antibodies or type I interferon resulted in upregulation of distinct subsets of multiple restriction factors. After infection of rhesus macaques with SIVmac239, the expression of most confirmed and putative restriction factors substantially increased in all CD4 + T cell memory subsets at the peak of acute infection. JejunalCCR5 + CD4 + T cells exhibited the highest levels of SIV RNA, corresponding to the lower restriction factor expression in this subset relative to peripheral blood prior to infection. These results illustrate the dynamic modulation of confirmed and putative restriction factor expression by memory differentiation, stimulation, tissue microenvironment and SIV infection and suggest that differential expression of restriction factors may play a key role in modulating the susceptibility of different populations of CD4 + T cells to lentiviral infection.
Respiratory syncytial virus (RSV) is a major cause of severe lower respiratory infection in infants and young children and causes disease in the elderly and persons with compromised cardiac, pulmonary, or immune systems. Despite the high morbidity rates of RSV infection, no highly effective treatment or vaccine is yet available. The RSV G protein is an important contributor to the disease process. A conserved CX3C chemokine-like motif in G likely contributes to the pathogenesis of disease. Through this motif, G protein binds to CX3CR1 present on various immune cells and affects immune responses to RSV, as has been shown in the mouse model of RSV infection. However, very little is known of the role of RSV CX3C-CX3CR1 interactions in human disease. In this study, we use an in vitro model of human RSV infection comprised of human peripheral blood mononuclear cells (PBMCs) separated by a permeable membrane from human airway epithelial cells (A549) infected with RSV with either an intact CX3C motif (CX3C) or a mutated motif (CX4C). We show that the CX4C virus induces higher levels of type I/III interferon (IFN) in A549 cells, increased IFN-α and tumor necrosis factor alpha (TNF-α) production by human plasmacytoid dendritic cells (pDCs) and monocytes, and increased IFN-γ production in effector/memory T cell subpopulations. Treatment of CX3C virus-infected cells with the F(ab′)2 form of an anti-G monoclonal antibody (MAb) that blocks binding to CX3CR1 gave results similar to those with the CX4C virus. Our data suggest that the RSV G protein CX3C motif impairs innate and adaptive human immune responses and may be important to vaccine and antiviral drug development.
HIV-1 assembly and release occurs at the plasma membrane in T lymphocytes, while intracellular sites of virus assembly or accumulation are apparent in macrophages. The host protein tetherin (BST-2) inhibits HIV release from the plasma membrane by retaining viral particles at the cell surface, but the role of tetherin at intracellular HIV assembly sites is unclear. We determined that tetherin is significantly upregulated upon macrophage infection and localizes to an intracellular virus-containing compartment (VCC). Tetherin localized at the virus-VCC membrane interface, suggesting that tetherin physically tethers virions in VCCs. Tetherin knockdown diminished and redistributed VCCs within macrophages and promoted HIV release and cell-cell transmission. The HIV Vpu protein, which downregulates tetherin from the plasma membrane, did not fully overcome tetherin-mediated restriction of particle release in macrophages. Thus, tetherin is essential for VCC formation, and may account for morphologic differences in the apparent HIV assembly sites in macrophages versus T cells.
Molecular epidemiology studies have provided convincing evidence of antigenic and sequence variability among respiratory syncytial virus (RSV) isolates. Circulating viruses have been classified into two antigenic groups (A and B) that correlate with well-delineated genetic groups. Most sequence and antigenic differences (both inter- and intra-groups) accumulate in two hypervariable segments of the G-protein gene. Sequences of the G gene have been used for phylogenetic analyses. These studies have shown a worldwide distribution of RSV strains with both local and global replacement of dominant viruses with time. Although data are still limited, there is evidence that strain variation may contribute to differences in pathogenicity. In addition, there is some but limited evidence that RSV variation may be, at least partially, immune (antibody) driven. However, there is the paradox in RSV that, in contrast to other viruses (e.g., influenza viruses) the epitopes recognized by the most effective RSV-neutralizing antibodies are highly conserved. In contrast, antibodies that recognize strainspecific epitopes are poorly neutralizing. It is likely that this apparent contradiction is due to the lack of a comprehensive knowledge of the duration and specificities of the human antibody response against RSV antigens. Since there are some data supporting a group- (or clade-) specific antibody response after a primary infection in humans, it may be wise to consider the incorporation of strains representative of groups A and B (or their antigens) in future RSV vaccine development.