Scientific Resources

Virus-specific CD8(+) T cells are associated with declining viremia in acute human immunodeficiency virus (HIV)1 infection,but do not correlate with control of viremia in chronic infection,suggesting a progressive functional defect not measured by interferon gamma assays presently used. Here,we demonstrate that HIV-1-specific CD8(+) T cells proliferate rapidly upon encounter with cognate antigen in acute infection,but lose this capacity with ongoing viral replication. This functional defect can be induced in vitro by depletion of CD4(+) T cells or addition of interleukin 2-neutralizing antibodies,and can be corrected in chronic infection in vitro by addition of autologous CD4(+) T cells isolated during acute infection and in vivo by vaccine-mediated induction of HIV-1-specific CD4(+) T helper cell responses. These data demonstrate a loss of HIV-1-specific CD8(+) T cell function that not only correlates with progressive infection,but also can be restored in chronic infection by augmentation of HIV-1-specific T helper cell function. This identification of a reversible defect in cell-mediated immunity in chronic HIV-1 infection has important implications for immunotherapeutic interventions. View Publication

High-titer,HIV-1-based lentiviral vector particles were found to transduce cytokine-mobilized rhesus macaque CD34(+) cells and clonogenic progenitors very poorly (textless 1%),reflecting the postentry restriction in rhesus cells to HIV infection. To overcome this barrier,we developed a simian immunodeficiency virus (SIV)-based vector system. A single exposure to a low concentration of amphotropic pseudotyped SIV vector particles encoding the green fluorescent protein (GFP) resulted in gene transfer into 68% +/- 1% of rhesus bulk CD34(+) cells and 75% +/- 1% of clonogenic progenitors. Polymerase chain reaction (PCR) analysis of DNA from individual hematopoietic colonies confirmed these relative transduction efficiencies. To evaluate SIV vector-mediated stem cell gene transfer in vivo,3 rhesus macaques underwent transplantation with transduced,autologous cytokine-mobilized peripheral blood CD34(+) cells following myeloablative conditioning. Hematopoietic reconstitution was rapid,and an average of 18% +/- 8% and 15% +/- 7% GFP-positive granulocytes and monocytes,respectively,were observed 4 to 6 months after transplantation,consistent with the average vector copy number of 0.19 +/- 0.05 in peripheral blood leukocytes as determined by real-time PCR. Vector insertion site analysis demonstrated polyclonal reconstitution with vector-containing cells. SIV vectors appear promising for evaluating gene therapy approaches in nonhuman primate models. View Publication

Gag-specific CD4 proliferative responses correlate inversely with HIV-1 RNA levels in infected adults,and robust responses are characteristic of long-term nonprogressive infection. However,strong responses are seldom detected in adult subjects with progressive infection and are not generally reconstituted on highly active antiretroviral therapy (HAART). To date,the role of HIV-1-specific Th responses in children has not been thoroughly examined. We characterized Gag-specific CD4 responses among 35 perinatally infected subjects,including 2 children who spontaneously control viremia without antiretroviral therapy,21 children with viral loads (VL) of textless400 on HAART,and 12 viremic children. Gag-specific Th activity was assessed by lymphoproliferative assay,and responses were mapped using overlapping Gag peptides in an IFN-gamma ELISPOT. Robust proliferative responses were detected in the children exhibiting spontaneous control of viremia,and mapping of targeted Gag regions in one such subject identified multiple epitopes. Among children textgreateror=5 years old,14 of 17 subjects with VL of textless400 on HAART demonstrated a significant p24 proliferative response (median p24 stimulation index,20),in contrast with only 1 of 9 viremic children (median p24 stimulation index,2.0; p = 0.0008). However,no subject younger than 5 years of age possessed a significant response,even when viremia was fully suppressed. When compared with adults with VL of textless400 on HAART,Th responses among children with VL of textless400 were both more frequent (p = 0.009) and of greater magnitude (p = 0.002). These data suggest that children may have a greater intrinsic capacity to reconstitute HIV-1-specific immunity than adults,and may be excellent candidates for immune-based therapies. View Publication

CD4+ T cells are required for immunity against many viral infections,including HIV-1 where a positive correlation has been observed between strong recall responses and low HIV-1 viral loads. Some HIV-1-specific CD4+ T cells are preferentially infected with HIV-1,whereas others escape infection by unknown mechanisms. One possibility is that some CD4+ T cells are protected from infection by the secretion of soluble HIV-suppressive factors,although it is not known whether these factors are produced during primary antigen-specific responses. Here,we show that soluble suppressive factors are produced against CXCR4 and CCR5 isolates of HIV-1 during the primary immune response of human CD4+ T cells. This activity requires antigenic stimulation of naïve CD4+ T cells. One anti-CXCR4 factor is macrophage-derived chemokine (chemokine ligand 22,CCL22),and anti-CCR5 factors include macrophage inflammatory protein-1 alpha (CCL3),macrophage inflammatory protein-1 beta (CCL4),and RANTES (regulated upon activation of normal T cells expressed and secreted) (CCL5). Intracellular staining confirms that CD3+CD4+ T cells are the source of the prototype HIV-1-inhibiting chemokines CCL22 and CCL4. These results show that CD4+ T cells secrete an evolving HIV-1-suppressive activity during the primary immune response and that this activity is comprised primarily of CC chemokines. The data also suggest that production of such factors should be considered in the design of vaccines against HIV-1 and as a mechanism whereby the host can control infections with this virus. View Publication

Human immunodeficiency virus type 1 (HIV-1) isolates from 20 chronically infected patients who participated in a structured treatment interruption (STI) trial were studied to determine whether viral fitness influences reestablishment of viremia. Viruses derived from individuals who spontaneously controlled viremia had significantly lower in vitro replication capacities than viruses derived from individuals that did not control viremia after interruption of antiretroviral therapy (ART),and replication capacities correlated with pre-ART and post-STI viral set points. Of note,no clinically relevant improvement of viral loads upon STI occurred. Virus isolates from controlling and noncontrolling patients were indistinguishable in terms of coreceptor usage,genetic subtype,and sensitivity to neutralizing antibodies. In contrast,viruses from controlling patients exhibited increased sensitivity to inhibition by chemokines. Sensitivity to inhibition by RANTES correlated strongly with slower replication kinetics of the virus isolates,suggesting a marked dependency of these virus isolates on high coreceptor densities on the target cells. In summary,our data indicate that viral fitness is a driving factor in determining the magnitude of viral rebound and viral set point in chronic HIV-1 infection,and thus fitness should be considered as a parameter influencing the outcome of therapeutic intervention in chronic infection. View Publication

Human immunodeficiency virus type 1 (HIV-1) subtype C viruses with different coreceptor usage profiles were isolated from 29 South African patients with advanced AIDS. All 24 R5 isolates were inhibited by the CCR5-specific agents,PRO 140 and RANTES,while the two X4 viruses and the three R5X4 viruses were sensitive to the CXCR4-specific inhibitor,AMD3100. The five X4 or R5X4 viruses were all able to replicate in peripheral blood mononuclear cells that did not express CCR5. When tested using coreceptor-transfected cell lines,one R5 virus was also able to use CXCR6,and another R5X4 virus could use CCR3,BOB/GPR15,and CXCR6. The R5X4 and X4 viruses contained more-diverse V3 loop sequences,with a higher overall positive charge,than the R5 viruses. Hence,some HIV-1 subtype C viruses are able to use CCR5,CXCR4,or both CXCR4 and CCR5 for entry,and they are sensitive to specific inhibitors of entry via these coreceptors. These observations are relevant to understanding the rapid spread of HIV-1 subtype C in the developing world and to the design of intervention and treatment strategies. View Publication

HIV-1 replication in simian cells is restricted at an early postentry step because of the presence of an inhibitory cellular factor. This block reduces the usefulness of HIV-1-based lentiviral vectors in primate animal models. Here,we demonstrate that substitution of the cyclophilin A (CyPA) binding region in the capsid of an HIV-1-based lentiviral vector (LV) with that of the macrophage tropic HIV-1 Ba-L resulted in a vector that was resistant to the inhibitory effect and efficiently transduced simian cells. Notably,the chimeric gag LV efficiently transduced primary simian hematopoietic progenitor cells,a critical cellular target in gene therapy. The alterations in the CyPA binding region did not affect CyPA incorporation; however,transduction by the gag chimeric LV seemed to be relatively insensitive to cyclosporin A,indicating that it does not require CyPA for early postentry steps. In dual infection experiments,the gag chimeric LV failed to remove the block to transduction of the WT LV,suggesting that the gag chimeric LV did not saturate the inhibitory simian cellular factor. These data suggest that the CyPA binding region of capsid contains a viral determinant involved in the postentry restriction of HIV-1-based lentiviral vectors. Overall,the findings demonstrate that the host range of HIV-1-based LV can be altered by modifications in the packaging construct. View Publication

Cellular immune responses play a critical role in the control of human immunodeficiency virus type 1 (HIV-1); however,the breadth of these responses at the single-epitope level has not been comprehensively assessed. We therefore screened peripheral blood mononuclear cells (PBMC) from 57 individuals at different stages of HIV-1 infection for virus-specific T-cell responses using a matrix of 504 overlapping peptides spanning all expressed HIV-1 proteins in a gamma interferon-enzyme-linked immunospot (Elispot) assay. HIV-1-specific T-cell responses were detectable in all study subjects,with a median of 14 individual epitopic regions targeted per person (range,2 to 42),and all 14 HIV-1 protein subunits were recognized. HIV-1 p24-Gag and Nef contained the highest epitope density and were also the most frequently recognized HIV-1 proteins. The total magnitude of the HIV-1-specific response ranged from 280 to 25,860 spot-forming cells (SFC)/10(6) PBMC (median,4,245) among all study participants. However,the number of epitopic regions targeted,the protein subunits recognized,and the total magnitude of HIV-1-specific responses varied significantly among the tested individuals,with the strongest and broadest responses detectable in individuals with untreated chronic HIV-1 infection. Neither the breadth nor the magnitude of the total HIV-1-specific CD8+-T-cell responses correlated with plasma viral load. We conclude that a peptide matrix-based Elispot assay allows for rapid,sensitive,specific,and efficient assessment of cellular immune responses directed against the entire expressed HIV-1 genome. These data also suggest that the impact of T-cell responses on control of viral replication cannot be explained by the mere quantification of the magnitude and breadth of the CD8+-T-cell response,even if a comprehensive pan-genome screening approach is applied. View Publication