Parameters influencing measurement of the Gag antigen-specific T-proliferative response to HIV type 1 infection

Evaluation of aldrithiol-2-inactivated preparations of HIV type 1 subtypes A, B, and D as reagents to monitor T cell responses

The development of HIV vaccines is an urgent priority and there is need to generate reagents representing multiple subtypes that can be used to screen HIV-1-specific responses. We used Aldrithiol-2 (AT-2), a mild oxidizing reagent, to eliminate the infectivity of HIV while maintaining its structure and ability to be processed for presentation to T cells. Inactivated subtype A, B, and D viruses were evaluated for their ability to stimulate T cell responses in PBMC samples from 18 U.S. subjects infected with HIV-1 subtype B and 32 Ugandan subjects infected with subtypes A and D or recombinants AC and AD. Five HIV-1-negative samples were also analyzed. T cell responses to AT-2-inactivated viral isolates were monitored by interferon-gamma (IFN-gamma) intracellular cytokine secretion (ICS) analysis; matched microvesicle preparations served as negative controls. Among the 18 subtype B infected subjects, 39% had CD3(+) CD4 (+) IFN-gamma responses and 67% had CD3(+) CD8(+) IFN-gamma responses. Of the 32 Ugandan subjects, 34% demonstrated CD3(+) CD4(+) IFN-gamma responses and 78% demonstrated CD3(+) CD8(+) IFN-gamma responses. Both subtype-specific and cross-reactive responses were observed. Responses to the AT-2 viruses tended to be lower in magnitude than those detected by a set of overlapping gag peptides. Robust lymphoproliferative responses to AT-2 viruses were seen in a subset of subjects. In conclusion, AT-2-inactivated HIV-1 virions stimulated both CD4 and CD8 HIV-1-specific responses and may provide an additional reagent for screening HIV-1-specific responses in HIV seropositives and vaccinees.

Enhanced rates and magnitude of immune responses detected against an HIV vaccine: effect of using an optimized process for isolating PBMC

Quantitative analysis of cell-mediated immune responses induced by candidate HIV vaccines requires robust procedures for collecting and processing human peripheral mononuclear blood cells (PBMCs). We evaluated several parameters in order to optimize a sample handling process that would be suitable for a multicenter clinical trial. Among the findings, systematic increases in the magnitude of IFN-gamma ELISpot responses were observed when the time from blood collection to PBMC freezing was reduced to <12 h. By implementing these improvements within an ongoing clinical trial, the estimated immunologic response rates to an adenovirus- based HIV vaccine increased by more than 20 percentage points to approximately 80% of the vaccine recipients against any of the vaccine antigens and the average levels of T cell response improved more than 3-fold. These studies establish the importance of optimal conditions for PBMC collection and handling to the success of a clinical development program.

Optimization of intracellular cytokine staining for the quantitation of antigen-specific CD4+ T cell responses in rhesus macaques

Standard proliferation assays used for analysis of CD4+ T cell function have significant shortcomings, including limited sensitivity, lack of truly quantitative readouts and significant variability. We have optimized an intracellular cytokine staining (ICS) assay in rhesus macaques which allows us to identify virus-specific CD4+ T cells at the single-cell level with high sensitivity while reducing background staining to a minimum. A variety of parameters were tested to determine the optimal experimental conditions necessary for the detection of antigen-specific CD4+ T cells in macaques. Central to our optimized protocol was the addition of cross-linked costimulatory anti-CD28 and anti-CD49d Mabs, a modification which resulted in up to threefold enhancement of the frequency of TNF-alpha-secreting CD4+ T cells following superantigen- or antigen-specific stimulation. The ICS protocol was also optimized with respect to antigen concentration and duration of antigenic stimulation. These modifications resulted in a convenient and highly reproducible assay with intra- and inter-assay variability of less than 10%. Although cryopreservation of PBMC generally led to a 40% to 80% decrease in the frequency of antigen-specific CD4+ T cells detected by ICS using stimulation with viral proteins, the use of overlapping peptide pools minimized the effects of cryopreservation on ICS responses. The use of more sensitive techniques such as ICS permits delineation of antigen-specific cells at the single cell level and should provide new insights into pathogen-specific immune responses in the rhesus macaque model.

Safety and immunogenicity of ALVAC vCP1452 and recombinant gp160 in newly human immunodeficiency virus type 1-infected patients treated with prolonged highly active antiretroviral therapy

In order to boost immune responses in persons in whom highly active antiretroviral therapy (HAART) was initiated within 120 days of the onset of symptoms of newly acquired human immunodeficiency virus type 1 (HIV-1) infection, we administered vaccines containing a canarypox virus vector, vCP1452, with HIV-1 genes encoding multiple HIV-1 proteins, and recombinant gp160. Fifteen HIV-1-infected subjects who achieved sustained suppression of plasma viremia for at least 2 years were enrolled. While continuing antiretroviral therapy, each subject received at least four intramuscular injections of the vaccines on days 0, 30, 90, and 180. Adverse events were mild, with the most common being transient tenderness at the vCP1452 injection site. Of the 14 patients who completed vaccination, 13 had significant increases in anti-gp120 or anti-p24 antibody titers, and 9 had transient augmentation of their T-cell proliferation responses to gp160 and/or p24. HIV-1-specific CD8(+) T cells were quantified using an intracellular gamma interferon staining assay. Among 11 patients who had increased CD8(+) T-cell responses, seven had responses to more than one HIV-1 antigen. In summary, vaccination with vCP1452 and recombinant gp160 appears safe and immunogenic in newly HIV-1-infected patients on HAART.

Characterization of HIV-specific proliferative T cell responses in HIV-infected persons

Virus-specific helper T cell responses are thought to be an important host defense in HIV infection. The proliferative responses to HIV p24, p55, and gp120 were tested in a cohort of 27 HIV-infected subjects. Vigorous proliferative responses directed at the Gag protein with stimulation indices in excess of 6 were detected in 10 of the individuals tested but an Env-specific response was present in only 1 subject. Viral load and proliferative activity to Gag were inversely correlated in untreated individuals. Proliferation was also observed in some individuals treated in the chronic phase of infection, and responses were maintained over time in the absence of detectable viremia. Positive proliferative responses could also occasionally be detected in treated persons with CD4(+) cell counts below 200/microl. Thus, vigorous Gag-specific proliferative responses are present in a minority of HIV-infected individuals and can be detected in individuals receiving highly active antiretroviral therapy at advanced disease stages. Proliferative responses are maintained for an extended time period in the presence of antiviral therapy.