Ann D. M. Rees

Anti-CD4-Binding Domain Antibodies Complexed with HIV Type 1 Glycoprotein 120 Inhibit CD4+ T Cell-Proliferative Responses to Glycoprotein 120

HIV-specific CD4+ helper T cell responses, particularly to the envelope glycoproteins, are usually weak or absent in the majority of HIV-seropositive individuals. Since antibodies, by their capacity to alter antigen uptake and processing, are known to have modulatory effects on CD4+ T cell responses, we investigated the effect of antibodies produced by HIV-infected individuals on the CD4+ T cell response to HIV-1 gp120. Proliferative responses of gp120-specific CD4+ T cells were inhibited in the presence of either serum immunoglobulin from HIV-infected individuals or human monoclonal antibodies specific for the CD4-binding domain (CD4bd) of gp120. Human monoclonal antibodies to other gp120 epitopes did not have the same effect. The anti-CD4bd antibodies complexed with gp120 suppressed T cell lines specific for varying gp120 epitopes but did not affect T cell proliferation to non-HIV antigens. Moreover, inhibition by the anti-CD4bd/gp120 complexes was observed regardless of the types of antigen-presenting cells used to stimulate the T cells. These results indicate that the presence of anti-CD4bd antibodies complexed with gp120 can strongly suppress CD4+ helper T responses to gp120.

Immunization with Human Immunodeficiency Virus Type 1 rgp120W61D in QS21/MPL Adjuvant Primes T Cell Proliferation and C-C Chemokine Production to Multiple Epitopes within Variable and Conserved Domains of gp120W61D

Human immunodeficiency virus type 1 (HIV-1) gp120W61D-specific T cell lines (TCL) were generated from an HIV-1-seronegative volunteer who received rgp120W61D in QS21/MPL adjuvant with emulsion. TCL were challenged with pools of consecutive, overlapping peptides spanning the gp120W61D sequence and then with the individual peptides of the immunostimulatory pool. T cell epitopes were found within both variable and conserved domains, and there was no evidence of a single immunodominant epitope. The two most frequently recognized peptides were located in the C1 domain and in the C-terminal region of the V3 loop. Several TCL were shown to recognize multiple peptides from nonoverlapping regions. Peptides from both conserved and variable domains were capable of inducing MIP-1alpha, MIP-1beta, and RANTES production. When tested against the equivalent peptide from the HIV-1IIIB sequence, however, TCL were able to tolerate only minor conserved changes in the amino acid sequence.

An early antigen‐presenting cell defect in HIV‐1‐infected patients correlates with CD4 dependency in human T‐cell clones

We have used a defined panel of nine HIV peptide‐specific T‐cell clones (TLC) generated from a healthy volunteer to evaluate the antigen‐presenting cell (APC) function of human immunodeficiency virus‐1 (HIV‐1)‐infected patients. Peripheral blood mononuclear cells (PBMC) from HLA‐matched seropositive and uninfected volunteers were compared for their capacity to present peptide to TLC specific for the V3 loop of HIV‐1 envelope glycoprotein gp120, influenza haemagglutinin or the mycobacterial 19 000 MW antigen. APC from uninfected volunteers (HIV−APC) invariably presented peptides to all TLC with comparable efficiency. In contrast, using APC from HIV‐1‐infected subjects (HIV+APC), three patterns of responsiveness were observed. The first group of TLC was not stimulated by HIV+APC, even early in infection. The second responded to all APC comparably. The third, and intermediate group, responded to APC from some clinically asymptomatic, but not acquired immune deficiency syndrome (AIDS), patients. The two additional TLC, derived from other donors and with specificity for non‐HIV peptides, showed similar variation in response to HIV+APC. The different patterns of response to HIV+APC did not correlate with the fine specificity or cytokine phenotypes of the TLC. Neither was the defect due to decreased levels of expression of APC molecules involved in delivering the first or second signal required for T‐cell activation. APC mixing experiments showed no evidence of APC‐derived inhibitory factors. Furthermore, the defect was independent of T cells or their products and was equally expressed in monocytes and dendritic cells. Instead, responsiveness was inversely related to the degree of CD4 dependency, suggesting that the underlying mechanism was a CD4 APC‐associated–gp120 interaction. The early appearance of this defect in HIV‐1 infection co‐incident with the loss of recall responses is consistent with a role for APC dysfunction in pathogenesis.

CD4+ T-cell recognition of diverse clade B HIV-1 isolates

Objectives:To evaluate the effect of sequence variation within the gp120 V3 loop on CD4 T-cell recognition. Design:CD4 T-cell clones were generated using synthetic peptides to circumvent the difficulties of using polyclonal T-cell responses. Peptides based on other HIV isolates were then used to determine the influence of single and multiple sequence differences. Results:Three of the panels of T-lymphocyte clones (TLC), which were all specific to diverse HIV-1 clade B gp120 V3-loop peptides differing in a limited number of residues, had heterogeneous patterns of response to peptides differing in length and sequence indicating that they recognized distinct but overlapping epitopes. The panels of TLC also differed in the extent to which they tolerated sequence differences between cell-culture-adapted or primary HIV-1 isolates. One panel responded to peptides based on several clade B and one clade D isolate. In contrast, two panels, generated from two different donors using the same peptide, only responded to a limited number of clade B isolates, whereas another only recognized HIV-1BRU. Two of the panels were also stimulated by peptides based on clinical isolates from one patient with some sequence changes enhancing T-cell recognition. Conclusions:These data are consistent with highly diverse CD4 T-cell recognition of the HIV-1 gp120 V3 loop, which is influenced by the sequence differences within the T-cell epitopic region and has implications for the pathogenesis and design of vaccines against HIV-1.

Tandem peptide epitopes facilitate CD4-dependent activation of T cell clones.

Peptides that consist of two tandemly repeated epitopes joined by a flexible linker have an increased affinity for class II molecules and are more potent at inducing prolireration of T cell clones than monomeric epitopes. The increase in potency of peptides with two epitopes for individual T cell clones is proportional to the relative CD4 dependence of the clones. We show that epitope dimers activate T cell clones that respond sub‐optimally to monomeric epitopes presented by APC from HIV‐infected donors. We hypothesize that HIV+ APC normally fail to stimulate the clones because virally encoded gpl20 sequesters CD4 from the activation complex, but epitope dimers overcome this effect because they are better able to recruit CD4.

Dendritic cells from HIV-1-infected patients naturally express HIV-1 gp120 V3 loop-derived peptide ligands

Little is known of the peptide ligands expressed in vivo on antigen‐presenting cells (APC) or of the APC lineages involved. In this study we have addressed this question using HLA‐DRβ1*0101‐restricted CD4 T cell clones (TLC) specific for a synthetic peptide based on the HIV‐1 gp120 V3 loop consensus sequence for the Clade B isolates predominantly found in European and North American patients. These TLC were found to respond, in a dose‐dependent manner, to freshly isolated HIV‐infected patient APC in the absence of exogenously added peptides. Further APC purification showed that the naturally expressed peptide ligands were present in both the APC lineages shown to be infected with the virus and were most strongly detectable on purified blood dendritic cells. Peptides based on consensus sequences of viruses isolated from one of the patients over the period when naturally expressed peptide ligands could be detected were all found to stimulate TLC proliferation. These studies, therefore, show that peptide ligands derived from natural infection are detectable on APC lineages, particularly on dendritic cells which play an important role in the immune response to viruses. Even small differences in sequence between the vaccine isolate and the natural infection, if they occur in the key residues of protective T cell epitopes, could therefore have a profound effect on the efficacy of vaccines against viruses with high rates of mutation.

Probing a repertoire of T cells responding to a mycobacterial antigen

Following infection, Mycobacterium tuberculosis may often persist in host tissues for years. This prolonged interaction may result in a dynamic equilibrium between host and parasite. The situation can be disturbed with reactivation of the infection. Ability to clone T cells and sustain them in long term culture allows the study of T cells in vitro. These studies can be used to understand the nature of the equilibrium between host and parasite. We have studied T cell immunity to M. tuberculosis by using a mycobacterial antigen purified by absorbance to a monoclonal (mab) to raise T cell clones. The mab, TB68, bound to antigenic determinant(s) in all strains of M. tuberculosis and M. bovis BCG and vallee [1]. T cell clones were generated from peripheral blood mononuclear cells (PBMC) of a normal BCG vaccinated individual [2]. Clonality was established by sub-cloning as previously described [3]. Clones of both helper/inducer (leu 1,3+, OKT4+) and suppressor/cytotoxic (leu 1,2+) phenotype were generated and examples of both will be discussed. All of these clones were found to be positive for the antigen recognised by the mab leu 8a. The antigenic specificity of individual clones was determined by co-culturing clone cells with feeders and a variety of antigenic preparations, some of which are known to contain, at least in part, determinants of the eliciting antigen [4].