Cellular immune responses, particularly those associated with CD3؉ CD8 ؉ cytotoxic T lymphocytes (CTL), play a primary role in controlling viral infection, including persistent infection with human immunodeficiency virus type 1 (HIV-1). Accordingly, recent HIV-1 vaccine research efforts have focused on establishing the optimal means of eliciting such antiviral CTL immune responses. We evaluated several DNA vaccine formulations, a modified vaccinia virus Ankara vector, and a replication-defective adenovirus serotype 5 (Ad5) vector, each expressing the same codon-optimized HIV-1 gag gene for immunogenicity in rhesus monkeys. The DNA vaccines were formulated with and without one of two chemical adjuvants (aluminum phosphate and CRL1005). The Ad5-gag vector was the most effective in eliciting anti-Gag CTL. The vaccine produced both CD4؉ and CD8 ؉ T-cell responses, with the latter consistently being the dominant component. To determine the effect of existing antiadenovirus immunity on Ad5-gag-induced immune responses, monkeys were exposed to adenovirus subtype 5 that did not encode antigen prior to immunization with Ad5-gag. The resulting anti-Gag T-cell responses were attenuated but not abolished. Regimens that involved priming with different DNA vaccine formulations followed by boosting with the adenovirus vector were also compared. Of the formulations tested, the DNA-CRL1005 vaccine primed T-cell responses most effectively and provided the best overall immune responses after boosting with Ad5-gag. These results are suggestive of an immunization strategy for humans that are centered on use of the adenovirus vector and in which existing adenovirus immunity may be overcome by combined immunization with adjuvanted DNA and adenovirus vector boosting.

The mechanism by which low affinity adhesion molecules function to produce stable cell-cell adhesion is unknown. In solution, the interaction of human CD2 with its ligand CD58 is of low affinity (500 mM ؊1 ) and the interaction of rat CD2 with its ligand CD48 is of still lower affinity (40 mM ؊1 ). At the molecular level, however, the two systems are likely to be topologically identical. Fluorescently labeled glycosylphosphatidylinositol-anchored CD48 and CD58 were prepared and incorporated into supported phospholipid bilayers, in which the ligands were capable of free lateral diffusion. Quantitative fluorescence imaging was used to study the binding of cell surface human and rat CD2 molecules to the fluorescent ligands in contact areas between Jurkat cells and the bilayers. These studies provide two major conclusions. First, CD2/ligand interactions cooperate to align membranes with nanometer precision leading to a physiologically effective two-dimensional affinity. This process does not require the intact cytoplasmic tail of CD2. Second, the degree of membrane alignment that can be achieved by topologically similar receptors deteriorates with decreasing affinity. This suggests an affinity limit for the ability of this mode of cooperativity to achieve stable cell-cell adhesion at approximately 10 mM ؊1 .Many biologically important events are initiated and sustained through low affinity binding interactions in cell-cell and cell-matrix contact areas. Several models suggest that active intracellular mechanisms are engaged to assist these low affinity interactions (1-3). This intracellular regulation can occur through the cytoplasmic domains of the adhesion molecules as in integrins and cadherins (4 -6). Other models hypothesize that the ectodomains of low affinity adhesion molecules can oligomerize to produce stable arrays that enhance the intrinsic affinity of the ectodomain interaction (7-9). Testing of these models has been limited by the absence of quantitative affinity measurements in contact areas. The fluid mosaic membrane can be viewed as a nearly two-dimensional solution in which diffusion is constrained to the plane of the membrane, with a small third dimension arising from the flexible tethering of the membrane anchored adhesion molecules (10). The contact area between two apposing membranes may have additional depth in the third dimension due to fluctuations in the distance between the two membranes. The thesis of this study is that low affinity adhesion interactions can succeed in forming many bonds between cells by organizing the two apposing membranes so that the depth of the third dimension is small and optimal for the relevant adhesion molecule pair. When the third dimension is minimized by this cooperativity, the adhesion molecule concentration is increased and bond formation is strongly favored.In this study, we tested this hypothesis using the human and rat CD2 adhesion systems. CD2 is an adhesion molecule expressed primarily on T lymphocytes in human, rat and other mammalian species. In all sp...

No abstract

No abstract