Cross-reactive neutralizing antibodies (NAbs) are found in the sera of many HIV-1–infected individuals, but the virologic basis of their neutralization remains poorly understood. We used knowledge of HIV-1 envelope structure to develop antigenically resurfaced glycoproteins specific for the structurally conserved site of initial CD4 receptor binding. These probes were used to identify sera with NAbs to the CD4-binding site (CD4bs) and to isolate individual B cells from such an HIV-1–infected donor. By expressing immunoglobulin genes from individual cells, we identified three monoclonal antibodies, including a pair of somatic variants that neutralized over 90% of circulating HIV-1 isolates. Exceptionally broad HIV-1 neutralization can be achieved with individual antibodies targeted to the functionally conserved CD4bs of glycoprotein 120, an important insight for future HIV-1 vaccine design.

Immunological memory is thought to depend upon a stem cell-like, self-renewing population of lymphocytes capable of differentiating into effector cells in response to antigen re-exposure. Here we describe a long-lived human memory T-cell population that displays enhanced self-renewal and multipotent capacity to derive central memory, effector memory and effector T cells. These cells, specific for multiple viral and self-tumor antigens, were found within a CD45RO−, CCR7+, CD45RA+, CD62L+, CD27+, CD28+ and IL-7Rα+ T-cell compartment characteristic of naïve T cells. However, they expressed increased levels of CD95, IL-2Rβ, CXCR3, and LFA-1, and exhibited numerous functional attributes distinctive of memory cells. Compared to known memory populations, these lymphocytes displayed increased proliferative capacity, more efficiently reconstituted immunodeficient hosts and mediated superior anti-tumor responses in a humanized mouse model. The identification of a human stem cell-like memory T-cell population is of direct relevance to the design of vaccines and T-cell therapies.

Establishing a CD8 ؉ T cell-mediated immune correlate of protection in HIV disease is crucial to the development of vaccines designed to generate cell-mediated immunity. Historically, neither the quantity nor breadth of the HIV-specific CD8 ؉ T-cell response has correlated conclusively with protection. Here, we assess the quality of the HIV-specific CD8 ؉ T-cell response by measuring 5 CD8 ؉ T-cell functions (degranulation, IFN-␥, MIP-1␤, TNF-␣, and IL-2) simultaneously in chronically HIV-infected individuals and elite nonprogressors. We find that the functional profile of HIV-specific CD8 ؉ T cells in progressors is limited compared to that of nonprogressors, who consistently maintain highly functional CD8 ؉ T cells. This limited functionality is independent of HLA type and T-cell memory phenotype, is HIV-specific rather than generalized, and is not effectively restored by therapeutic intervention. Whereas the total HIV-specific CD8 ؉ T-cell frequency did not correlate with viral load, the frequency and proportion of the HIV-specific T-cell response with highest functionality inversely correlated with viral load in the progressors. Thus, rather than quantity or phenotype, the quality of the CD8 ؉ T-cell functional response serves as an immune correlate of HIV disease progression and a potential qualifying factor for evaluation of HIV vaccine efficacy. (Blood. 2006;107:4781-4789)