Broadly reactive HIV-2 and SIVmac specific antibody-dependent cellular cytotoxicity in immunized and infected cynomolgus monkeys

Innovative approaches to develop prophylactic and therapeutic vaccines against HIV/AIDS

The acquired immunodeficiency syndrome (AIDS) emerged in the human population in the summer of 1981. According to the latest United Nations estimates, worldwide over 33 million people are infected with human immunodeficiency virus (HIV) and the prevalence rates continue to rise globally. To control the alarming spread of HIV, an urgent need exists for developing a safe and effective vaccine that prevents individuals from becoming infected or progressing to disease. To be effective, an HIV/AIDS vaccine should induce broad and long-lasting humoral and cellular immune responses, at both mucosal and systemic level. However, the nature of protective immune responses remains largely elusive and this represents one of the major roadblocks preventing the development of an effective vaccine. Here we summarize our present understanding of the factors responsible for resistance to infection or control of progression to disease in human and monkey that may be relevant to vaccine development and briefly review recent approaches which are currently being tested in clinical trials. Finally, the rationale and the current status of novel strategies based on nonstructural HIV-1 proteins, such as Tat, Nef and Rev, used alone or in combination with modified structural HIV-1 Env proteins are discussed.

A simplified method for the rapid fluorometric assessment of antibody-dependent cell-mediated cytotoxicity

We demonstrate that the FATAL cytolysis assay can be adapted into a rapid and fluorometric antibody-dependent cellular cytotoxicity assay (RFADCC). The RFADCC relies on double-staining target cells with a membrane dye (PKH-26) and a viability dye (CFSE) prior to the addition of antibody and effector cells. We used the RFADCC to assess dose-dependent and envelope-specific anti-human immunodeficiency virus (HIV) ADCC responses mediated by monoclonal antibody-2G12 and human sera. Using the assay, we also detected early anti-simian immunodeficiency virus (SIV) ADCC responses in rhesus macaques infected with pathogenic SIV(mac251). Importantly, the RFADCC was further useful in monitoring anti-HIV and anti-SIV ADCC responses elicited by immunizing chimpanzees and rhesus macaques with replicating adenovirus-based AIDS vaccine candidates. In comparison to the standard chromium release assay, the RFADCC provides a higher cell killing readout and is advantageous in allowing use of viably frozen as well as fresh effector cells, thus facilitating assay standardization. The RFADCC is therefore a simple, reliable, and highly sensitive method that can be applied to assess the ADCC activity of monoclonal antibodies as well as ADCC responses elicited by HIV or SIV infection or by AIDS vaccine candidates.

Antibody-dependent cell-mediated cytotoxic responses in participants enrolled in a phase I/II ALVAC-HIV/AIDSVAX B/E prime-boost HIV-1 vaccine trial in Thailand

Antibody-dependent cell-mediated cytotoxicity (ADCC) was assessed in volunteers participating in an ALVAC-HIV (vCP1521)/AIDSVAX B/E gp120 prime-boost vaccine trial in Thailand. ADCC activity was measured using chromium release from gp120 subtype B- and CRF01_AE-coated targets in 95 vaccinees and 28 placebo recipients. There was a significant difference in the magnitude of the ADCC response to both targets between vaccinees and placebo recipients. The frequency of responders to subtype B and to CRF01_AE was 96% and 84% in the vaccine group versus 11% and 7% in the placebo group. The results demonstrate that this HIV vaccine is a potent inducer of ADCC activity and may be an additional protection of this prime-boost vaccine in preventing HIV disease.

Vaccine-elicited antibodies mediate antibody-dependent cellular cytotoxicity correlated with significantly reduced acute viremia in rhesus macaques challenged with SIVmac251

Effector cells armed with Abs can eliminate virus-infected target cells by Ab-dependent cellular cytotoxicity (ADCC), an immune mechanism that has been largely overlooked in HIV vaccine development. Here, we show that a prime/boost AIDS vaccine approach elicits potent ADCC activity correlating with protection against SIV in rhesus macaques (Macacca mulatta). Priming with replicating adenovirus type 5 host range mutant-SIV recombinants, followed by boosting with SIV gp120, elicited Abs with ADCC activity against SIV(mac251)-infected cells. In vitro ADCC activity correlated with in vivo reduced acute viremia after a mucosal challenge with pathogenic SIV. Our findings expose ADCC activity as an immune correlate that may be relevant in the rational design of an efficacious vaccine against HIV.

Antibody-dependent cellular cytotoxicity in HIV type 1-infected patients receiving VaxSyn, a recombinant gp160 envelope vaccine

Antibody-dependent cellular cytotoxicity (ADCC) activity was measured in 60 human immunodeficiency virus (HIV-1)-infected patients receiving a recombinant gp160 (rgp160) envelope protein of HIV-1(NL4-3) in alum and 64 receiving placebo over a 5-year study period. There was no difference in the percentage of ADCC responders when comparing rgp160-immunized patients (mean, 78.4%) with those receiving placebo alone (mean, 81.5%) at any time point examined. Patients were further divided into progression groups regardless of their vaccine status. ADCC activity was somewhat higher in rapid than in slow-progressing groups, although the number that had detectable ADCC activity was equivalent in each group. ADCC activity of sera from rapid- and slow-progressing groups against primary or laboratory isolate envelopes was similar. This study showed that transcription with rgp160 did not appear to enhance HIV-specific ADCC activity. ADCC activity did not appear to correlate with protection against AIDS in this cohort of HIV-1-infected people.

HIV-2 and T cell recognition

HIV-2 is less pathogenic and less transmissible than HIV-1. Recent research in relation to deletions in the HIV nef gene and to immune cross-reactions between infections by HIV-2, HIV-1 and simian immunodeficiency virus suggests that T cell recognition and the control of viral replication may be more efficient in HIV-2 infection than in HIV-1 infection. These insights may be crucial to the design of effective vaccines.