Comparative evaluation of oral and intranasal priming with replication-competent adenovirus 5 host range mutant (Ad5hr)-simian immunodeficiency virus (SIV) recombinant vaccines on immunogenicity and protective efficacy against SIV(mac251).

Oral, replication-competent Ad-HIV vaccines are advancing to human trials. Previous evaluation of protective efficacy in non-human primates has primarily followed upper respiratory tract administrations. Here we compared sequential oral (O/O) versus intranasal/oral (I/O) priming of rhesus macaques with Ad5 host range mutant-SIV recombinants expressing SIV env/rev, gag, and nef genes followed by boosting with SIV gp120 protein. Cellular immune responses in PBMC were stronger and more frequent after I/O administration. Both groups developed mucosal immunity, including memory cells in bronchial alveolar lavage, and gut-homing receptors on PBMC. Following intrarectal SIV(mac251) challenge, both groups exhibited equivalent, significant protection and robust post-challenge cellular immunity. Our results illustrate the promise of oral replication-competent Ad-recombinant vaccines. Pre-challenge PBMC ELISPOT and proliferative responses did not predict protection in the O/O group, highlighting the need for simple, non-invasive methods to reliably assess mucosal immunity.

An adenovirus-based HIV subtype B prime/boost vaccine regimen elicits antibodies mediating broad antibody-dependent cellular cytotoxicity against non-subtype B HIV strains.

Although HIV subtype B predominates in North America and Western Europe, most HIV infections worldwide are non-subtype B. Globally effective AIDS vaccines need to elicit broad immunity against multiple HIV strains. In this study, 10 chimpanzees were intranasally primed sequentially with adenovirus type 5 (Ad5)- and Ad7-HIVMNenv/rev recombinants and boosted twice intramuscularly with heterologous oligomeric HIVSF162 gp140DeltaV2 protein in MF59 adjuvant. Sera were evaluated for binding, neutralizing, and antibody-dependent cellular cytotoxicity (ADCC) against HIV clades A, B, C, and CRF01_AE. The vaccine regimen elicited high-titered HIV subtype A, B, C and CRF01_AE gp120-binding antibodies. Sera from 7 of 10 vaccinated chimpanzees cross-neutralized the heterologous South African subtype C primary HIVTV-1 isolate. Significant cross-clade neutralization against other subtype A, C and E isolates was not observed. Sera from all animals mediated ADCC of cells coated with gp120 from HIV subtypes A and B. Nine of 10 animals also exhibited ADCC activity against HIV subtype C and CRF01_AE gp120-coated targets. This subtype B Ad-HIV recombinant prime/envelope protein boost regimen is a promising approach for eliciting broad ADCC activity against diverse HIV clades. Incorporating additional non-subtype B envelope genes and protein boosts in a multivalent strategy may be required to elicit broader neutralizing antibodies against non-subtype B HIV strains.

Oral delivery of replication-competent adenovirus vectors is well tolerated by SIV- and SHIV-infected rhesus macaques.

Although replication-competent adenovirus (Ad) vectors are promising in AIDS vaccine design, their safety in immune compromised hosts is unknown. To initially address this question, enteric-coated tablets containing a replicating Ad vector were orally administered to SHIV- and SIV-infected rhesus macaques with normal, intermediate or low CD4 T cell counts and stable disease. The vector was detected within a week after tablet administration in stools of all animals but not in nasal secretions, indicating no spread of virus to the upper respiratory tract. CD4 T cell counts and viral loads remained stable in all animals and no signs of fever, weight loss, or other clinical symptoms of Ad-induced disease were observed during 10 weeks of follow-up. Oral delivery of the replicating Ad vector was safe and well tolerated by SHIV- and SIV-infected hosts. Oral enteric-coated tablets may prove safe for administering replicating Ad-vectored vaccines in areas with high HIV prevalence.

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.

Evaluation of envelope vaccines derived from the South African subtype C human immunodeficiency virus type 1 TV1 strain.

Human immunodeficiency virus type 1 (HIV-1) subtype C infections are on the rise in Sub-Saharan Africa and Asia. Therefore, there is a need to develop an HIV vaccine capable of eliciting broadly reactive immune responses against members of this subtype. We show here that modified HIV envelope (env) DNA vaccines derived from the South African subtype C TV1 strain are able to prime for humoral responses in rabbits and rhesus macaques. Priming rabbits with DNA plasmids encoding V2-deleted TV1 gp140 (gp140TV1DeltaV2), followed by boosting with oligomeric protein (o-gp140TV1DeltaV2) in MF59 adjuvant, elicited higher titers of env-binding and autologous neutralizing antibodies than priming with DNA vaccines encoding the full-length TV1 env (gp160) or the intact TV1 gp140. Immunization with V2-deleted subtype B SF162 env and V2-deleted TV1 env together using a multivalent vaccine approach induced high titers of oligomeric env-binding antibodies and autologous neutralizing antibodies against both the subtypes B and C vaccine strains, HIV-1 SF162 and TV1, respectively. Low-level neutralizing activity against the heterologous South African subtype C TV2 strain, as well as a small subset of viruses in a panel of 13 heterologous primary isolates, was observed in some rabbits immunized with the V2-deleted vaccines. Immunization of rhesus macaques with the V2-deleted TV1 DNA prime/protein boost also elicited high titers of env-binding antibodies and moderate titers of autologous TV1 neutralizing antibodies. The pilot-scale production of the various TV1 DNA vaccine constructs and env proteins described here should provide an initial platform upon which to improve the immunogenicity of these subtype C HIV envelope vaccines.

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.