CCR5 targeted SIV vaccination strategy preventing or inhibiting SIV infection

Cell-surface CCR5 is a major coreceptor with CD4 glycoprotein, mediating cellular entry of CCR5 strains of HIV-1 or SIV. We targeted the SIV CCR5 coreceptor in a combined CCR5-SIV antigen immunization strategy. Rhesus macaques were immunized i.m. with the 70 kDa heat shock protein (HSP70) covalently linked to the CCR5 peptides, SIV gpl20 and p27. Intravenous challenge with SIV mac 8980 prevented SIV infection or decreased the viral load with the CCR5-SIV combined vaccine. CC chemokines and antibodies which block and downmodulateCCR5 were induced, as well as immune responses to the subunit SIV antigens. This novel vaccination strategy complements cognate immunity to SIV with innate immunity to the CCR5 coreceptor of SIV.

Evidence for viral virulence as a predominant factor limiting human immunodeficiency virus vaccine efficacy

Current strategies in human immunodeficiency virus type 1 (HIV-1) vaccine development are often based on the production of different vaccine antigens according to particular genetic clades of HIV-1 variants. To determine if virus virulence or genetic distance had a greater impact on HIV-1 vaccine efficacy, we designed a series of heterologous chimeric simian/human immunodeficiency virus (SHIV) challenge experiments in HIV-1 subunit-vaccinated rhesus macaques. Of a total of 22 animals, 10 nonimmunized animals served as controls; the remainder were vaccinated with the CCR5 binding envelope of HIV-1(W6.1D). In the first study, heterologous challenge included two nonpathogenic SHIV chimeras encoding the envelopes of the divergent clade B HIV-1(han2) and HIV-1(sf13) strains. In the second study, all immunized animals were rechallenged with SHIV(89. 6p), a virus closely related to the vaccine strain but highly virulent. Protection from either of the divergent SHIV(sf13) or SHIV(han2) challenges was demonstrated in the majority of the vaccinated animals. In contrast, upon challenge with the more related but virulent SHIV(89.6p), protection was achieved in only one of the previously protected vaccinees. A secondary but beneficial effect of immunization on virus load and CD4(+) T-cell counts was observed despite failure to protect from infection. In addition to revealing different levels of protective immunity, these results suggest the importance of developing vaccine strategies capable of protecting from particularly virulent variants of HIV-1.

Efforts to broaden HIV-1-specific immunity by boosting with heterologous peptides or envelope protein and the influence of prior exposure to virus

In two previous studies, we have demonstrated the successful protection of human immunodeficiency virus type 1 (HIV-1)-vaccinated rhesus macaques from challenge with SHIV(SF13) with envelop immunogens derived from the closely related HIV-1(SF2) strain. Here we report on two follow-up studies in which we aimed to broaden immunity in order to elicit protection from a more diverse heterologous challenge with SHIV(SF33). In the first study, animals were boosted once with HIV-1(SF33) V2 and V3 peptides that were cross-linked to influenza immune-stimulating complexes (ISCOMs). In the second study, monkeys were boosted twice at 12-week intervals, using a heterologous recombinant gp120 derived from HIV-1(SF33) that was either incorporated into ISCOMs or mixed with the MF59 adjuvant. In both studies, the animals were challenged with 50 monkey infectious doses of SHIV(SF33) 4 weeks after the final boost. All controls became readily infected with the heterologous challenge virus SHIV(SF33). Neither boosting with heterologous SF33 peptides or gp120 afforded protection from infection to SF2-vaccinated animals that had previously resisted SHIV(SF13) challenge. These results demonstrate the importance of developing vaccine strategies that are capable of generating broad immune responses early in the immunization protocol. Furthermore, these findings may illustrate the potential pitfalls of early antigenic sin.

Comparison of immunity generated by nucleic acid-, MF59-, and ISCOM-formulated human immunodeficiency virus type 1 vaccines in Rhesus macaques: evidence for viral clearance

The kinetics of T-helper immune responses generated in 16 mature outbred rhesus monkeys (Macaca mulatta) within a 10-month period by three different human immunodeficiency virus type 1 (HIV-1) vaccine strategies were compared. Immune responses to monomeric recombinant gp120SF2 (rgp120) when the protein was expressed in vivo by DNA immunization or when it was delivered as a subunit protein vaccine formulated either with the MF59 adjuvant or by incorporation into immune-stimulating complexes (ISCOMs) were compared. Virus-neutralizing antibodies (NA) against HIV-1SF2 reached similar titers in the two rgp120SF2 protein-immunized groups, but the responses showed different kinetics, while NA were delayed and their levels were low in the DNA-immunized animals. Antigen-specific gamma interferon (IFN-gamma) T-helper (type 1-like) responses were detected in the DNA-immunized group, but only after the fourth immunization, and the rgp120/MF59 group generated both IFN-gamma and interleukin-4 (IL-4) (type 2-like) responses that appeared after the third immunization. In contrast, rgp120/ISCOM-immunized animals rapidly developed marked IL-2, IFN-gamma (type 1-like), and IL-4 responses that peaked after the second immunization. To determine which type of immune responses correlated with protection from infection, all animals were challenged intravenously with 50 50% infective doses of a rhesus cell-propagated, in vivo-titrated stock of a chimeric simian immunodeficiency virus-HIVSF13 construct. Protection was observed in the two groups receiving the rgp120 subunit vaccines. Half of the animals in the ISCOM group were completely protected from infection. In other subunit vaccinees there was evidence by multiple assays that virus detected at 2 weeks postchallenge was effectively cleared. Early induction of potent type 1- as well as type 2-like T-helper responses induced the most-effective immunity.