Heterologous human immunodeficiency virus type 1 priming-boosting immunization strategies involving replication-defective adenovirus and poxvirus vaccine vectors

Abstract

We compared the human immunodeficiency virus type 1 (HIV-1)-specific cellular immune responses elicited in nonhuman primates by HIV-1 gag-expressing replication-defective adenovirus serotype 5 (Ad5) or poxvirus vectors, used either alone or in combination with each other. The responses arising from a heterologous Ad5 priming-poxvirus boosting regimen were significantly greater than those elicited by homologous regimens with the individual vectors or by a heterologous poxvirus priming-Ad5 boosting regimen. The heterologous Ad5 priming-poxvirus boosting approach may have potential utility in humans as a means of inducing high levels of cellular immunity.

FIG. 1.

Frequencies of Gag-specific IFN-γ-secreting cells from macaques immunized with homologous or heterologous priming-boosting regimens of Ad5-gag and/or MVA-gag. Two priming immunizations were given at weeks 0 and 4, followed by a single booster inoculation at week 26 or 27. The frequencies are expressed as the number of SFC/10⁶ PBMC and were calculated as the differences in responses between the PBMC stimulated with the Gag 20-aa peptide pool and the mock-treated PBMC; animal identification numbers are indicated along the x axis. The responses were determined prior to immunization (pre), at weeks 4 (post-dose 1) and 8 (post-dose 2), at time of boosting (pre-boost), and at 4 and 8 weeks postboosting. NA, not available.

FIG. 2.

ALVAC and MVA vectors as boosters, following priming with Ad vectors. Macaques were immunized at weeks 0, 4, and 26 with either 10⁹ vp of Ad5-gag (animals 99C117 and 99D227), 10⁷ vp of Ad5-gag (animals 99D021 and 99D156), 10⁹ vp of Ad6-gag (animals 99D126 and 99D128), or 10⁷ vp of Ad6-gag (animals 99D147 and 99D151). At weeks 56 and 119, animals were given either 10⁸ PFU of ALVAC-gag or 10⁸ PFU of MVA-gag. Numbers of SFC/10⁶ PBMC were calculated as noted in the legend to Fig. 1.

FIG. 3.

Comparison of the Gag-specific cellular immune response elicited by heterologous poxvirus priming-Ad5 boosting and Ad5 priming-poxvirus boosting. Priming doses of the gag-expressing ALVAC and NYVAC vectors were given at weeks 0 and 4, followed by the Ad5 booster at week 27; dose levels are indicated. MVA-gag was given at week 0, 4, and 27, and the Ad5 booster was given at week 65. In the final group, the Ad5 vector priming inoculations were delivered at weeks 0 and 4, with the MVA vector boosting delivered at week 27. The frequencies are expressed as the numbers of SFC/10⁶ PBMC and were calculated as the differences in responses between the PBMC stimulated with the Gag 20-aa peptide pool and the mock-treated PBMC. These values were determined at the start of the treatment (pre), at week 8 (post-prime), at the time of the boosting (pre-boost), and at 4 and 8 weeks postboosting; animals are indicated along the x axis.

FIG. 4.

Percentages of Gag-specific T-cells that are CD3⁺ CD8⁺ in rhesus macaques immunized with either the Ad priming-Ad boosting (Ad/Ad) or Ad priming-poxvirus boosting (Ad/pox) regimen. The Ad/Ad cohort consisted of animals given two priming doses of either Ad5 or Ad6 (at a 10⁹- to 10¹¹-vp dose) followed by a homologous Ad booster. This cohort includes four of six Ad5-primed-Ad5-boosted animals that are represented in Fig. 1 (open squares) and for which responses were detectable by the IFN-γ cytokine staining method. The data for Ad priming-poxvirus boosting cohorts were collected for animals at 4 weeks following boosting with ALVAC (gray circles) or MVA (black circles, data for macaques from Fig. 1; black diamonds, data for macaques from Fig. 2; black triangles, data for macaques from Fig. 3). Also shown are the cohort arithmetic means and the associated standard errors.