Simian immunodeficiency virus (SIV) gag DNA-vaccinated rhesus monkeys develop secondary cytotoxic T-lymphocyte responses and control viral replication after pathogenic SIV infection

Abstract

The potential contribution of a plasmid DNA construct to vaccine-elicited protective immunity was explored in the simian immunodeficiency virus (SIV)/macaque model of AIDS. Making use of soluble major histocompatibility class I/peptide tetramers and peptide-specific killing assays to monitor CD8(+) T-lymphocyte responses to a dominant SIV Gag epitope in genetically selected rhesus monkeys, a codon-optimized SIV gag DNA vaccine construct was shown to elicit a high-frequency SIV-specific cytotoxic T-lymphocyte (CTL) response. This CTL response was demonstrable in both peripheral blood and lymph node lymphocytes. Following an intravenous challenge with the highly pathogenic viral isolate SIVsm E660, these vaccinated monkeys developed a secondary CTL response that arose with more rapid kinetics and reached a higher frequency than did the postchallenge CTL response in control plasmid-vaccinated monkeys. While peak plasma SIV RNA levels were comparable in the experimentally and control-vaccinated monkeys during the period of primary infection, the gag plasmid DNA-vaccinated monkeys demonstrated better containment of viral replication by 50 days following SIV challenge. These findings indicate that a plasmid DNA vaccine can elicit SIV-specific CTL responses in rhesus monkeys, and this vaccine-elicited immunity can facilitate the generation of secondary CTL responses and control of viral replication following a pathogenic SIV challenge. These observations suggest that plasmid DNA may prove a useful component of a human immunodeficiency virus type 1 vaccine.

FIG. 1

SIV gag DNA expression vector V1R-SIV gag. Kan(R), kanamycin resistance gene; CMV, cytomegalovirus; ori, origin of replication; bGH, bovine growth hormone.

FIG. 2

In vitro expression of the V1R-SIV gag DNA vaccine construct in transiently transfected human RD cells. Human RD cells were transfected with either mock preparation (PBS; lanes 1 and 2) or 10 μg of V1R-SIV gag DNA construct (lanes 3 and 4) using calcium phosphate. Twenty-four hours later, the cells were washed and lysed, and the proteins were then resolved by SDS-PAGE. Sizes are indicated in kilodaltons.

FIG. 3

SIV Gag p11C tetramer binding to peripheral blood CD8⁺ lymphocytes of SIV gag DNA-immunized Mamu-A*-01⁺ rhesus monkeys. Arrows indicate the weeks at which the monkeys were immunized. Percent p11C tetramer binding represents Mamu-A*01/p11C tetramer-binding CD8αβ⁺ T cells in unstimulated whole blood samples at each time point tested.

FIG. 4

SIV Gag p11C tetramer binding-CD8αβ⁺ T cells in whole blood of SIV gag DNA-immunized Mamu-A*-01⁺ rhesus monkeys 2 weeks after the fourth immunization. Cells were gated on CD8αβ⁺ CD3⁺ lymphocytes. (A) Staining of unstimulated whole blood; (B) staining of lymphocytes after in vitro expansion with p11C.

FIG. 5

Plasmid DNA vaccine-induced Gag epitope-specific functional CTL activity in PBL of vaccinated monkeys 2 weeks after the fourth immunization. PBL of the vaccinated monkeys were activated in vitro with p11C in IL-2-containing medium and assessed for lysis of p11C-pulsed (■) and control peptide p11B-pulsed (▴) B-LCL target cells.

FIG. 6

SIV Gag p11C tetramer binding CD8αβ⁺ T cells in whole blood after SIVsm E660 challenge in control DNA- and SIV gag DNA-immunized monkeys. Percent p11C tetramer binding represents Mamu-A*01/p11C tetramer-binding CD8αβ⁺ T cells in unstimulated whole blood samples at each time point tested.

FIG. 7

Peripheral blood CD4⁺ T-lymphocyte counts after intravenous SIVsm E660 challenge in Mamu-A*01⁺ rhesus monkeys immunized with the control (A) or the SIV gag (B) DNA vaccine.

FIG. 8

Plasma viral load analysis after intravenous SIVsm E660 challenge in Mamu-A*01⁺ rhesus monkeys immunized with the control (A) or the SIV gag (B) DNA vaccine.