Pathogenicity and mucosal transmissibility of the R5-tropic simian/human immunodeficiency virus SHIV(AD8) in rhesus macaques: implications for use in vaccine studies

Abstract

There is an urgent need to develop new pathogenic R5 simian/human immunodeficiency viruses (SHIVs) for the evaluation of candidate anti-HIV vaccines in nonhuman primates. Here, we characterize swarm SHIV(AD8) stocks, prepared from three infected rhesus macaques with documented immunodeficiency at the time of euthanasia, for their capacity to establish durable infections in macaques following inoculation by the intravenous (i.v.) or intrarectal (i.r.) route. All three viral stocks (SHIV(AD8-CE8J), SHIV(AD8-CK15), and SHIV(AD8-CL98)) exhibited robust replication in vivo and caused marked depletion of CD4(+) T cells affecting both memory and naïve CD4(+) T lymphocyte subsets following administration by either route. Eleven of 22 macaques inoculated with the new SHIV(AD8) stocks were euthanized with clinical symptoms of immunodeficiency and evidence of opportunistic infections (Pneumocystis, Candida, and Mycobacterium). A single but unique founder virus, also present in the SHIV(AD8-CE8J) swarm stock, was transmitted to two animals following a single i.r. inoculation of approximately 3 50% animal infectious doses, which is close to the threshold required to establish infection in all exposed animals. Because the three new SHIV(AD8) viruses are mucosally transmissible, exhibited tier 2 sensitivity to anti-HIV-1 neutralizing antibodies, deplete CD4(+) T lymphocytes in vivo, and induce AIDS in macaques, they are eminently suitable as challenge viruses in vaccine experiments.

Fig 1

Gp120 sequence alignments of SHIV_AD8 viral stocks (CE8J, CK15, and CL98). Six independent clones amplified from each virus stock by RT-PCR were sequenced, and the deduced amino acid sequences of the V1 and V2 (a), V3 and C3 (b), V4 (c), and V5 (d) regions of gp120 were aligned with the HIV_AD8 sequence at the top. Amino acid changes are highlighted in yellow.

Fig 2

SHIV_AD8 induces sustained plasma viremia and loss of CD4⁺ T cells in intravenously inoculated rhesus macaques. The levels of plasma viremia (A); absolute numbers of peripheral CD4⁺ T cells (B), memory CD4⁺ T cells (C), and naïve CD4⁺ T cells (D); and percentages of BAL fluid CD4⁺ T cells (E) are shown. Note that purple symbols denote animals infected with SHIV_AD8-CE8J, maroon symbols denote animals infected with SHIV_AD8-CL98, and orange symbols denote animals infected with SHIV_AD8-CK15. Macaques euthanized with AIDS are indicated (†).

Fig 3

Intrarectal inoculation of SHIV_AD8 viral stocks in rhesus macaques. The colors in the graphs represent the challenge virus as described in the legend for Fig. 2. Macaques euthanized with AIDS are indicated (†).

Fig 4

Loss of CD4⁺ T cell lymphocyte subsets following i.r. inoculation of SHIV_AD8 virus stocks. Absolute numbers of memory CD4⁺ T cells (A, B, and C), and naïve CD4⁺ T cells (D, E, and F) are shown. The colors in the graphs represent the challenge virus as described in the legend for Fig. 2. Macaques euthanized with AIDS are indicated (†).

Fig 5

Loss of CD4⁺ T cell lymphocytes at an effector site (BAL fluid). Macaques euthanized with AIDS are indicated (†).

Fig 6

Composite phylogenic tree of env gene sequences present in the SHIV_AD8-CE8J stock and in plasma from macaques (DBJE and DBX9) on day 14 after i.r. inoculation. Animal-derived sequences from plasma at peak viremia are color coded, and inoculum-derived sequences are shown in black.