Two-step nature of human T-cell leukemia virus type 1 replication in experimentally infected squirrel monkeys (Saimiri sciureus)

Abstract

After experimental infection of squirrel monkeys (Saimiri sciureus) with human T-cell leukemia virus type 1 (HTLV-1)-infected cells, the virus is transcribed only transiently in circulating blood, spleen, and lymph nodes. Stable disappearance of viral expression occurs at 2 to 3 weeks after inoculation. This coincides with the development of the anti-HTLV-1 immune response and persistent detection of the provirus in peripheral blood mononuclear cells (PBMCs). In this study, the HTLV-1 replication pattern was analyzed over time in PBMCs and various organs from two HTLV-1-infected squirrel monkeys. Real-time quantitative PCR confirmed that PBMCs and lymphoid organs constitute the major reservoirs for HTLV-1. The PCR amplification of HTLV-1 flanking sequences from PBMCs evidenced a pattern of clonal expansion of infected cells identical to that observed in humans. Dissemination of the virus in body compartments appeared to result from cellular transport of the integrated provirus. The circulating proviral burden increased as a function of time in one animal studied over a period of 4 years. The high proviral loads observed in the last samples resulted from the accumulation of infected cells via the extensive proliferation of a restricted number of persistent clones on a background of polyclonally expanded HTLV-1-positive cells. Therefore, HTLV-1 primary infection in squirrel monkeys is a two-step process involving a transient phase of reverse transcription followed by persistent multiplication of infected cells. This suggests that the choice of the target for blocking HTLV-1 replication might depend on the stage of infection.

FIG. 1

Quadruplicate LMPCR analysis of HTLV-1 integration sites in DNA samples from experimentally infected squirrel monkeys. DNA was submitted to quadruplicate LMPCR; amplified products were subjected to runoff analysis with an HTLV-1 3′ long terminal repeat-specific oligonucleotide. Run-off products were resolved on a sequencing gel. M, molecular weight marker (positions are indicated in base pairs). (A) E1540 cell line, PBMCs and organs from animal S1657; (B) E798 cell line, PBMCs from animal S1491 collected over 4 years with 1-year intervals (abundant persistent clones are identified by arrows).

FIG. 2

Temporal evolution of circulating HTLV-1 proviral load and anti-HTLV-1 antibody titers in animal S1491. The first sample was collected 3 months after experimental infection. For the proviral load, the mean viral copy number obtained after three experiments is given at each time point. For the five samples, the standard deviation ranged from 3.3 to 11.8 and the mean coefficient of variance was 6%. O.D., optical density.