Evidence for both Lytic Replication and Tightly Regulated Human Herpesvirus 8 Latency in Circulating Mononuclear Cells, with Virus Loads Frequently below Common Thresholds of Detection

Abstract

To address whether human herpesvirus 8 (HHV-8) DNA in peripheral blood mononuclear cells (PBMCs) might be the product of latent or lytic infection and to shed light on sporadic detection of HHV-8 DNA in individuals seropositive for the virus, we studied the frequency of infected cells, total virus load, and virus load per infected cell in PBMCs from men coinfected with HHV-8 and human immunodeficiency virus (HIV), some of whom had Kaposi's sarcoma. The low frequencies of infected cells detected (fewer than one per million cells in some individuals) suggest that the prevalence of the virus in circulating leukocytes was underestimated in previous studies that employed more conventional sampling methods (single, small-volume specimens). Mean virus loads ranged from 3 to 330 copies per infected PBMC; these numbers can represent much higher loads in individual lytically infected cells (>10 3 genomes/cell) in mixtures that consist predominantly of latently (relatively few genomes) infected cells. The presence in some subjects of high HHV-8 mean genome copy numbers per infected cell, together with viral DNA being found in plasma only from subjects with positive PBMCs, supports earlier suggestions that the virus can actively replicate in PBMCs. In some individuals, mean virus loads were less than 10 genomes per infected cell, suggesting a tightly controlled purely latent state. HHV-8 genome copy numbers are substantially higher in latently infected cells derived from primary effusion lymphomas; thus, it appears that HHV-8 is able to adopt more than one latency program, perhaps analogous to the several types of Epstein-Barr virus latency.

Impact of Kaposi Sarcoma–Associated Herpesvirus (KSHV) Burden and HIV Coinfection on the Detection of T Cell Responses to KSHV ORF73 and ORF65 Proteins

“…The 1 positive PCR from a KSHV-seronegative sample was derived from a woman with HIV coinfection and detectable ORF73-and ORF65-specific responses. Thus, although the PCR amplification appeared to be even less sensitive than serologic testing, we were able to identify 1 individual who had negative KSHV serologic results but was PCR positive and who showed detectable KSHV-specific T cell activity (table 2) [31]. Thus, the combined ELISPOT and PCR data, as well as epidemiological considerations, strongly suggest that the subjects with positive ELISPOT responses were indeed KSHV infected but did not show a detectable serologic response at the time when mounting detectable T cell responses.…”

Simultaneous quantification of human herpesvirus 8 DNA by real time PCR in different tissues of HIV infected cuban patients with Kaposi's sarcoma

“…The lower copy number of HHV-8 detected in PBMC in comparison to KS tissue, could be due to its latent state within this compartment, in contrast to viral expression present in lesional spindle cells [17]. …”

Human herpesvirus 8 presence and viral load are associated with the progression of AIDS-associated Kaposi's sarcoma

“…Positive reactions were confirmed with a second PCR amplification using the HHV-8 orf 37 primers and probes [12]. HIV viral loads were measured with reverse transcription-PCR Taqman as described [13].…”