Lack of Evidence of HHV-8 DNA in Blood Cells From Heart Transplant Recipients

To the Editor:

The human herpesvirus type 8 (HHV-8), previously named as Kaposi's sarcoma-associated herpesvirus (KSHV),1 has been suggested to play a major role in the etiology and the pathogenesis of acquired immunodeficiency syndrome (AIDS)-associated and iatrogenic Kaposi's sarcoma (KS). In addition, evidence for HHV-8 involvement in primary effusion and possibly other human B-cell lymphomas has been recently provided.2 Although a role for HHV-8 in the pathogenesis of the above neoplasms is presently accepted by most investigators, controversial results have been obtained in molecular epidemiology studies with regard to the distribution of the virus in the healthy population. Two recent reports have shown detection of HHV-8 DNA sequences in semen from the vast majority of healthy adults3 and in peripheral blood mononuclear cells (PBMC) from ∼10% of healthy subjects,4 suggesting that HHV-8 is a fairly common virus latently infecting humans. Thus, the involvement of HHV-8 in KS lesions1 and in non-KS skin lesions from immunosuppressed transplant recipients5 raises the possibility that the virus can reactivate in the presence of various immunosuppression conditions. By contrast, other investigators have failed to identify HHV-8 DNA in non-KS skin lesions from immunosuppressed transplant patients6 and in PBMC from a healthy adult population.7,8 

We looked for the presence of HHV-8 DNA in 54 buffy-coat samples from 28 KS-negative immunosuppressed heart transplant recipients and 134 control buffy-coat samples from healthy blood donors. Periodical shell-vial culturing of oropharyngeal washing showed reactivation of cytomegalovirus (CMV), and/or herpes simplex virus 1 (HSV-1) in 18 of the 28 (64.3%) transplant patients during immunosuppressive treatment. DNA from buffy-coat cells was prepared by a “salting out” procedure and polymerase chain reaction (PCR) suitability of the samples was assessed by amplification of a human β-globin gene region. One microgram of each DNA sample was tested for the presence of HHV-8 DNA sequences by nested PCR amplification.7 HHV-8 PCR was performed on 1 to 4 serial samples per transplant patient, of whom at least one was drawn at the time when CMV and/or HSV-1 reactivation was demonstrated. Reconstruction experiments with titrated cloned HHV-8 templates showed that the nested amplification procedure used was able to detect five copies of target DNA sequence. However, HHV-8 DNA was found neither in the blood donors nor in the transplant patients, including those with concomitant reactivation of CMV and/or HSV-1.

Our failure to detect HHV-8 DNA sequences in buffy-coat cells from the healthy blood donors and the transplant patients examined does not support that HHV-8 is a common infectious agent typically reactivating in the course of immunosuppression. Actually, CD19⁺ B cells are a target for HHV-8 infection in KS patients.1 Although the lymphoid system has been suggested to represent a possible reservoir of HHV-8–infected cells4 it is not presently known whether B cells are also a site of viral latency. Most human herpesviruses are in fact ubiquitous and lymphotropic. In particular, Epstein-Barr virus (EBV) shares nucleotide sequence homology with HHV-8 and is well known to establish a latent infection in B cells and to be a relevant cofactor in different lymphomas. Nevertheless, EBV genome is hardly detectable in the blood of the vast majority of healthy subjects even when sensitive PCR methods are used.7 Thus, a low HHV-8 load could similarly not be detected during latent infection. However, it is worth considering that HHV-8 genome has been demonstrated in endothelial and spindle cells present in KS lesions9 and in sensory ganglia from KS-positive patients,10 raising the possibility that HHV-8 establishes a latent infection in tissues other than lymphocytes. The high prevalence of HHV-8 in semen from healthy subjects recently reported3 merits further investigation in light of this hypothesis. In conclusion, we consider that data presently available are not at all sufficient to claim that HHV-8 is as ubiquitous as other human herpesviruses. Accordingly, KS typically develops in homosexual males, and the rare occurrences of KS in women appear to be related to sexual contacts with bisexual males. In addition, HHV-8 DNA has been detected at high frequency in human immunodeficiency virus–infected homosexual males with and without KS.2,8 It is also worth reminding that another human herpesvirus, HSV-2, is an almost exclusively sexually transmitted agent. Thus, it may be reasonably conceived that transmission of HHV-8 infection requires specific sexual practices and that development of HHV-8–related diseases is critically favored by underlying immunosuppression.