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Journal of Clinical Microbiology, October 2002, p. 3883-3884, Vol. 40, No. 10
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.10.3883-3884.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
Quantification of Human Immunodeficiency Virus Type 1 Proviral DNA by the TaqMan Real-Time PCR Assay

LETTER
A variety of real-time PCR assays have been applied for quantification
of human immunodeficiency virus type 1 (HIV-1) (
4-
7). Recently,
Désiré et al. have reported a TaqMan PCR for quantification
of HIV-1 provirus in peripheral blood mononuclear cells (PBMCs)
(
3). This method targets the polymerase (
pol) gene of HIV-1
subtype B. Based on their data, Désiré et al.
have concluded that HIV-1 proviral DNA load in PBMCs does not
correlate with HIV-1 RNA level in plasma and CD4
+ lymphocyte
counts. This conclusion is contradictory to those previously
drawn by us (
2) and recently drawn by others (
8). In order to
clarify if the use of different DNA quantification methods may
have contributed to this controversy, we decided to compare
the TaqMan PCR by Désiré et al. with a TaqMan
PCR recently developed in our laboratory. Our TaqMan PCR targeted
the long terminal repeat region (LTR) of the HIV-1 major group.
The sequences of the sense and antisense primers were 5'-GCCTCAATAAAGCTTGCCTTGA-3'
and 5'-GGGCGCCACTGCTAGAGA-3'. The probe sequence was 5'-CCAGAGTCACACAACAGACGGGCACA-3'.
The 5' and 3' ends of the probe were labeled with FAM and TAMRA
dyes. The sensitivity of the assay was estimated to be five
copies of HIV-1 plasmid DNA (Applied Biosystems). We randomly
selected 25 PBMC samples, which had been earlier confirmed to
be HIV-1 DNA positive by a nested PCR (
1). The HIV-1 DNA was
extracted from the PBMCs with the Qiagen blood kit. Five microliters
of each DNA extract (equivalent to 2
x 10
5 PBMCs) was tested
with both the
pol- and LTR-based TaqMan PCR assays on the same
plate for <45 PCR cycles. The threshold cycle numbers (Ct)
obtained by the two TaqMan PCR assays are listed in Table
1.
Compared with the LTR TaqMan PCR, markedly higher Ct values
(>2 cycles) were obtained by the
pol TaqMan PCR (Table
1).
Furthermore, HIV-1 DNA in seven HIV-1-positive PBMC samples
was not detected by the
pol TaqMan assay. Among those seven
HIV-1 false-negative samples, three were PBMC culture positive
for HIV-1. Our results suggest that the
pol TaqMan PCR exhibits
an unsatisfactory low sensitivity on the selected sample panel.
The fact that some of the tested samples belonged to a subtype
other than B may partly contribute to the high false negativity
of the HIV-1
pol TaqMan PCR assay. However, the lower sensitivity
was also seen when HIV-1 subtype B SF2 strain was tested with
the
pol TaqMan PCR (Table
1). Therefore, we further examined
the
pol TaqMan PCR design by using PrimerExpress software (version
2.0). The melting temperature of the reverse primer P2 was significantly
lower than that of the forward primer P1 (50.4 versus 60.5°C).
At the reported annealing temperature (60°C), an asymmetric
amplification could have been taking place during PCR due to
the poor hybridization of the P2 primer with the template, resulting
in decreased amplification efficiency. Considering that HIV-1
load turns out to be extremely low after efficient antiretroviral
therapy (ART), we believe that a highly sensitive real-time
PCR is demanded for the purpose of ART monitoring.

ACKNOWLEDGMENTS
We thank the Swedish Physicians against AIDS Foundation for
support.

FOOTNOTES
Ed. Note: The authors of the published article did not respond. 

REFERENCES
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Zhibing Yun* Eva Fredriksson Anders Sönnerborg
Division of Clinical Virology Karolinska Institute at Huddinge University Hospital F68 S-141 86 Stockholm, Sweden
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* Phone: (46) 8 58581319 Fax: (46) 8 58581305 E-mail: zhyu{at}labd01.hs.sll.se. |
Journal of Clinical Microbiology, October 2002, p. 3883-3884, Vol. 40, No. 10
0095-1137/02/$04.00+0 DOI: 10.1128/JCM.40.10.3883-3884.2002
Copyright © 2002, American Society for Microbiology. All Rights Reserved.
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