Background: HTLV-1/HIV co-infection is known to elevate the CD4+ T-cell counts of
treatment-naïve persons. We investigated whether HTLV-1/HIV co-infected patients continued to
have elevated CD4+ T-cell counts after developing virologic failure on antiretroviral therapy (ART).
Methods: The data is taken from a drug resistance study located in the KwaZulu-Natal province of
South Africa. All participants (N=383) presented for repeated CD4+ T-cell count and HIV viral load
level testing between January 2006 and March 2014. We used a random-coefficient model to estimate
the change in CD4+ T-cell count and HIV viral load level by HTLV-1/HIV co-infection status
over time, adjusting for age, sex, and duration of virologic failure.
Results: HTLV-1/HIV co-infected participants (n=8) had higher CD4+ T-cell counts, with a positive
difference of 117.2 cells/μL at the ART initiation date (p-value=0.001), 114.7 cells/μL (pvalue<
0.001) 12 months after this date, and 112.3 cells/μL (p-value=0.005) 24 months after this
date, holding all else constant. In contrast, there was no difference in the HIV viral load level by
HTLV-1/HIV co-infected status throughout the observation period.
Conclusion: We show that HTLV-1/HIV co-infected participants continued to have elevated CD4+ T-cell
counts after developing virologic failure on ART, despite no difference in their HIV viral load levels when
compared with HIV mono-infected participants. Our results indicate that CD4+ T-cell count testing may
not be a useful strategy to monitor ART response in the presence of HTLV-1/HIV co-infection.