Between December 1984 and April 1994, the SBBC blood donor D36 had a stable CD4 T-cell count but subsequently experienced CD4 T-cell loss at an average rate of 97.48 cells/μL/y until diagnosis of HIV-associated dementia (HIVD) was made in December 1998.15,16 CD4 T-cell loss was accompanied by a steady increase in plasma HIV-1 RNA levels at an average rate of 3408 RNA copies/mL/y, peaking at approximately 20,000 copies/mL in August 1998. At diagnosis of HIVD, cerebrospinal fluid (CSF) HIV-1 RNA levels were recorded at >750,000 copies/mL. After commencement of highly active antiretroviral therapy (HAART),15,16 plasma and CSF HIV-1 RNA were suppressed to lower than detectable levels. D36 subsequently experienced neurologic improvement and CD4 T-cell recovery to approximately 700 cells/μL in August 2006. D36 remains clinically well.
C98 died of non-HIV-1-related causes at the age of 64 years but experienced significant CD4 T-cell loss before death. This individual commenced prednisone for treatment of asthma in 199513 and was diagnosed with pulmonary amyloidosis in 1998. With this background, C98 commenced HAART in November 199914 because of CD4 T-cell loss at an average rate of approximately 60 cells/μL/y. CD4 T-cell loss was accompanied by low steady-state plasma HIV-1 RNA levels, with the median level between December 1994 and August 1999 recorded at 690 copies/mL. Plasma HIV-1 RNA levels were suppressed to lower than detectable levels on HAART, but the decline in CD4 T-cell count continued. C98 died of amyloidosis in March 2002.
C18 died from causes unrelated to HIV-1 infection in 1995 and has been described in detail previously.13 Although asymptomatic and with a preserved CD4 T-cell count before death, this subject had persistently detectable plasma HIV-1 RNA levels, with the median level between July 1994 and October 1995 recorded at 1400 copies/mL.13
Subjects C49, C64, and C135 have been infected for 23, 24, and 26 years, respectively, without antiretroviral therapy, and they have consistently had undetectable plasma HIV-1 RNA levels. C49 suffers with type II diabetes and chronic alcoholism. For the first 14 years after infection, C49 had stable CD4 T-cell counts,13 but inclusion of more recent data demonstrated a marginal decline in CD4 T cells that was not considered significant. The median CD4 T-cell count since June 1987 was recorded at 918 cells/μL. C64 and C135 have had steady CD4 T-cell counts, with median values since December 1987 and January 1996 recorded at 968 and 503 cells/μL, respectively. Of note, C135 carries the heterozygous CCR5Δ32 and HLA-B57 genotypes,18,19 both of which are associated with slow HIV-1 progression.20,21 Thus, the host genotype of C135 may have contributed to further attenuated infection.
Our studies show that D36, C98, and C54, who had persistently detectable plasma HIV-1 RNA, all experienced HIV-1 progression highlighted by significant CD4 T-cell losses over time. Progression was more dramatic in D36, who experienced HIVD as an initial AIDS-defining illness. The neurologic improvement and restoration of CD4 T-cell count in D36 by inhibiting the in vivo HIV-1 replication kinetics with HAART unequivocally demonstrates the pathogenic potential of nef-deleted HIV-1. Thus, eventual HIV-1 disease progression was demonstrated in 3 of 4 subjects who had persistent low-level viremia. The other viremic individual, C18, died after only 12 years of infection.13 Although C18 showed no evidence of CD4 T-cell loss before death, our results suggest that persistently detectable plasma HIV-1 RNA levels placed this individual at risk of eventual HIV-1 progression had death not occurred from unrelated causes. In contrast, 3 of 3 subjects with persistently undetectable HIV-1 RNA levels remain long-term nonprogressors 23 to 26 years after infection. Two additional SBBC subjects not reported here, C83 and C124, died before 1995.13 A lack of laboratory measures from C83 and C124, including plasma HIV-1 RNA levels, prevents assessment of whether HIV-1 infection was progressive in these subjects. SBBC subjects harbor closely related HIV-1 variants.7 Furthermore, detailed longitudinal studies of the evolution of nef/LTR sequences,14 HIV-1 coreceptor use,22 envelope gene diversity,23 and rev sequence/function24 were unable to segregate SBBC nonprogressors from progressors. Together, these studies suggest that nef-deleted HIV-1 may be nonpathogenic in humans only if additional host factors are present to suppress replication persistently to lower than detectable levels.
Together, these studies provide valuable insights into the long-term pathogenicity of nef-deleted HIV-1. Importantly, we show that even weakened highly attenuated HIV-1 strains with nef deletions are ultimately pathogenic in humans unless replication is completely and persistently suppressed in vivo. Furthermore, only low-level persistent viremia was necessary to mediate the long-term pathogenic effects of nef-deleted virus. Thus, our studies underscore the importance of aiming to achieve nothing less than complete and sustained suppression of HIV-1 replication by antiretroviral drugs and vaccines.
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