In 2004, we described two cases of the sexual transmission of multidrug-resistant (MDR) HIV-1, defined as triple class resistant, which persisted for 2 years without antiretroviral treatment . Those observations support the theory that new infections involve the transmission of a single predominantly resistant viral strain, rather than the entire diverse quasispecies generally present in chronically infected individuals. In clonal analysis, the lack of detection of wild-type quasispecies in source patients confirmed the transmission of viruses only harbouring resistance-associated mutations. These viruses serve as a new starting point for the HIV-1 evolution in newly infected patients, as suggested by archival information and the persistence over time of highly resistant viruses. The long-term persistence of MDR infections (2–7 years) has also been documented in other studies [2–7].
Markowitz et al.  recently described a rapid progression to AIDS after acute HIV-1 infection with multidrug-resistant viruses in one patient. The patient was a 40-year-old man who had been sexually active with many male partners over the years, often in conjunction with the use of metamphetamine. A diagnosis of HIV-1 was established in January 2005, but all biological tests suggested a previous date of contamination, probably approximately 4–20 months earlier. The patient had been infected by a viral variant of HIV-1 resistant to multiple classes of antiretroviral drugs. Interestingly, his virus population was dual tropic for cells that express CCR5 and CXCR4 co-receptors, although it was believed that CCR5 viruses had probably dominated in the early period of infection . Moreover, the infection resulted in rapid progression to symptomatic AIDS in 4–20 months.
This observation led us to study the clinical, immunological and virological outcomes of our two case reports 5 years after their primary infection. Longitudinal plasma samples from both patients were obtained with informed written consent. Data were collected since those published previously  over 5 years of follow-up. To compare virological specificity with the case from New York reported by Markowitz et al. , the genotypic tropism of the virus of source cases (before transmission) and index cases (at the time of primary infection and each year during the follow-up) were also determined. The predictor co-receptor usage of HIV-1 was determined from the V3 env region nucleotide sequence using Geno2pheno (http://coreceptor.bioinf.mpi-sb.mpg.de/cgi-bin/coreceptor.pl)  and amino acid sequence with position-specific scoring matrices (http://ubik.microbiol.washington.edu/computing/pssm/)  algorithms.
Viral loads, CD4 cell counts and genotypic resistance tests are described for patients A and B in Figure 1. For patient A, during the first 32 months, levels of CD4 cell count and HIV-1-RNA load were stable with a mean of 600 cell/μl and a mean of 4 log10 copies/ml, respectively. Then, a decrease of 150 CD4 lymphocytes was observed between month 32 and month 50 without a concomitant increase in the plasma viral load. To date, this patient has not received antiretroviral treatment. With regard to resistance-associated mutations in the plasma, we previously described the rapid loss of detection of the M184V lamivudine mutation, known to impair viral fitness and the switch over time of T215Y to the substitution T215D, which is a transient intermediate, less resistant but with a better competitive advantage without treatment . Only one major protease gene mutation, I84V, was replaced by a wild-type codon at month 38, concomitantly with the decrease in the CD4 cell count. In patient B, an increase in the HIV-1-RNA viral load to month 45 to 5.3 log10 copies/ml concomitant with a CD4 cell count decrease to 77 cells/μl led the physician to initiate antiretroviral therapy with lamivudine, tenofovir and lopinavir/ritonavir. The viral load was undetectable (threshold 50 copies/ml, Cobas Amplicor; Roche Diagnostics, Marcy l'Etoile, France) from 12 weeks post-therapy and maintained at 24 weeks associated with a dramatic increase in CD4 lymphocytes (+468 cell/μl). The protease M46I mutation was the only switch to wild-type codon over time at month 36, previously described in the first report , also associated with a close temporal relationship with the CD4 cell count decrease. In the absence of HIV-1 RNA being detectable in the plasma, resistance analysis of HIV-1 DNA in peripheral blood mononuclear cells on the last available sample showed the detection of M46I with the same backbone baseline mutation, reflecting the archive of all resistance mutations at the time of primary infection. Analysis of genotypic tropism showed that the source and index cases A and B tested harboured R5 variants.
To compare with the case from New York reported by Markowitz et al. , neither of the two patients infected with MDR HIV-1 had experienced rapid progression to AIDS during the follow-up of 5 years. This finding could be explained partly by the transmission of CCR5 viruses, which are less virulent and associated less with the rapid progression of disease.
Acquired resistant viruses establish themselves as the dominant viral population at primary infection and persist over time even if antiretroviral treatment is initiated and is associated with therapeutic success. Ghosn et al.  recently reported that HIV-1-resistant strains acquired at the time of primary infection massively fuel the cellular reservoir, and their prolonged persistence is supported by the early expansion of a dominant homogenous and resistant viral population.
Over time, a rare genetic event occurred because only one stepwise back mutation in the protease gene at codon 84 (patient A) and one at codon 46 (patient B) to wild-type codon were observed during 5 years of follow-up. In both cases, these genetic changes were probably associated with an increase in viral replicative capacity because this was temporally correlated with a marked decrease in CD4 cell numbers, as shown previously in primary and chronically infected patients [12,13].
There is concern that the transmission of MDR viruses in primary HIV-1 infection may limit future therapeutic options. It is accepted that treatment failure has been observed in several individuals harbouring MDR infections [13–17]. In most cases, empirical treatment began before the results of genotypic resistance testing were obtained, and may have been suboptimal, resulting in the acquisition of additional mutations in these already MDR viruses, as shown in a large cohort of HAART-treated patients at the time of HIV primary infection [6,16]. French guidelines recommend performing resistance testing prospectively in patients with HIV primary infection, so that the results are available soon after the initiation of HAART.
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