Background:  HIV-1 uses CCR5 and CXCR4 as co-receptors. The R5 viral strains are less pathogenic as opposed to their X4 counterparts. Several reports suggest that during HAART there is preponderance of R5-using strains, but the mechanism by which this process occurs is not clear. It is unclear how ART may influence the in vitro usage of CCR5 and CXCR4 co-receptors in relation to their surface expression, a finding which may assist in the designing of better alternative therapeutic strategies for HIV-1 control. We studied 6 patients on non-interrupted HAART, 4 patients on structured treatment interruption and 6 treatment-naïve patients, over time.

Methods:  This study was designed to address the surface co-receptor expression of CCR5 and CXCR4 on purified CD4⁺ T cells using flow cytometry and appropriate antibodies. Further, the co-receptor usage in vitro was assessed with autologous HIV-1 strains over time during HAART, along with viral replication kinetics on CD4⁺ T cells using p24 antigen monitoring. Molecular nature of HIV-1 strains was also analyzed longitudinally in the V3 loop region. To further confirm the in vitro usage of CCR5 and CXCR4, we used position-specific scoring matrices. Statistical analysis was performed using a paired t-test for comparison of means, and the c² analysis test for categorical variables. The p value (two-tailed) of < 0.05 was considered statistically significant.

Results:  These analyses are unique in demonstrating:  the predominant usage of CCR5 and reduced or no usage of CXCR4 during HAART, which was in concordance with the V3 loop architecture of HIV-1 strains derived over time; significant down-modulation of CXCR4 during HAART, over time; and the first evidence in favor of reduction in bioavailability of cell-surface CXCR4 on CD4⁺ T cells during both forms of HAART. This was consistent with the predominance of CCR5 using strains further confirmed by the PSSM prediction and in vitro co-receptor usage. We believe that via this mechanism, HAART may encourage the emergence less pathogenic CCR5 using HIV-1 strains.

Conclusions:  Certain antiretroviral drug combinations may affect the cell surface expression of CXCR4. These studies, which were statistically significant, may have implications also in HIV neuropathogenesis in the era of HAART, as CCR5 using strains are macrophage tropic and are critical in HIV infection of the brain.

Keywords: Immunology; Pathogenesis; Adult antiretroviral therapy