Immunological and virological response to fostemsavir in routine US clinical care: An OPERA cohort study.

Objectives: Fostemsavir is a novel attachment inhibitor used with other antiretrovirals in heavily treatment-experienced (HTE) adults with multidrug-resistant HIV-1. Real-world immunological and virological responses were assessed in individuals starting fostemsavir in the OPERA cohort.

Methods: Among adults with HIV-1 starting fostemsavir between 2 July 2020 and 1 September 2022, 6-month and 12-month changes in CD4 T-cell count and CD4%, and maintenance/achievement of viral load (VL) <50 copies/mL were described and stratified by baseline VL (suppressed: <50 copies/mL; viraemic: ≥50 copies/mL) and CD4 count (high: ≥350 cells/μL; low: <350 cells/μL).

Results: Of 182 individuals starting fostemsavir, 64% were viraemic (34% low CD4, 30% high CD4) and 36% were suppressed (16% low CD4, 20% high CD4). The suppressed/low CD4 group had the largest median increases in CD4 count (6-month: 30 cells/μL [interquartile range {IQR} 9-66], 12-month: 66 cells/μL [IQR 17-125]), and CD4% (6-month: 1.0% [IQR -0.3-2.8], 12-month: 1.9% [IQR 1.3-3.9]). Regardless of baseline VL, those with a high baseline CD4 count experienced a greater variability in immunological response than those with low CD4 counts (12-month standard deviation range 172-231 cells/μL vs. 69-90 cells/μL). VL <50 copies/mL was maintained in most suppressed individuals; nearly half of the viraemic/high CD4 group and a third of the viraemic/low CD4 group achieved a VL <50 copies/mL at either timepoint.

Conclusions: After 6 or 12 months of fostemsavir use, virological response was low in viraemic individuals, although most suppressed individuals did maintain suppression. While immunological response varied across individuals, virologically suppressed HTE individuals with low CD4 counts may benefit from immunological improvements with fostemsavir.