ABSTRACT: Background:Complete recovery of the CD4 T cell count is uncommon among chronically HIV-infected individuals with very low pre-treatment CD4 count. We studied the prevalence of chronically immune recovery and its associated factors including immune characteristics chronic HIV-infected Thais. Methods:Treatment-naïve participants (n ?= ?375) from the HIV-NAT 006 cohort with a pre-treatment CD4 T cell count after initiating antiretroviral therapy (ART) and having achieved a suppressed viremia (HIV-RNA level ?< ?400 copies/mL) were retrospectively followed at the Thai Red Cross AIDS Research Centre, Bangkok, Thailand. Suboptimal immune recovery (SIR) was defined as having a CD4+ T cell count <200 ?cells/mm3 for 3 years after ART initiation. A case-control sub-study matched for age, sex and pre-ART CD4 T cell count was conducted to compare immunological characteristics between SIR (n ?= ?17) and non-SIR (n ?= ?24) participants. Immunological biomarkers such as interleukin-7 (IL-7) and soluble CD14 (sCD14) and other covariates including cytomegalovirus (CMV) DNA level, baseline hemoglobin level, hepatitis B and C co-infections, and T cell subsets associated with immune activation and exhaustion were evaluated. Results:Among 375 participants with pre-ART CD4 T cell counts < 200 ?cells/mm3, the prevalence of SIR was 39.7%, 19.7% and 7.7% at years 1, 2 and 3 after starting ART, respectively. In a multivariate analysis, a pre-ART CD4 T cell count ?100 ?cells/mm3 (adjusted odds ratio [aOR] 9.45, 95% CI 2.92-30.61, p ?< ?0.001), older age (aOR 1.07, 95% CI 1.01-1.13, p ?= ?0.029) and baseline HIV-RNA level (aOR 0.36, 95% CI 0.21-0.59, p ?< ?0.001) were independently associated with SIR at year 3 after ART initiation. In the matched case-control sub-study (cases ?= ?17, controls ?= ?24), there was a higher prevalence of hepatitis C co-infection (18.8% vs. 0%, p ?= ?0.05), lower sCD14 levels (mean, 6.23 vs. 6.27 log10 ?pg/mL, p ?= ?0.04), lower CD8 T cell counts (mean, 514 vs. 876, p ?= ?0.0003), lower CD4/CD8 T cell ratio (mean, 0.27 vs. 0.41, p ?= ?0.01) and higher expression of PD1 on CD8+ T cells (74.2% vs. 65.1%, p ?= ?0.02) observed in SIR participants compared to their non-SIR counterparts at year 3 after ART initiation. Conclusions:Nearly 10% of the study participants who had achieved virological suppression failed to recover a CD4 T cell count > 200 cells/mm3 after 3 years of ART which was with a very low pre-ART CD4 T cell count and older age. The long-term clinical outcomes of SIR participants need to be further explored.