Abstract Background The extension of HIV reservoir in the rectal gut associated lymphoid tissue (GALT) and the ART influence on this compartment are still poorly studied. We aimed to evaluate the extent of HIV-DNA in GALT and peripheral blood of virologically suppressed patients (VS) Methods 40 HIV-1+ VS pts were enrolled. Blood and GALT HIV-DNA levels and residual plasma viremia (RV) were quantified by droplet digital-PCR. Rectal biopsies were collected during high resolution anoscopy. Lymphocyte (L) phenotype and antiretroviral drug concentrations were analysed in tissue and peripheral blood Results Pts median age (IQR) was 37 (32-45) yrs, 39 (97.5%) were males. At HIV-1 diagnosis, median (IQR) viremia and CD4+ were 4.7 (4.3-5) Log10cps/mL and 469 (299-627) cells/”L, respectively. 27 (67.5%) pts had HIV-1 B subtype. At the enrolment, median (IQR) CD4+ was 720 (583-1041) cells/”L and RV was 3 (2-6) cps/mL. All pts were on 2 NRTI-regimen with a 3rd drug (20 INSTI, 15 NNRTI, 5 PI). A positive correlation emerged among HIV-DNA levels in the GALT and PBMC (Rho= 0.432; p=0.005), CD8+ L counts (Rho=0.367; p=0.02), and a negative correlation emerged with blood CD3+ L percentage (Rho=-0.489; p=0.006). Peripheral blood HIV-DNA values were inversely correlated with the CD4+ nadir (Rho= -0.379; p=0.017) and blood CD4+/CD8+ ratio (Rho= -0.362; p=0.022), and directly correlated with GALT CD4+CD38+ (Rho= 0.414; p=0.028) and blood CD8+CD38+ L (%) (Rho= 0.400; p=0.026). A positive correlation among GALT and peripheral blood CD4+CD38+ (Rho= 0.555; p=0.005), CD8+CD38+ (Rho= 0.417; p=0.030), and CD19+CD38+ L (Rho= 0.498; p=0.007) was found. There was no difference in HIV-DNA levels in the GALT and PBMCs according to the ART 3rd drug. In a subgroup of 20 pts the analysis of rectal tissue and blood drug concentrations showed that tissue/plasma ratio was higher in pts on Elvitegravir (EVG) and Rilpivirine (RPV) (median ratio 2.8 and 1.7, respectively) GALT and Blood HIV-DNA levels Tissue-Plasma Drug concentration Conclusion HIV-DNA from rectal GALT is a valid marker to characterize viral reservoir. The correlation of higher GALT HIV-DNA levels, CD8+ T L counts and CD4 and CD8 activation levels suggests that a greater amount of virus in the anorectal reservoir can perpetuate the inflammatory state characteristic of HIV+ pts. EVG and RPV showed higher tissue exposure than other ART regimens Disclosures All Authors: No reported disclosures.