Anti-Tat immunity defines CD4+ T-cell dynamics in people living with HIV on long-term cART

Abstract

Background: Low-level HIV viremia originating from virus reactivation in HIV reservoirs is often present in cART treated individuals and represents a persisting source of immune stimulation associated with sub-optimal recovery of CD4⁺ T cells. The HIV-1 Tat protein is released in the extracellular milieu and activates immune cells and latent HIV, leading to virus production and release. However, the relation of anti-Tat immunity with residual viremia, persistent immune activation and CD4⁺ T-cell dynamics has not yet been defined.

Methods: Volunteers enrolled in a 3-year longitudinal observational study were stratified by residual viremia, Tat serostatus and frequency of anti-Tat cellular immune responses. The impact of anti-Tat immunity on low-level viremia, persistent immune activation and CD4⁺ T-cell recovery was investigated by test for partitions, longitudinal regression analysis for repeated measures and generalized estimating equations.

Findings: Anti-Tat immunity is significantly associated with higher nadir CD4⁺ T-cell numbers, control of low-level viremia and long-lasting CD4⁺ T-cell recovery, but not with decreased immune activation. In adjusted analysis, the extent of CD4⁺ T-cell restoration reflects the interplay among Tat immunity, residual viremia and immunological determinants including CD8⁺ T cells and B cells. Anti-Env immunity was not related to CD4⁺ T-cell recovery.

Interpretation: Therapeutic approaches aiming at reinforcing anti-Tat immunity should be investigated to improve immune reconstitution in people living with HIV on long-term cART.

Trial registration: ISS OBS T-002 ClinicalTrials.gov identifier: NCT01024556 FUNDING: Italian Ministry of Health, special project on the Development of a vaccine against HIV based on the Tat protein and Ricerca Corrente 2019/2020.

Keywords: Anti-Tat antibodies; Anti-Tat cellular immunity; CD4+ T cells; HIV immune activation; HIV reservoirs; HIV residual viremia; HIV-1 Tat; Perspective for clinical implications.

Fig. 1

Dynamics of immune parameters over 3 years of follow up in participants stratified by anti-Tat antibodies or cellular immune responses to Tat. CD4⁺ T cells, CD8⁺ T cells and CD4⁺/CD8⁺ T-cell ratio over time were analysed according to anti-Tat humoral and cellular responses in a longitudinal regression analysis for repeated measures using a mixed model with random-effects; N = 95 anti-Tat Ab⁻, 23 anti-Tat Ab⁺, 40 infrequent responders, 48 frequent responders. (a, b, c) CD4⁺ T-cell dynamics over time. (a) Regression analysis of the whole study population (β = 0.028 cells/day, p = 0.0125); (b) Participants stratified by humoral responses to Tat (anti-Tat Ab⁺: β = 0.09 cells/day, p < 0.0001; anti-Tat Ab⁻: β = 0.01 cells/day, p = 0.4326); (c) Volunteers stratified by cellular immune responses to Tat (frequent responders: β = 0.03 cells/day, p = 0.0242; infrequent responders: β = 0.01 cells/day, p = 0.6146). (d, e, f) CD8⁺ T-cell kinetics. (d) Regression analysis of the whole study population (β = -0.051 cells/day, p = 0.0265) (e) Regression analysis according to anti-Tat humoral responses (anti-Tat Ab⁺: β = 0.04 cells/day, p = 0.4045; anti-Tat Ab⁻: β = -0.08 cells/day, p = 0.0022); (f) Analysis according to cellular immune responses to Tat (frequent responders: β = -0.06 cells/day, p = 0.0739; infrequent responders: β = -0.07 cells/day, p = 0.0248); (g, h, i) CD4⁺/CD8⁺ T-cell ratio dynamics over time. (g) Regression analysis of the whole study population (β = 0.0002 cells/day, p < 0.0001) (h) Participants stratified by anti-Tat humoral responses (anti-Tat Ab⁺: β = 0.0002/day, p < 0.0001; anti-Tat Ab⁻: β = 0.0001/day, p < 0.0001); (i) Participants stratified by cellular immune responses (frequent responders: β=0.00015/day, p < 0.0001; infrequent responders β = 0.00016/day, p < 0.0001). β: slope of the regression line; p-values: probability β ≠ 0.

Fig. 2

Volunteers’ immunological dynamics according to Tat humoral and cellular responses. Summary of the results of longitudinal regression analysis of immune-cell variations over time in volunteers cross-stratified for Tat serostatus and frequency of cellular responses to Tat. Dark green with arrow pointing upwards: significant increase over time; light green with arrow pointing downwards: significant decrease along time; intermediate green and absence of arrow: non-significant variations. CD4⁺ and CD8⁺ T cells in anti-Tat Ab⁺ infrequent responders showed non-significant increases and decreases, respectively, resulting in a significant increase of the CD4⁺/CD8⁺ T-cell ratio over time (For interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.).

Fig. 3

Residual viremia over 3 years of follow up in participants stratified by anti-Tat antibodies or cellular immune responses to Tat. Percentages of individuals that remained persistently aviremic (VL = undetectable) or had episodes of transient residual viremia (VL ≤ 40 HIV-1 RNA copies/mL) or viral blips (VL > 40 HIV-1 RNA copies/mL) during the study. (A) Participants stratified by anti-Tat humoral response (p = 0.0037) (anti-Tat Ab⁻: VL = undetectable: n. 31; VL ≤ 40: n. 30; VL > 40: n.34; anti-Tat Ab⁺: VL = undetectable: n. 14; VL ≤ 40: n. 0; VL > 40: n. 9); (B) Participants stratified by frequency of cellular responses to Tat (p = 0.7730) (infrequent responders: VL = undetectable: n.12; VL ≤ 40: n. 10; VL > 40: n.18; frequent responders: VL = undetectable: n. 16; VL ≤ 40: n. 14; VL > 40: n. 18). A chi-square test was utilized.