In this exploratory cross-sectional analysis including well-defined viro-immunological phenotypes and HIV-negative controls, virally suppressed INRs showed the highest plasma GDF-15 levels. Importantly, INR status remained independently associated with higher GDF-15 concentrations, after adjustment for age and CD4+ T-cell nadir. These findings suggest that elevated GDF-15 is not merely a marker of chronological aging or low historically CD4+ T-cell counts but may capture residual biological stress linked to incomplete immune recovery in treated HIV infection. To our knowledge, this is the first study to compare plasma GDF-15 levels across distinct HIV viro-immunological phenotypes, including INRs, ART-treated IRs, ECs, ART-naïve individuals, and HIV-negative controls.

GDF-15 correlated positively with age, duration of HIV infection, and time on ART, and inversely with indices of immune restoration, including CD4+ nadir and CD4/CD8 ratio. This profile is consistent with the role of GDF-15 as a stress-responsive cytokine and aligns with current concepts of INR pathophysiology, in which persistent immune activation, immunosenescence, impaired immune restoration, and mitochondrial or bioenergetic dysfunction may coexist despite virological suppression. Although these upstream biological processes were not directly measured, the marked elevation of GDF-15 in INRs supports the hypothesis that this biomarker may reflect a cumulative burden of cellular stress and immune dysfunction [5, 6].

The inclusion of contrasting viro-immunological groups strengthens the interpretation of these findings. ECs and ART-treated IRs showed GDF-15 concentrations comparable to those observed in HIV-negative controls, whereas INRs displayed a markedly different profile. This suggests that elevated levels of GDF-15 are more closely related to persistent immune dysfunction than to HIV infection, viral control, or ART exposure alone. The comparison with ECs is particularly informative, as these individuals maintained spontaneous viral control without ART and generally preserve CD4+ T-cell counts, whereas IRs represent successful immune restoration under ART.

These results extend our previous evidence supporting the relevance of GDF-15 in PWH. We recently reported that elevated plasma levels of GDF-15 were associated with aging, multimorbidity, and tobacco exposure in PWH, suggesting that this biomarker may capture biological vulnerability beyond conventional clinical markers [8]. Although the INR group was older than the other study groups, age was included in the multivariable regression model and the association between GDF-15 levels and the INR phenotype remained statistically significant. Nevertheless, given the well-established relationship between GDF-15 and biological aging, the contribution of age to the observed differences cannot be completely excluded and should be further explored in larger, age-matched studies. Recent evidence has also linked plasma GDF-15 levels to HIV reservoir markers in ART-treated PWH, independently of classical inflammatory markers, supporting a potential connection between viral persistence, mitochondrial stress, and comorbidity risk in treated HIV infection [9]. Together with our findings, these data suggest that GDF-15 may reflect a broader biological stress signature in PWH, encompassing immune dysfunction, HIV-related persistence, and comorbidity-associated pathways.

Importantly, a recent prospective study has shown that the INR phenotype is associated with a markedly increased long-term risk of both AIDS-defining and non-AIDS-defining diseases, highlighting that conventional CD4+ T-cell monitoring alone may not fully capture the clinical vulnerability of this subgroup [13]. Within this context, our findings support the hypothesis that GDF-15 may reflect the cumulative burden of biological processes underlying the INR phenotype and reinforce its potential as a candidate biomarker for improving the biological characterization of INR (Fig. 2). Although the present cross-sectional study was not designed to evaluate the prognostic value of GDF-15, our results provide a rationale for future longitudinal studies assessing whether GDF-15 may contribute to risk assessment beyond conventional immunological markers.

Biological interpretation of elevated plasma GDF-15 levels in immune non-responders (INRs). The diagram integrates previous evidence with the findings of the present study to illustrate a potential biological interpretation of the elevated plasma growth differentiation factor 15 (GDF-15) levels observed in immune non-responders (INRs). ART antiretroviral therapy. Created in BioRender. Pérez-González, A. (2026) https://BioRender.com/7br1fhf

This study has several strengths, including clinically relevant and well-defined HIV viro-immunological phenotypes, HIV-negative controls, standardized sample handling, duplicate GDF-15 measurements, and multivariable adjustment for key covariates. The stringent INR definition strengthened phenotypic specificity by identifying participants with marked incomplete immune recovery, although this may limit generalizability to broader populations with less severe immune non-response. Limitations of this study include the cross-sectional design, limiting the assessment of temporal changes in GDF-15 levels and causal relationships with immune recovery, modest sample size, and limited ability to adjust for multiple covariates. Although predefined viro-immunological criteria were applied consistently across groups, the possibility of selection bias cannot be completely excluded. The sample size limited adequately powered analyses of individual comorbid conditions, and therefore multimorbidity rather than disease-specific variables was used in the multivariable models. Ethnicity data were not available and therefore could not be considered in the analyses. In addition, information on cytomegalovirus serostatus or viremia was also unavailable, and its potential contribution to immune activation and GDF-15 variability cannot be excluded. In addition, participants were recruited from different cohorts and clinical centers, and residual confounding or pre-analytical differences cannot be fully excluded. Direct measurements of inflammatory, metabolic, mitochondrial, aging-related, and HIV reservoir markers were not available. Therefore, these findings should be interpreted as exploratory and hypothesis-generating rather than confirmatory. Future studies should validate these findings in larger, prospectively followed cohorts and investigate whether GDF-15 may serve as a dynamic marker of immune recovery over time. Further research should also explore the biological mechanisms underlying the association between GDF-15 and the INR phenotype.