Serum levels of the biomarkers associated with immune activation and inflammation, with the exception of IL-6 and CRP, were seen to be decreased, but not normalized, following the initiation of HAART. It is assumed that these decreased levels of serum biomarkers of inflammation and B-cell activation result primarily from the virological suppression mediated by HAART. IL-6 levels were elevated prior to HAART initiation and appeared to be unaffected by HAART. CRP levels were modestly elevated prior to HAART and increased over time, a pattern seen in a previous longitudinal study of untreated HIV-infected men from the MACS [37
Only one-third of study participants achieved immediate and sustained virologic responses. In the subgroup that did not achieve optimal HIV suppression, increases in CD4 cell number were still apparent, with significant reductions in serum sCD27 and sCD30 levels. Results of subgroup analyses suggest that the effects of HAART on serum biomarkers was most pronounced in those persons who were naïve to ART prior to HAART initiation, consistent with previous studies [43
]. Therefore, persons who have experienced therapeutic failure with prior nonfully suppressive ART regimens, with resultant accumulation of drug resistance, may have a decreased probability of immune normalization with subsequent regimens.
There is a paucity of data examining the effect of HAART on the biomarkers measured in this study, and no published study has measured this group of biomarkers simultaneously. Atlas et al.
] and De Milito et al.
] examined the effect of HAART on plasma sCD27 levels. Atlas et al.
reported results from a study of 64 persons (primarily of African ethnicity living in Sweden) with mixed HIV-1 subtypes, who were ART-naive at HAART initiation and experienced effective viral responses to HAART. When comparing results from a subgroup infected with HIV-1 subtype B, the predominant viral subtype in North America, to our results, Atlas et al.
showed a more modest 9% decrease in sCD27 levels. De Milito et al.
found that HAART-induced significant and progressive reductions, but not normalization, of plasma sCD27 levels in 26 HIV-infected persons after 27 months.
The results of our study are consistent with a previous pilot study of 34 MACS participants that examined the effect of HAART on CXCL13 serum levels [15
], which reported a 21% decrease in CXCL13 serum levels after 1 year of HAART. Our results, in a larger study population, demonstrated greater than 40% decreases in CXCL13 after 2–3 years of HAART. Interestingly, baseline CD4 cell count appeared to modify the effect of HAART use on CXCL13 level, with higher CD4 being associated a greater decrease in CXCL13 levels following HAART initiation. CXCL13 is produced by follicular helper T cells (TFH
), which is the T-cell subset that interacts with activated germinal-center B cells in secondary lymphoid organs [35
]. Little is known about the effect of HIV infection on TFH
cells, or about how these cells are normally regulated. A recent study identified a novel regulatory CD8+
T-cell subset in mice, which can suppress the activity of TFH
]. When these CD8+
regulatory T cells were disrupted, this resulted in the enhanced production of auto-antibodies and in autoimmunity, and in a 10-fold increase in the size of germinal-center area [46
]. It is interesting to speculate that more advanced HIV disease, for which low CD4 number can act as a marker, results in a more pronounced loss of such regulatory T-cell subsets, making it more difficult for HAART to restore the activity of such cells and dampen TFH
activity, thereby resulting in a less marked decrease in CXCL13 levels post HAART. Clearly, additional research is needed to better define the effect of HIV infection, and of HAART, on TFH
cells and on potential regulatory T-cell subsets that may act on those cells.
Several studies have examined the association between HAART and hypergammaglobulinemia [47
]. Overall, these studies report a reduction in IgG with HAART use, and in some cases, normalization. Our results are consistent with these prior studies, but show much more modest decreases in serum IgG levels. In a case–control study, Chong et al.
] reported 65% lower IgG levels among virologic responders who were compared with an ART-untreated group. Notermans et al.
] reported complete normalization of IgG in 13 persons with virologic responses to HAART after 1.5 years of therapy, using a population-based reference range determined for the specific methodology in the testing hospital. Jacobson et al.
] and Redgrave et al.
] reported findings that were fairly consistent with ours, noting significant decreases, but not normalization, of IgG levels in persons who achieved effective HAART responses, with 45% (Jacobson et al.
) and 37% (Redgrave et al.
) of IgG values continuing to exceed reference limits.
Our results indicate that serum CRP levels were unaffected by HAART, and in fact appear to increase over time following HAART initiation. A similar pattern was seen in a study by Lau et al.
], who reported a general increase in CRP over time in untreated HIV-infected men in the MACS, with a 4.5 and 8% increase per year for men who remained AIDS-free and for men who progressed to AIDS, respectively.
Overall, these findings suggest that HAART resulted in near normalization of some biomarkers, whereas others continue to be markedly elevated post-HAART. It is possible that such sustained immune system alterations occurring among HAART recipients may lead to ongoing or new pathological processes. It is also possible that immune dysfunction is resolving slowly, and will eventually normalize over time, with resultant normalization in markers of immune activation and inflammation. However, our findings do not support this, in that we saw fairly consistent results between the two post-HAART measurements. Perhaps more extended longitudinal study of immune activation biomarkers among successfully treated HAART recipients is warranted, to determine whether and when full immune function is restored. It would be expected that the longer a state of chronic B-cell hyperactivation exists, the greater the risk for accumulation of genetic errors that can lead to the development of AIDS-related NHL. Therefore, even if immune normalization is ultimately achieved, it would be expected that the excess risk of NHL among HIV-infected persons would be reduced, but not eliminated, with HAART use. This is consistent with the results of epidemiologic studies, which have noted whereas HAART is associated with a decreased incidence of AIDS-NHL, a significant elevation in NHL risk remains in HIV-positive persons receiving HAART [31
Previous studies have shown that although HAART results in viral suppression to undetectable levels in peripheral blood, viral eradication is not achieved, even after years of continuous therapy [52
], and there is quick rebound of plasma viremia with therapy interruption. Viral persistence is thought to be the result of long-term survival of infected memory CD4 cells, permitting a steady-state low level of viral replication in lymphoid tissue that is not detectable in the peripheral blood [53
]. This low-level HIV replication may contribute to persisting B-cell hyperactivation in those on HAART. The progressive increases in serum CRP levels seen in this study suggest ongoing immune activation may continue post-HAART.
We found no apparent effect of HAART upon IL-6 levels. The SMART study, a study of HAART administration, with one arm based on minimizing drug use using target CD4 number (drug conservation arm) and another aiming at maximal suppression of HIV plasma levels (viral suppression arm), found that IL-6 levels increased by 30% over the first month of the trial in the drug conservation arm but were unchanged in the viral suppression arm, and also that the risk of death was associated with higher IL-6 levels at study entry [36
]. In another study, plasma IL-6 levels did not seem to change in most HAART recipients following initiation of treatment, except in those who developed immune restoration and inflammatory syndrome (IRIS), who showed an increase in plasma IL-6 post-HAART [54
]. IL-6 is a B-cell-stimulatory cytokine that is involved in promoting IgH
class switching and also has antiapoptotic effects on B cells, effects that have the potential to promote the development of B-cell cancers. In addition, a persistent excess of IL-6 may promote nascent lymphoma clones through its anti-apoptotic effects. Therefore, even if levels of other cytokines are normalized in HAART recipients, there still may be increased risks for those forms of AIDS-related NHL that are associated with errors in IgH
class switch DNA recombination, which may be promoted by IL-6. If this is true, one would expect to observe excess levels of those forms of AIDS-NHL associated with this genetic error among HAART-treated persons. In light of this, it is informative to note that whereas the incidence of EBV-associated AIDS-related NHLs has decreased in the first decade of the HAART era, the incidence of Burkitt’s lymphoma has not decreased significantly [32
Because this study did not include concurrent HAART-naive HIV-infected controls, we cannot adequately account for temporal changes that may have confounded this analysis (i.e. changes in patient management strategies over time, and better management of comorbidities including other opportunistic illnesses). However, our results were generally consistent within each time period studied, and significant changes in biomarker levels were seen within the fairly brief time periods closest to HAART initiation, often as short as a 1-year interval. Results from historical controls selected from the MACS cohort suggest that these biomarker levels are relatively stable over a period of three to five years (data not shown).
Most of the HIV-infected men in our study sample are long-term survivors. In this group of 467 participants, 81% were HIV-infected by early 1988, and may have been infected as early as 1978. Hence, this is a population that survived between 8 (seroincident participants) and 14 years (seroprevalent participants), respectively, prior to the introduction of HAART. These survivors are healthier and slower progressors than other MACS participants, who progressed to AIDS and died prior to HAART availability, and therefore could not have participated in this study. Obviously, the results obtained in this study cannot provide information on HAART’s impact upon serum B-cell activation associated molecules in these faster progressors.
Another potential source of error can occur with spurious events that cause transient increases in B-cell activation, such as responses to acute infection. Since effective HAART will potentially decrease the likelihood of acute infections, it is probable that acute infections will more likely occur prior to exposure to HAART.
Ultimately we would like to have been able to evaluate most closely those persons who developed AIDS-related NHL during the course of their infection and HAART treatment. However, with only 12 men this group developing AIDS-NHL, it was not possible to provide a formal analysis of this subgroup. Descriptive analyses suggest the NHL subgroup had a similar HAART response to that seen in the larger group of HIV-infected persons, with substantial decreases, but not normalization, of biomarker levels following HAART. Further studies in a larger NHL group are needed to support these findings.
Overall, our study indicates that HAART is associated with reductions in, but not normalization of, some markers of B-cell activation. None of the biomarkers were completely normalized in all individuals; 65% of individuals continued to have at least one elevated biomarker 2–3 years after HAART initiation. It is clear that good virologic and CD4 responses to HAART do not necessarily equate with normalization of these B-cell activation-associated molecules. Perhaps, markers of immune recovery should include routine assessment of markers of both B-cell and T-cell function. Finally, our results suggest that an altered immune environment still exists 2–3 years after HAART initiation, which has the potential to contribute to the increased risk of AIDS-related NHL that persists in those receiving effective antiretroviral treatment.