Mechanisms involved in CD4 cell gains in HIV-infected patients switched to raltegravir

Pharmacokinetic/pharmacodynamic modelling approaches in paediatric infectious diseases and immunology

Pharmacokinetic/pharmacodynamic (PKPD) modelling is used to describe and quantify dose-concentration-effect relationships. Within paediatric studies in infectious diseases and immunology these methods are often applied to developing guidance on appropriate dosing. In this paper, an introduction to the field of PKPD modelling is given, followed by a review of the PKPD studies that have been undertaken in paediatric infectious diseases and immunology. The main focus is on identifying the methodological approaches used to define the PKPD relationship in these studies. The major findings were that most studies of infectious diseases have developed a PK model and then used simulations to define a dose recommendation based on a pre-defined PD target, which may have been defined in adults or in vitro. For immunological studies much of the modelling has focused on either PK or PD, and since multiple drugs are usually used, delineating the relative contributions of each is challenging. The use of dynamical modelling of in vitro antibacterial studies, and paediatric HIV mechanistic PD models linked with the PK of all drugs, are emerging methods that should enhance PKPD-based recommendations in the future.

Antiretroviral therapy increases thymic output in children with HIV

OBJECTIVE

Disease progression and response to antiretroviral therapy (ART) in HIV-infected children is different to that of adults. Immune reconstitution in adults is mainly from memory T cells, whereas in children it occurs predominantly from the naive T-cell pool. It is unclear however what proportion of reconstituted CD4 T cells comes from thymic export and homeostatic proliferation in the periphery. Thymic output is often estimated by measuring T-cell receptor excision circles and markers such as CD31 expressed on recent thymic emigrants but these are confounded by peripheral T-cell division and cannot in themselves be used as quantitative estimates of thymic output.

DESIGN

To compare thymic output in HIV-infected children on ART, HIV-infected children not on ART and uninfected children of different ages.

METHOD

Combined T-cell receptor excision circle (TREC) and proliferation data are used with a recently described mathematical model to give explicit measures of thymic output.

RESULTS

We found that age-adjusted thymic output is reduced in untreated children with HIV, which increases significantly with length of time on ART.

CONCLUSION

Our results suggest that a highly active thymus in early childhood may contribute to better immune reconstitution if ART is initiated early in life.

Improvements in Immune Function and Activation with 48-Week Darunavir/Ritonavir-Based Therapy: GRACE Substudy

Objective. During the course of HIV infection, progressive immune deficiency occurs. The aim of this prospective substudy was to evaluate the recovery of functional immunity in a subset of patients from the GRACE (Gender, Race, And Clinical Experience) study treated with a DRV/r-based regimen. Methods. The recovery of functional immunity with a darunavir/ritonavir-based regimen was assessed in a subset of treatment-experienced, HIV-1 infected patients from the GRACE study. Results. 19/32 patients (59%) enrolled in the substudy were virologically suppressed (<50 copies/mL). In these patients, median (range) CD4+ cell count increased from 222 (2, 398) cells/mm³ at baseline to 398 (119, 812) cells/mm³ at Week 48. CD8+% decreased significantly from baseline to Week 48 (P = .03). Proliferation of CD4+ lymphocytes in response to CD3+/CD28+, phytohemagglutinin, and pokeweed was significantly increased (P < .01) by Week 12. Proliferation in response to Candida and tetanus was significantly increased by Week 48 (P < .01 and P = .014, resp.). Staphylococcal enterotoxin B-stimulated tumor necrosis factor-alpha and interleukin-2 in CD4+ cells was significantly increased by Week 12 (P = .046) and Week 48 (P < .01), respectively. Conclusions. Darunavir/ritonavir-based therapy demonstrated improvements in CD4+ cell recovery and association with progressive functional immune recovery over 48 weeks. This trial is registered with NCT00381303.

c-Jun NH2 -terminal kinase is a critical node in the death of CD4+ CD8+ thymocytes during Salmonella enterica serovar Typhimurium infection

Thymic atrophy, due to the depletion of CD4(+) CD8(+) thymocytes, is observed during infections with numerous pathogens. Several mechanisms, such as glucocorticoids and inflammatory cytokines, are known to be involved in this process; however, the roles of intracellular signaling molecules have not been investigated. In this study, the functional role of c-Jun NH2 -terminal kinase (JNK) during infection-induced thymic atrophy was addressed. The levels of phosphorylated JNK in immature CD4(+) CD8(+) thymocytes from C57BL/6 (Nramp-deficient) and 129/SvJ (Nramp-sufficient) mice were increased upon oral infection of mice with Salmonella enterica serovar Typhimurium (S. typhimurium). Furthermore, inhibition of JNK signaling, but not ERK or p38 MAPK, prevented the in vitro death of infected thymocytes. Importantly, the in vivo inhibition of JNK signaling with SP600125 protected C57BL/6 CD4(+) CD8(+) thymocytes from depletion via multiple mechanisms as follows: lower intracellular ROS, inflammatory cytokines, Bax and caspase 3 activity, increase in Bcl-xL amounts, and prevention of the loss in mitochondrial membrane potential. Notably, thymic architecture was preserved in infected mice treated with SP600125. Overall, this study identifies a novel role for JNK as a crucial regulator of the death of CD4(+) CD8(+) thymocytes during S. typhimurium infection.

Dynamics of CD8 T-cell activation after discontinuation of HIV treatment intensification

BACKGROUND

Detection of episomal HIV cDNA has been associated with greater levels of CD8 and CD4 T-cell activation in HIV-1-infected highly active antiretroviral therapy (HAART)-suppressed individuals. However, HAART intensification exclusively reduced CD8 T-cell activation.

METHODS

We evaluated activation markers 12 weeks after raltegravir withdrawal in a previously described 48-week raltegravir intensification study. The subjects (n = 34) were subgrouped into 2-LTR(+) (n = 12) or 2-LTR(-) (n = 22) subgroups according to delectability of 2-LTR episomes during the intensification period.

RESULTS

The initial differences in CD8 T-cell activation between subgroups were lost after intensification. Linear mixed models revealed significant reductions in CD8 T-cell activation in both 2-LTR(-) and 2-LTR(+) subgroups, suggesting that raltegravir impacts subjects irrespective of 2-LTR detection. Remarkably, a partial rebound in CD8 activation markers after raltegravir discontinuation was observed in the 2-LTR(+) subgroup. This restored the differences between subgroups observed at study entry, particularly in terms of CD38 expression within CD8 memory T-cells. Conversely, CD4 T-cell activation remained unchanged in both subgroups during the study period, although an early and transient CD45RA(-) CD4 T-cell redistribution from tissues was apparent.

CONCLUSIONS

CD8 T-cell activation undergoes reversible changes during raltegravir intensification and discontinuation in patients showing detectable 2-LTR circles. The general decrease in CD8 T-cell activation and a transient CD45RA(-) CD4 T-cell redistribution in intensified individuals may reflect residual viral replication during apparently suppressive HAART.

Interferon-γ- and glucocorticoid-mediated pathways synergize to enhance death of CD4(+) CD8(+) thymocytes during Salmonella enterica serovar Typhimurium infection

Thymic atrophy is known to occur during infections; however, there is limited understanding of its causes and of the cross-talk between different pathways. This study investigates mechanisms involved in thymic atrophy during a model of oral infection by Salmonella enterica serovar Typhimurium (S. typhimurium). Significant death of CD4(+) CD8(+) thymocytes, but not of single-positive thymocytes or peripheral lymphocytes, is observed at later stages during infection with live, but not heat-killed, bacteria. The death of CD4(+) CD8(+) thymocytes is Fas-independent as shown by infection studies with lpr mice. However, apoptosis occurs with lowering of mitochondrial potential and higher caspase-3 activity. The amounts of cortisol, a glucocorticoid, and interferon-γ (IFN-γ), an inflammatory cytokine, increase upon infection. To investigate the functional roles of these molecules, studies were performed using Ifnγ(-/-) mice together with RU486, a glucocorticoid receptor antagonist. Treatment of C57BL/6 mice with RU486 does not affect colony-forming units (CFU), amounts of IFN-γ and mouse survival; however, there is partial rescue in thymocyte death. Upon infection, Ifnγ(-/-) mice display higher CFU and lower survival but more surviving thymocytes are recovered. However, there is no difference in cortisol amounts in C57BL/6 and Ifnγ(-/-) mice. Importantly, the number of CD4(+) CD8(+) thymocytes is significantly higher in Ifnγ(-/-) mice treated with RU486 along with lower caspase-3 activity and mitochondrial damage. Hence, endogenous glucocorticoid and IFN-γ-mediated pathways are parallel but synergize in an additive manner to induce death of CD4(+) CD8(+) thymocytes during S. typhimurium infection. The implications of this study for host responses during infection are discussed.

Raltegravir intensification shows differing effects on CD8 and CD4 T cells in HIV-infected HAART-suppressed individuals with poor CD4 T-cell recovery

BACKGROUND

Immunodiscordant HIV-infected patients show viral suppression during antiretroviral therapy but fail to recover CD4 T cells. Immunodiscordance is characterized by partial CD4 T-cell immunodeficiency and increased inflammation, activation and immunosenescence in both CD4 and CD8 T cells.

METHODS

A randomized, controlled, 48-week intensification study to assess the effect of raltegravir on immunological parameters in immunodiscordant patients (CD4 cell counts <350 cells/μl; viral load <50 copies/ml for >2 years). Patients were randomized (2 : 1) to intensify therapy with raltegravir (intensified arm, n = 30) or continue with the same therapy (control arm, n = 14).

RESULTS

Both groups showed similar immunological baseline characteristics. CD4 T-cell counts increased faster in the intensified arm (P = 0.01, week 12). However, no differences between groups were observed at week 48. Additionally, no changes in thymic output (CD45RA(+)CD31(+) cells), activation (HLA-DR(+)CD95(+) cells) or ex-vivo cell death were observed in CD4 T cells at any time point intergroups or intragroups. Conversely, intensified arm showed significant decreases in the expression of the CD8 T-cell activation marker CD38 at weeks 24-48, which were more evident in memory cells. Despite this, the levels of HLA-DR expression in CD8 T cells and plasma soluble CD14 remained stable in both arms overtime.

CONCLUSION

Long-term (48-week) raltegravir intensification failed to counterbalance CD4 T-cell deficiency and its associated features: hyperactivation and death of CD4 T cells. However, raltegravir induced a specific reduction of CD38 expression in CD8 T cells, suggesting a beneficial effect on CD8 T-cell hyperactivation, which has been linked with HIV-associated comorbidities.