Curr HIV/AIDS Rep DOI 10.1007/s11904-014-0213-0
COMPLICATIONS OF ANTIRETROVIRAL THERAPY (JM KILBY, SECTION EDITOR)
Immune Reconstitution Disorders in Patients With HIV Infection: From Pathogenesis to Prevention and Treatment C. C. Chang & V. Sheikh & I. Sereti & M. A. French
# Springer Science+Business Media New York 2014
Abstract An immune reconstitution disorder occurs in up to 40 % of severely immunodeficient HIV patients who commence antiretroviral therapy (ART), with an immune reconstitution inflammatory syndrome (IRIS) being encountered most commonly. Differences in the immunopathogenesis of an IRIS associated with different types of pathogen have become apparent but common features have also been defined. These include severe immunodeficiency prior to commencing ART associated with a high pathogen load and ‘compensatory’ immune responses, particularly innate immune responses, which inadequately control the pathogen and increase the risk of immunopathology as the immune system recovers on ART. Prevention of an IRIS may be achieved by optimising therapy for opportunistic infections before ART is commenced, delaying ART or using immunomodulatory therapy to prevent or suppress the immune response that causes the immunopathology. However, further
C. C. Chang Department of Infectious Diseases, Alfred Hospital and Monash University, Melbourne 3000, Australia
clinical studies are required to examine these options in a systematic manner for the various types of IRIS. Keywords HIV . Immune reconstitution disorders . Immune reconstitution inflammatory syndrome (IRIS)
Introduction Severe HIV-induced immunodeficiency is hazardous to an affected patient not only because of the increased risk of opportunistic infections and cancers but also because it confers an increased risk of an immune reconstitution disorder (IRD) during recovery of the immune system after antiretroviral therapy (ART) is commenced. Clinical and laboratory studies over the last two decades have defined three categories of IRD (Table 1). Here, we review recent developments in knowledge about the pathogenesis and treatment of the most clinically significant types of IRD.
C. C. Chang Center for Biomedical Research, Burnet Institute, Melbourne 3000, Australia
Tuberculosis-associated Immune Reconstitution Inflammatory Syndrome (TB-IRIS)
V. Sheikh : I. Sereti Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 10 Center Drive, Bethesda, MD 20892, USA
Data from prospective clinical studies demonstrate that paradoxical TB-IRIS occurs in 20-25 % of HIV patients with treated TB after commencing ART [1–3], but is an uncommon cause of death and usually can be managed conservatively [4–6]. An exception is TB-IRIS complicating TB meningitis (TBM), which affects about 50 % of patients commencing ART and often causes morbidity or mortality [7]. In regions of the world where M. tuberculosis infection is endemic, TB presents in about 6 % of HIV patients after ART is commenced [8] and sometimes presents as an IRIS (unmasking TB-IRIS).
M. A. French (*) School of Pathology and Laboratory Medicine, University of Western Australia, Perth 6009, Australia e-mail: [email protected] M. A. French Department of Clinical Immunology, Royal Perth Hospital and PathWest Laboratory Medicine, Perth 6000, Australia
Curr HIV/AIDS Rep Table 1 Immune reconstitution disorders in HIV patients receiving ART • Inflammatory disease or cancer resulting from the restoration of an immune response against an opportunistic pathogen that causes immunopathology at sites of infection, and sometimes systemically, which presents in one of two ways: ○ An immune reconstitution inflammatory syndrome (IRIS), characterised by inflammation that is exaggerated and/or atypical, in patients with a treated opportunistic infection (paradoxical IRIS) or subclinical infection (unmasking IRIS). ○ Disease presentation that cannot be distinguished from typical disease events, such as tuberculosis, herpes zoster and flares of hepatitis caused by hepatitis B virus (HBV) and hepatitis C virus (HCV) infection during the first three months of ART. • Immune reconstitution-associated autoimmune diseases, of which the most common type is Graves’ disease. • Immune reconstitution-associated immune-mediated inflammatory diseases, of which the most common type is sarcoidosis.
A low CD4+ T-cell count, disseminated TB and a short period of time between treating the TB and commencing ART are risk factors for developing TB-IRIS, suggesting that the risk is highest when the pathogen load is high. Direct evidence of this was provided by the observation that TB-IRIS is more frequent in patients with mycobacterial lipoaribinomannan detectable in urine before commencing ART [9]. In addition, Marais et al. demonstrated that a positive cerebrospinal fluid (CSF) culture for M. tuberculosis prior to commencing ART in HIV patients with treated TBM conferred a relative risk of 9.3 for developing TB-IRIS [10]. A higher mycobacterial load in patients who develop TBIRIS is a possible explanation for differences in T cell responses to M. tuberculosis antigens observed before ART is commenced. Vignesh et al. used intracellular flow cytometry to show that patients who developed TB-IRIS had higher frequencies of CD4+ T-cells producing interferon (IFN)-gamma after stimulation with PPD and ESAT-6 before ART was commenced and that these cells expanded after ART [11•]. Moreover, the group led by Meintjes and Wilkinson have demonstrated that TB-IRIS is more common in patients infected with drug-resistant M. tuberculosis [12] and that these patients exhibit low IFN-gamma/interleukin (IL)-10 ratios in cultures of PBMC stimulated with heat-killed H37Rv strain of M. tuberculosis [13]. It was argued that this was a consequence of poorly controlled mycobacterial growth in patients with drug-resistant TB. An increasing amount of evidence indicates that aberrant innate immune responses against M. tuberculosis increase susceptibility to, and contribute to an exaggerated inflammatory response in, TB-IRIS. Higher production of IL-18 and CXCL10 (also known as interferon-inducible protein-10 [IP10]) in TB-IRIS patients, compared with controls, provided evidence of activated innate immune responses, probably mediated by monocytes and macrophages [14]. Higher expression levels of multiple gene transcripts in monocytes from
patients with TB-IRIS, compared with controls, provided evidence of monocyte activation before and two weeks after commencing ART [15•]. Gene transcripts of molecules associated with infection and inflammation, especially pattern recognition receptors for bacteria and viruses, and of complement system components were particularly affected. In support of these findings, Tan et al. demonstrated that monocytes from patients who had previously experienced TB-IRIS expressed higher amounts of TLR2 [16]. In a study focussing on complement abnormalities in monocytes [17], Tran et al. demonstrated increased gene transcripts of C1q (a component of the classical pathway of complement activation) and C5 (a component of the membrane attack complex of the complement system) but decreased gene transcripts of C1 inhibitor (a complement activation regulatory protein). It was argued that activation of the complement system might contribute to inflammation in TB-IRIS, but evidence of complement activation in plasma was not presented. It is therefore likely that aberrant production of complement system proteins is a marker of monocyte activation and/or dysfunction. Activation of monocytes and macrophages is also a likely explanation for the higher production of matrix metalloproteinases (MMPs) by peripheral blood mononuclear cells (PBMC) stimulated with M. tuberculosis antigens, and higher plasma levels of these molecules, demonstrated in TB-IRIS patients [18•]. MMPs induce the production of inflammatory mediators and tissue remodelling and their activity may therefore be a cause of the pronounced suppuration that occurs in some patients with TB-IRIS [19]. Natural killer (NK) cells and neutrophils may also contribute to innate immune responses against M. tuberculosis before ART is commenced in patients who develop TB-IRIS. Pean et al. demonstrated in a randomised controlled trial of early versus late ART in HIV patients with treated TB that patients who developed TB-IRIS exhibited a higher proportion of NK cells expressing markers of cytotoxicity [20]. Marais et al. demonstrated that HIV patients with TBM who develop TBIRIS have higher CSF neutrophil counts prior to ART [10]. Recognition that TB-IRIS may be caused in part by innate immune responses against M. tuberculosis has led to studies of plasma biomarkers of those immune responses, which might be used in the diagnosis and/or prediction of TB-IRIS. Increased production of pro-inflammatory cytokines, including IL-6, TNF-alpha and IL-18, and chemokines, such as CXCL10 and CXCL8 (also known as IL-8), and of antiinflammatory cytokines, such as IL-10, has been observed before and/or during TB-IRIS in several studies [14, 21, 22•, 23, 24•, 25, 26•]. However, it is unclear which of these potential biomarkers might have clinical utility in predicting TB-IRIS. Haddow et al. did not observe higher plasma levels of any pro-inflammatory cytokine before ART in South African patients who developed paradoxical TB-IRIS, though did observe higher serum levels of CRP (which is induced by
Curr HIV/AIDS Rep
IL-6) in patients who developed unmasking TB-IRIS [23]. In a study of Ugandan patients, paradoxical TB-IRIS was independently associated with lower plasma levels of IL-6 before ART and higher levels of IL-6 at the time of TB-IRIS [22•]. In contrast, a study conducted in India demonstrated that patients who developed paradoxical TB-IRIS had higher plasma levels of IL-6 and CRP before ART was commenced [24•]. Finally, another study of South African patients demonstrated only higher pre-ART plasma levels of IFN-gamma in patients who developed paradoxical TB-IRIS [21]. Thus, while TB-IRIS is associated with increased production of multiple cytokines and chemokines, none has provided a clinically useful biomarker for disease prediction, so far.
Cryptococcosis-associated IRIS (C-IRIS) Most prospective clinical studies of C-IRIS have been performed in HIV patients co-infected with Cryptococcus neoformans and have focused on paradoxical C-IRIS of the central nervous system (CNS) [27], as this bears a higher morbidity and mortality than non-CNS C-IRIS. Several recent studies have increased knowledge about the pathogenesis of C-IRIS and identified risk factors and potential disease biomarkers. Predictors of C-IRIS include a lower baseline CD4+ T-cell count [28] and reduced CSF inflammation [29]. The UgandanUnited States group led by Boulware and Bohjanen has proposed a 3-phase model of C-IRIS [30, 31] based on their findings [29, 30, 32, 33]. Prior to ART commencement, a paucity of innate inflammatory responses, or inappropriately high Th2 responses, result in reduced inflammation that promotes ineffective antigen clearance. Second, early after ART initiation, persistent antigen primes for inflammation by promoting pro-inflammatory cytokines, such as IL-6, yet despite this, the effector response is poor and secondary activation of the coagulation cascade occurs. Third, at the time of C-IRIS, a generalised cytokine storm occurs with activation of multiple innate and adaptive immune pathways and the coagulation cascade. CSF Cryptococcal Culture Negativity and Higher CD4+ T cell Increase Are Protective for C-IRIS In a prospective study of 130 ART-naive HIV patients treated for CM who commenced ART, patients with a negative CSF cryptococcal culture pre-ART experienced fewer episodes of neurological deterioration (ND), C-IRIS and cryptococcal relapse/persistence than patients with culture positivity [34••]. Furthermore, increased CD4+ T-cell counts over 24-weeks of ART were independently associated with a decreased rate of C-IRIS, in contrast to the findings of a previous study [35].
IFN-gamma Is Beneficial in CM and C-IRIS The importance of IFN-gamma in the control of cryptococcal infection was highlighted by a Zimbabwean study, which demonstrated that 60 % of HIV patients with CM had undetectable IFN-gamma in CSF [36], and a Thai study where patient survival was associated with a higher CSF concentrations of pro-inflammatory cytokines, including IFN-gamma, and only the antifungal therapy regimen and CSF IFN-gamma concentration were independently associated with rate of fungal clearance [37]. Recently, a randomised controlled trial (RCT) in 90 patients from Cape Town, found that adjuvant IFN-gamma therapy led to faster rates of CSF fungal clearance, but had no impact on mortality [38]. In addition, patients who survived CM had higher IFN-gamma and TNF-alpha production from PBMC stimulated with cryptococcal antigens [39]. Chang et al. undertook an analysis of cryptococcal-specific T-cell responses in HIV-infected patients with treated CM before and during the first 24-weeks of ART using whole blood assays of T cells activated with cryptococcal mannoproteins (CMP) [40]. C-IRIS patients, compared to patients with no ND, had lower CMP-induced IFN-gamma production in blood collected pre-ART and 4-weeks post-ART and lower proportions of CMP-activated CD4+ T-cells (expressing CD25 and CD134) pre-ART. Preserved T-cell function pre-ART, as demonstrated by higher proportions of mitogen-activated CD4+ T-cells, and higher IL-10 and CXCL10 production in CMP-stimulated whole blood cultures, was also associated with better survival at 24-weeks post-ART [40]. Such whole blood assays may be useful in risk-stratification algorithms for the management of HIV patients with CM. CNS Compartmentalisation of Immune Responses in C-IRIS While the pathogenesis of C-IRIS is unclear, it seems likely that examination of blood may not always reflect immunopathology in the CNS. Chang et al. explored the CSF compartment of HIV patients with treated CM and demonstrated a distinct immunological profile compared to blood [41••]. The T-cell CD4+/CD8+ ratio was lower in CSF than in blood and the proportion of CD4+ and CD8+ T-cells that expressed both CXCR3+ and CCR5+ and the concentration of CXCL10, CCL2 and CCL3 were all increased in CSF compared to blood prior to ART initiation. Patients who subsequently developed C-IRIS exhibited an increased ratio of CCL2/CXCL10 and CCL3/CXCL10 in CSF and an increased proportion of CXCR3+CCR5+CD8+ T-cells in CSF relative to blood. A higher CSF CCL2/CXCL10 ratio was also associated with persistent CSF cryptococcal growth and death during ART. In an allied study, it was shown that relative to blood, the CSF was enriched with immunoregulatory
Curr HIV/AIDS Rep
(CD56bright) NK cells [42]. Immunoregulatory NK cells were also more activated (CD69+) and tended to secrete higher levels of CXCL10 and lower levels of TNF-alpha. CSF was also enriched with non-classical monocytes. Together, these findings suggest that enhanced recruitment and/or retention of activated CD8+ T-cells and NK cells, and a chemokine profile that recruits monocytes into the CSF, characterises the immune response against cryptococci in the context of CD4+ T-cell and IFN-gamma deficiency and may predispose to C-IRIS after ART is commenced. Potential Strategies for Preventing C-IRIS Given that a high cryptococcal antigen load in CSF is a risk factor for C-IRIS, particularly when associated with active infection, prevention of C-IRIS might be achieved by ensuring that cryptococcal infection is optimally controlled before ART is commenced. This might be achieved by optimising antifungal therapy, using adjunctive IFN-gamma therapy or deferring ART. Choice and duration of induction antifungal therapy impacts on CSF cryptococcal clearance and is likely to affect the occurrence of C-IRIS in HIV patients with CM. Day et al. [43] published definitive data showing a reduction of mortality using amphotericin and 5-FC in a RCT of 299 patients with CM. This should be tested as a strategy for preventing C-IRIS in HIV patients with CM. Timing of ART commencement in the setting of newly diagnosed opportunistic infections has been long debated, where the risk of an IRIS after early ART commencement is measured against the risk of new AIDS-defining disease after late ART commencement. Several studies have addressed this issue in HIV patients with CM. A Zimbabwean study, in which fluconazole was used as induction therapy, was terminated after 54 patients were enrolled because the early ART arm (initiated within 72 hours of CM diagnosis) had almost three times the risk of mortality compared to the delayed ART arm (initiated more than 10 weeks after CM diagnosis) [44]. It was postulated that the higher death rate associated with early ART was due to C-IRIS. A recently published, smaller, randomised study of 27 patients from Botswana showed no difference in mortality but reported an increased rate of CIRIS in the early arm [45]. A large multicentre prospective study—the Cryptococcal Optimal Antiretroviral Timing (COAT) study—was also recently terminated at 35 % enrolment as mortality was significantly higher in the early ART arm (commenced at 7-13 days after CM diagnosis) compared to the late ART arm (commenced more than 5 weeks after CM diagnosis). However, the rate of C-IRIS was reported as being not different between the early and deferred ART arms [46]. Taken together, the findings of these studies suggest that later commencement of ART is desirable in HIV patients with CM, with expert opinion arguing that ART
should be deferred until 4-6 week after CM diagnosis [47]. However, judicious interpretation of data from these RCTs is necessary. While it seems clear that very early (at 3-11 days) commencement of ART is harmful, by virtue of RCT designs, there remains an unexplored time-window between 2 and 4 weeks after CM diagnosis where ART could plausibly be initiated, particularly in the context of optimal antifungal therapy. In the study of Chang et al., ART was commenced based on clinical response, at a median time of 18 days after CM diagnosis and the 6-month post-ART survival rate was 80.2 % [34••]. Therefore, while very early ART initiation is not recommended in HIV patients with CM, deferring to 4-6 weeks may be too long. Instead, it is suggested that care should be individualised taking into account clinical recovery from CM, CSF sterility and other comorbidities.
Immune Reconstitution Inflammatory Syndromes Associated With Virus Infections Kaposi’s Sarcoma-associated IRIS (KS-IRIS) Kaposi’s sarcoma herpesvirus (KSHV) is the aetiologic agent for a spectrum of conditions that may complicate HIV-induced immunodeficiency, including Kaposi’s sarcoma (KS), Multicentric Castleman’s Disease (KSHV-MCD), primary effusion lymphoma (PEL) and a recently described inflammatory condition termed KSHV inflammatory cytokine syndrome (KICS) [48]. Both human and viral IL-6 contribute to the immunopathology of these diseases [49]. KS is the most common HIV-associated malignancy in HIV patients in Sub-Saharan Africa [50] and disease exacerbation (paradoxical KS-IRIS) or presentation (unmasking KS-IRIS) after ART are common. However, disease progression without ART is also common and distinguishing this from KS-IRIS clinically is difficult. Importantly, there is no consensus definition for KS-IRIS or KS-MCD-IRIS. Paradoxical KS-IRIS has been reported in up to 29 % of HIV patients with KS during the first year of ART, with higher rates reported in patients with visceral disease and from Africa [51, 52]. High plasma HIV RNA and KSHV DNA and T1 KS stage are risk factors for KS-IRIS [52]. The risk of unmasking KS-IRIS is particularly high in the first 3 months after ART initiation, especially in patients with severe CD4+ T-cell deficiency, men-who-have-sex-with-men (MSM) and African migrants [53]. In a retrospective study, KS-IRIS was reported in 22 % of children commencing ART in Malawi and Botswana [54]. There are no studies examining the optimal timing of ART in HIV patients with KS or the use of chemotherapy with ART.
Curr HIV/AIDS Rep
Progressive Multifocal Leukoencephalopathy-associated IRIS (PML-IRIS)
Autoimmunity and Other Immune-mediated Inflammatory Disease During Immune Reconstitution
Both paradoxical and unmasking IRIS may occur in HIV patients with progressive multifocal leukoencephalopathy (PML) of brain white matter, which is caused by infection with JC polyomavirus (JCV). Distinguishing between progressive PML and PML-IRIS is difficult clinically and radiologically. Cases of PML-IRIS have been reported more than 24-weeks following ART commencement [55]. A CD4+ Tcell count of
COMPLICATIONS OF ANTIRETROVIRAL THERAPY (JM KILBY, SECTION EDITOR)
Immune Reconstitution Disorders in Patients With HIV Infection: From Pathogenesis to Prevention and Treatment C. C. Chang & V. Sheikh & I. Sereti & M. A. French
# Springer Science+Business Media New York 2014
Abstract An immune reconstitution disorder occurs in up to 40 % of severely immunodeficient HIV patients who commence antiretroviral therapy (ART), with an immune reconstitution inflammatory syndrome (IRIS) being encountered most commonly. Differences in the immunopathogenesis of an IRIS associated with different types of pathogen have become apparent but common features have also been defined. These include severe immunodeficiency prior to commencing ART associated with a high pathogen load and ‘compensatory’ immune responses, particularly innate immune responses, which inadequately control the pathogen and increase the risk of immunopathology as the immune system recovers on ART. Prevention of an IRIS may be achieved by optimising therapy for opportunistic infections before ART is commenced, delaying ART or using immunomodulatory therapy to prevent or suppress the immune response that causes the immunopathology. However, further
C. C. Chang Department of Infectious Diseases, Alfred Hospital and Monash University, Melbourne 3000, Australia
clinical studies are required to examine these options in a systematic manner for the various types of IRIS. Keywords HIV . Immune reconstitution disorders . Immune reconstitution inflammatory syndrome (IRIS)
Introduction Severe HIV-induced immunodeficiency is hazardous to an affected patient not only because of the increased risk of opportunistic infections and cancers but also because it confers an increased risk of an immune reconstitution disorder (IRD) during recovery of the immune system after antiretroviral therapy (ART) is commenced. Clinical and laboratory studies over the last two decades have defined three categories of IRD (Table 1). Here, we review recent developments in knowledge about the pathogenesis and treatment of the most clinically significant types of IRD.
C. C. Chang Center for Biomedical Research, Burnet Institute, Melbourne 3000, Australia
Tuberculosis-associated Immune Reconstitution Inflammatory Syndrome (TB-IRIS)
V. Sheikh : I. Sereti Laboratory of Immunoregulation, National Institute of Allergy and Infectious Diseases, National Institutes of Health, 10 Center Drive, Bethesda, MD 20892, USA
Data from prospective clinical studies demonstrate that paradoxical TB-IRIS occurs in 20-25 % of HIV patients with treated TB after commencing ART [1–3], but is an uncommon cause of death and usually can be managed conservatively [4–6]. An exception is TB-IRIS complicating TB meningitis (TBM), which affects about 50 % of patients commencing ART and often causes morbidity or mortality [7]. In regions of the world where M. tuberculosis infection is endemic, TB presents in about 6 % of HIV patients after ART is commenced [8] and sometimes presents as an IRIS (unmasking TB-IRIS).
M. A. French (*) School of Pathology and Laboratory Medicine, University of Western Australia, Perth 6009, Australia e-mail: [email protected] M. A. French Department of Clinical Immunology, Royal Perth Hospital and PathWest Laboratory Medicine, Perth 6000, Australia
Curr HIV/AIDS Rep Table 1 Immune reconstitution disorders in HIV patients receiving ART • Inflammatory disease or cancer resulting from the restoration of an immune response against an opportunistic pathogen that causes immunopathology at sites of infection, and sometimes systemically, which presents in one of two ways: ○ An immune reconstitution inflammatory syndrome (IRIS), characterised by inflammation that is exaggerated and/or atypical, in patients with a treated opportunistic infection (paradoxical IRIS) or subclinical infection (unmasking IRIS). ○ Disease presentation that cannot be distinguished from typical disease events, such as tuberculosis, herpes zoster and flares of hepatitis caused by hepatitis B virus (HBV) and hepatitis C virus (HCV) infection during the first three months of ART. • Immune reconstitution-associated autoimmune diseases, of which the most common type is Graves’ disease. • Immune reconstitution-associated immune-mediated inflammatory diseases, of which the most common type is sarcoidosis.
A low CD4+ T-cell count, disseminated TB and a short period of time between treating the TB and commencing ART are risk factors for developing TB-IRIS, suggesting that the risk is highest when the pathogen load is high. Direct evidence of this was provided by the observation that TB-IRIS is more frequent in patients with mycobacterial lipoaribinomannan detectable in urine before commencing ART [9]. In addition, Marais et al. demonstrated that a positive cerebrospinal fluid (CSF) culture for M. tuberculosis prior to commencing ART in HIV patients with treated TBM conferred a relative risk of 9.3 for developing TB-IRIS [10]. A higher mycobacterial load in patients who develop TBIRIS is a possible explanation for differences in T cell responses to M. tuberculosis antigens observed before ART is commenced. Vignesh et al. used intracellular flow cytometry to show that patients who developed TB-IRIS had higher frequencies of CD4+ T-cells producing interferon (IFN)-gamma after stimulation with PPD and ESAT-6 before ART was commenced and that these cells expanded after ART [11•]. Moreover, the group led by Meintjes and Wilkinson have demonstrated that TB-IRIS is more common in patients infected with drug-resistant M. tuberculosis [12] and that these patients exhibit low IFN-gamma/interleukin (IL)-10 ratios in cultures of PBMC stimulated with heat-killed H37Rv strain of M. tuberculosis [13]. It was argued that this was a consequence of poorly controlled mycobacterial growth in patients with drug-resistant TB. An increasing amount of evidence indicates that aberrant innate immune responses against M. tuberculosis increase susceptibility to, and contribute to an exaggerated inflammatory response in, TB-IRIS. Higher production of IL-18 and CXCL10 (also known as interferon-inducible protein-10 [IP10]) in TB-IRIS patients, compared with controls, provided evidence of activated innate immune responses, probably mediated by monocytes and macrophages [14]. Higher expression levels of multiple gene transcripts in monocytes from
patients with TB-IRIS, compared with controls, provided evidence of monocyte activation before and two weeks after commencing ART [15•]. Gene transcripts of molecules associated with infection and inflammation, especially pattern recognition receptors for bacteria and viruses, and of complement system components were particularly affected. In support of these findings, Tan et al. demonstrated that monocytes from patients who had previously experienced TB-IRIS expressed higher amounts of TLR2 [16]. In a study focussing on complement abnormalities in monocytes [17], Tran et al. demonstrated increased gene transcripts of C1q (a component of the classical pathway of complement activation) and C5 (a component of the membrane attack complex of the complement system) but decreased gene transcripts of C1 inhibitor (a complement activation regulatory protein). It was argued that activation of the complement system might contribute to inflammation in TB-IRIS, but evidence of complement activation in plasma was not presented. It is therefore likely that aberrant production of complement system proteins is a marker of monocyte activation and/or dysfunction. Activation of monocytes and macrophages is also a likely explanation for the higher production of matrix metalloproteinases (MMPs) by peripheral blood mononuclear cells (PBMC) stimulated with M. tuberculosis antigens, and higher plasma levels of these molecules, demonstrated in TB-IRIS patients [18•]. MMPs induce the production of inflammatory mediators and tissue remodelling and their activity may therefore be a cause of the pronounced suppuration that occurs in some patients with TB-IRIS [19]. Natural killer (NK) cells and neutrophils may also contribute to innate immune responses against M. tuberculosis before ART is commenced in patients who develop TB-IRIS. Pean et al. demonstrated in a randomised controlled trial of early versus late ART in HIV patients with treated TB that patients who developed TB-IRIS exhibited a higher proportion of NK cells expressing markers of cytotoxicity [20]. Marais et al. demonstrated that HIV patients with TBM who develop TBIRIS have higher CSF neutrophil counts prior to ART [10]. Recognition that TB-IRIS may be caused in part by innate immune responses against M. tuberculosis has led to studies of plasma biomarkers of those immune responses, which might be used in the diagnosis and/or prediction of TB-IRIS. Increased production of pro-inflammatory cytokines, including IL-6, TNF-alpha and IL-18, and chemokines, such as CXCL10 and CXCL8 (also known as IL-8), and of antiinflammatory cytokines, such as IL-10, has been observed before and/or during TB-IRIS in several studies [14, 21, 22•, 23, 24•, 25, 26•]. However, it is unclear which of these potential biomarkers might have clinical utility in predicting TB-IRIS. Haddow et al. did not observe higher plasma levels of any pro-inflammatory cytokine before ART in South African patients who developed paradoxical TB-IRIS, though did observe higher serum levels of CRP (which is induced by
Curr HIV/AIDS Rep
IL-6) in patients who developed unmasking TB-IRIS [23]. In a study of Ugandan patients, paradoxical TB-IRIS was independently associated with lower plasma levels of IL-6 before ART and higher levels of IL-6 at the time of TB-IRIS [22•]. In contrast, a study conducted in India demonstrated that patients who developed paradoxical TB-IRIS had higher plasma levels of IL-6 and CRP before ART was commenced [24•]. Finally, another study of South African patients demonstrated only higher pre-ART plasma levels of IFN-gamma in patients who developed paradoxical TB-IRIS [21]. Thus, while TB-IRIS is associated with increased production of multiple cytokines and chemokines, none has provided a clinically useful biomarker for disease prediction, so far.
Cryptococcosis-associated IRIS (C-IRIS) Most prospective clinical studies of C-IRIS have been performed in HIV patients co-infected with Cryptococcus neoformans and have focused on paradoxical C-IRIS of the central nervous system (CNS) [27], as this bears a higher morbidity and mortality than non-CNS C-IRIS. Several recent studies have increased knowledge about the pathogenesis of C-IRIS and identified risk factors and potential disease biomarkers. Predictors of C-IRIS include a lower baseline CD4+ T-cell count [28] and reduced CSF inflammation [29]. The UgandanUnited States group led by Boulware and Bohjanen has proposed a 3-phase model of C-IRIS [30, 31] based on their findings [29, 30, 32, 33]. Prior to ART commencement, a paucity of innate inflammatory responses, or inappropriately high Th2 responses, result in reduced inflammation that promotes ineffective antigen clearance. Second, early after ART initiation, persistent antigen primes for inflammation by promoting pro-inflammatory cytokines, such as IL-6, yet despite this, the effector response is poor and secondary activation of the coagulation cascade occurs. Third, at the time of C-IRIS, a generalised cytokine storm occurs with activation of multiple innate and adaptive immune pathways and the coagulation cascade. CSF Cryptococcal Culture Negativity and Higher CD4+ T cell Increase Are Protective for C-IRIS In a prospective study of 130 ART-naive HIV patients treated for CM who commenced ART, patients with a negative CSF cryptococcal culture pre-ART experienced fewer episodes of neurological deterioration (ND), C-IRIS and cryptococcal relapse/persistence than patients with culture positivity [34••]. Furthermore, increased CD4+ T-cell counts over 24-weeks of ART were independently associated with a decreased rate of C-IRIS, in contrast to the findings of a previous study [35].
IFN-gamma Is Beneficial in CM and C-IRIS The importance of IFN-gamma in the control of cryptococcal infection was highlighted by a Zimbabwean study, which demonstrated that 60 % of HIV patients with CM had undetectable IFN-gamma in CSF [36], and a Thai study where patient survival was associated with a higher CSF concentrations of pro-inflammatory cytokines, including IFN-gamma, and only the antifungal therapy regimen and CSF IFN-gamma concentration were independently associated with rate of fungal clearance [37]. Recently, a randomised controlled trial (RCT) in 90 patients from Cape Town, found that adjuvant IFN-gamma therapy led to faster rates of CSF fungal clearance, but had no impact on mortality [38]. In addition, patients who survived CM had higher IFN-gamma and TNF-alpha production from PBMC stimulated with cryptococcal antigens [39]. Chang et al. undertook an analysis of cryptococcal-specific T-cell responses in HIV-infected patients with treated CM before and during the first 24-weeks of ART using whole blood assays of T cells activated with cryptococcal mannoproteins (CMP) [40]. C-IRIS patients, compared to patients with no ND, had lower CMP-induced IFN-gamma production in blood collected pre-ART and 4-weeks post-ART and lower proportions of CMP-activated CD4+ T-cells (expressing CD25 and CD134) pre-ART. Preserved T-cell function pre-ART, as demonstrated by higher proportions of mitogen-activated CD4+ T-cells, and higher IL-10 and CXCL10 production in CMP-stimulated whole blood cultures, was also associated with better survival at 24-weeks post-ART [40]. Such whole blood assays may be useful in risk-stratification algorithms for the management of HIV patients with CM. CNS Compartmentalisation of Immune Responses in C-IRIS While the pathogenesis of C-IRIS is unclear, it seems likely that examination of blood may not always reflect immunopathology in the CNS. Chang et al. explored the CSF compartment of HIV patients with treated CM and demonstrated a distinct immunological profile compared to blood [41••]. The T-cell CD4+/CD8+ ratio was lower in CSF than in blood and the proportion of CD4+ and CD8+ T-cells that expressed both CXCR3+ and CCR5+ and the concentration of CXCL10, CCL2 and CCL3 were all increased in CSF compared to blood prior to ART initiation. Patients who subsequently developed C-IRIS exhibited an increased ratio of CCL2/CXCL10 and CCL3/CXCL10 in CSF and an increased proportion of CXCR3+CCR5+CD8+ T-cells in CSF relative to blood. A higher CSF CCL2/CXCL10 ratio was also associated with persistent CSF cryptococcal growth and death during ART. In an allied study, it was shown that relative to blood, the CSF was enriched with immunoregulatory
Curr HIV/AIDS Rep
(CD56bright) NK cells [42]. Immunoregulatory NK cells were also more activated (CD69+) and tended to secrete higher levels of CXCL10 and lower levels of TNF-alpha. CSF was also enriched with non-classical monocytes. Together, these findings suggest that enhanced recruitment and/or retention of activated CD8+ T-cells and NK cells, and a chemokine profile that recruits monocytes into the CSF, characterises the immune response against cryptococci in the context of CD4+ T-cell and IFN-gamma deficiency and may predispose to C-IRIS after ART is commenced. Potential Strategies for Preventing C-IRIS Given that a high cryptococcal antigen load in CSF is a risk factor for C-IRIS, particularly when associated with active infection, prevention of C-IRIS might be achieved by ensuring that cryptococcal infection is optimally controlled before ART is commenced. This might be achieved by optimising antifungal therapy, using adjunctive IFN-gamma therapy or deferring ART. Choice and duration of induction antifungal therapy impacts on CSF cryptococcal clearance and is likely to affect the occurrence of C-IRIS in HIV patients with CM. Day et al. [43] published definitive data showing a reduction of mortality using amphotericin and 5-FC in a RCT of 299 patients with CM. This should be tested as a strategy for preventing C-IRIS in HIV patients with CM. Timing of ART commencement in the setting of newly diagnosed opportunistic infections has been long debated, where the risk of an IRIS after early ART commencement is measured against the risk of new AIDS-defining disease after late ART commencement. Several studies have addressed this issue in HIV patients with CM. A Zimbabwean study, in which fluconazole was used as induction therapy, was terminated after 54 patients were enrolled because the early ART arm (initiated within 72 hours of CM diagnosis) had almost three times the risk of mortality compared to the delayed ART arm (initiated more than 10 weeks after CM diagnosis) [44]. It was postulated that the higher death rate associated with early ART was due to C-IRIS. A recently published, smaller, randomised study of 27 patients from Botswana showed no difference in mortality but reported an increased rate of CIRIS in the early arm [45]. A large multicentre prospective study—the Cryptococcal Optimal Antiretroviral Timing (COAT) study—was also recently terminated at 35 % enrolment as mortality was significantly higher in the early ART arm (commenced at 7-13 days after CM diagnosis) compared to the late ART arm (commenced more than 5 weeks after CM diagnosis). However, the rate of C-IRIS was reported as being not different between the early and deferred ART arms [46]. Taken together, the findings of these studies suggest that later commencement of ART is desirable in HIV patients with CM, with expert opinion arguing that ART
should be deferred until 4-6 week after CM diagnosis [47]. However, judicious interpretation of data from these RCTs is necessary. While it seems clear that very early (at 3-11 days) commencement of ART is harmful, by virtue of RCT designs, there remains an unexplored time-window between 2 and 4 weeks after CM diagnosis where ART could plausibly be initiated, particularly in the context of optimal antifungal therapy. In the study of Chang et al., ART was commenced based on clinical response, at a median time of 18 days after CM diagnosis and the 6-month post-ART survival rate was 80.2 % [34••]. Therefore, while very early ART initiation is not recommended in HIV patients with CM, deferring to 4-6 weeks may be too long. Instead, it is suggested that care should be individualised taking into account clinical recovery from CM, CSF sterility and other comorbidities.
Immune Reconstitution Inflammatory Syndromes Associated With Virus Infections Kaposi’s Sarcoma-associated IRIS (KS-IRIS) Kaposi’s sarcoma herpesvirus (KSHV) is the aetiologic agent for a spectrum of conditions that may complicate HIV-induced immunodeficiency, including Kaposi’s sarcoma (KS), Multicentric Castleman’s Disease (KSHV-MCD), primary effusion lymphoma (PEL) and a recently described inflammatory condition termed KSHV inflammatory cytokine syndrome (KICS) [48]. Both human and viral IL-6 contribute to the immunopathology of these diseases [49]. KS is the most common HIV-associated malignancy in HIV patients in Sub-Saharan Africa [50] and disease exacerbation (paradoxical KS-IRIS) or presentation (unmasking KS-IRIS) after ART are common. However, disease progression without ART is also common and distinguishing this from KS-IRIS clinically is difficult. Importantly, there is no consensus definition for KS-IRIS or KS-MCD-IRIS. Paradoxical KS-IRIS has been reported in up to 29 % of HIV patients with KS during the first year of ART, with higher rates reported in patients with visceral disease and from Africa [51, 52]. High plasma HIV RNA and KSHV DNA and T1 KS stage are risk factors for KS-IRIS [52]. The risk of unmasking KS-IRIS is particularly high in the first 3 months after ART initiation, especially in patients with severe CD4+ T-cell deficiency, men-who-have-sex-with-men (MSM) and African migrants [53]. In a retrospective study, KS-IRIS was reported in 22 % of children commencing ART in Malawi and Botswana [54]. There are no studies examining the optimal timing of ART in HIV patients with KS or the use of chemotherapy with ART.
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Progressive Multifocal Leukoencephalopathy-associated IRIS (PML-IRIS)
Autoimmunity and Other Immune-mediated Inflammatory Disease During Immune Reconstitution
Both paradoxical and unmasking IRIS may occur in HIV patients with progressive multifocal leukoencephalopathy (PML) of brain white matter, which is caused by infection with JC polyomavirus (JCV). Distinguishing between progressive PML and PML-IRIS is difficult clinically and radiologically. Cases of PML-IRIS have been reported more than 24-weeks following ART commencement [55]. A CD4+ Tcell count of
