Evidence of thymic reconstitution after highly active antiretroviral therapy in HIV-1 infection

HIV-related Malignancies and Mimics: Imaging Findings and Management

The risk of developing malignancy is higher in patients with human immunodeficiency virus (HIV) infection than in non-HIV-infected patients. Several factors including immunosuppression, viral coinfection, and high-risk lifestyle choices lead to higher rates of cancer in the HIV-infected population. A subset of HIV-related malignancies are considered to be acquired immunodeficiency syndrome (AIDS)-defining malignancies, as their presence confirms the diagnosis of AIDS in an HIV-infected patient. The introduction of highly active antiretroviral therapy (HAART) has led to a significant drop in the rate of AIDS-defining malignancies, including Kaposi sarcoma, non-Hodgkin lymphoma, and invasive cervical carcinoma. However, non-AIDS-defining malignancies (eg, Hodgkin lymphoma, lung cancer, hepatocellular carcinoma, and head and neck cancers) now account for an increasing number of cancer cases diagnosed in HIV-infected patients. Although the number has decreased, AIDS-defining malignancies account for 15%-19% of all deaths in HIV-infected patients in the post-HAART era. Most HIV-related malignancies in HIV-infected patients manifest at an earlier age with a more aggressive course than that of non-HIV-related malignancies. Understanding common HIV-related malignancies and their specific imaging features is crucial for making an accurate and early diagnosis, which impacts management. Owing to the weakened immune system of HIV-infected patients, other entities such as various infections, particularly opportunistic infections, are prevalent in these patients. These processes can have confounding clinical and imaging manifestations that mimic malignancy. This article reviews the most common AIDS-defining and non-AIDS-defining malignancies, the role of imaging in their diagnosis, and the imaging mimics of malignancies in HIV-infected patients. ^©RSNA, 2018.

The Role of Nuclear Medicine in the Staging and Management of Human Immune Deficiency Virus Infection and Associated Diseases

Human immune deficiency virus (HIV) is a leading cause of death. It attacks the immune system, thereby rendering the infected host susceptible to many HIV-associated infections, malignancies and neurocognitive disorders. The altered immune system affects the way the human host responds to disease, resulting in atypical presentation of these disorders. This presents a diagnostic challenge and the clinician must use all diagnostic avenues available to diagnose and manage these conditions. The advent of highly active antiretroviral therapy (HAART) has markedly reduced the mortality associated with HIV infection but has also brought in its wake problems associated with adverse effects or drug interaction and may even modulate some of the HIV-associated disorders to the detriment of the infected human host. Nuclear medicine techniques allow non-invasive visualisation of tissues in the body. By using this principle, pathophysiology in the body can be targeted and the treatment of diseases can be monitored. Being a functional imaging modality, it is able to detect diseases at the molecular level, and thus it has increased our understanding of the immunological changes in the infected host at different stages of the HIV infection. It also detects pathological changes much earlier than conventional imaging based on anatomical changes. This is important in the immunocompromised host as in some of the associated disorders a delay in diagnosis may have dire consequences. Nuclear medicine has played a huge role in the management of many HIV-associated disorders in the past and continues to help in the diagnosis, prognosis, staging, monitoring and assessing the response to treatment of many HIV-associated disorders. As our understanding of the molecular basis of disease increases nuclear medicine is poised to play an even greater role. In this review we highlight the functional basis of the clinicopathological correlation of HIV from a metabolic view and discuss how the use of nuclear medicine techniques, with particular emphasis of F-18 fluorodeoxyglucose, may have impact in the setting of HIV. We also provide an overview of the role of nuclear medicine techniques in the management of HIV-associated disorders.

Levels of CD56+TIM-3- effector CD8 T cells distinguish HIV natural virus suppressors from patients receiving antiretroviral therapy

Prolonged antiretroviral therapy (ART) with effective HIV suppression and reconstitution of CD4 T cells, fails to restore CD8 T cell lytic effector function that is needed to eradicate the viral reservoir. Better understanding of the phenotype and function of circulating CD8 cells in HIV patients will contribute to new targeted therapies directed at increasing CD8 T cell lytic effector function and destruction of the viral reservoir. We show that CD8 T cells from ART treated patients had sharply reduced expression of CD56 (neural cell adhesion molecule-1), a marker associated with cytolytic function whereas elite patients who control HIV in the absence of ART had CD56+ CD8 T cell levels similar to uninfected controls. The CD56+ CD8 T cells had higher perforin upregulation as well as degranulation following stimulation with HIV gag peptides compared with CD56 negative CD8 T cells. Elite patients had the highest frequencies of perforin producing CD56+ CD8 T cells among all HIV+ groups. In patients receiving ART we noted high levels of the exhaustion marker TIM-3 on CD56+ CD8 T cells, implying that defective effector function was related to immune exhaustion. CD56+ CD8 T cells from elite or treated HIV patients responded to PMA plus ionomycin stimulation, and expressed transcription factors T-bet and EOMES at levels similar to uninfected controls. Consequently, the lytic effector defect in chronic HIV disease is due to immune exhaustion and quantitative loss of CD56+ CD8 T cells and this defect is not repaired in patients where viremia is suppressed and CD4 T cells are recovered after ART.

Reconstituting the cytotoxic CD56+ subset of CD8+ T cells through new interventions might improve the lytic effector capacity and contribute to reducing the viral reservoir. Our initial studies indicate that IL-15 treatment partly reverses the CD56 defect, implying that myeloid cell defects could be targeted for immune therapy during chronic HIV disease.

FDG-PET imaging in HIV infection and tuberculosis

The intersection and syndemic interaction between the human immunodeficiency virus (HIV) and tuberculosis (TB) epidemics have global prevalence with devastating morbidity and massive mortality. Using FDG-PET imaging it was shown that in HIV-infected individuals, involvement of the head and neck precedes that of the chest and of the abdomen. The sequence of lymph node involvement observed suggests the existence of a diffusible activation mediator that may be targeted via therapeutic intervention strategies. Furthermore, the degree of FDG uptake proved directly related to viral load and inversely related to CD4 cell count. Available data in acquired immune deficiency syndrome (AIDS)-defining cancers further suggest that FDG-PET/CT imaging may be useful for prognostication of cervical cancer and for identifying appropriate sites for biopsy, staging, and monitoring lymphoproliferative activity owing to HIV-associated Kaposi sarcoma and multicentric Castleman disease. Inversely, in HIV-associated lymphoma, FDG uptake in HIV-involved lymphoid tissue was shown to reduce the specificity of FDG-PET imaging findings, the effect of which in clinical practice warrants further investigation. In the latter setting, knowledge of viremia appears to be essential for FDG-PET image interpretation. Early HIV-associated neurocognitive disorder, formerly known as AIDS dementia complex, proved to be characterized by striatal hypermetabolism and progressive HIV-associated neurocognitive disorder or AIDS dementia complex by a decrease in subcortical and cortical metabolism. In lipodystrophic HIV-infected individuals, lipodystrophy proved associated with increased glucose uptake by adipose tissue, likely resulting from the metabolic stress of adipose tissue in response to highly active antiretroviral therapy. Furthermore, ongoing chronic low-grade infection in arteries of HIV-infected individuals could be depicted by FDG-PET/CT imaging. And there is promising data that FDG-PET/CT in HIV may serve as a new marker for the evaluation of thymic function in HIV-infected patients. In the setting of TB, FDG-PET has proven unable to differentiate malignancy from TB in patients presenting with solitary pulmonary nodules, including those suffering from HIV, and thus cannot be used as a tool to reduce futile biopsy or thoracotomy in these patients. In patients presenting with extrapulmonary TB, FDG-PET imaging was found to be significantly more efficient when compared with CT for the identification of more sites of involvement. Thus supporting that FDG-PET/CT can demonstrate lesion extent, serve as guide for biopsy with aspiration for culture, assist surgery planning and contribute to follow-up. Limited available data suggest that quantitative FDG-PET findings may allow for prediction or rapid assessment, at 4 months following treatment instigation, of response to antituberculostatics in TB-infected HIV patients. These results and more recent findings suggest a role for FDG-PET/CT imaging in the evaluation of therapeutic response in TB patients.

Reduced thymic output is a major mechanism of immune reconstitution failure in HIV-infected patients after long-term antiretroviral therapy

BACKGROUND

Approximately 20% of human immunodeficiency virus type 1 (HIV-1)--infected adults do not normalize their CD4(+) T lymphocytes after long-term effective highly active antiretroviral therapy (HAART). The mechanistic basis for this failure is unclear.

METHODS

Seventy-four patients were followed up regularly for 3-7 years. Patients with undetectable plasma viral load (<50 copies/mL) for over 12 months were further classified into 2 groups: (1) immunological nonresponders, whose CD4(+) T-cell count was < 200/μL or <20% compared with baseline; and (2) immunological responders, whose CD4(+) T-cell count was > 300/μL or >30% compared with baseline.

RESULTS

Compared with 17 immunological responders, 13 immunological nonresponders had a lower magnitude of naive CD4(+) T-cell increase, a lower percentage of recent thymic immigrants (CD31(+)%), and a higher percentage of activated CD8(+) T cells. Furthermore, unlike CD4(+) T cells, which increased along with the decrease of viral load, the percentage of recent thymic immigrants (CD31(+)%) had little change in the majority of patients. These data were fit into a mathematical model, , from which we deduced that the initial rate of CD4(+) T-cell restoration is associated significantly with the percentage of recent thymic immigrants (CD31(+)%).

CONCLUSIONS

Our data indicate that the failure to restore CD4(+) T-cell count following HAART was associated primarily with a defect in recent thymic immigrants, which suggests the existence of thymus exhaustion.

Thymic tissue is not evident on high-resolution computed tomography and [¹⁸F]fluoro-deoxy-glucose positron emission tomography scans of aviraemic HIV patients with poor recovery of CD4⁺ T cells

Some previously immunodeficient HIV patients responding to antiretroviral therapy display poor recovery of CD4⁺ T cells. Evaluation of the contribution of thymic function requires sensitive detection and quantitation of metabolically active thymic tissue. We describe patients with low but detectable thymopoiesis assessed as circulating CD4⁺ naive T cells expressing CD31. High-resolution computed tomography and PET scans found no residual thymic tissue even though metabolic activity was demonstrable by PET in lymph nodes.

Thymopoietic and bone marrow response to murine Pneumocystis pneumonia

CD4(+) T cells play a key role in host defense against Pneumocystis infection. To define the role of naïve CD4(+) T cell production through the thymopoietic response in host defense against Pneumocystis infection, Pneumocystis murina infection in the lung was induced in adult male C57BL/6 mice with and without prior thymectomy. Pneumocystis infection caused a significant increase in the number of CCR9(+) multipotent progenitor (MPP) cells in the bone marrow and peripheral circulation, an increase in populations of earliest thymic progenitors (ETPs) and double negative (DN) thymocytes in the thymus, and recruitment of naïve and total CD4(+) T cells into the alveolar space. The level of murine signal joint T cell receptor excision circles (msjTRECs) in spleen CD4(+) cells was increased at 5 weeks post-Pneumocystis infection. In thymectomized mice, the numbers of naïve, central memory, and total CD4(+) T cells in all tissues examined were markedly reduced following Pneumocystis infection. This deficiency of naïve and central memory CD4(+) T cells was associated with delayed pulmonary clearance of Pneumocystis. Extracts of Pneumocystis resulted in an increase in the number of CCR9(+) MPPs in the cultured bone marrow cells. Stimulation of cultured bone marrow cells with ligands to Toll-like receptor 2 ([TLR-2] zymosan) and TLR-9 (ODN M362) each caused a similar increase in CCR9(+) MPP cells via activation of the Jun N-terminal protein kinase (JNK) pathway. These results demonstrate that enhanced production of naïve CD4(+) T lymphocytes through the thymopoietic response and enhanced delivery of lymphopoietic precursors from the bone marrow play an important role in host defense against Pneumocystis infection.

CD4+ T cell depletion, immune activation and increased production of regulatory T cells in the thymus of HIV-infected individuals

Mechanisms by which HIV affects the thymus are multiple and only partially known, and the role of thymic dysfunction in HIV/AIDS immunopathogenesis remains poorly understood. To evaluate the effects of HIV infection on intra-thymic precursors of T cells in HIV-infected adults, we conducted a detailed immunophenotypic study of thymic tissue isolated from 7 HIV-infected and 10 HIV-negative adults who were to undergo heart surgery. We found that thymuses of HIV-infected individuals were characterized by a relative depletion of CD4+ single positive T cells and a corresponding enrichment of CD8+ single positive T cells. In addition, thymocytes derived from HIV-infected subjects showed increased levels of activated and proliferating cells. Our analysis also revealed a decreased expression of interleukin-7 receptor in early thymocytes from HIV-infected individuals, along with an increase in this same expression in mature double- and single-positive cells. Frequency of regulatory T cells (CD25+FoxP3+) was significantly increased in HIV-infected thymuses, particularly in priorly-committed CD4 single positive cells. Our data suggest that HIV infection is associated with a complex set of changes in the immunophenotype of thymocytes, including a reduction of intrathymic CD4+ T cell precursors, increased expression of activation markers, changes in the expression pattern of IL-7R and enrichment of T regulatory cells generation.

Restoration of the antibody response upon rabies vaccination in HIV-infected patients treated with HAART

DESIGN

Rabies vaccine was used as a T-cell-dependent neoantigen to investigate several aspects of the primary and booster immune response in vivo in HIV-infected individuals receiving antiretroviral treatment.

METHODS

Study participants received rabies vaccination twice, within a 3-month interval. Serum samples were taken before and 1, 2 and 4 weeks after both vaccinations and 1 and 5 years after the primary vaccination. Antirabies antibodies [immunoglobulin G (IgG), IgG subclasses, immunoglobulin A (IgA) and immunoglobulin M (IgM)] were determined; antibody avidity was measured after both vaccinations. T-cell subsets were characterized by flow cytometry.

RESULTS

Eighteen healthy controls and 30 HIV-infected adults, treated with HAART for almost 4 years, with a median CD4(+) T-cell count of 537 cells/microl, were immunized. The postvaccination concentrations of antirabies IgG and IgM were significantly lower in HIV-infected individuals as compared with controls. Three T-cell-dependent processes, a true booster response, a class switch from IgM to IgG and avidity maturation were present in both healthy controls and HIV-infected individuals. Higher age was associated with lower postvaccination antirabies IgG and IgM titers. Five years after the primary vaccination, 63% of the HIV-infected individuals still had antibody titers above the protection threshold.

CONCLUSION

Immune restoration in HIV-infected individuals treated with HAART, resulting in a CD4(+) T-cell count greater than 500 cells/microl, is incomplete. However, the majority of HIV-infected individuals are capable of mounting a long-lasting immune response, including several pivotal T-cell-dependent processes, upon vaccination with a neoantigen such as the rabies vaccine.

Premature immunosenescence in HIV-infected patients on highly active antiretroviral therapy with low-level CD4 T cell repopulation

OBJECTIVES

To analyse the role of thymic function and its association with cellular immunosenescence markers in patients with low-level CD4 T cell repopulation, despite complete HIV RNA replication control on highly active antiretroviral therapy (HAART).

METHODS

Cellular immunosenescence markers comparing patients with CD4 T cell counts <or=250 cells/mm(3) for >or=48 weeks (n = 11) and patients with a CD4 T cell count >or=500 cells/mm(3) (n = 11) were investigated. Both groups were also compared with 11 healthy volunteers of similar age. Naive CD4 T cell counts, beta- and delta-T cell rearrangement excision circles, recent thymic emigrants, replicative senescence marker, cell activation, and rate of apoptosis were analysed. The Mann-Whitney U-test was used to compare parameters between both low-level and high-level CD4 T cell repopulation groups, and healthy volunteers.

RESULTS

Our results showed a lower thymic activity in patients with low-level CD4 T cell repopulation, leading to a decline in CD4 T cell production. On the other hand, a higher activation along with a higher replicative senescence of CD4 T cells contributed to a higher rate of apoptotic CD4 T cells in this group of patients.

CONCLUSIONS

We propose a model with several different related mechanisms involved in premature immune senescence in HIV-infected patients with low-level CD4 repopulation on HAART. The understanding of such different mechanisms could help find effective strategies to prevent immune decay.

PET/CT in the evaluation of lymphoma in patients with HIV-1 with suppressed viral loads

OBJECTIVE

Positron emission tomography (PET) with F-18 fluorodeoxyglucose detects active lymphoid tissue during HIV-1 infection, with distinct patterns of lymphoid activation correlating to various stages of disease activity. Patients with HIV-1 are at risk for lymphoma, making the differential diagnosis between benign and malignant lymphadenopathy imperative. This study retrospectively evaluated the role of PET/computed tomography (CT) in differentiating active lymphoma from persistent generalized lymphadenopathy in patients with HIV-1.

MATERIALS AND METHODS

Seven patients with HIV-1 underwent PET/CT. Six, with known non-Hodgkin lymphoma underwent a total of 16 PET/CT scans; 5/16 scans were performed for initial staging, and 10/16 for evaluating treatment response and follow-up. One patient was referred for evaluation of lymphadenopathy suspected of being lymphoma. PET/CT findings were compared with concurrent clinical, immunologic, and virological data.

RESULTS

PET/CT accurately depicted the extent of lymphoma in 12/16 patients' scans (75%), yet in 4/16 (25%) scans increased fluorodeoxyglucose uptake was noted in lymph nodes of normal CT appearance (PET+/CT-). Viral loads ranged from 0 to 84,000 copies/mL, CD4 T-cell count ranged from 130 to 474 cells/muL in the group. The highest values of both laboratory parameters were concurrent with the discrepant PET+/CT- scans, seen in 4 scans, in 2 patients. The PET+/CT- findings in both these patients were observed in neck, axillae, mediastinum, spleen, and inguinal regions, and sample biopsies of the PET (+) nodes consequently proved benign findings in both patients. All PET+/CT+ findings correctly indicated lymphoma status, as proven by clinical follow-up.

CONCLUSION

PET/CT accurately detected lymphoma in patients with HIV-1 and had been used confidently as a management tool in this patient group. In the context of discrepant PET/CT findings, increased viral loads and CD4 levels may imply benign HIV-related lymphadenopathy.

Human T cell reconstitution in DiGeorge syndrome and HIV-1 infection

The thymus is essential for proper development and maintenance of a broad T cell repertoire capable of recognizing a wide-range of foreign antigens. Recent advances in multicolor flow cytometry, non-invasive imaging techniques, and molecular assessments of thymic function have enabled a more comprehensive characterization of human thymic output in clinical settings than in the past. These techniques have been particularly valuable in monitoring human T cells after therapeutic thymic grafting for complete DiGeorge syndrome and during HIV-1 infection and AIDS. By defining the degree and mechanisms of T cell reconstitution in these settings, clinical investigators and primary caregivers have been able to better diagnose, treat and care for individuals with congenital or acquired immune deficiencies associated with loss of thymic function.

Regeneration of the adult thymus is preceded by the expansion of K5+K8+ epithelial cell progenitors and by increased expression of Trp63, cMyc and Tcf3 transcription factors in the thymic stroma

Studies of HIV-1-infected individuals on anti-retroviral therapies and of patients receiving lymphoablating treatments indicate that the thymus retains restorative capacity even in adults. The contributions of the thymic epithelial cells (TECs) to the regeneration of the thymus and the identity of epithelial cell progenitors were evaluated in murine models of transient thymic atrophy followed by a complete regeneration. Using microarray approach, we analyzed the pattern of gene expression in TECs sorted from mice that were depleted of thymocytes by steroid treatment or by irradiation. The initial analysis identified significant increases in the mRNA for cMyc, Trp63 and Tcf3 transcription factors known to be expressed in early epithelial cell progenitors in tissues other than the thymus. Immunohistochemistry showed that in involuted thymuses, the cMyc and Trp63 proteins were expressed in a subset of cortical thymic epithelial cells (cTECs) that were keratin 5 positive (K5(+)), typifying cTEC precursors. Importantly, confocal microscopy established that epithelial cells with the phenotype of putative TEC progenitors (i.e. K5(+)K8(+)) expressed the Trp63 protein and confirmed that K5(+)K8(+) TEC progenitors expanded significantly during atrophy and prior to the thymic regeneration. Thus, our data demonstrated for the first time that critical steps in the recovery of the adult thymus include expansion of TEC progenitors and elevated expression of Trp63, cMyc and Tcf3 transcription factors in the thymic stroma. These results suggest that TEC progenitors could be reactivated in the adult thymus and, therefore, reactivation of TEC progenitors could provide a new approach for thymic reconstitution.

Complexity of Anti-immunosenescence Strategies in Humans

Immunosenescence is characterized by three main aspects: (i) the shrinkage of the T cell repertoire and the accumulation of oligoclonal expansions (megaclones) of memory/effector cells directed toward ubiquitary infectious agents; (ii) the involution of the thymus and the exhaustion of naïve T cells; and (iii) a chronic inflammatory status called inflamm-aging. We present here possible strategies to counteract these main aspects of immunosenescence in humans with particular attention to the reduction of antigenic load by pathogens, such as CMV, and the normalization of intestinal microflora, the possible utilization of IL-7 to reverse thymic involution, the purging of megaclones, the forced expression of CD28 on T lymphocytes, the reduction of inflamm-aging and the administration of nutrients such as vitamin D. Possible drawbacks of all these strategies are discussed. Finally, the complexity of a rejuvenation approach is stressed, with particular attention to the inhibitory role played by the "old microenvironment" on the performance of progenitor cells, the best candidate to counteract the decline in regenerative potential characteristic of organs and tissues from old organisms.

Graves' Disease as an Immune Reconstitution Syndrome in an HIV-1–Positive Patient Commencing Effective Antiretroviral Therapy: Case Report and Literature Review

Combination antiretroviral therapy (cART) reduces morbidity and mortality in human immunodeficiency virus (HIV) infection, but it may also alter the clinical course of subclinical opportunistic infections and can even induce autoimmune disease. These atypical presentations are known as immune restoration disease (IRD), immune reconstitution syndrome/immune recovery syndrome (IRS), or immune restoration inflammatory syndrome (IRIS). We report the case of a 27-year-old, HIV-1-positive woman who developed hyperthyroidism attributable to Graves' disease (GD) after commencing potent cART. At the initiation of cART, her CD4 T cell count was 15 cells/microL and plasma HIV RNA 35 000 copies/mL. Her commencement of cART resulted in complete viral suppression and subsequent improvement of the CD4 T-cell count. Three years later, the diagnosis of GD was established based on a typical clinical picture and the results of hormonal and immunological analyses. It coincided with a 58-fold rise of the CD4 T cells. Retrospective analysis of serum samples revealed normal thyroid function and lack of anti-thyroid peroxidase (anti-TPO), anti- thyroid-stimulating hormone receptor (anti-TSHR), and anti-thyroglobulin (anti-TG) autoantibodies at the beginning of cART. HLA class II gene examination did not reveal susceptibility for the GD development in this patient. We suggest that GD in our patient was an IRD, and advise this as a possible differential diagnosis in patients presenting with hyperthyroidism on cART. To provide further details relevant to this case, we also review the literature concerning IRD-GD.

Thymic function in HIV infection

Current models hold that CD4+ depletion occurs as a result of direct and indirect effects of HIV, which both kill peripheral CD4+ cells and prevent adequate regeneration. Although age-associated involution diminishes thymic reserve and HIV is clearly thymotoxic, clinical trials have nonetheless shown that large proportions of patients who sustain adequate control of viral replication with highly active antiretroviral therapy (HAART) will demonstrate some evidence for thymic-dependent immune reconstitution, which is associated with improved immune competence. Furthermore, patients with insufficient or absent immune reconstitution following HAART generally lack evidence for thymopoiesis. Current studies are focused on improving our understanding of the causes for thymic failure in HIV infection. Recent work has demonstrated that some HIV strains, especially those that are CXCR4 trophic, are more thymotoxic and may contribute to irreversible thymic damage in this population.

Evolving role of positron emission tomography in the management of patients with inflammatory and other benign disorders

Fluoro-2-deoxyglucose (FDG) positron emission tomography (PET) has evolved from a research imaging modality assessing brain function in physiologic and pathologic states to a pure clinical necessity. It has been successfully used for diagnosing, staging, and monitoring a variety of malignancies. FDG-PET imaging also is evolving into a powerful imaging modality that can be effectively used for the diagnosis and monitoring of a certain nononcological diseases. PET has been shown to be very useful in the diagnosis of osteomyelitis, painful prostheses, sarcoidosis, fever of unknown etiology, and acquired immunodeficiency syndrome. Based on recent observations, several other disorders, such as environment-induced lung diseases, atherosclerosis, vasculitis, back pain, transplantation, and blood clot, can be successfully assessed with this technique. With the development and the introduction of several new PET radiotracers, it is expected that PET will secure a major role in the management of patients with inflammatory and other benign disorders.