Role of CD4+ and CD8+ T-cell responses against JC virus in the outcome of patients with progressive multifocal leukoencephalopathy (PML) and PML with immune reconstitution inflammatory syndrome

Effect of the Antibody-mediated Immune Responses on COPD, Asthma, and Lung Function: A Mendelian Randomization Study

INTRODUCTION

The precise cause of antibody-mediated immune responses on chronic obstructive pulmonary disease (COPD), asthma, and lung function remains unclear. We characterized the relationship between antibody-mediated immune responses to COPD, asthma, and lung function, ultimately achieve the prevention or treatment.

METHODS

We obtained summary data from published genome-wide association studies, including antibody-mediated immune responses, COPD, asthma, forced expiratory volume in the first second (FEV1), forced expiratory volume (FVC), and FEV1/FVC. Bidirectional two-sample mendelian randomization (MR) analysis was used to assess causal relationships of antibody-mediated immune responses, COPD, asthma, FEV1, FVC, and FEV1/FVC.

RESULTS

A total of 20 antibody-mediated immune responses were identified have a significant causal effect on COPD, asthma, FEV1, and FVC, with six exhibiting reverse causality. Importantly, the results of the five MR analyses were almost identical with respect to the causal effect of anti-polyomavirus 2 IgG seropositivity and varicella zoster virus glycoprotein E and I antibody levels on the risk of COPD, asthma, FEV1, and FVC.

CONCLUSIONS

This study contributes to existing knowledge by investigating the causal relationship between antibody-mediated immune responses and respiratory conditions, including COPD, asthma, and lung function, using a two-sample MR design. The key findings can aid in identifying individuals at risk of these conditions and facilitate early prevention and diagnosis.

Signal detection of adverse reactions for bendamustine based on FDA adverse event reporting system

BACKGROUND

This study aimed to analyze the adverse events to bendamustine using data obtained from the Food and Drug Administration open public data project (openFDA) and to provide a reference for its use in clinical practice.

RESEARCH DESIGN AND METHODS

Adverse events (AEs) due to bendamustine usage reported from 1 January 2008 to 31 March 2023 were collected from the FDA Adverse Event Reporting System (FAERS). The reporting odds ratio (ROR), proportional reporting ratio (PRR), Bayesian plausible propagation neural network (BCPNN), and multinomial gamma-Poisson distribution shrinking (MGPS) algorithms were used to identify signs of adverse reactions caused by bendamustine.

RESULTS

A total of 4214 AE reports where bendamustine was considered as the first suspected drug were obtained from FAERS. The analysis revealed 214 AE risk signals, among which 141 met the criteria but they were not listed as possible side effects on the drug information sheet provided in the package.

CONCLUSION

Our findings identified numerous common AEs with previously reported clinical observations. We also identified some signs of potential new AEs, indicating the need of careful clinical monitoring of patients treated with bendamustine and further risk identification research about this drug.

The CD4 T cell-independent IgG response during persistent virus infection favors emergence of neutralization-escape variants

How changes in the quality of anti-viral antibody (Ab) responses due to pre-existing or acquired CD4 T cell insufficiency affect virus evolution during persistent infection are unknown. Using mouse polyomavirus (MuPyV), we found that CD4 T cell depletion before infection results in short-lived plasma cells secreting low-avidity antiviral IgG with limited BCR diversity and weak virus-neutralizing ability. CD4 T cell deficiency during persistent infection incurs a shift from a T-dependent (TD) to T-independent (TI) Ab response, resembling the pre-existing TI Ab response. CD4 T cell loss before infection or during persistent infection is conducive for emergence of Ab-escape variants. Cryo-EM reconstruction of complexes of MuPyV virions with polyclonal IgG directly from infected mice with pre-existing or acquired CD4 T cell deficiency enabled visualization of shortfalls in TI IgG binding. By debilitating the antiviral IgG response, CD4 T cell deficiency sets the stage for outgrowth of variant viruses resistant to neutralization.

Antigen-Specific T Cell Receptor Discovery for Treating Progressive Multifocal Leukoencephalopathy

Background

Progressive multifocal leukoencephalopathy (PML) is a frequently fatal disease of the central nervous system caused by JC virus (JCV). Survival is dependent on early diagnosis and ability to re-establish anti-viral T cell immunity. Adoptive transfer of polyomavirus-specific T cells has shown promise; however, there are no readily available HLA-matched anti-viral T cells to facilitate rapid treatment.

Objective

Identify epitopes of the JCV major capsid protein VP1 that elicit an immune response in the context of human leukocyte antigen allele A*02:01 (HLA-A2) and isolate cognate T cell receptors (TCRs) from healthy donors. Evaluate individual VP1-specific TCRs for their capacity to be expressed in T cells and clear JCV in vitro .

Methods

PBMCs from HLA-A2+ healthy donors were stimulated with peptide libraries tiled across the JCV VP1 protein. Multiple rounds of stimulation were performed to identify the antigens that induced the largest expansion and CD8 + T cell response (measured as INF γ , TNF α , CD137, and CD69 expression). High-affinity, antigen-specific CD8 + T cells were isolated based on intensity of tetramer binding for downstream single-cell TCR sequencing. Candidate TCRs were selected based on tetramer binding affinity and activation assays. Promising TCRs were introduced into the T cell genome via viral transduction for in vitro validation including peptide-pulsed K562 cells and astrocyte cells, and JCV-infected astrocytes.

Results

Four conserved JCV VP1 epitopes (amino acids 100-108, 251-259, 253-262, and 274-283) presented by HLA-A2 were identified. VP1(100-108) consistently elicited the highest level of IFN- γ production from multiple donors and this peptide is in a highly conserved region of VP1. We next identified fourteen high avidity TCRs specific for VP1(100-108). When virally transduced into primary human T cells, seven of these TCRs demonstrated specific binding to VP1(100-108):HLA-A2 tetramers, and four showed increased IFN- γ response when incubated with peptide. Primary CD8 + T cells expressing two of these TCRs cleared both HLA-A2 positive K562 cells and HLA-A2 positive SVG astrocyte cell line presenting exogenously added VP1 peptide at a range of E:T ratios. In addition, both TCR-transduced T cell populations effectively lysed JCV-infected astrocytes.

Conclusions

We identified JCV VP1 epitopes that are immunogenic in the context of HLA-A2 MHC-I, including epitopes that have not been previously described. The VP1(100-108) epitope was used to isolate HLA-A2-restricted TCRs. When cloned into primary human CD8 + T cells, these TCRs recognized VP1 (100-108)-presenting targets, and the transduced T cells conferred cytotoxic activity and eliminated K562 and astrocyte cells displaying the VP1(100-108) peptide and not sham peptide, as well as JCV-infected astrocytes. Taken together, these data suggest that JCV VP1-specific TCRs could be appealing therapeutics for HLA-A2+ individuals with PML in whom intrinsic T cell immunity cannot be rescued.

Development of progressive multifocal leukoencephalopathy after cord blood transplantation in a patient with refractory angioimmunoblastic T-cell lymphoma

A patient undergoing cord blood transplantation for refractory angioimmunoblastic T-cell lymphoma was subsequently managed with long-term immunosuppressants for chronic graft-versus-host disease (GVHD). On day 591 post-transplant, she exhibited disorientation and cognitive dysfunction. Magnetic resonance imaging (MRI) of the brain revealed two hyperintense foci in the white matter, suggestive of progressive multifocal leukoencephalopathy (PML). However, we did not include PML in the differential diagnosis at that time. Unfortunately, she developed progressive cognitive impairment, and repeated brain MRIs showed a progression in lesion size. She was still taking immunosuppressants to control her GVHD, therefore we suspected PML. The diagnosis of PML was confirmed through the detection of a John Cunningham (JC) virus in the cerebrospinal fluid on day 640 post-transplant. This report highlights the critical need to consider PML in differential diagnoses for post-allogeneic transplant patients, especially those who exhibit progressive neurological symptoms while on prolonged immunosuppressant therapy.

Chemokine-mediated cell migration into the central nervous system in progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) has been associated with different forms of immune compromise. This study analyzes the chemokine signals and attracted immune cells in cerebrospinal fluid (CSF) during PML to define immune cell subpopulations relevant for the PML immune response. In addition to chemokines that indicate a general state of inflammation, like CCL5 and CXCL10, the CSF of PML patients specifically contains CCL2 and CCL4. Single-cell transcriptomics of CSF cells suggests an enrichment of distinct CD4+ and CD8+ T cells expressing chemokine receptors CCR2, CCR5, and CXCR3, in addition to ITGA4 and the genetic PML risk genes STXBP2 and LY9. This suggests that specific immune cell subpopulations migrate into the central nervous system to mitigate PML, and their absence might coincide with PML development. Monitoring them might hold clues for PML risk, and boosting their recruitment or function before therapeutic immune reconstitution might improve its risk-benefit ratio.

Upregulation of the NKG2D Ligand ULBP2 by JC Polyomavirus Infection Promotes Immune Recognition by Natural Killer Cells

BACKGROUND

JC polyomavirus (JCPyV) causes progressive multifocal leukoencephalopathy (PML), a potentially fatal complication of severe immune suppression with no effective treatment. Natural killer (NK) cells play critical roles in defense against viral infections; however, NK-cell response to JCPyV infection remains unexplored.

METHODS

NK- and T-cell responses against the JCPyV VP1 were compared using intracellular cytokine staining upon stimulation with peptide pools. A novel flow cytometry-based assay was developed to determine NK-cell killing efficiency of JCPyV-infected astrocyte-derived SVG-A cells. Blocking antibodies were used to evaluate the contribution of NK-cell receptors in immune recognition of JCPyV-infected cells.

RESULTS

In about 40% of healthy donors, we detected robust CD107a upregulation and IFN-γ production by NK cells, extending beyond T-cell responses. Next, using the NK-cell-mediated killing assay, we showed that coculture of NK cells and JCPyV-infected SVG-A cells leads to a 60% reduction in infection, on average. JCPyV-infected cells had enhanced expression of ULBP2-a ligand for the activating NK-cell receptor NKG2D, and addition of NKG2D blocking antibodies decreased NK-cell degranulation.

CONCLUSIONS

NKG2D-mediated activation of NK cells plays a key role in controlling JCPyV replication and may be a promising immunotherapeutic target to boost NK-cell anti-JCPyV activity.

Biomarkers for progressive multifocal leukoencephalopathy: emerging data for use of JC virus DNA copy number in clinical trials

Progressive multifocal leukoencephalopathy is a rare but devastating demyelinating disease caused by the JC virus (JCV), for which no therapeutics are approved. To make progress towards addressing this unmet medical need, innovations in clinical trial design are needed. Quantitative JCV DNA in CSF has the potential to serve as a valuable biomarker of progressive multifocal leukoencephalopathy disease and treatment response in clinical trials to expedite therapeutic development, as do neuroimaging and other fluid biomarkers such as neurofilament light chain. Specifically, JCV DNA in CSF could be used in clinical trials as an entry criterion, stratification factor, or predictor of clinical outcomes. Insights from the investigation of candidate biomarkers for progressive multifocal leukoencephalopathy might inform approaches to biomarker development for other rare diseases.

Structural vaccinology, molecular simulation and immune simulation approaches to design multi-epitopes vaccine against John Cunningham virus

The JCV (John Cunningham Virus) is known to cause progressive multifocal leukoencephalopathy, a condition that results in the formation of tumors. Symptoms of this condition such as sensory defects, cognitive dysfunction, muscle weakness, homonosapobia, difficulties with coordination, and aphasia. To date, there is no specific and effective treatment to completely cure or prevent John Cunningham polyomavirus infections. Since the best way to control the disease is vaccination. In this study, the immunoinformatic tools were used to predict the high immunogenic and non-allergenic B cells, helper T cells (HTL), and cytotoxic T cells (CTL) epitopes from capsid, major capsid, and T antigen proteins of JC virus to design the highly efficient subunit vaccines. The specific immunogenic linkers were used to link together the predicted epitopes and subjected to 3D modeling by using the Robetta server. MD simulation was used to confirm that the newly constructed vaccines are stable and properly fold. Additionally, the molecular docking approach revealed that the vaccines have a strong binding affinity with human TLR-7. The codon adaptation index (CAI) and GC content values verified that the constructed vaccines would be highly expressed in E. coli pET28a (+) plasmid. The immune simulation analysis indicated that the human immune system would have a strong response to the vaccines, with a high titer of IgM and IgG antibodies being produced. In conclusion, this study will provide a pre-clinical concept to construct an effective, highly antigenic, non-allergenic, and thermostable vaccine to combat the infection of the John Cunningham virus.

Pembrolizumab for the treatment of progressive multifocal leukoencephalopathy in China

The aim of this study is to analyze the clinical characteristics and outcomes of Chinese patients with progressive multifocal leukoencephalopathy (PML) who were treated with programmed cell death protein 1 (PD1) blockade therapies. We retrospectively analyzed patients who were admitted to our hospital between October 1, 2020, and October 1, 2022, diagnosed with PML and treated with PD1 blockade therapies. Four patients with PML who were treated with PD1 blockade therapies were identified. All patients were male, and their ages ranged from 19 to 54 years old. One patient (Case 2) exhibited mild pleocytosis, while three patients (Cases 2-4) had markedly reduced T lymphocyte cell counts prior to treatment. The time interval between symptom onset and treatment initiation ranged from six to 54 weeks. All patients received pembrolizumab treatment, with a total of two to four doses administered. Three patients who responded to pembrolizumab treatment showed clinical improvement starting around 8 weeks after the initiation of therapy. Although one patient did not show clinical improvement, they ultimately survived until the last follow-up. None of the patients in this study exhibited immune-related adverse events or immune reconstitution inflammatory syndrome. PD1 blockade appears to be a promising novel therapeutic option for PML; additional prospective studies are necessary to confirm its efficacy.

Polyomavirus Wakes Up and Chooses Neurovirulence

JC polyomavirus (JCPyV) is a human-specific polyomavirus that establishes a silent lifelong infection in multiple peripheral organs, predominantly those of the urinary tract, of immunocompetent individuals. In immunocompromised settings, however, JCPyV can infiltrate the central nervous system (CNS), where it causes several encephalopathies of high morbidity and mortality. JCPyV-induced progressive multifocal leukoencephalopathy (PML), a devastating demyelinating brain disease, was an AIDS-defining illness before antiretroviral therapy that has "reemerged" as a complication of immunomodulating and chemotherapeutic agents. No effective anti-polyomavirus therapeutics are currently available. How depressed immune status sets the stage for JCPyV resurgence in the urinary tract, how the virus evades pre-existing antiviral antibodies to become viremic, and where/how it enters the CNS are incompletely understood. Addressing these questions requires a tractable animal model of JCPyV CNS infection. Although no animal model can replicate all aspects of any human disease, mouse polyomavirus (MuPyV) in mice and JCPyV in humans share key features of peripheral and CNS infection and antiviral immunity. In this review, we discuss the evidence suggesting how JCPyV migrates from the periphery to the CNS, innate and adaptive immune responses to polyomavirus infection, and how the MuPyV-mouse model provides insights into the pathogenesis of JCPyV CNS disease.

Progressive Multifocal Leukoencephalopathy Initially Suspected As Brain Relapse From Classical Hodgkin's Lymphoma

HIV-negative progressive multifocal leukoencephalopathy (PML) has a poor prognosis due to a lack of standard treatment. Herein, we report a patient with HIV-negative PML which occurred after the treatment for classical Hodgkin's lymphoma (CHL). A 71-year-old male patient was admitted to our hospital due to various neurological symptoms, including memory disturbance, dysgraphia, ataxia, and ideomotor apraxia, at 16 months after high-dose salvage chemotherapy with autologous peripheral blood stem cell transplantation (PBSCT) for primary treatment-refractory CHL. The patient's blood and serological examination results were mainly normal, including CD4-positive T lymphocyte count and serum immunoglobulin levels. T2-weighted fluid-attenuated inversion recovery MRI showed high-intensity lesions from the left occipital lobe to the corpus callosum. Moreover, the rapid intraoperative pathological assessment of biopsy specimens obtained from abnormal brain lesions suggested brain relapse of CHL. The patient's symptoms progressed rapidly; therefore, treatment with high-dose methotrexate was started, which significantly improved the patient's symptoms and MRI findings within a week. However, further examinations of the biopsy specimens with in situ hybridization and immunohistochemical examinations showed reactivation of the John Cunningham virus (JCV) in the astrocytes. Further, cells initially believed to be Hodgkin cells based on the rapid intraoperative pathological assessment were found to be destructive astrocytes, thereby confirming the diagnosis of PML. The patient was then successfully treated with combined mefloquine and mirtazapine and did not have any fatal outcomes. Based on this case, a differential diagnosis of PML from CNS involvement of CHL is important even in cases without evident biomarkers for immunodeficiency. Moreover, methotrexate was likely to be effective in improving neurological symptoms by decreasing brain parenchyma inflammation in the acute phase in this particular patient.

A human T-lymphotropic virus-1 carrier who developed progressive multifocal leukoencephalopathy following immunotherapy for sarcoidosis: a case report

BACKGROUND

Progressive multifocal leukoencephalopathy (PML) is a devastating demyelinating disorder of the central nervous system caused by opportunistic infection of the JC virus (JCV).

CASE PRESENTATION

A 58-year-old Japanese woman was admitted to our hospital for aphasia. She had a 5-year history of untreated sarcoidosis and was a human T cell lymphotropic virus-1 (HTLV-1) carrier. Serum angiotensin-converting enzyme, soluble interleukin-2 receptor, lysozyme, and calcium levels were elevated. JCV-DNA was not detected in cerebrospinal fluid by PCR testing. Skin biopsy revealed noncaseating granuloma formation. Bilateral multiple nodular lesions were present on chest X-ray. Brain magnetic resonance imaging showed left frontal and temporal lesions without gadolinium enhancement. As we suspected that systemic sarcoidosis had developed into neurosarcoidosis, we started steroid and infliximab administration. After treatment, the chest X-ray and serum abnormalities ameliorated, but the neurological deficits remained. At 1 month after immunotherapy, she developed right hemiparesis. Cerebrospinal fluid was positive for prototype (PML-type) JCV on repeated PCR testing. Brain biopsy revealed demyelinating lesions with macrophage infiltration, atypical astrocytes, and JCV antigen-positive cells. We diagnosed her with PML and started mefloquine, leading to partial remission.

CONCLUSIONS

Sarcoidosis and HTLV-1 infection both affect T cell function, especially CD4⁺ T cells, and may developped the patient's PML. The comorbidity of sarcoidosis, PML, and HTLV-1 infection has not been reported, and this is the world's first report of PML associated with HTLV-1 infection and sarcoidosis.

Progressive Multifocal Leukoencephalopathy Treated by Immune Checkpoint Inhibitors

OBJECTIVE

Our aim was to assess the real-world effectiveness of immune checkpoint inhibitors for treatment of patients with progressive multifocal leukoencephalopathy (PML).

METHODS

We conducted a multicenter survey compiling retrospective data from 79 PML patients, including 38 published cases and 41 unpublished cases, who received immune checkpoint inhibitors as add-on to standard of care. One-year follow-up data were analyzed to determine clinical outcomes and safety profile. Logistic regression was used to identify variables associated with 1-year survival.

RESULTS

Predisposing conditions included hematological malignancy (n = 38, 48.1%), primary immunodeficiency (n = 14, 17.7%), human immunodeficiency virus/acquired immunodeficiency syndrome (n = 12, 15.2%), inflammatory disease (n = 8, 10.1%), neoplasm (n = 5, 6.3%), and transplantation (n = 2, 2.5%). Pembrolizumab was most commonly used (n = 53, 67.1%). One-year survival was 51.9% (41/79). PML-immune reconstitution inflammatory syndrome (IRIS) was reported in 15 of 79 patients (19%). Pretreatment expression of programmed cell death-1 on circulating T cells did not differ between survivors and nonsurvivors. Development of contrast enhancement on follow-up magnetic resonance imaging at least once during follow-up (OR = 3.16, 95% confidence interval = 1.20-8.72, p = 0.02) was associated with 1-year survival. Cerebrospinal fluid JC polyomavirus DNA load decreased significantly by 1-month follow-up in survivors compared to nonsurvivors (p < 0.0001). Thirty-two adverse events occurred among 24 of 79 patients (30.4%), and led to treatment discontinuation in 7 of 24 patients (29.1%).

INTERPRETATION

In this noncontrolled retrospective study of patients with PML who were treated with immune checkpoint inhibitors, mortality remains high. Development of inflammatory features or overt PML-IRIS was commonly observed. This study highlights that use of immune checkpoint inhibitors should be strictly personalized toward characteristics of the individual PML patient. ANN NEUROL 2023;93:257-270.

BK virus-specific T cells for immunotherapy of progressive multifocal leukoencephalopathy: an open-label, single-cohort pilot study

BACKGROUND

Progressive multifocal leukoencephalopathy, a rare disease of the CNS caused by JC virus and occurring in immunosuppressed people, is typically fatal unless adaptive immunity is restored. JC virus is a member of the human polyomavirus family and is closely related to the BK virus. We hypothesised that use of partly HLA-matched donor-derived BK virus-specific T cells for immunotherapy in progressive multifocal leukoencephalopathy would be feasible and safe.

METHODS

We did an open-label, single-cohort pilot study in patients (aged 18 years or older) with clinically definite progressive multifocal leukoencephalopathy and disease progression in the previous month at the National Institutes of Health (NIH) Clinical Center (Bethesda, MD, USA). Overlapping peptide libraries derived from large T antigen and major capsid protein VP1 of BK virus with high sequence homology to JC virus counterparts were used to generate polyomavirus-specific T cells cross-recognising JC virus antigens. Polyomavirus-specific T cells were manufactured from peripheral blood mononuclear cells of first-degree relative donors aged 18 years or older. These cells were administered to patients by intravenous infusion at 1 × 10⁶ polyomavirus-specific T cells per kg, followed by up to two additional infusions at 2 × 10⁶ polyomavirus-specific T cells per kg. The primary endpoints were feasibility (no manufacturing failure based on meeting release criteria, achieving adequate numbers of cell product for clinical use, and showing measurable antiviral activity) and safety in all patients. The safety monitoring period was 28 days after each infusion. Patients were followed up with serial MRI for up to 12 months after the final infusion. This trial is registered at ClinicalTrials.gov, NCT02694783.

FINDINGS

Between April 7, 2016, and Oct 19, 2018, 26 patients were screened, of whom 12 were confirmed eligible and received treatment derived from 14 matched donors. All administered polyomavirus-specific T cells met the release criteria and recognised cognate antigens in vitro. 12 patients received at least one infusion, ten received at least two, and seven received a total of three infusions. The median on-study follow-up was 109·5 days (range 23-699). All infusions were tolerated well, and no serious treatment-related adverse events were observed. Seven patients survived progressive multifocal leukoencephalopathy for longer than 1 year after the first infusion, whereas five died of progressive multifocal leukoencephalopathy within 3 months.

INTERPRETATION

We showed that generation of polyomavirus-specific T cells from healthy related donors is feasible, and these cells can be safely used as an infusion for adoptive immunotherapy of progressive multifocal leukoencephalopathy. Although not powered to assess efficacy, our data provide additional support for this strategy as a potential life-saving therapy for some patients.

FUNDING

Intramural Research Program of the National Institute of Neurological Disorders and Stroke of the NIH.

Advances in Treatment of Progressive Multifocal Leukoencephalopathy

Progressive multifocal encephalopathy (PML) is a severe demyelinating disease of the central nervous system (CNS) caused by JC virus (JCV), which occurs in immunocompromised individuals. Management of PML relies on restoration of immunity within the CNS. However, when this restoration cannot be readily achieved, PML has a grim prognosis. Innovative strategies have shown promise in promoting anti‐JCV immune responses, and include T‐cell adoptive transfer or immune checkpoint inhibitor therapies. Conversely, management of immune reconstitution inflammatory syndrome, particularly in iatrogenic PML, remains a major challenge. In this paper, we review recent development in the treatment of PML. ANN NEUROL 2021;90:865–873

A retrospective analysis of changes in lymphocyte levels in patients with multiple sclerosis during and after Tecfidera® treatment

Background

There are currently no best practice recommendations for lymphocyte subset monitoring for patients with multiple sclerosis (pwMS) on disease-modifying therapies including Tecfidera® (dimethyl fumarate, DMF). However, there have been several cases of pwMS on DMF without severe lymphopenia who had high CD4:CD8 T cell ratios and went on to develop progressive multifocal leukoencephalopathy.

Objective

Our objective was to characterize the changes in immune profile during and after DMF treatment in pwMS.

Methods

A retrospective analysis of longitudinal data from 299 pwMS who have been treated with DMF at the Fraser Health Multiple Sclerosis Clinic in British Columbia, Canada. The blood test results were taken from January 1, 2013 to April 1, 2020.

Results

Our results suggest that CD8+ T cells had the highest proportional decrease compared to other lymphocyte subset populations and overall lymphocyte count in response to DMF treatment. CD56+ Natural Killer cells were similarly decreased in response to DMF treatment. CD4:CD8 T cell ratio was the measurement that had the highest rate of change in response to DMF initiation and discontinuation.

Conclusion

CD8+ T cell count and CD4:CD8 T cell ratio may be a more sensitive measurement of the immune landscape of patients with MS on DMF.

Progressive multifocal leukoencephalopathy and the spectrum of JC virus-related disease

Progressive multifocal leukoencephalopathy (PML) is a devastating CNS infection caused by JC virus (JCV), a polyomavirus that commonly establishes persistent, asymptomatic infection in the general population. Emerging evidence that PML can be ameliorated with novel immunotherapeutic approaches calls for reassessment of PML pathophysiology and clinical course. PML results from JCV reactivation in the setting of impaired cellular immunity, and no antiviral therapies are available, so survival depends on reversal of the underlying immunosuppression. Antiretroviral therapies greatly reduce the risk of HIV-related PML, but many modern treatments for cancers, organ transplantation and chronic inflammatory disease cause immunosuppression that can be difficult to reverse. These treatments — most notably natalizumab for multiple sclerosis — have led to a surge of iatrogenic PML. The spectrum of presentations of JCV-related disease has evolved over time and may challenge current diagnostic criteria. Immunotherapeutic interventions, such as use of checkpoint inhibitors and adoptive T cell transfer, have shown promise but caution is needed in the management of immune reconstitution inflammatory syndrome, an exuberant immune response that can contribute to morbidity and death. Many people who survive PML are left with neurological sequelae and some with persistent, low-level viral replication in the CNS. As the number of people who survive PML increases, this lack of viral clearance could create challenges in the subsequent management of some underlying diseases.

In this Review, Cortese et al. provide an overview of the pathobiology and evolving presentations of progressive multifocal leukoencephalopathy and other diseases caused by JC virus, and discuss emerging immunotherapeutic approaches that could increase survival.

Progressive multifocal leukoencephalopathy (PML) is a rare, debilitating and often fatal disease of the CNS caused by JC virus (JCV).

JCV establishes asymptomatic, lifelong persistent or latent infection in immune competent hosts, but impairment of cellular immunity can lead to reactivation of JCV and PML.

PML most commonly occurs in patients with HIV infection or lymphoproliferative disease and in patients who are receiving natalizumab for treatment of multiple sclerosis.

The clinical phenotype of PML varies and is shaped primarily by the host immune response; changes in the treatment of underlying diseases associated with PML have changed phenotypes over time.

Other clinical manifestations of JCV infection have been described, including granule cell neuronopathy.

Survival of PML depends on reversal of the underlying immunosuppression; emerging immunotherapeutic strategies include use of checkpoint inhibitors and adoptive T cell transfer.

IL-21 from high-affinity CD4 T cells drives differentiation of brain-resident CD8 T cells during persistent viral infection

Development of tissue-resident memory (T_RM) CD8 T cells depends on CD4 T cells. In polyomavirus central nervous system infection, brain CXCR5^hi PD-1^hi CD4 T cells produce interleukin-21 (IL-21), and CD8 T cells lacking IL-21 receptors (IL21R^-/-) fail to become bT_RM IL-21⁺ CD4 T cells exhibit elevated T cell receptor (TCR) affinity and higher TCR density. IL21R^-/- brain CD8 T cells do not express CD103, depend on vascular CD8 T cells for maintenance, are antigen recall defective, and lack T_RM core signature genes. CD4 T cell-deficient and IL21R^-/- brain CD8 T cells show similar deficiencies in expression of genes for oxidative metabolism, and intrathecal delivery of IL-21 to CD4 T cell-depleted mice restores expression of electron transport genes in CD8 T cells to wild-type levels. Thus, high-affinity CXCR5^hi PD-1^hi CD4 T cells in the brain produce IL-21, which drives CD8 bT_RM differentiation in response to a persistent viral infection.

Long-Term Survival after Progressive Multifocal Leukoencephalopathy in a Patient with Primary Immune Deficiency and NFKB1 Mutation

PURPOSE

To describe the development of progressive multifocal leukoencephalopathy (PML) in a patient with primary immune deficiency (PID) due to a NFKB1 (nuclear factor kB subunit 1) mutation, who was treated successfully with a combination of mirtazapine and mefloquine.

METHODS

We've based the treatment of our patient on literature research and provide a review of PML in CVID patients.

RESULTS

Only a few reports have been published on the occurrence of PML in PID. PML is mainly observed in patients with reduced cellular immunity, which was not the case in our patient. Successful treatment options in this population are limited. Though severely disabled, our patient still survives, more than 4 years after symptom onset and shows consistent improvement on MRI (magnetic resonance imaging) and CSF (cerebrospinal fluid) analysis.

CONCLUSION

We conclude that some patients with PML might be treatable and can show long-term survival although neurological deficits remain. Involvement of humoral immunity in the pathogenesis of PML as well as the possible role of NFKB1 mutations in response to specific pathogens deserves further investigation.

Fifty Years of JC Polyomavirus: A Brief Overview and Remaining Questions

In the fifty years since the discovery of JC polyomavirus (JCPyV), the body of research representing our collective knowledge on this virus has grown substantially. As the causative agent of progressive multifocal leukoencephalopathy (PML), an often fatal central nervous system disease, JCPyV remains enigmatic in its ability to live a dual lifestyle. In most individuals, JCPyV reproduces benignly in renal tissues, but in a subset of immunocompromised individuals, JCPyV undergoes rearrangement and begins lytic infection of the central nervous system, subsequently becoming highly debilitating-and in many cases, deadly. Understanding the mechanisms allowing this process to occur is vital to the development of new and more effective diagnosis and treatment options for those at risk of developing PML. Here, we discuss the current state of affairs with regards to JCPyV and PML; first summarizing the history of PML as a disease and then discussing current treatment options and the viral biology of JCPyV as we understand it. We highlight the foundational research published in recent years on PML and JCPyV and attempt to outline which next steps are most necessary to reduce the disease burden of PML in populations at risk.

Progressive multifocal leukoencephalopathy in dimethyl fumarate-treated multiple sclerosis patients

Dimethyl fumarate (DMF), a fumaric acid with antioxidant and immunomodulatory properties, is among the most commonly used oral therapies for relapsing multiple sclerosis (MS). Progressive multifocal leukoencephalopathy (PML) has been associated with several disease-modifying therapies (DMTs), including DMF in treating MS. We present detailed clinical characteristics of nine PML cases and show that the PML incidence in DMF-treated patients is 0.02 per 1000 patients. In addition to persistent severe lymphopenia, older age appears to be a potential risk for PML. However, younger patients without lymphopenia were also observed to develop PML. DMF-associated PML has occurred in patients with absolute lymphocyte counts (ALCs) above the guideline threshold, suggesting that changes in specific subsets might be more important than total ALC. Furthermore, since DMF has been found to decrease immune cell migration by decreasing the expression of adhesive molecules, the cerebrospinal fluid (CSF) immune profile may also be useful for assessing PML risk in DMF-treated patients. This review provides an up-to-date assessment of PML cases occurring in DMF-treated patients and discusses other potential considerations in light of our current understanding of DMF's mechanism of action on the immune system in the periphery and in the central nervous system (CNS).

Progressive multifocal leukoencephalopathy on dimethyl fumarate with preserved lymphocyte count but deep T-cells exhaustion

BACKGROUND

Progressive multifocal leukoencephalopathy (PML) among multiple sclerosis (MS) patients receiving dimethyl fumarate (DMF) is associated with iatrogenic lymphopenia, predominating on CD8+ T-cells.

OBJECTIVES AND METHODS

We report an unusual case of DMF-related PML in a 66-year-old MS patient with preserved lymphocyte count (nadir: 810/mm³) and normal CD8+ T-cells count.

RESULTS

A massive overexpression of the inhibitory receptor Programmed Cell Death 1 (PD-1) on CD8+ and memory effector T-cells together with an impaired anti-JC virus (JCV) specific T-cells response were found, compatible with exhaustion. Following DMF withdrawal, PML progressively regressed, PD-1 was downregulated, and a functional anti-JCV response was established.

CONCLUSION

T-cells exhaustion may favor PML onset on DMF independently of lymphocyte count.

Brief Report: Decreased JC Virus-Specific Antibody-Dependent Cellular Cytotoxicity in HIV-Seropositive PML Survivors

BACKGROUND

Progressive multifocal leukoencephalopathy (PML) is an often fatal disease caused by JC virus (JCV) in severely immunocompromised patients, including HIV patients. Development of therapeutics to prevent or treat PML is an urgent medical need. While JCV-specific T cells are crucial to control JCV and recover from PML, the role played by antibodies remains unclear. Anti-JCV antibodies, including potent neutralizing antibodies, can be detected in most infected adults, yet in PML patients, JCV seems to escape from neutralization. Whether antibodies can contribute to JCV control by eliciting Fc-mediated effector functions activity has not been evaluated.

METHODS

We measured the capacity of plasma anti-JCV VP1 antibodies to recruit Fc receptor (FcR)-bearing effector cell functions in 28 HIV patients, comparing subjects without PML with PML survivors (PML S) who were alive 1 year after disease onset or PML progressors (PML P) who succumbed within the first year. Antibody titers against JCV VP1 and HIV gp140 trimer were determined by end-point titer dilution ELISA. FcR-mediated natural killer cell degranulation and IFN-γ production were measured as surrogate for in vitro antibody-dependent cellular cytotoxicity (ADCC).

RESULTS

PML S had higher JCV antibody titers than PML P and patients without PML. However, anti-JCV antibodies had a higher ability to functionally engage FcR in PML P than PML S. Antibody titers and ADCC activity did not vary over time in PML S. Anti-HIV antibody titers and ADCC activity were similar among groups.

CONCLUSIONS

The ability of anti-JCV antibodies to stimulate FcR-bearing effector cell activity might contribute to the outcome of PML. Further studies are warranted to define Fc-mediated functions of anti-JCV antibodies and evaluate whether ADCC can contain JCV replication.

Checkpoint inhibitors for the treatment of JC virus-related progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a frequently fatal brain infection caused by the JC polyomavirus (JCV). PML occurs in people with impaired cellular immunity, and the only effective treatment is restoration of immune function. Infection in immunocompromised hosts is often associated with immune exhaustion, which is mediated by inhibitory cell surface receptors known as immune checkpoints, leading to loss of T cell effector function. Blockade of immune checkpoints can reinvigorate host responses to fight infection. Recently, there have been several reports of checkpoint blockade to treat PML in patients in whom immune reconstitution is otherwise not possible, with some evidence for positive response. Larger studies are needed to better understand efficacy of checkpoint blockade in PML and factors that determine response.

JCPyV NCCR analysis in PML patients with different risk factors: exploring common rearrangements as essential changes for neuropathogenesis

Background

During severe immunosuppression or treatment with specific biological drugs, human polyomavirus JC (JCPyV) may establish a lytic infection in oligodendrocytes, leading to progressive multifocal leukoencephalopathy (PML). Beyond AIDS, which represents the most common predisposing condition, several biological drugs have been associated to the development of PML, such as natalizumab, fingolimod and dimethyl fumarate, which have been showed to increase the risk of PML in the multiple sclerosis (MS) population. JCPyV non-coding control region (NCCR) can be found in two different forms: a virulent neurotropic pathogenic form and a latent non-pathogenic form. The neurotropic forms contain a rearranged NCCR and are typically found in the cerebrospinal fluid, brain or blood of PML patients.

Case presentation

We sequenced and critically examined JCPyV NCCR from isolates detected in the cerebrospinal fluid of four newly diagnosed progressive multifocal leukoencephalopathy patients: two HIV-positive and two HIV-negative multiple sclerosis patients. More complex NCCR rearrangements were observed in the two HIV-positive patients compared to the HIV-negative multiple sclerosis patients with PML.

Conclusions

The comparison of HIV-positive and HIV-negative MS patients with PML, allowed us to evidence the presence of a common pattern of JCPyV NCCR rearrangement, characterized by the deletion of the D-block, which could be one of the initial rearrangements of JCPyV NCCR needed for the development of PML.

Host-Immune Interactions in JC Virus Reactivation and Development of Progressive Multifocal Leukoencephalopathy (PML)

With the advent of immunomodulatory therapies and the HIV epidemic, the impact of JC Virus (JCV) on the public health system has grown significantly due to the increased incidence of Progressive Multifocal Leukoencephalopathy (PML). Currently, there are no pharmaceutical agents targeting JCV infection for the treatment and the prevention of viral reactivation leading to the development of PML. As JCV primarily reactivates in immunocompromised patients, it is proposed that the immune system (mainly the cellular-immunity component) plays a key role in the regulation of JCV to prevent productive infection and PML development. However, the exact mechanism of JCV immune regulation and reactivation is not well understood. Likewise, the impact of host factors on JCV regulation and reactivation is another understudied area. Here we discuss the current literature on host factor-mediated and immune factor-mediated regulation of JCV gene expression with the purpose of developing a model of the factors that are bypassed during JCV reactivation, and thus are potential targets for the development of therapeutic interventions to suppress PML initiation. Graphical Abstract.

Children with Narcolepsy type 1 have increased T-cell responses to orexins

Narcolepsy type 1 (NT1) is caused by severe loss of the orexin neurons, and is highly associated with HLA DQB1*06:02. Using intracellular cytokine staining, we observed a higher frequency of IFN‐γ‐ and TNF‐α‐producing CD4⁺ and CD8⁺ T‐cells in response to orexins in 27 children with NT1 compared to 15 healthy control children. Conversely, no such difference was observed between 14 NT1 and 16 HC adults. In addition, priming with flu peptides amplified the T‐cell response to orexins in children with NT1. Our data suggests that NT1 may be caused by an autoimmune T‐cell response to orexins, possibly triggered by flu antigens.

Sustained Response and Rationale of Programmed Cell Death-1-Targeting for Progressive Multifocal Leukoencephalopathy

In this study, we report a complete (clinical, radiological, and virological) sustained (1 year) response after nivolumab salvage therapy in a progressive multifocal leukoencephalopathy patient. Analyses of the cells infiltrate in a pretreatment brain biopsy suggest that parenchymal programmed cell death-L1⁺ macrophages could be the T-cells partnership in immune exhaustion and virus escape.

Progressive multifocal leukoencephalopathy secondary to hepatitis C virus infection-related T-cell lymphopenia

Progressive multifocal leukoencephalopathy (PML) is an uncommon neurological condition known to occur in the setting of T-cell immune suppression. We report a case of hepatitis C virus (HCV) infection-related T-cell lymphopenia manifesting as PML. HCV treatment and transient viral suppression resulted in immunological recovery with clinical stabilisation.

The "milky way" galaxy of HIV-related central nervous system immune reaction syndromes

The landscape of central nervous system HIV infection is rapidly changing, leading to the recognition of a new constellation of overlapping syndromes and to a better insight for the elder ones. Among these, progressive multifocal leukoencephalopathy (PML) still poses several diagnostic and therapeutic challenges; nevertheless, recent developments in understanding PML in patients with multiple sclerosis may have benefitted HIV-positive patients suffering from PML too. We describe a peculiar case of PML-immune reconstitution inflammatory syndrome (IRIS) presenting a punctate pattern with "milky way" appearance on magnetic resonance imaging. Despite the fact that brain imaging and histopathology remain the mainstays for extricating through the expanding galaxy of HIV-related central nervous system dysimmune syndromes and although punctate pattern has been already well acknowledged as a suggestive finding of PML among patients on natalizumab, this radiological presentation is still poorly recognised in AIDS-related PML cases, leading to possible life-threatening diagnostic delays. This is also the first report about intravenous immunoglobulin treatment in AIDS-related PML-IRIS; the favourable clinical and radiological outcome of our case and the preliminary administrations of intravenous immunoglobulins in natalizumab-associated PML-IRIS from literature support probable benefits also among HIV-positive patients.

Fumaric acid ester-induced T-cell lymphopenia in the real-life treatment of psoriasis

BACKGROUND

Fumaric acid esters (FAEs) are used to treat psoriasis and are known to cause lymphopenia in roughly 60% of the patients. Much remains to be elucidated about the biological effects of FAEs on lymphocytes.

OBJECTIVE

To evaluate the influence of long-term FAE (Fumaderm® ) treatment on peripheral blood CD4+ and CD8+ T cells, CD19+ B cells and CD56+ natural killer (NK) cells in psoriasis.

METHODS

In this single-centre retrospective observational subcohort study, we obtained leucocyte and lymphocyte subset counts before initiating FAE therapy in 371 psoriasis patients (mean age, 47.8 years; 63.3% males) and monitored them during treatment (mean treatment duration, 2.9 years). Multiparametric flow cytometry was used for immunophenotyping.

RESULTS

FAEs significantly reduced the numbers of CD4+ T, CD8+ T, CD19+ B and CD56+ NK cells. Among lymphocyte subsets, the mean percentage reduction from baseline was always highest for CD8+ T cells, with a peak of 55.7% after 2 years of therapy. The risk of T-cell lymphopenia increased significantly with the age of the psoriasis patients at the time that FAE therapy was initiated. It was significantly decreased for the combination therapy with methotrexate and folic acid (vitamin B9) supplementation. Supporting evidence was found suggesting that T-cell lymphopenia enhances the effectiveness of FAE therapy.

CONCLUSIONS

Monitoring distinct T-cell subsets rather than just absolute lymphocyte counts may provide more meaningful insights into both the FAE treatment safety and efficacy. We therefore suggest optimizing pharmacovigilance by additionally monitoring CD4+ and CD8+ T-cell counts at regular intervals, especially in patients of middle to older age. Thus, further prospective studies are needed to establish evidence-based recommendations to guide dermatologists in the management of psoriasis patients who are taking FAEs and who develop low absolute T-cell counts.

Effect of dimethyl fumarate on lymphocytes in RRMS: Implications for clinical practice

OBJECTIVE

To assess functional changes in lymphocyte repertoire and subsequent clinical implications during delayed-release dimethyl fumarate (DMF) treatment in patients with multiple sclerosis.

METHODS

Using peripheral blood from several clinical trials of DMF, immune cell subsets were quantified using flow cytometry. For some patients, lymphocyte counts were assessed after DMF discontinuation. Incidence of adverse events, including serious and opportunistic infections, was assessed.

RESULTS

In DMF-treated patients, absolute lymphocyte counts (ALCs) demonstrated a pattern of decline followed by stabilization, which also was reflected in the global reduction in numbers of circulating functional lymphocyte subsets. The relative frequencies of circulating memory T- and B-cell populations declined and naive cells increased. No increased incidence of serious infection or malignancy was observed for patients treated with DMF, even when stratified by ALC or T-cell subset frequencies. For patients who discontinued DMF due to lymphopenia, ALCs increased after DMF discontinuation; recovery time varied by ALC level at discontinuation. T-cell subsets closely correlated with ALCs in both longitudinal and cross-sectional analyses.

CONCLUSIONS

DMF shifted the immunophenotype of circulating lymphocyte subsets. ALCs were closely correlated with CD4⁺ and CD8⁺ T-cell counts, indicating that lymphocyte subset monitoring is not required for safety vigilance. No increased risk of serious infection was observed in patients with low T-cell subset counts. Monitoring ALC remains the most effective way of identifying patients at risk of subsequently developing prolonged moderate to severe lymphopenia, a risk factor for progressive multifocal leukoencephalopathy in DMF-treated patients.

TRIAL REGISTRATION NUMBERS

EUDRA CT 2015-001973-42, NCT00168701, NCT00420212, NCT00451451, and NCT00835770.

A controlled inflammation and a regulatory immune system are associated with more favorable prognosis of progressive multifocal leukoencephalopathy

OBJECTIVE

In the present study, we analyzed the inflammatory profiles of brain tissues obtained from patients with progressive multifocal leukoencephalopathy (PML) due to John Cunningham (JC) virus infection to identify potential prognostic factors.

METHODS

The study included seven patients (two men, five women) who had been pathologically diagnosed with PML, and all of whom were HIV negative. Fixed brain samples were analyzed via hematoxylin and eosin (HE) staining and Klüver-Barrera (KB) staining. We then performed immunohistochemistry (IHC) specific to JC virus capsid proteins (VP1 and VP2/3) and lymphocyte surface markers (CD4, CD8, CD138, and PD-1).

RESULTS

The mean age at onset was 53.4, while the mean duration until biopsy/autopsy was 4.7 months. Four patients were included in the good prognosis (GP) group, while three were included in the poor prognosis (PP) group. Pathological analysis revealed a significantly larger number of CD4-positive T-cell infiltrations (P = .029) in the GP group, along with a preserved CD4:CD8 ratio. Larger numbers of CD138-positive plasma cells were also observed in the GP group (P = .029) than in the PP group. Linear regression analyses revealed a significant association between the numbers of CD138-positive plasma cells and PD-1-positive cells (R² = 0.80).

CONCLUSIONS

Viral loads in the cerebrospinal fluid, a controlled inflammatory response mediated by CD4- and CD8-positive T cells, and plasma cells are associated with PML prognosis. Our findings further indicate that regulatory plasma cells may regulate inflammatory T-cell activity via a PD-1/PD-L1 immuno-checkpoint pathway, thereby protecting the uninfected brain from excessive immune-mediated damage during an active JC virus infection.

Successful treatment of progressive multifocal leukoencephalopathy with recombinant interleukin-7 and maraviroc in a patient with idiopathic CD4 lymphocytopenia

Progressive multifocal leukoencephalopathy (PML) is a rapidly progressive, often fatal viral infection of the brain without a known treatment. Recently, case reports have demonstrated survival from PML with therapies that improve cell-mediated immunity, including interleukin-7 (IL-7) or the chemokine receptor type 5 (CCR5) antagonist, maraviroc (MVC). We present the first known case of a patient with PML successfully treated with both IL-7 and MVC. A 63-year-old woman presented to our center with a 6-month history of progressive left hemiparesis. Extensive laboratory testing was negative except for a severe CD4 lymphocytopenia (140/μL). Serial brain MRIs done prior to presentation revealed an enlarging, non-enhancing T2-hyperintense lesion in the right fronto-parietal white matter. PML was confirmed through detection of the JC virus by PCR in the cerebrospinal fluid and by brain biopsy, and she was started on mirtazapine and mefloquine. She continued to deteriorate and was then given a course of recombinant IL-7. Though she remained clinically stable after IL-7 treatment and serum JCV PCR decreased from 1000 copies/mL to a nadir of 238 copies/mL, a repeat MRI 3 months later showed lesion enlargement. MVC was then initiated. Now, more than 2 years after initial presentation, she remains stable and serum JCV PCR is undetectable. This case demonstrates successful treatment of PML in a patient with idiopathic CD4 lymphocytopenia and highlights the potential benefits of IL-7 and MVC in the treatment of PML. Treatment with IL-7 and MVC led to clinical stability and improvement in JC virus titers.

JC Virus-DNA Detection Is Associated with CD8 Effector Accumulation in Peripheral Blood of Patients with Multiple Sclerosis under Natalizumab Treatment, Independently from JC Virus Serostatus

Although natalizumab (anti-α4 integrin) represents an effective therapy for relapsing remitting multiple sclerosis (RRMS), it is associated with an increased risk of developing progressive multifocal leukoencephalopathy (PML), caused by the polyomavirus JC (JCV). The aim of this study was to explore natalizumab-induced phenotypic changes in peripheral blood T-lymphocytes and their relationship with JCV reactivation. Forty-four patients affected by RRMS were enrolled. Blood and urine samples were classified according to natalizumab infusion number: 0 (N0), 1–12 (N12), 13–24 (N24), 25–36 (N36), and over 36 (N > 36) infusions. JCV-DNA was detected in plasma and urine. T-lymphocyte phenotype was evaluated with flow cytometry. JCV serostatus was assessed. Ten healthy donors (HD), whose ages and sexes matched with the RRMS patients of the N0 group, were enrolled. CD8 effector (CD8 E) percentages were increased in natalizumab treated patients with detectable JCV-DNA in plasma or urine compared to JCV-DNA negative patients (JCV−) (p < 0.01 and p < 0.001, resp.). Patients with CD8 E percentages above 10.4% tended to show detectable JCV-DNA in plasma and/or urine (ROC curve p = 0.001). The CD8 E was increased when JCV-DNA was detectable in plasma or urine, independently from JCV serology, for N12 and N24 groups (p < 0.01). As long as PML can affect RRMS patients under natalizumab treatment with a negative JCV serology, the assessment of CD8 E could help in the evaluation of JCV reactivation.

T cell deficiencies as a common risk factor for drug associated progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is a disease of the central nervous system caused by neuropathogenic prototypes of ubiquitous community-acquired JC virus (JCV). The disease became of particular concern following its association with certain therapies that modulate immune system function without heavy immunosuppression. Due to lack of prophylactic/treatment options and poor outcomes, which often include severe disability or death, PML is a considerable concern for development of new drugs that interfere with immune system functions. In this review of clinical and research findings, we discuss the evidence that deficiencies in CD4⁺ T helper cells, cytotoxic CD8⁺ T cells, and interferon gamma are of crucial importance for development of PML under a variety of circumstances, including those associated with use of various drugs, regardless of differences in their mechanisms of action. These deficiencies apparently enable transformation of the harmless JCV archetype into neuropathogenic prototypes, but the site(s), and the mechanisms, of this transformation are yet to be elucidated. Here we discuss the evidence for brain as one of the sites of this transformation, and propose a model of PML pathogenesis that emphasizes the central role of T cell deficiencies in the two life cycles of the JCV, one non-pathogenic and one neuropathogenic. Finally, we conclude that the development of clinical grade T cell functional tests and more consistent use of already available laboratory tests for T cell subset analysis would greatly aid the effort to more accurately predict and assess the magnitude of PML risk for concerned therapeutic interventions.

Understanding Progressive Multifocal Leukoencephalopathy Risk in Multiple Sclerosis Patients Treated with Immunomodulatory Therapies: A Bird's Eye View

The increased use of newer potent immunomodulatory therapies for multiple sclerosis (MS), including natalizumab, fingolimod, and dimethyl fumarate, has expanded the patient population at risk for developing progressive multifocal leukoencephalopathy (PML). These MS therapies shift the profile of lymphocytes within the central nervous system (CNS) leading to increased anti-inflammatory subsets and decreased immunosurveillance. Similar to MS, PML is a demyelinating disease of the CNS, but it is caused by the JC virus. The manifestation of PML requires the presence of an active, genetically rearranged form of the JC virus within CNS glial cells, coupled with the loss of appropriate JC virus-specific immune responses. The reliability of metrics used to predict risk for PML could be improved if all three components, i.e., viral genetic strain, localization, and host immune function, were taken into account. Advances in our understanding of the critical lymphocyte subpopulation changes induced by these MS therapies and ability to detect viral mutation and reactivation will facilitate efforts to develop these metrics.

Emerging Understanding of the Mechanism of Action for Dimethyl Fumarate in the Treatment of Multiple Sclerosis

Dimethyl fumarate (DMF) is an effective treatment option for relapsing-remitting multiple sclerosis (MS), but its therapeutic mechanism of action has not been fully elucidated. A better understanding of its mechanism will allow for the development of assays to monitor its clinical efficacy and safety in patients, as well as guide the development of the next generation of therapies for MS. In order to build the foundation for determining its mechanism, we reviewed the manner in which DMF alters lymphocyte subsets in MS patients, its impact on clinical efficacy and safety, as well as its molecular effects in cellular and animal models. DMF decreases absolute lymphocyte counts, but does not affect all subsets uniformly. CD8⁺ T-cells are the most profoundly affected, but reduction also occurs in the CD4⁺ population, particularly within the pro-inflammatory T-helper Th1 and Th17 subsets, creating a bias toward more anti-inflammatory Th2 and regulatory subsets. Similarly, B-lymphocyte, myeloid, and natural killer populations are also shifted toward a more anti-inflammatory state. In vitro and animal models demonstrate a role for DMF within the central nervous system (CNS) in promoting neuronal survival in an Nrf2 pathway-dependent manner. However, the impact of DMF directly within the CNS of MS patients remains largely unknown.