Progressive Multifocal Leukoencephalopathy Onset Research Articles

Use of quantitative susceptibility mapping (QSM) in progressive multifocal leukoencephalopathy

Progressive multifocal leukoencephalopathy (PML) is an opportunistic demyelinating encephalopathy related to JC virus. Its characteristics on conventional brain MRI are well known and are important for the diagnosis. To analyze SWI hypointensities recently described in U-fibers and cortex adjacent to the white matter lesions of PML. Prospective study including four patients with an history of definite diagnosis of PML. Clinical data were collected retrospectively. Brain MRI exams were done on a 3T magnet, including FLAIR, T2 GRE sequences and SWI. Four males were included (mean age: 47 years, mean PML duration: 24.2 months). Immunosuppression was related to AIDS (n=2), natalizumab for multiple sclerosis (n=1), B-cell lymphoma treated by chemotherapeutic agents and rituximab (n=1). All patients had SWI hypointensities in cortex and/or U-fibers adjacent to the white matter lesions. QSM always suggested a paramagnetic effect. SWI and T2 GRE hypointensities in cortex and U-fibers adjacent to the white matter lesions seem highly prevalent in PML, irrespective of the delay between PML onset and the MRI. QSM data suggest a paramagnetic effect.

Drug-Induced Progressive Multifocal Leukoencephalopathy: A Comprehensive Analysis of the WHO Adverse Drug Reaction Database.

To identify safety signals concerning the association between the use of various drug classes and the onset of progressive multifocal leukoencephalopathy (PML). All reports containing suspected or interacting PML-related or leukoencephalopathy-related drugs, held in the World Health Organization spontaneous individual case safety reports database as at 1 September 2014, were retrieved. We identified safety signals by analysing the drug-reaction pairs, using the reporting odds ratio as a measure of disproportionality. A safety signal was defined if a drug was reported more than twice in PML cases with a reporting odds ratio >2 and a lower 95 % confidence limit >1. We retrieved 2452 reports associated with PML (N = 1612), leukoencephalopathy (N = 835) or both (N = 5), corresponding to 343 different drugs. PML was reported similarly in male and female adults (18-64 years), and almost 30 % of the cases had a fatal outcome. The most frequent Anatomical Therapeutic Chemical (ATC) classification groups concerned antineoplastic agents (23.5 %), antivirals for systemic use (10.1 %) or immunostimulants (4.6 %). Significant disproportionality was found for 88 drugs in the overall analysis (of cases with 'progressive multifocal leukoencephalopathy' or 'leukoencephalopathy' as the Preferred Term), and a new safety signal was identified for 59 active substances (e.g. muromonab-CD3, basiliximab and antithymocyte Ig), as no information on a possible risk of PML was acknowledged in their Summary of Product Characteristics documents. Some safety signals were confirmed also after sensitivity analysis adjustment for several confounding factors (underlying diseases and considering only 'progressive multifocal leukoencephalopathy' as the Preferred Term). We report a possible association between several drugs and PML that has not been previously described. In addition, we have confirmed previously reported signals in a number of drugs. We highlight the need for follow-up by regulatory agencies.

Synthetic antibodies and peptides recognizing progressive multifocal leukoencephalopathy-specific point mutations in polyomavirus JC capsid viral protein 1

Polyomavirus JC (JCV) is the causative agent of progressive multifocal leukoencephalopathy (PML), a rare and frequently fatal brain disease that afflicts a small fraction of the immune-compromised population, including those affected by AIDS and transplantation recipients on immunosuppressive drug therapy. Currently there is no specific therapy for PML. The major capsid viral protein 1 (VP1) involved in binding to sialic acid cell receptors is believed to be a key player in pathogenesis. PML-specific mutations in JCV VP1 sequences present at the binding pocket of sialic acid cell receptors, such as L55F and S269F, abolish sialic acid recognition and might favor PML onset. Early diagnosis of these PML-specific mutations may help identify patients at high risk of PML, thus reducing the risks associated with immunosuppressive therapy. As a first step in the development of such early diagnostic tools, we report identification and characterization of affinity reagents that specifically recognize PML-specific mutations in VP1 variants using phage display technology. We first identified 2 peptides targeting wild type VP1 with moderate specificity. Fine-tuning via selection of biased libraries designed based on 2 parental peptides yielded peptides with different, yet still moderate, bindinspecificities. In contrast, we had great success in identifying synthetic antibodies that recognize one of the PML-specific mutations (L55F) with high specificity from the phage-displayed libraries. These peptides and synthetic antibodies represent potential candidates for developing tailored immune-based assays for PML risk stratification in addition to complementing affinity reagents currently available for the study of PML and JCV.

Progressive multifocal leukoencephalopathy during fumarate monotherapy of psoriasis.

In September 2013, a 69-year-old Caucasian man who was anti–JC virus (JCV) antibody positive was admitted to our hospital with slowly progressing right hemiparesis and aphasia lasting for approximately 6 months. Medical history revealed arterial hypertension, biological aortic valve replacement, and psoriasis vulgaris, treated with 3–6 tablets daily of dimethylfumarate (DMF; 120 mg)/ethylhydrogenfumarate (EHF; 95 mg) (Fumaderm, Biogen Idec, Ismaning, Germany) since December 2008 (table e-1 at [Neurology.org/nn][1]). No other immunosuppressive pretreatment had been given. In April/May 2013, the patient recognized a steadily progressing weakness of the right leg. In June 2013, an external diagnosis of ischemic stroke was made. An MRI scan (figure e-1), which was performed after deterioration of clinical symptoms, revealed a subcortical left hemispheric lesion; biopsy demonstrated macrophage-dominated inflammation, dysmorphic astrocytes, simian virus 40 positivity, and several p53- and MiB1-positive cells, suggestive of a JCV encephalitis (figure e-2). JCV DNA was detected in CSF at 2 different time points using a highly sensitive PCR protocol (September 24, 2013, 16 copies/mL; October 7, 2013, 42 copies/mL),1 leading to the diagnosis of progressive multifocal leukoencephalopathy (PML) in September 2013. Further diagnostic workup (table e-2) unmasked toxic bone marrow damage (figure e-3) and an increased excretion of kappa light chains in urine without any evidence for a plasmocytoma. Taking into account the patient's initial presentation with a slowly progressive paresis since April/May 2013 as well as the initial MRI scan (figure e-1), which is compatible with the PML diagnosis, we believe that the onset of PML was in April/May without preexisting leukopenia and only moderate lymphopenia (grade 2 lymphopenia: 724–738 cells/µL, figure). Several weeks later, white blood cell count dropped to a minimum of 4,800 cells/µL with 288 cells/µL lymphocytes under continuous Fumaderm treatment. Fumaderm was discontinued, and treatment with mirtazapine (45 mg/day; Remergil, MSD Sharp und Dohme GmbH, Haar, Germany), mefloquine (250 mg/week; Lariam, Roche Pharma AG, Grenzach-Wyhlen, Germany), and levetiracetam (1,000 mg/day; Keppra, UCB Pharma GmbH, Monheim, Germany) was initiated.2 Acknowledgment: The authors thank Prof. Dr. med. Anke Reinacher-Schick for her great support in hemato-oncologic diagnostics and Prof. Dr. med. Andrea Tannapfel/Dr. med. M. Gruener for providing pictures of the bone marrow biopsy. [1]: http://Neurology.org/nn

Molecular diagnostic tests to predict the risk of progressive multifocal leukoencephalopathy in natalizumab-treated multiple sclerosis patients

Natalizumab is a humanized monoclonal antibody against the alpha4 chain of the alpha4beta1 and alpha4beta7 integrin heterodimers used with high effectiveness in the treatment of multiple sclerosis. The use of this drug can unfortunately be associated with the onset of progressive multifocal leukoencephalopathy, a possibly fatal infection of the central nervous system, caused by polyomavirus JC. To understand and quantify the risk of developing PML is important for patients who are about to start therapy with natalizumab and for patients who already are under treatment with this drug. In this review we describe and critique molecular diagnostic tests proposed in the last years to assess the risk of PML.

Natalizumab treatment for multiple sclerosis: updates and considerations for safer treatment in JCV positive patients.

Natalizumab is currently one of the best options for treatment of patients with Multiple Sclerosis who have failed traditional prior therapies. However, prolonged use, prior immunosuppressive therapy and anti-JCV antibody status have been associated with increased risk of developing progressive multifocal leukoencephalopathy (PML). The evaluation of these conditions has been used to estimate risks of PML in these patients, and distinct (sometimes extreme) approaches are used to avoid the PML onset. At this time, the biggest issue facing the use of Natalizumab is how to get a balance between the risks and the benefits of the treatment. Hence, strategies for monitor JCV-positive patients undergoing Natalizumab treatment are deeply necessary. To illustrate it, we monitored JCV/DNA in blood and urine of a patient receiving Natalizumab for 12 months. We also bring to discussion the effectiveness of the current methods used for risk evaluation, and the real implications of viral reactivation.

Molecular targeted therapy against the blood–brain barrier in multiple sclerosis

AbstractPrevious therapeutic strategies for multiple sclerosis (MS) include the non‐selective suppression of systemic immunity (immunosuppressive agents, such as glucocorticoids, mitoxantrone and azathioprine) and immunomodulation (type I interferons or intravenous immunoglobulin). The recent development of two pivotal drugs, fingolimod and natalizumab, has resulted in a third category of MS treatment, namely the sequestration of pathogenic T cells. Natalizumab, a humanized monoclonal antibody that binds to the α4‐integrin molecule on the surface of circulating lymphocytes and thus blocks very late antigen‐4/vascular cell adhesion molecule‐1 interactions at the blood–brain barrier (BBB), is now widely accepted as a potent tool for treating relapsing–remitting MS. This drug is epoch‐making, as it is the first agent to confirm the efficacy of merely inhibiting the transfer of T cells across the BBB in the treatment of MS; however, the risk of a potentially fatal central nervous system opportunistic infection, progressive multifocal leukoencephalopathy, should always be kept in mind. Because the onset of progressive multifocal leukoencephalopathy might be partly due to the almost total blockage of T cells, including those participating in immune surveillance, the development of novel therapies that selectively inhibit only the entrance of pathogenic T cells is now eagerly awaited. In addition to the blockade of mononuclear cell intrusion, restoring the integrity of the BBB might quickly terminate the process of local inflammation. In addition, manipulating the BBB to enhance the transfer of useful molecules, including a variety of growth factors, could facilitate axonal regeneration. Therefore, the BBB is a promising target of future therapeutic strategies in MS.

Association between Infratentorial Onset of Progressive Multifocal Leukoencephalopathy (PML) and Long-Term Exposure to Natalizumab (NAT) (P2.248)

Association between Infratentorial Onset of Progressive Multifocal Leukoencephalopathy (PML) and Long-Term Exposure to Natalizumab (NAT) (P2.248)

Adhesion Molecules as a Therapeutic Target in IBD

Recruitment of circulating leukocytes to areas of inflammation is a key process in the pathophysiology of inflammatory bowel diseases, including ulcerative colitis (UC). This is a finely regulated multistep process in which specialised adhesion and signalling molecules mediate a series of sequential steps. Following activation, integrins expressed on the surface of leukocytes become the key mediators of firm adhesion and emigration through interaction with immunoglobulin superfamily molecules expressed on the vascular endothelium. The anti α4 antibody natalizumab has shown efficacy in inducing and maintaining response and remission in patients with moderate and severe Crohn’s disease. However, a major safety setback involving the onset of progressive multifocal leukoencephalopathy (PML) in 1/1000 treated cases led to limitations on its clinical use and application in UC. The more selective anti α4β7 antibody vedolizumab has proven efficacious for inducing clinical and endoscopic remission in UC. Selective expression of the α4β7 receptor MAdCAM-1, which occurs predominantly in the intestine, may avoid the risk of those central nervous system infectious complications associated with the nonselective blockade of all α4 integrins. Moreover, treatment with anti-MAdCAM-1 or anti-α7 antibody (etrolizumab) showed promising results for inducing remission in UC. In conclusion, the development of safe and effective drugs that target these molecular components of the inflammatory response may yield novel, improved therapies for inflammatory bowel disease (IBD) that address as yet unmet needs.

Immune surveillance and response to JC virus infection and PML

The ubiquitous human polyomavirus JC virus (JCV) is the established etiological agent of the debilitating and often fatal demyelinating disease, progressive multifocal leukoencephalopathy (PML). Most healthy individuals have been infected with JCV and generate an immune response to the virus, yet remain persistently infected at subclinical levels. The onset of PML is rare in the general population, but has become an increasing concern in immunocompromised patients, where reactivation of JCV leads to uncontrolled replication in the CNS. Understanding viral persistence and the normal immune response to JCV provides insight into the circumstances which could lead to viral resurgence. Further, clues on the potential mechanisms of reactivation may be gleaned from the crosstalk among JCV and HIV-1, as well as the impact of monoclonal antibody therapies used for the treatment of autoimmune disorders, including multiple sclerosis, on the development of PML. In this review, we will discuss what is known about viral persistence and the immune response to JCV replication in immunocompromised individuals to elucidate the deficiencies in viral containment that permit viral reactivation and spread.

Natalizumab treatment alters the expression of T-cell trafficking marker LFA-1 α-chain (CD11a) in MS patients

Objective: To determine the long-term effect of natalizumab (NTZ) treatment on the expression of integrins and chemokine receptors involved in the migration of T cells towards the central nervous system (CNS). Methods: We drew the blood of 23 patients just before starting NTZ therapy and every 12 months thereafter, for up to 48 months of treatment. We assessed the ex-vivo expression of phenotype markers (CCR7 and CD45RA), CNS-addressing integrins (CD11a, CD49d and CD29) and chemokine receptors (CXCR3 and CCR6) in CD4+ or CD8+ T-cell subsets by flow cytometry. Results: As compared to the pre-NTZ values, there was a marked increase in central memory (CCR7+/CD45RA-) CD4+ T cells and in effector memory (CCR7-/CD45RA-) CD8+ T cells at 12 and 24 months. In addition to an expected downregulation of both VLA-4 subunits (CD49d/CD29), we also found decreased T-cell expression of CXCR3 at 12 months, and of CD11a (LFA-1 αL subunit) at 12 months, but mostly at 24 months of NTZ treatment. Conclusion: Our data show a nadir of CD11a expression at 2 years of NTZ treatment, at the peak of incidence of progressive multifocal leukoencephalopathy (PML), indirectly suggesting that a lack of these molecules may play a role in the onset of PML in NTZ-treated patients.

A bird's-eye view of T cells during natalizumab therapy

Natalizumab binds to α4 integrins expressed on lymphocytes and monocytes. It blocks the interaction of these integrins with their binding partners on vascular endothelial cells, and thereby prevents immune cells from entering inflamed tissues. Natalizumab is an effective treatment, but it carries the risk of progressive multifocal leukoencephalopathy (PML). Results reported in this issue of Neurology ® are relevant to both the beneficial and adverse effects of natalizumab.1 The authors investigated how natalizumab affects the T-cell receptor (TCR) repertoire of patients with multiple sclerosis (MS). Their main observations are that 1) the TCR repertoire seems to “normalize” during natalizumab treatment, that is, revert to the state observed in healthy subjects, and 2) the onset of PML and immune reconstitution inflammatory syndrome (IRIS) is accompanied or preceded by the appearance of distinct clonal T-cell expansions in blood or CSF.

Changes to anti-JCV antibody levels in a Swedish national MS cohort

BackgroundThe anti-JC virus (JCV) antibody status has been introduced to stratify patients with multiple sclerosis (MS) for higher or lower risk of progressive multifocal leukoencephalopathy (PML).ObjectiveTo assess the potential utility...

Failure of mefloquine therapy in progressive multifocal leukoencephalopathy: Report of two Japanese patients without human immunodeficiency virus infection

Although progressive multifocal leukoencephalopathy (PML) cases showing responses to mefloquine therapy have been reported, the efficacy of mefloquine for PML remains unclear. We report on the failure of mefloquine therapy in two Japanese patients with PML unrelated to human immunodeficiency virus. One of the patients was a 47-year-old male who had been treated with chemotherapy for Waldenström macroglobulinemia, and the other was an 81-year-old male with idiopathic CD4+ lymphocytopenia. Diagnosis of PML was established based on MRI findings and increased JC virus DNA in the cerebrospinal fluid in both patients. Mefloquine was initiated about 5months and 2months after the onset of PML, respectively. During mefloquine therapy, clinical and radiological progression was observed, and JC virus DNA in the cerebrospinal fluid was increased in both patients. Both patients died about 4months and 2months after initiation of mefloquine, respectively. Further studies are necessary to clarify the differences between mefloquine responders and non-responders in PML.

Progressive multifocal leukoencephalopathy associated with immunosuppressive therapy in rheumatic diseases: Evolving role of biologic therapies

To evaluate the association of progressive multifocal leukoencephalopathy (PML) with immunosuppressive therapy for autoimmune rheumatic diseases (ARDs). A Freedom of Information Act request was submitted for all cases of PML within the Food and Drug Administration Adverse Event Reporting System database. ARD cases were selected for further analysis. A total of 34 confirmed cases of PML in the setting of ARDs were identified: 17 had systemic lupus erythematosus, 10 had rheumatoid arthritis, 4 had vasculitis, and 3 had dermatomyositis. Fifteen of these patients were treated with one or more biologic agents: 14 received rituximab (RTX), 6 received anti-tumor necrosis factor (anti-TNF) therapy (5 treated with anti-TNF agent prior to RTX). Four RTX-treated patients were not receiving additional immunosuppressive therapy at the time of PML onset, other than an antimalarial drug and/or low-dose glucocorticoids; all others who were receiving a biologic agent were also receiving one or more synthetic disease-modifying agents. All but 1 patient receiving a biologic agent had at least 1 potential confounding factor for the diagnosis of PML. The remaining 19 confirmed cases of PML among ARD patients were treated with synthetic disease-modifying antirheumatic drugs only, 14 of whom had received an alkylating agent. PML has been reported in patients with ARD treated with various immunosuppressive agents. The limitations of this study preclude definitive attribution of causality. While the paucity of confirmed cases recently exposed to anti-TNF therapy suggests a causal relationship is unlikely, a specific signal is emerging with regard to rituximab and PML. Although this is a rare adverse event associated with RTX therapy, the devastating nature of PML mandates continued vigilance, particularly in patients with current or prior exposure to an alkylating agent.

Reactivation of human polyomavirus JC in patients affected by psoriasis vulgaris and psoriatic arthritis and treated with biological drugs: Preliminary results

Psoriasis vulgaris (PsV) and psoriatic arthritis (PSA) are inter-related heritable inflammatory skin diseases. Psoriatic lesions develop as a result of abnormal immune responses, hyperproliferation and altered differentiation of keratinocytes, and a notable subset of psoriatic patients develops PsA, characterized by joints inflammation. Recently, biological drugs were introduced to treat these diseases. However, this therapy has already been associated with the development of serious life-threatening infections, such as the reactivation of human polyomavirus JC (JCV), responsible for the progressive multifocal leukoencephalopathy (PML), a lethal demyelinating disease caused by oligodendrocytes lytic infection. Therefore, the aims of our study were the investigation of the possible JCV reactivation in PsV and PsA patients treated with adalimumab, etanercept, and methotrexate, performing quantitative real-time PCR in sera and skin biopsies at the time of recruitment (T0) and after 3 (T3) and 6 (T6) months of treatment, and the sequencing analysis of the JCV non-coding control region (NCCR). We found JCV DNA in 5/15 PsV patients and in 2/15 PsA patients and JCV NCCR sequence analysis always showed a structure similar to non-pathogenic CY archetype, with random occurrence of a few irrelevant point mutations. Nevertheless the poor number of patients analyzed, our preliminary data can pave the way for taking into account that the follow-up of JCV DNA detection and the JCV NCCR sequence analysis in psoriatic patients may be important to evaluate the risk of PML onset, considering that patients affected by autoimmune diseases and treated with biologics continue to rise.

Metabolic profile of PML lesions in patients with and without IRIS

To characterize progressive multifocal leukoencephalopathy (PML) lesions by contrast-enhanced MRI and evaluate their metabolism using proton magnetic resonance spectroscopy ((1)H- MRS) in the setting of immune reconstitution inflammatory syndrome (IRIS). A total of 42 patients with PML underwent a clinical evaluation as well as brain MRI and (1)H-MRS at baseline and 3, 6, and 12 months later. The presence of IRIS was determined based on clinical and laboratory criteria. Ratios of N-acetylaspartate (NAA), choline (Cho), myo-inositol (mI), and lipid/lactate (Lip1 and Lip2) to creatine (Cr) were measured and correlated with the presence of contrast enhancement (CE) in PML lesions. IRIS occurred in 16 of 28 (57.1%) PML survivors (PML-S) and 1 of 14 (7.1%) PML progressors (PML-P). Lesions of patients with PML-IRIS showed significantly higher Cho/Cr (p = 0.0001), mI/Cr (p = 0.02), Lip1/Cr (p < 0.0001), and Lip2/Cr (p = 0.002) ratios and lower NAA/Cr (p = 0.02) ratios than patients with PML who did not have IRIS. An elevated Cho/Cr ratio was associated with CE within the (1)H-MRS voxel, whereas lipid/Cr ratios were elevated in PML-IRIS lesions independently of CE. Follow-up until 33 months from PML onset showed persistent elevation of the mI/Cr ratio in lesions of patients with PML-IRIS. A Lip1/Cr ratio greater than 1.5 combined with the presence of CE yielded a 79% probability of IRIS compared with 13% in the absence of these criteria. (1)H-MRS is a valuable tool to recognize and track IRIS in PML and may prove useful in the clinical management of these patients.

Pre-Existing T- and B-Cell Defects in One Progressive Multifocal Leukoencephalopathy Patient

Progressive multifocal leukoencephalopathy (PML) usually occurs in patients with severe immunosuppression, hematological malignancies, chronic inflammatory conditions or receiving organ transplant. Recently, PML has also been observed in patients treated with monoclonal antibodies. By taking advantage of the availability of samples from a multiple sclerosis (MS) patient treated with natalizumab, the antibody anti-α4 integrin, who developed PML and was monitored starting before therapy initiation, we investigated the fate of T and B lymphocytes in the onset of PML. Real-time PCR was used to measure new T- and B-cell production by means of T-cell receptor excision circle (TREC) and K-deleting recombination excision circle (KREC) analysis and to quantify transcripts for CD34, terminal-deoxynucleotidyltransferase, and V pre-B lymphocyte gene 1. T- and B-cell subsets and T-cell heterogeneity were measured by flow cytometry and spectratyping. The data were compared to those of untreated and natalizumab-treated MS patients and healthy donors. Before therapy, a patient who developed PML had a low TREC and KREC number; TRECs remained low, while KRECs and pre-B lymphocyte gene 1 transcripts peaked at 6 months of therapy and then decreased at PML diagnosis. Flow cytometry confirmed the deficient number of newly produced T lymphocytes, counterbalanced by an increase in TEMRA cells. The percentage of naive B cells increased by approximately 70% after 6 months of therapy, but B lymphocyte number remained low for the entire treatment period. T-cell heterogeneity and immunoglobulins were reduced.Although performed in a single patient, all results showed that an immune deficit, together with an increase in newly produced B cells a few months after therapy initiation, may predispose the patient to PML. These findings indicate the TREC/KREC assay is a potential tool to identify patients at risk of developing PML and may provide insights into the immunological involvement of monoclonal antibody-associated therapies.

Immune Defects of B- and T-Cell Compartments in Natalizumab-Induced Progressive Multifocal Leukoencephalopathy,

Abstract 3228▪▪This icon denotes a clinically relevant abstract Objective:Progressive multifocal leukoencephalopathy (PML) is a rare, but often fatal demyelinating brain disease caused by the JC virus, which usually occurs in immunosuppressed patients, including those with hematological malignancies or receiving monoclonal antibodies-based immunotherapies. PML is likely the result of a complex combination of several pathogenic mechanisms, such as alterations of peripheral cell-mediated immunity and mobilization of JC virus-carrying CD34+-hematopoetic stem cells and pre-B-cells. Taking advantage of the availability of samples from a multiple sclerosis (MS) patient treated with the anti-α4β1 monoclonal antibody natalizumab who developed PML, which was monitored for 35 months since before therapy initiation, we investigated the role of B and T lymphocytes in PML onset. Methods:Real-Time PCR was used to measure the release of T and B cells from the production sites by means of T-cell receptor excision circles (TRECs) and K-deleting excision circles (KRECs) analysis and to quantify transcripts for immature hematopoietic cells such as terminal deoxynucleotidyl transferase, CD34, and pre-B lymphocyte gene 1. Naïve and mature T- and B-cell subsets were identified by flow cytometry, T-cell heterogeneity was quantified by spectratyping and IgA, IgG and IgM by turbidimetric assay. Data were compared to those of untreated and natalizumab-treated MS patients and healthy donors. Results:After 34 months of natalizumab therapy, a 42 years old female developed PML, diagnosed on the basis of magnetic resonance imaging and JC virus positivity in cerebrospinal fluid. Before therapy, her thymus and bone marrow produced a significant low number of TRECs+ and KRECs+ cells. While TRECs remained low during all therapy period, KRECs and transcripts for pre-B lymphocyte gene 1, which is selectively expressed in pre-B cells, peaked after 6 months of therapy, remained high at 12 and 15 months of treatment, and then decreased at the moment of PML onset. Flow cytometry confirmed a deficient production of CD4+CD45RA+CCR7+CD31+ recent T emigrants, counterbalanced by an increased number of CD8+CCR7–CD45RA+ TEMRA cells for all observation period, but showed a modification of peripheral CD4 and CD8 cell number only at the moment of PML. While the percentage of naïve B cells increased by about 70% after 6 months of therapy, the number of B lymphocytes within each B-cell subpopulations remained low for the entire treatment period. T-cell repertoire and immunoglobulin production were altered. Interpretation:Although performed in a single patient, data all agree in demonstrating that a deficient production of new TRECs+ T lymphocytes, together with an increase of newly produced KRECs+ B cells just few months after therapy beginning may predispose to PML. These findings encourage further researches on the utility of the TRECs/KRECs assay as a potential tool for the identification of patients at risk of developing PML after monoclonal antibodies-based therapies. Disclosures:No relevant conflicts of interest to declare.

Progressive Multifocal Leukoencephalopathy (PML) Development Is Associated With Mutations in JC Virus Capsid Protein VP1 That Change Its Receptor Specificity

Progressive multifocal leukoencephalopathy (PML), a fatal demyelinating disease caused by JC virus (JCV) infection of oligodendrocytes, may develop in patients with immune disorders following reactivation of chronic benign infection. Mutations of JCV capsid viral protein 1 (VP1), the capsid protein involved in binding to sialic acid cell receptors, might favor PML onset. Cerebrospinal fluid sequences from 37/40 PML patients contained one of several JCV VP1 amino acid mutations, which were also present in paired plasma but not urine sequences despite the same viral genetic background. VP1-derived virus-like particles (VLPs) carrying these mutations lost hemagglutination ability, showed different ganglioside specificity, and abolished binding to different peripheral cell types compared with wild-type VLPs. However, mutants still bound brain-derived cells, and binding was not affected by sialic acid removal by neuraminidase. JCV VP1 substitutions are acquired intrapatient and might favor JCV brain invasion through abrogation of sialic acid binding with peripheral cells, while maintaining sialic acid-independent binding with brain cells.