To the Editor
Progressive multifocal leukoencephalopathy (PML), caused by JC virus (JCV), has remained one of the deadliest opportunistic infections in HIV-infected patients despite combined antiretroviral therapy (cART), with only a 50% one-year survival rate. PML has also been diagnosed in patients with autoimmune diseases treated with immunomodulators such as natalizumab1. A consistent feature of PML is the predominant location of lesions in the subcortical white matter on MRI, with corresponding demyelinating areas at the gray-white junction (GWJ) on histology. Interestingly, 64% of brain metastases are also found at the GWJ2. This is likely due to hemodynamic factors, where emboli of cancerous cells bind to endothelial receptors and remain in areas of sudden reduction of vascular caliber. Ultrastructural studies of the cortical microvasculature showed abrupt narrowing of perforating end-arterioles coming from the brain surface into the cortical gray matter, with a dense bed of deep cortical capillaries at the GWJ3.
JC virions may circulate either cell-free or in association with B-lymphocytes4. The virions can attach to the surface of a number of cell types, and have the capability to aggregate type O erythrocytes, which is the basis of the hemagglutination inhibition assay (HAI), for detection of JCV antibody in patients’ serum. The presence of JCV on the surface of B lymphocytes in individuals with type O blood may promote the aggregation of lymphocytes and erythrocytes, causing cell clumping that becomes impacted in narrow cortical capillaries with low blood flow at the GWJ. We sought to determine whether type O blood was a risk factor for PML.
Methods
We characterized ABO blood group antigen on blood samples of 76 PML patients (62 Caucasians and 14 African Americans (AA)) followed in our neurology clinic. Due to their low number and different distribution of ABO blood group, AA were excluded from statistical analyses. Of the 62 Caucasian patients with PML, 36 (58%) were HIV+, 14 (23%) had underlying hematologic or oncologic diseases, and 12 (19%) included patients with autoimmune diseases, transplant recipients, idiopathic lymphocytopenia or other forms of minimal immunosuppression. One patient had natalizumab-treated multiple sclerosis (MS).
Results
Of 62 PML patients, 31 (50%) were type O, 20 (32%) type A, 8 (13%) type B, and 3 (5%) type AB (Table). By comparison to the blood type frequency of Caucasians in the United States5, the odds ratio of PML in type O patients compared with all other blood types was 1.22 (95%CI 0.72 to 2.07; p=0.45), while it was 0.71 (95%CI 0.39 to 1.24; p=0.24) in type A patients compared to patients with all other blood types. Based on this pilot data, to reject the null hypothesis that blood type has no influence on PML risk would require 794 PML patients with type O and 295 PML patients with type A blood.
Table.
Distribution of ABO blood types amongst Caucasian PML patients and the general population.
| Blood type | ||||
|---|---|---|---|---|
| O | A | B | AB | |
| Caucasian-PML | 50% (31) | 33% (20) | 13% (8) | 5% (3) |
| Caucasian-USA | 45% | 40% | 11% | 4% |
Discussion
As of March 2013, approximately 112,200 patients have received natalizumab, mainly for treatment of MS, and 343 have developed PML. Patients with anti-JC virus antibodies, prior use of immunosuppressants, and treatment with natalizumab for 24 months or longer have an approximate 1 in 90 risk of developing PML6. If our data are reproduced in other studies, the implication is that among these high risk individuals, extrapolation of our pilot data would predict one extra case of PML per 409 type O patients and 1 fewer case of PML per 310 type A patients. Larger PML cohort studies, including MS patients treated with natalizumab or other immunosuppressants, and a more diverse ethnic population will be necessary to determine the role of O and A blood types in PML risk stratification. Future algorithms might include type O blood testing in addition to the currently accepted risk factors mentioned above when deciding whether MS patients are suitable candidates for natalizumab. If verified, our hypothesis could also pave the way for new avenues of research on PML pathogenesis.
Acknowledgments
This work was supported in part by grants BU-CHART/NIH grant T32 AI052074 (NIAID) to MNK, and R01 NS 074995 and 047029 and K24 NS 060950 to IJK for design of the study, collection of the data, and preparation and review of the manuscript. This work was conducted with support from Harvard Catalyst | The Harvard Clinical and Translational Science Center (National Center for Research Resources and the National Center for Advancing Translational Sciences, National Institutes of Health Award 8UL1TR000170-05 and financial contributions from Harvard University and its affiliated academic health care centers) in the management, analysis, and interpretation of the data.
Footnotes
The authors have no conflicts of interest to disclose.
The content is solely the responsibility of the authors and does not necessarily represent the official views of Harvard Catalyst, Harvard University and its affiliated academic health care centers, or the National Institutes of Health. The authors have full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis.
This article is also available online: http://archneur.jamanetwork.com/article.aspx?articleid=1754577
Contributor Information
Michael N. Khoury, Email: mkhoury1@bidmc.harvard.edu.
Murray A. Mittleman, Email: mmittlem@bidmc.harvard.edu.
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