Detection of JC virus-specific immune responses in a novel humanized mouse model

Abstract

Progressive Multifocal Leukoencephalopathy (PML) is an often fatal disease caused by the reactivation of the JC virus (JCV). Better understanding of viral-host interactions has been hampered by the lack of an animal model. Engrafting NOD/SCID/IL-2-Rg (null) mice with human lymphocytes and thymus, we generated a novel animal model for JCV infection. Mice were inoculated with either a PML isolate, JCV Mad-4, or with JCV CY, found in the kidney and urine of healthy individuals. While mice remained asymptomatic following inoculation, JCV DNA was occasionally detected in both the blood and the urine compartments. Mice generated both humoral and cellular immune responses against JCV. Expressions of immune exhaustion marker, PD-1, on lymphocytes were consistent with response to infection. Using this model we present the first in vivo demonstration of virological and immunological differences between JCV Mad-4 and CY. This model may prove valuable for studying JCV host immune responses.

Figure 1. Detection of JCV DNA in the urine and blood of JCV inoculated humanized BLT mice.

Only positive data are shown. (A) Urine samples were collected day 7, 22, 35, 49, 77, 91, and 104 post inoculation. JCV CY inoculation resulted in an early detection of JCV DNA in the urine on day 7 compared to first detection of JCV Mad-4 in the urine on day 77. (B) Blood samples were collected 24, 44, 65, 86, and 106 days post inoculation. Inoculation with JCV Mad-4 resulted in more frequent detection of JCV DNA in the blood compared to JCV CY. Unique symbols are used for individual mice; CY: JCV CY; Mad-4: JCV Mad-4.

Figure 2. Humoral immune responses in JCV-inoculated humanized BLT mice.

Anti-JCV IgM were detected 42–103 days post inoculation. JCV Mad-4 inoculation elicited a stronger humoral immune response than JCV CY inoculation. Quantitative IgM values are expressed on a logarithmic scale. Dashed line: cut-off for positive values (OD450 nm = 0.039).

Figure 3. Humanized BLT mice inoculated with JCV displayed cellular immune responses against JCV VP1 antigens.

(A) Intracellular staining (ICS) of splenocytes detected an increased IFN-γ expression on both CD4⁺ and CD8⁺ T cells, after stimulation with JCV peptides. (B) Culturing splenocytes with JCV capsid protein VP1 peptide pools for 12 days and then stimulated with the peptide pool a second time for ICS increased IFN-γ expression on both CD4⁺ and CD8⁺ T cells in a mouse inoculated with Mad-4, but not in a PBS-injected mouse. (C) Tetramer staining detected JCV VP1 epitope-specific CD8⁺ T cells after stimulation with A*0201-restricted JCV VP1 p100 peptide in mice inoculated with either JCV Mad-4 or CY, but not in a PBS-injected mouse. Percentages of positive cells are indicated.

Figure 4. JCV-inoculated humanized BLT mice showed increased expression of the cell exhaustion marker, PD-1, on splenocytes.

PD-1 expression was measured on splenocytes after stimulation with JCV VP1 peptide pools. A significantly higher percentage of CD4⁺ and CD8⁺ T cells expressed PD-1 in either the JCV Mad-4 or CY mice as compared to the PBS mice. Bars illustrate the means and standard deviation above the means in each group.

Figure 5. JCV-inoculated humanized BLT mice showed rare detection of JCV VP1 protein in the kidney.

Immunohistochemistry staining of JCV VP1 protein was not detected in the kidney of PBS-inoculated mice (A), but was detected in rare kidney cells in JCV Mad-4 inoculated mice (B). The images are magnified 40-fold, and the inset is magnified 100-fold. Scale bar = 100 µm.