Increased Peripheral T Cell Responses to EBV-Infected Cells with Frequent Detection of EBV-DNA In Plasma and Viral mRNA In Peripheral B-Cells In Immunocompetent EBV-Positive Diffuse Large B-Cell Lymphoma Patients

It is well known that immunocompromised patients(pts) such as post-transplantation or HIV infection are at increased risk of EBV-associated B-cell lymphoproliferaitive disorders. However, the immunological status of immunocompetent EBV-positive diffuse large B-cell Lymphoma (DLBCL) has not been well elucidated. For example, EBV-positive DLBCL in the elderly is defined as an EBV-positive clonal B-cell lymphoid proliferation occurring in pts more than 50 years of age and without any known immunodeficiency in WHO classification 2008, accounting for 5 – 10% of DLBCL in Japan. This disease is speculated to be related to the immunological deterioration accompanying the aging process. We conducted a multi-center prospective study to assess EBV status and the T cell response to EBV of peripheral blood (PB) in EBV-positive DLBCL in comparison with EBV-negative DLBCL pts and normal old-healthy persons (old-HPs).

Fifteen newly-diagnosed pts with EBV-positive DLBCL, 8 pts with EBV-negative DLBCL, and 16 old-HPs were enrolled. Median ages of pts with EBV-positive DLBCL, pts with EBV-negative DLBCL, and old-HPs were 74.5 years (range 29–82 years), 71 years (48-79), and 65 years (60-74), respectively. Among the 15 pts with EBV-positive DLBCL, 2 were pyothorax-associated lymphoma, 2 were treated with methotrexate for rheumatoid arthritis, and the remaining 11 pts were without past histories predisposing to immunodeficiency. The diagnosis of EBV-positive DLBCL was made by positive signals for in situ hybridization using EBV-encoded small RNA (EBER) on paraffin section. To analyze T cell reactivity to autologous EBV-infected B-cell lymphoblastoid cell lines (LCL), CFSE-labeled peripheral blood mononuclear cells (PBMCs) were co-cultured with irradiated autologous LCL, and the division indices (DI) of CD4⁺ and CD8⁺ T cells were determined on day 5 (Cytometry 34:143, 1998). Percentage of proliferating CFSE^low IFN-γ⁺CD4⁺ T cells and CFSE^low IFN-γ⁺CD8⁺ T cells was assessed on day 7. EBV DNA load in PBMCs and plasma was determined by quantitative real-time PCR. CD19⁺ B cells were separated from of PBMCs by immunomagnetic sorting, and viral mRNA expression of B cells was quantified by one-step multiplex real-time RT-PCR.

(1) Plasma EBV-DNA was detectable in 13 of the 15 EBV-positive DLBCL pts but in none of the 8 EBV-negative DLBCL pts or the 16 old-HPs. Copy number of EBV-positive DLBCL was significantly higher than EBV-negative DLBCL (p<0.00001) or old-HPs (p=0.0001). EBV-DNA in PBMC was positive in 10 of the 15 EBV-positive DLBCL pts, 2 of 8 EBV-negative DLBCL pts, and 2 of 15 old-HPs. (2) EBER1 of PB B cells was detected in all 10 EBV-positive DLBCL pts, 4 of 7 EBV-negative DLBCL pts, and 7 of 14 old-HPs. BamHI A rightward transcripts (BARTs) of B-cells was detected in 8 of 10 EBV-positive DLBCL pts, 3 of 10 EBV-negative DLBCL pts, and 2 of 14 old-HPs. Latent membrane protein 2 (LMP2) of B cells was detected in 2 of 10 EBV-positive DLBCL pts, 2 of 14 old-HPs, and none of 5 EBV-negative DLBCL pts. LMP1 of B cells was detected in 1 of 10 EBV-positive DLBCL pts, none of 7 EBV-negative DLBCL pts, and none of 14 old-HPs. EBV-encoded nuclear antigen 1 (EBNA1) or EBNA2 were not detected in any of the pts nor old-HPs. (3) DI of CD4⁺ T cells for 5 days in EBV-positive DLBCL (median 1.41) was significantly higher than in old-HPs (median 0.53) (p=0.0009), and DI of CD8⁺ T cells of EBV-positive DLBCL (median 1.94) showed a higher tendency than old-HP (median 1.35). (4) Percentage of CFSE-low IFN-γ⁺CD4⁺ T cells in EBV-positive DLBCL (median 9.8%) was significantly higher than in old-HPs (median 2.2%) (p=0.002), and percentage of CFSE-low IFN-γ⁺CD8⁺ T cells in EBV-positive DLBCL (median 12.0%) was significantly higher than in old-HPs (median 6.6%)(p=0.025).

Measurement of the plasma EBV-DNA copy number is a good indicator for the diagnosis of EBV-positive DLBCL, and the frequent detection of EBV viral mRNA of peripheral B-cells in EBV-positive DLBCL pts might be associated with greater viral load. Proliferative and INF-γ secreting responses of both peripheral CD4⁺ T cells and CD8⁺ T cells to EBV-infected cells were increased in EBV-positive DLBCL compared to old-HPs, which might be driven by an elevated viral load. These findings suggest that systemic immunological reaction to EBV might be intact in EBV-positive DLBCL.

No relevant conflicts of interest to declare.