Frequent expression of activation-induced cytidine deaminase in diffuse large B-cell lymphoma tissues from persons living with HIV

Abstract

Objective: The increased risk for persons living with HIV to develop diffuse large B-cell lymphoma (DLBCL) even in the post-antiretroviral therapy eras suggests a role beyond immunosuppression in lymphoma development. However, the mechanisms leading to lymphoma in the HIV setting are not fully understood. HIV is known to induce activation-induced cytidine deaminase (AID) levels in nonneoplastic B cells in vitro and chronic AID expression may play an important role in lymphomagenesis. Although AID expression is observed in B-cell lymphoma, studies in HIV-associated DLBCL are limited.

Design: In this study, we conducted a retrospective review of DLBCL tissues from patients with and without HIV infection to compare expression of AID and B-cell receptors potentially involved in HIV and B-cell interaction.

Methods: We evaluated DLBCL formalin-fixed paraffin-embedded tissues from 72 HIV-seropositive and 58 HIV-seronegative patients for AID, DC-SIGN, and CD40 protein expression. BCL2 and MYC, two well established prognostically significant oncoproteins in DLBCL, were also assessed at the protein and mRNA levels. Subset analysis was performed according to DLBCL subtype and EBV status.

Results: Of note, AID expression was more frequent in HIV-associated DLBCL compared with non-HIV-associated DLBCL regardless of cell-of-origin subtype, and also displayed significantly less BCL2 expression. Despite no direct correlation with AID expression, the HIV-DLBCL tissues also exhibited high levels of the DC-SIGN receptor.

Conclusion: Collectively, these findings support a potential role for AID in the pathogenesis of HIV-associated lymphomas and suggest the need of further investigations into the involvement of the DC-SIGN receptor-signaling pathway.

Fig. 1.

EBV co-infection in HIV(+) DLBCL and comparison of BCL2 and MYC expression in HIV(−) and HIV(+) DLBCL. (a) Number of GCB and non-GCB DLBCL cases according to EBV co-infection in HIV(+) DLBCL samples. EBV status was determined by EBER. Differences between the proportions were determined by Fisher’s exact test with *P < 0.05. Percent tumor cells stained positive for BCL2 (b) and MYC (c) protein in HIV(−) and HIV(+) DLBCL. Log2 transformed BCL2 (e) and MYC (f) mRNA levels in HIV(−) and HIV(+) DLBCL. Each dot represents an individual tumor with mean ± SEM. Differences were determined by the Student’s t-test and P-values were adjusted using Sidak’s multiple test correction with ** P < 0.01 and ***P < 0.001.

Fig. 2.

AID expression in HIV(+) DLBCL tissues compared to HIV(−) DLBCL. (a-c) Representative images of positive AID immunohistochemical staining in a tonsil control tissue (a), and in HIV(−) and HIV(+) DLBCL tissues (b and c, respectively). Original magnification, 200x (a, inset at 600x) and 600x (b,c) with scale bars, 200 and 20 μm. (d) Comparison of AID expression in HIV(−) and HIV(+) DLBCL as percent tumors cells staining positive. The Student’s t-test was used to determine a significant difference with *P < 0.05. Each dot represents an individual tumor with mean ± SEM. (e) Number of HIV(−) and HIV(+) DLBCL tissues with positive AID staining at 5%, 25%, and 75% cutoffs. Differences between the proportions were determined by Fisher’s exact test with ** P < 0.01. (f) Percent tumor cells positive for AID in GCB and non-GCB DLBCL tissues according to HIV sero-status. Each dot represents an individual tumor with mean ± SEM.

Fig. 3.

DC-SIGN expression in HIV(+) DLBCL tissues compared to HIV(−) DLBCL. (a-c) Representative images of positive DC-SIGN immunohistochemical staining in a tonsil control tissue (a), and in HIV(−) and HIV(+) DLBCL tissues (b and c, respectively). Original magnification, 200x (a, inset 600x) and 600x (b,c) with scale bars, 200 and 20 μm. (d) Comparison of DC-SIGN expression in HIV(−) and HIV(+) DLBCL as percent tumors cells staining positive. The Student’s t-test was used to determine a significant difference with *P < 0.05. Each dot represents an individual tumor with mean ± SEM. (e) Number of HIV(−) and HIV(+) DLBCL tissues with positive DC-SIGN staining at 5%, 25%, and 75% cutoffs. Differences between the proportions were determined by Fisher’s exact test with ** P < 0.01. (f) Percent tumor cells positive for DC-SIGN in GCB and non-GCB DLBCL tissues according to HIV sero-status. Each dot represents an individual tumor with mean ± SEM.

Fig. 4.

CD40 expression in HIV(+) DLBCL tissues compared to HIV(−) DLBCL. (a-c) Representative images of positive CD40 immunohistochemical staining in a tonsil control tissue (a), and in HIV(−) and HIV(+) DLBCL tissues (b and c, respectively). Original magnification, 200x (a, inset at 600x) and 600x (b,c) with scale bars, 200 and 20 μm. (d) Comparison of CD40 expression in HIV(−) and HIV(+) DLBCL as percent tumors cells staining positive. The Student’s t-test was used to determine there was no significant difference. Each dot represents an individual tumor with mean ± SEM. (e) Number of HIV(−) and HIV(+) DLBCL tissues with positive CD40 staining at 5%, 25%, and 75% cutoffs. Differences between the proportions were determined by Fisher’s exact test. (f) Percent tumor cells positive for CD40 in GCB and non-GCB DLBCL tissues according to HIV sero-status. Each dot represents an individual tumor with mean ± SEM.

Figure 5.

AID expression in HIV(+) DLBCL according to DC-SIGN and CD40. (a,b) Spearman correlations between percent AID positive tumor cells in HIV(+) DLBCL and either percent DC-SIGN (a) or percent CD40 (b) positive tumor cells within the same DLBCL tissue. Each dot represents an individual tumor and the dashed lines show the 95% confidence interval.