The effect of the BK polyomavirus large T antigen on the function and maturity of the CD4+ T cell subsets in kidney transplant recipients

Abstract

Background: In kidney transplant recipients (KTRs) who are immunosuppressed, human BK polyomavirus (BKPyV) infection can be reactivated, resulting in BKPyV-associated nephropathy (BKPyVN). Considering that BKPyV inhibits CD4⁺ T cell differentiation, we investigated the effect of BKPyV large T antigen (LT-Ag) on the maturation of CD4⁺ T cell subsets during active BKPyV infection.

Methods: In this cross-sectional study, we examined the following groups: 1) five KTRs with active viral infection (BKPyV⁺ KTRs), 2) five KTRs without active viral infection (BKPyV^-KTRs), and 3) five healthy controls. We measured the frequency of CD4⁺ T cells and their different subsets, such as naive T cells, central memory T cells (Tcm), and effector memory T cells (Tem). All these subsets were analyzed by flow cytometry in peripheral blood mononuclear cells (PBMCs) stimulated with the overlapping BKPyV LT-Ag peptide pool. In addition, CD4⁺ T cell subsets were analyzed by flow cytometry for the presence of CD4, CCR7, CD45RO, CD107a, and granzyme B (GB). In addition, mRNA expression of transcription factors (TFs) such as T-bet, GATA-3, STAT-3, and STAT-6 was examined. The probability of inflammation with perforin protein was examined by SYBR Green real-time PCR.

Results: After stimulation of PBMCs, naive T cells (CD4⁺CCR7⁺CD45RO^-) (p = 0.9) and CD4⁺ T cells which release CD107a⁺ (CD4⁺CD107a⁺Geranzyme B^-) (p = 0.9) T cells were more abundant in BKPyV⁺ KTRs than in BKPyV^- KTRs. In contrast, central memory T cells (CD4⁺CCR7⁺CD45RO⁺) (p = 0.1) and effector memory T cells (CD4⁺CCR7^-CD45RO⁺) (p = 0.1) were more abundant in BKPyV^- KTRs than in BKPyV⁺ KTRs. The mRNA expression levels of T-bet, GATA-3, STAT-3, and STAT-6 were significantly higher (p < 0.05) in BKPyV^- KTRs than in BKPyV⁺ KTRs which may be due to a higher differentiation level of CD4⁺ T cells. Due to inflammation, the mRNA expression level of perforin was higher in BKPyV⁺ KTRs, than in BKPyV^- KTRs, but the difference was not significant (p = 0.175).

Conclusions: The high number of naive T cells after PBMC stimulation with the LT-Ag peptide pool was observed in BKPyV⁺ KTRs due to the interaction of LT-Ag with T cells. This means that BKPyV by using its LT-Ag can inhibit the naive T cell differentiation to other T cell subsets like central and effector memory T cells. However, the frequency of CD4⁺ T cell subsets and the combination of the activities of these cells with the expression profile of the target genes in this study may be efficient in treating and diagnosing BKPyV infections in kidney recipients.

Keywords: BK polyomavirus; CD4(+) T cell; Kidney transplantation; Large T antigen.