Functional Characterization of BK Virus-Specific CD4⁺T Cells with Cytotoxic Potential in Seropositive Adults

Abstract

BK polyomavirus (BKV) reactivation is associated with a failure of T cell immunity in kidney transplant patients, and may lead to BKV-associated nephropathy (BKVN) and loss of the allograft. BKV reactivation in hematopoietic stem cell transplant recipients is associated with hemorrhagic cystitis. We have investigated T cell responses to overlapping peptide mixtures corresponding to the whole BKV major T antigen (TAg) and major capsid protein (VP1) in peripheral blood mononuclear cell samples from a cohort of healthy BKV-seropositive subjects. The majority of these individuals possessed populations of both CD8(+) and CD4(+) T cells specific for these BKV antigens. After expansion in culture, the majority of the BKV-specific CD4(+) T cells, in addition to expressing CD40L (CD154), secreted both interferon (IFN)-gamma and tumor necrosis factor (TNF)-alpha, contained both granzyme A and granzyme B, and degranulated/mobilized CD107 in response to antigen-specific stimulation. These T cells thus represent potentially functional BKV-specific cytotoxic CD4(+) T lymphocytes. Secretion of both TNF-alpha and IFN-gamma by CD154(+)CD4(+) T cells on BKV-specific stimulation was associated with higher levels of granzyme B and a higher proportion of degranulating cells compared with CD154(+)CD4(+) T cells producing only IFN-gamma or neither cytokine. These healthy subjects also harbored populations of functional CD8(+) T cells specific for one or more of three newly defined HLA-A 02-restricted cytotoxic T lymphocyte epitopes within the BKV TAg as well as two HLA-A 02-restricted epitopes within the BKV VP1 we have previously described. The BKV-specific CD4(+) T cells characterized in this study may play a part in maintaining persistent memory T cell responses to the virus and thus contribute to the immune control of BKV in healthy individuals.

The Polyomavirus BK Large T-Antigen-Derived Peptide Elicits an HLA-DR Promiscuous and Polyfunctional CD4+T-Cell Response

“…Similar to our findings, BKV-sensitized T cells were noted to produce both IFN-␥ and TNF-␣ in a prior study of healthy subjects (49). P313-specific CD4 ϩ T-cell clones also expressed CD107a, a marker that correlates with release of perforin and granzyme B (19).…”

“…Notably, several other studies also found it necessary to expand peripheral blood mononuclear cells for comparable durations prior to being able to detect virus-sensitized cells. The responses detected in this fashion appear to be functionally important, since high frequencies of cytotoxic T cells correlate with resolution of BKV infection in kidney transplant patients (6,14,41,49) and of the related polyomavirus JCV infection in patients with progressive multifocal encephalopathy (10). The resulting increase in frequency of detectable BKV-reactive T cells could be due to expansion of preexisting memory cells, since the majority of the subjects tested (12/15 subjects) were BKV seropositive.…”

“…As reported by others, we were unable to detect T-cell responses to BKV LTA without initial expansion of PBMC in vitro. This problem likely reflects low frequencies of BKV-sensitized cells in peripheral blood (6,41,49) and could be overcome by culturing PBMC with BKV LTA PepMix in the presence of IL-2 prior to ELISPOT testing. Notably, several other studies also found it necessary to expand peripheral blood mononuclear cells for comparable durations prior to being able to detect virus-sensitized cells.…”

Stimulation of BK Virus DNA Replication by NFI Family Transcription Factors

“…Immune suppression is associated with the activation of BKV replication (2,26,89), and stress-related injury, repair, regeneration, and differentiation are also associated (27,37), but the responsible mechanisms have not been defined.…”

Perforin level in CD4+ T cells from patients with systemic lupus erythematosus

“…The PRF1 gene is expressed primarily in NK cells and effector CD8 + T cells [31,32]. PRF1 is also expressed in a subpopulation of cytotoxic CD4 + T cells, which may combat various pathogens (33)(34)(35)(36)(37)(38)(39). An increased number of cytotoxic CD4 + T cells has been observed in patients with multiple sclerosis, rheumatoid arthritis, inflammatory bowel disease, and acute coronary syndromes [20][21][22][23].…”