Kinetics of CD8⁺ effector T cell responses and induced CD4⁺ regulatory T cell responses during Friend retrovirus infection

Abstract

Cytolytic CD8 + T cells are critical for the control of acute Friend virus (FV) infection yet they fail to completely eliminate the virus during chronic infection because they are functionally impaired by regulatory T cells (Treg). We performed a kinetic analysis of T cell responses during FV infection to determine when dysfunction of CD8 + T cells and suppressive activity of CD4 + regulatory T cells develops. At 1 week post infection, virusspecific CD8 + T cells with effector phenotype and cytolytic potential expanded. Peak expansion was found at 12 days post infection, correlating with peak viral loads. After 2 weeks when viral loads dropped, numbers of activated CD8 + T cells started to decline. However, a population of virus-specific CD8 + T cells with effector phenotype was still detectable subsequently, but these cells had lost their ability to produce granzymes and to degranulate cytotoxic molecules. Contemporaneous with the development of CD8 + T cell dysfunction, different CD4 + T cell populations expressing cell surface markers for Treg and the Treg-associated transcription factor Foxp3 expanded. Transfer as well as depletion experiments indicated that regulatory CD4 + cells developed during the second week of FV infection and subsequently suppressed CD8 + T cell functions, which was associated with impaired virus clearance.

CD137 Agonist Therapy Can Reprogram Regulatory T Cells into Cytotoxic CD4+ T Cells with Antitumor Activity

“…Intracellular granzyme B (monoclonal anti-human granzyme B Ab allophycocyaninconjugated; Invitrogen) was performed as described previously (20). Dead cells for cell-surface and intracellular staining were excluded by using Fixable Viability Dye (eBioscience).…”

Premature Terminal Exhaustion of Friend Virus-Specific Effector CD8+ T Cells by Rapid Induction of Multiple Inhibitory Receptors

“…The pentamer used was purchased from ProImmune (Oxford, U.K.). All three cysteine residues in the epitope peptide were replaced with aminobutyric acid to prevent interpeptide disulfide bonding (25). This variant peptide was shown to be recognized by CD8 + T cells specific for gag 75-83 /D b (25).…”

“…All three cysteine residues in the epitope peptide were replaced with aminobutyric acid to prevent interpeptide disulfide bonding (25). This variant peptide was shown to be recognized by CD8 + T cells specific for gag 75-83 /D b (25). Abs to the following molecules were purchased from BD Biosciences (CD3, CD4, CD8, Ter119, and CD11b), BioLegend (CD43 [1B11], CD25, PD-1, CD69, CD62L, CD122, CD127, Tim-3, LAG-3, CTLA-4, FasL, TRAIL, PD-L1, PD-L2, CD11c, and FoxP3), or Invitrogen (Carlsbad, CA; granzyme B).…”

“…Previous studies reported that although virus-specific CD8 + T cells acquired effector functions at an early stage of infection, these cells displayed a profound functional impairment during the chronic phase (24)(25)(26). This virus-specific memory CD8 + T cell dysfunction in the chronic phase has been attributed to suppression by virus-induced regulatory T (Treg) cells, because FV infection results in more Treg cells during the chronic phase (24).…”

“…Support for these ideas has mainly come through an adoptive transfer approach by which TCRtransgenic CD8 + T cells transferred into acutely infected mice developed proper effector function, whereas cells transferred into chronically infected animals showed weaker cytokine production (24). Another piece of evidence for Treg cell-mediated CD8 + T cell dysfunction in chronically infected mice was that endogenous CD8 + T cells in acutely infected mice produced significant amounts of granzymes, whereas the production of granzymes by CD8 + T cells during the chronic phase of FV infection was much weaker (25,26). Because these studies did not take into consideration the potentially differential priming conditions (e.g., Ag doses and inflammatory stimuli between the acute and memory phases of FV infection and the stages of CD8 + T cell differentiation from effector to memory), it is unclear whether the dysfunction of FV-specific CD8 + T cells is due solely to the presence of virus-induced Treg cells, as is when and how FV-specific CD8 + T cells suffer functional defects throughout the entire course of FV infection.…”