Different responses are elicited in cytotoxic T lymphocytes by different levels of T cell receptor occupancy.

Abstract

SummaryWe have investigated the level of TCR occupancy required to elicit different biological responses in human CTL clones specific for an influenza matrix peptide. Specific cytotoxicity could be detected at extremely low peptide concentrations (10 -t2 to 10 -15 M). However, IFN-',/production, responsiveness to IL-2 and Ca ++ fluxes were observed only at peptide concentrations > 10 -9 M, while autonomous proliferation required even higher peptide concentrations. In parallel experiments we measured TCR downregulation to estimate the number of TCRs triggered. We observed that at low peptide concentrations, where only cytotoxicity is triggered, TCI( downregulation was hardly detectable. Conversely, induction of IFN-~/production and proliferation required triggering of at least 20-50% of TCRs.Taken together these results indicate that a single CTL can graduate different biological responses as a function of antigen concentration and that killing of the specific target does not necessarily result in full activation. It is well known that naive CD8 § T cells and mature CTL have different requirements for activation. On the one hand it has been shown that naive T cells require high antigen concentrations (1-3), professional APCs (4, 5) and T cell help (1, 6-8) in order to proliferate and mature into effector cells. On the other hand, mature CTL can kill any target cell displaying very low numbers of peptide-MHC complexes (9), even lower than that required to trigger Th cells (10, 11). These findings have generally been interpreted as evidence that the responsiveness of CTL to antigen is increased after activation and that CTL are far more sensitive than Th cells.We have recently demonstrated that TCP-, downregulanon can be used to measure the number of TCRs triggered at the level of T-APC interaction. Using this assay we observed that in Th clones activation to IFN-~ production requires that ~30% of the TCt(s are triggered (12). Here we investigated the relationship between antigen concentration, TCR occupancy, and the induction of different biological responses in CTL. We found that in human CTL clones, cytotoxicity can be elicited by triggering a very small number of TCt(s, in conditions where no other responses can be detected. At increasing levels of TCR. occupancy, helper-dependent and -independent proliferation and IFN-~/production were observed as a function of the number of TCRs triggered. These results demonstrate that different responses can be elicited in cytotoxic T lymphocytes by different levels of TCR occupancy. Materials and MethodsT Cell Clones and Target Cells. Clones speczfic for the influenza matrix peptide 58-66 (M58-66, reference 13) were isolated from polyclonal cell lines derived from two different donors and maintamed as described (14). The clones were used 10-30 d after restimulation. An HLA-A2 + EBV-transformed B cell line 0"Y) was used as antigen presenting/target cell.Cytotoxicity. Cytotoxicity was measured in a standard 4 h 51Cr release assay using 5,000 target cells/well and different E...

Reduced antigen concentration and costimulatory blockade increase IFN‐γ secretion in naive CD8+ T cells

“…In contrast to our data, other experiments show that the more peptide that is added to CD8 + T cells, the more IFNc is released into the culture supernatants [26,27]. Possible differences in relation to our work include the use of antigen-experienced [26] versus naive T cells (our study), but a more important aspect may be the different methods used to measure IFN-c production.…”

“…Possible differences in relation to our work include the use of antigen-experienced [26] versus naive T cells (our study), but a more important aspect may be the different methods used to measure IFN-c production. While FACS measures IFN-c in individual T cells at fixed time points, ELISA reflects accumulated IFN-c over the entire period of culturre.…”

Functional balance between T cell chimeric receptor density and tumor associated antigen density: CTL mediated cytolysis and lymphokine production

“…1 The different T lymphocyte effector responses that can be elicited, ie quality and magnitude of the response, depend on the density of the T lymphocyte receptors as well as on target cell density. [10][11][12][13][14] A detailed understanding of antigen-receptor/antigen relationships is important for the efficient generation and expansion of optimally reactive, tumor-specific CTLs for immunotherapy, since adoptive transfer of tumor-specific CTLs has shown significant clinical benefit. 15,18 However, tumor-specific CTLs are difficult to isolate from cancer patients and their expansion to therapeutic numbers is time-consuming and the succes rate unpredictable.…”

“…Chimeric receptor and TAA densities also co-determine levels of T lymphocyte IFN-␥ and TNF-␣ production Individual CTLs can exercise distinct biological responses as a function of percentage of TCR occupancy, 8,[10][11][12][13][14] which in turn is determined by ligand density and potency. 12 Therefore we studied the capacity of chRec LOW and HIGH POS T lymphocytes to secrete INF-␥ and TNF-␣ in response to G250 TAA LOW and HIGH POS RCCs.…”

“…Also, different antigen densities or potencies result in different levels of TCR engagements and elicit the triggering of distinct effector functions. 8,[10][11][12][13] The limited data that are available on the effect of low versus high TCR densities on antigen reactive T lymphocyte responses show a correlation with T lymphocyte activities. 11,13,14 A detailed understanding of the functional balance between TCR and TAA densities is therefore essential for the generation of optimally antitumor reactive T lymphocytes for cancer gene-immunotherapy now that adoptive transfer of tumor-specific CTLs to patients has demonstrated clinical benefit.…”