ALLOGENEIC DENDRITIC CELLS INDUCE CORD T CELL CD40L EXPRESSION AND INTERFERON-g PRODUCTION

ALLOGENEIC DENDRITIC CELLS INDUCE CORD T CELL CD40L EXPRESSION AND INTERFERON-g PRODUCTION.
N.C.Matthews, M.Wadhwa*, F.E.Borras, C.Bird* and C.V.Navarrete, Department of Histocompatibility & Immunogenetics, NBS-London and S.E.Zone, London, UK and *Division of Immunobiology, National Institute of Biological Standards and Controls, Herts, UK

Cord blood T cells are immunocompetent and proliferate as strongly as adult T cells in conventional MLR assays, but generate very low numbers of CTLs. However, since cord T cells are phenotypically naive (CD45RA+) and require optimal stimulation by dendritic cells, the full potential magnitude of the frequency of CTL generated by allostimulation in vivo might be underestimated. Blockade of T cell - dendritic cell CD40L-CD40 interactions in vitro reduces DC IL12 secretion, DC and T cell viability, and abolishes TH1 and CTL effector generation. Naive CTL priming is therefore critically dependent on CD40L-CD40 costimulation. To verify whether cord T cells can provide DC help for CTL priming, we have used 2-colour flow cytometry to measure adult and cord blood T cell CD40L expression in response to optimal allostimulation with adult monocyte derived dendritic cells.
CD40L expression was assessed after 5 days of stimulation with alloDC (T cell:DC ratio of 20:1). Analysis of forward and side scatter showed that both cord and adult T cells had equally high viability, but cord T cells had twice as many large proliferating blast cells as adult T cells. At this point of harvest, there was no significant difference in total CD40L expression between adult and cord T cells (4.4±2.8% and 6±5.2%, respectively, n=6). Virtually all CD40L expression was restricted to the blast population. Analysis of DC-T cell supernatants by ELISA revealed that cord T cells produced nearly as much IFN-g as adult T cells (207±182 and 279±145 pg/ml, repectively, n=8). These data show, in contrast to previous MLR data, that allostimulated cord T cells, in the acute term, can provide sufficient CD40L-CD40 costimulation for naive CTL priming and effector generation.