The Journal of Immunology, Vol 159, Issue 12 5821-5833, Copyright © 1997 by American Association of Immunologists

ARTICLES

Anti-CD3 epsilon F(ab')2 fragments inhibit T cell expansion in vivo during graft-versus-host disease or the primary immune response to nominal antigen

BR Blazar, MK Jenkins, PA Taylor, J White, A Panoskaltsis-Mortari, R Korngold and DA Vallera
Department of Pediatrics, University of Minnesota Hospital, Minneapolis 55455, USA. blaza001@maroon.tc.umn.edu

This study was undertaken to distinguish between several mechanisms responsible for graft-vs-host disease (GVHD) protection in anti- CD3epsilonF(ab')2 fragment (Fr)-treated recipients: TCR down- modulation, deletion, failure of expansion, or anergy induction. To quantify alloreactive T cell expansion and function, thoracic duct lymphocytes (TDL) were analyzed. Sixfold fewer donor TDL T cells were recoverable from anti-CD3epsilonF(ab')2 Fr as compared with irrelevant F(ab')2 Fr-treated recipients at the time of peak T cell expansion in vivo. Kinetic analysis revealed that donor T cell expansion was inhibited and not simply delayed by anti-CD3epsilonF(ab')2 Fr. Similar proportions of TDL T cells in irrelevant and anti-CD3epsilonF(ab')2 Fr were undergoing apoptosis. Although TCR modulation was observed, donor TDL T cells had intact anti-host alloresponses as compared with irrelevant F(ab')2 Fr-treated recipients. Because donor CD4+ T cells are primarily responsible for GVHD in this model, an adoptive transfer system was used in which the function and kinetics of expansion of OVA- specific CD4+ TCR transgenic cells could be physically tracked. Relevant Fr severely blunted CD4+ TCR transgenic T cell clonal expansion after OVA administration. Nonviable transgenic and nontransgenic T cells were proportionally similar in OVA-pulsed recipients, regardless of whether relevant or irrelevant F(ab')2 Fr were given. After discontinuing Fr, transgenic T cells were found to have intact in vitro OVA-specific responses. Our current and previous results suggest that reduced donor T cell expansion and T cell depletion both contribute to GVHD protection by anti-CD3epsilonF(ab')2 Fr. These data have implications for designing therapeutic approaches directed toward TCR targeting in humans.

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