Phenotypic and functional analysis of T-cell recovery after anti-CD3 immunotoxin treatment for tolerance induction in rhesus macaques

T-cell reduction utilizing specific antibody has been widely used in human transplantation, and is a cornerstone of several tolerance induction strate gies in nonhuman primates. We have established a population of long-term to lerant rhesus macaques induced with an anti-CD3 epsilon immunotoxin (IT). T his treatment effects transient, specific and profound ablation of T cells in blood and lymphoid tissues. Tn most instances the IT was used in combina tion with the NF-kappaB inhibitor, 15-Deoxyspergualin. This 2-week long pro tocol produces a "window of opportunity" for tolerization in which the anim al exhibits an enduring quiescent state of unresponsiveness to the allograf t, all accomplished without maintenance immunosuppressive drugs. During thi s induction period, the treated immune system bears some resemblance to tha t of the neonate, in that T cell numbers are abnormally low and antigen pre sentation by dendritic cells is precluded by an arrest in their NF-kappaB d ependant maturation. In addition, IL-4 production is prominent during and a fter the tolerance induction interval. For this study we focused on measuri ng the monkey's ability to repopulate T cells with particular emphasis on t he memory T-cell phenotype. Three "memory" phenotypes were utilized; CD3(+) CD45RO(+), CD3(+)CRTH2(+), and CD3(+)CD4(+)CD8(+). All three phenotypes exh ibited different patterns of recovery, all of which included transient burs ts in their numbers during repopulation. We also estimated thymic activity after T-cell ablation with the use of a newly-described RTE or recent thymi c emigre phenotype (a naive CD8(+)CD103(+) T cell). This marker revealed pr oduction of RTE cells including supranormal levels at approximately 6 month s post-transplant, implicating thymic function in the repopulation of T-cel ls. Finally, we measured antibody responses to a panel of antigens (vaccine s, environmental antigen, and foreign proteins) that indicated there was no apparent loss of immunologic function during or after the tolerance induct ion period. Results of studies of T-cell receptor repertoire expression sug gest preservation of the pretreatment repertoire, which is consistent with rapid recovery of immune competence to the test antigens. Taken together, t hese results suggest that while aggressive, this tolerance induction proroc ol does not appear to incur a prolonged immunologically-compromised state, if at all. (C) American Society for Histocompatibility and Immunogenetics, 2001. Published by Elsevier Science Inc.