DIFFERENTIAL CD26-MEDIATED ACTIVATION OF THE CD3 AND CD2 PATHWAYS AFTER CD6-DEPLETED ALLOGENEIC BONE-MARROW TRANSPLANTATION

Patients who have undergone allogeneic bone marrow transplantation (al lo-BMT) are susceptible to a variety of opportunistic infectious compl ications in the months to years after engraftment. Impaired in vitro T -cell functions have been documented in these patients, and these T-ce ll dysfunctions contribute to the prolonged immune deficiency after al lo-BMT. In the present study, we examined the expression of CD26 as we ll as the reconstitution of CD26-mediated T-cell costimulation via the CD3 and CD2 pathways at various times in patients aged greater than 1 8 years after CD6-positive, T-cell depleted allo-BMT. We found that th e percentage of CD26- and CD3-positive cells, as well as the levels of expression of both antigens, was lower than in normal controls during the first 4 months after CD6-depleted allo-BMT. Subsequently, the num ber of lymphocytes expressing CD3 and CD26 and the quantitative surfac e expression of CD3 and CD26 were not significantly different in patie nts and normal controls. Functional studies showed that CD26-mediated T-cell proliferation via the CD3 pathway was considerably improved and almost reached normal levels by 1 year, whereas recovery of CD26-medi ated T-cell proliferation via the CD2 pathway was delayed for at least 2 years after CD6-depleted allo-BMT, As CD26 involvement in the regul ation of human thymocyte activation is restricted preferentially to th e CD3 pathway-unlike its involvement with both CD3 and CD2 pathways of peripheral T cells-our results suggest that the different effects of CD26-mediated costimulation via the CD3 and CD2 pathways after CD6-dep leted allo-BMT may be a reflection of peripheral T-cell immaturity in those individuals, similar to that seen in mature medullary thymocytes or cord T lymphocytes. (C) 1995 by The American Society of Hematology ,