E. Roux et al., Recovery of immune reactivity after T-cell-depleted bone marrow transplantation depends on thymic activity, BLOOD, 96(6), 2000, pp. 2299-2303
To evaluate the importance of the thymus for the reconstitution of immunity
in recipients of a T-cell-depleted bone marrow, we measured the appearance
of CD4(+)CD45RA(+)RO(-) naive T cells (thymic rebound), restoration of the
diversity of the T-cell-receptor (TCR) repertoire and the response to vacc
inations with tetanus toroid (TT). Repopulation by CD4(+)CD45RA(+)RO(-) thy
mic emigrants varied among patients, starting at approximately 6 months aft
er transplantation. Young patients reconstituted swiftly, whereas in older
patients, the recovery of normal numbers of naive CD4(+) T cells could take
several years. Restoration of TCR diversity was correlated with the number
of naive CD4(+)CD45RA(+)RO(-) T cells. Moreover, the extent of the thymic
rebound correlated with the patient's capacity to respond to vaccinations.
Patients without a significant thymic rebound at the moment of vaccination
(CD4(+)CD45RA(+)RO(-) T cells less than 30 mu L) did not respond, or respon
ded only marginally even after 3 boosts with TT. We conclude that during th
e first year after transplantation, the absence of an immune response is du
e mainly to the loss of an adequate T-cell repertoire. Restoration of the r
epertoire can come only from a thymic rebound that can be monitored by meas
uring the increase of CD4(+)CD45RA(+)RO(-) naive T cells, This will allow p
ostponing revaccinations to a moment when the patient will be able to respo
nd more effectively. This may be particularly useful in the elderly patient
who, owing to low thymic activity, might not yet be able to respond 1 year
after transplant when revaccinations are usually scheduled. (Blood. 2000;9
6:2299-2303) (C) 2000 by The American Society of Hematology.