Transplants are more likely to be rejected in CLL than in other conditions. The rejection rate in follicular lymphoma is between 3 and 6%. For CLL it may be as high as 20%. One study from Nebraska showed that the the graft failed to take completely in 35% of cases. This particularly a problem with T-depleted grafts - rejections of close to 20% compared with less than 10% with unmanipulated grafts. Factors that might play a part in this are the level of CLL infiltration in the marrow and a deficiency of host dendritic cells.
Another specific factor for CLL transplants is prior immunodeficiency. 60% of non-relapse deaths are due to infection. Patients who have had prior fludarabine or alemtuzumab are particularly susceptible.
For patients with mixed chimerism (both donor and graft cells are present in blood or marrow) and especially if there is evidence of persistent disease, donor lymphocyte infusions are indicated, though they are usually ineffective in progressive disease. Graft-versus-host disease is of course a risk of DLI and they have found greater favor with units using T-depleted grafts.
Another particular feature of CLL transplants is the occurrence of late relapses. One possible reason for this seems to be the existence of the CLL in sanctuary sites that do not communicate with blood or marrow - blood and marrow being the sites that are tested for minimal residual disease. Imaging studies for lymph node involvement are therefore necessary post transplant before declaring cure.