the autologous marrow to graft and establish normal hematopoiesis 
rapidly. The combination of busulfan and cytoxan is highly effective as 
a preparative regimen for allogeneic marrow transplant in AML and 
has acceptable defined toxicides. This combination apparently 
eliminates leukemic cells in a high percentage of patients and permits 
engraftment. 
A number of studies in AML using autologous marrow engraftment 
after preparation with busulfan/cytoxan have shown promising results. 
In studies from Johns Hopkins Hospital, AML patients in second or 
subsequent complete remission who had autologous marrow removed, 
treated with 4HC and then reinfused after treatment with 
busulfan/cytoxan had an estimated event-free survival at 2 years of 30%. 
By historical review, none of these patients would remain disease free 
with conventional chemotherapy for relapsed AML more than a 
median of 6 months. 
Mechanism of Relapse 
Although autologous BMT (ABMT) may offer advantages over conventional 
chemotherapy, the major cause of treatment failure remains relapse or disease 
progression. When ABMT is undertaken for solid tumors, relapse is generally 
at the site of original disease, implying that supralethal chemo-radiotherapy 
has not eradicated the malignancy. The mechanism of relapse following 
ABMT for marrow cell derived malignancies such as AML is less clear. As 
the incidence of relapse in these diseases is far higher after autologous BMT 
than it is after allogeneic marrow transplantation, two explanations have been 
offered. The first is that the alloreactive T lymphocytes present in allogeneic 
marrow have a major role in recognition and elimination of residual host 
malignant cells. Since these cells are absent from autologous marrow, relapse 
is more likely after autologous BMT. This explanation suggests that relapse 
after ABMT for hematological malignancy occurs for the same reason as 
relapse after ABMT for solid tumor - persistence of residual disease in the 
host . An alternative explanation is that even though cryopreserved autologous 
marrow is harvested in remission, it nonetheless contains residual malignant 
cells. In this case, relapse is due to residual disease not in the host, but in the 
rescuing marrow . It is likely that both factors contribute to relapse, although 
the relative contribution of each in any given disease is unknown. 
The mechanism of relapse following ABMT for marrow derived malignancy 
is an important issue to resolve. The fear that stored marrow contains residual 
malignant cells has led to intensive investigation of the value of marrow 
purging prior to storage and subsequent reinfusion. Purging may be 
Recombinant DNA Research, Volume 14 
