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Lymphocyte transfusion from the marrow donor (DLT) is well established as an effective therapy for relapse of CML post allogeneic BMT. Reports thus far have been mostly limited to patients who received DLT from a matched sibling donor. We compared the efficacy and toxicity of DLT in 30 patients who were treated with cells from their HLA-identical sibling (n = 18) or from their phenotypically HLA-matched unrelated marrow donor (n = 12). The overall probability of obtaining a cytogenetic remission was 69% (95%CI: 51-83%) and was not significantly different between the two groups. The disease stage at the time of DLT was the only factor associated with cytogenetic remission by multivariate analysis; patients treated in cytogenetic or molecular relapse (n = 11) were seven times more likely (RR = 7.4, 95%CI: 2.4-22.4, P = 0.0005) to respond compared to patients treated for hematologic relapse (n = 19). There was a trend towards more acute GVHD II-IV in the unrelated donor group (58 vs 39%, P = 0.09), but the probability of developing extensive chronic GVHD was not significantly different (56 vs 39%, P = 0.4). We conclude that transfusion of donor cells from HLA-matched volunteer donors does not appreciably increase the risk of GVHD compared with transfusion of cells from HLA-identical siblings in patients with CML who relapse following allogeneic BMT. Conversely, there is no evidence for an increased graft-versus-leukemia effect after DLT from volunteer donors.

Serial quantification of residual disease in CML patients after allogeneic BMT is useful for early detection of relapse. However, the fact that some cytogenetic relapses appear to be transient may complicate protocols for early therapeutic intervention based on molecular analysis and could result in the unnecessary treatment of some patients. To determine the frequency and significance of transient cytogenetic relapse, we have studied serial samples from 98 CML patients after allogeneic BMT by conventional cytogenetics and competitive RT-PCR for BCR-ABL mRNA. During the period of study, 26 patients had cytogenetic or haematologic evidence or relapse. In four cases (15% of those who relapsed; 4% of all patients) relapse appeared to be transient; i.e., subsequent marrow samples were completely Ph chromosome-negative despite the fact that there had been no change in treatment, including the level of immunosuppression. BCR-ABL mRNA levels broadly paralleled the cytogenetic findings. Of these four patients, two subsequently progressed to frank haematologic relapse and two remained strongly positive for BCR-ABL transcripts and are therefore presumably still at risk of relapse. Analysis of B cell-enriched, T cell-enriched and lymphoid-depleted fractions for three patients demonstrated that transient relapse was not due to the proliferations of BCR-ABL-positive lymphoid cells. In contrast, BCR-ABL-positive myeloid precursor cells were detected in two of three patients tested. We conclude that transient cytogenetic relapse followed by sustained remission is a relatively infrequent occurrence after current allogeneic transplant regimens.

Interferon-alpha (IFN-alpha) induces cytogenetic responses of variable degree in patients with CML. We sought to establish the relationship between BCR-ABL transcript numbers measured by competitive two-step reverse transcription polymerase chain reaction (RT-PCR) and cytogenetic status in CML patients treated with IFN-alpha. All 305 samples from 133 patients investigated by RT-PCR were positive for BCR-ABL transcripts. In order to standardize results for variability in RNA and cDNA quality, we quantified total ABL transcripts in each sample as an internal control. The BCR-ABL : ABL ratios correlated well with the cytogenetic results. Quantitative nested PCR allowed the detection of residual BCR-ABL transcripts in all complete cytogenetic responders on IFN-alpha. We conclude that competitive PCR with internal controls is a reliable method for monitoring patients on IFN-alpha and reduces the need for repeated marrow investigations.

We report a 33-year-old man with Ph chromosome-positive CML who underwent an allogeneic BMT from an unrelated donor. DNA microsatellite studies showed complete donor chimaerism immediately after BMT followed by mixed chimaerism; by day + 45 haematopoiesis was exclusively of recipient origin. Throughout the first year post-transplant all marrow metaphases were Ph negative but with non-clonal rearrangements consistent with autologous recovery. Cytogenetic relapse of leukaemia was first detected 15 months post-transplant. This case is unusual in that non-malignant stem cells of recipient origin survived the transplant and reconstituted haematopoiesis very early after BMT. Later the leukaemic cells reasserted their 'proliferative' advantage.

The clinical status of a homogeneous cohort of long-term survivors of allogeneic marrow transplantation was assessed and residual leukaemia was studied by reverse transcription polymerase chain reaction for leukaemia specific BCR-ABL mRNA. The group comprised 34 consecutive patients with CML in chronic phase treated by chemoradiotherapy and transplantation of bone marrow from HLA-identical sibling donors between February 1981 and December 1983 in the joint Hammersmith-Northwick Park programme. The probability of survival at 10 years was 59 +/- 17%. Eighteen of the 19 surviving (95%) patients have Karnofsky scores of 90 or 100% indicative of a good performance status. One of the survivors had evidence of relapse 6.5 years after transplant but has since been restored to complete remission by treatment with interferon-alpha followed by donor leucocyte transfusions. Surprisingly, 2 of the 19 patients who have been in remission for over 10 years have molecular evidence of persisting leukaemic cells. Quantification by competitive PCR indicated that the malignant clone persisted at low levels. The data suggest that the majority of long-term survivors after BMT for CML are in good health and may be regarded as cured. Some long-term survivors, however, may still harbour residual leukaemic cells and continued monitoring for late relapse is warranted. Late relapse is amenable to further therapy with leukocyte transfusions from the original marrow donor.

Between January 1985 and March 1992, 48 patients with chronic phase CML underwent BMT from volunteer unrelated donors (MUD) serologically identical at HLA-A, B and DR loci. 19 patients received donor marrow ex vivo T-cell depleted (EX-TCD) with Campath monoclonal antibodies. 29 patients received unmanipulated donor marrow with CsA/MTX GVHD prophylaxis; 28 received additional intravenous antilymphocyte therapy from day +1 to +5 (IN-TCD). Overall 26 patients survive at median follow up of 362 days; actuarial survival at 3 years is 50%. 3 patients have sustained haematological relapse; actuarial leukaemia-free survival is 38%. There is no difference in overall survival between the EX-TCD and IN-TCD groups, but primary graft failure (n = 4) occurred only in the EX-TCD group, while GVHD (grade II or greater) occurred more frequently in the IN-TCD group (61% vs. 29%, p = 0.084). The optimum method for GVHD prophylaxis in MUD BMT remains uncertain.