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The Philadelphia chromosome t(9;22)(q34;q11) is a cytogenetic marker for chronic myelogenous leukaemia (CML), and is also present in some acute leukaemias. The translocation in CML gives rise to two BCR/ABL chimeric transcripts (b3a2 and b2a2) encoding a 210-kD tyrosine kinase protein. These leukaemia-specific transcripts can be detected easily by the reverse transcriptase polymerase chain reaction (PCR). PCR has improved the possibility of detecting minimal residual leukaemia cells in Ph-positive patients, especially after bone marrow transplantation (BMT). With PCR, we looked for BCR/ABL transcripts in 30 patients with CML and 4 with essential thrombocythaemia at time of diagnosis, finding a significant difference in the platelet counts of CML patients carrying b3a2 or b2a2 transcripts. The BCR/ABL transcript was monitored by PCR in 6 CML patients after BMT. The usefulness of PCR in clinical practice at time of diagnosis, and the biological and clinical significance of positive/negative PCR results, in patients with transplants, are discussed.

We report on 24 patients with leukemia (19 pts), congenital disorders (4 pts) or severe aplastic anemia (1 pt) who received bone marrow transplantation from unrelated volunteer donors in 8 Italian Institutions. All the donor/recipient pairs were serologically HLA-A,B,DR matched; MLR was non reactive in 21 out of 24 cases. Preparative regimens were in accord with standards for diagnosis and disease status and included TBI in 15 patients, busulfan in 8, cyclophosphamide alone in one patient with SAA. GvHD prophylaxis consisted of cyclosporine/methotrexate in the majority of cases; 6 patients received additional immunotherapy with anti-lymphocyte globulin and 1 patient in vivo Campath-1G. The bone marrow was T-cell depleted in 2 cases. Acute GvHD grade II-IV occurred in 87% of patients (gr.III-IV: 57%) and was the main cause of death in 8 cases. Six patients (25%) survive with a median follow-up of 9 months, (16% actuarial survival at 3 years). A trend in favour of a better outcome has been found for age < 20 yrs at BMT (33% vs 22%), intensified GvHD prophylaxis (33% vs 22%) and transplants performed in more recent years (31% vs 18%).

We evaluated the cytotoxicity of the immunotoxin OKT1-SAP on fresh B-chronic lymphocytic leukemia (B-CLL) cells from 31 consecutive patients. OKT1-SAP comprised the OKT1 (CD5) monoclonal antibody disulfide linked to saporin-6 (SAP) ribosome-inactivating protein from the plant Saponaria officinalis. The effect of OKT1-SAP on target CD5-positive B-CLL cells was estimated using an in vitro proliferation inhibition assay in which control or OKT1-SAP-treated B-CLL cells were induced to proliferate by sequential stimulation with insolubilized anti-C3b receptor CB04 (CD35) antibody and low molecular weight B-cell growth factor. In 90% of patients, OKT1-SAP specifically suppressed B-CLL cell proliferation in a dose-related manner (50% inhibitory concentration, 4.0-6.8 nM). Taken together the findings reported in this article provide information relevant to the clinical development of immunotoxins because: (a) the in vitro conditions under which B-CLL cell proliferation is inhibited by OKT1-SAP are achievable in vivo without nonspecific toxicity according to our previous toxicology and pharmacokinetics studies in primates; and (b) the B-CLL cell proliferation inhibition assay described here provides a basis for future comparative studies.