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TITLE: HEMIZYGOSITY DETECTED AT 13 OF 14 VNTR/STR LOCI IN CD45/19+ LEUKEMIA CELLS FROM A PATIENT WITH ALL

A. G. Smith,¹ C. McFarland,¹ H. Hertenstein,¹ C. Kellum,¹ T. Allina,¹ D. Gulley,¹ J. A. Hansen.<sup>2

1</sup>Clinical Immunogenetics, Seattle Cancer Care Alliance, Seattle, WA; ²Human Immunogenetics, Fred Hutchinson Cancer Research Center, Seattle, WA

Extensive publications document chromosome abnormalities in patients with malignant hematologic diseases. In our experience these abnormalities are rarely detected during routine post–transplant DNA analysis of short tandem repeat (STR) or variable number tandem repeat (VNTR) loci. We report here on the detection of extensive chromosome loss in flow cytometry sorted leukemia cells from a patient with Acute Lymphocytic Leukemia (ALL) during engraftment monitoring after hematopoietic stem cell transplantation. The proband was transplanted with an HLA–A,B,C,DRB1 matched unrelated donor. On day 72 and day 97 post–transplant, peripheral blood was collected and flow cytometry sorted for CD3+ (T–cells) and CD33+ (myeloid) and bone marrow aspirate samples were sorted for CD45/19+ tumor cells. DNA from post–transplant samples along with patient pretransplant and donor samples were amplified using primers for 4 VNTR/STR loci, D1S80, D1S111, SE–33 and ApoB. Patient pretransplant exhibited 2 distinct alleles at all 4 loci. The unrelated donor showed 2 alleles at 3 loci, but a single allele band at D1S80. All 4 loci provided at least one unique patient allele. The post–transplant CD3+ and CD33+ samples revealed the presence of approximately 1–5% host on both draw dates. Interestingly the CD45/19+ leukemia cells exhibited a single allele consistent with one of the patient alleles at all 4 loci. Subsequently, 11 additional loci, including 9 loci from the ABI AmpFISTR Profiler Plus system were analyzed in the tumor cells. Samples from both parents were included in order to determine which parental allele was missing. In total, 15 different VNTR/STR loci, representing 13 different chromosomes, were tested. These results showed that 6 loci exhibited loss of the allele inherited from 1 parent and 7 different loci were missing an allele from the other parent, suggesting that chromosome loss was not haplotype specific. One locus was not informative since the patient inherited the same allele from both parents. Only a single locus, D5S818 on chromosome 5, showed inheritance of both parent alleles in the leukemia cell samples.