Lack of Utility of Chimerism Studies at Day 80 after Myeloablative Hematopoietic Cell Transplantation for Acute Lymphocytic Leukemia.

Between January 1998 and December 2004, 89 adults (≥18 years old) received allogeneic myeloablative hematopoietic stem cell transplants for treatment of acute lymphocytic leukemia (ALL) and had chimerism studies performed at a median of 77 days (range = 65–113 days) after transplant to assess the degree of donor engraftment. Median patient age was 33.5 yrs (range = 18.1–55.9 yrs). Seventy-eight patients had B-cell ALL, 8 had T-cell ALL, and 3 were not phenotyped. Conventional cytogenetic analyses were available for 70 patients at diagnosis: 19 had normal karyotypes, 24 were Philadelphia chromosome positive (Ph⁺), and 27 were Ph⁻, but had other clonal abnormalities. Four of the 19 patients without conventional cytogenetic studies had fluorescent in-situ hybridization (FISH) or polymerase chain reaction (PCR) studies positive for the bcr/abl gene rearrangement. Thirty-nine patients were transplanted in first remission, 29 in ≥2nd remission, and 21 in relapse. Eighty-four of the 89 patients received preparative regimens of cyclophosphamide (120 mg/kg) plus 12 or 13.2 Gy TBI. Thirty-two donors were HLA-identical family members, 2 were HLA-mismatched relatives, 36 were HLA-identical unrelated donors (URDs), and 19 were HLA-mismatched URDs. Thirty-four patients received stem cells from a bone marrow (BM) harvest, 54 received peripheral blood (PB) stem cells, and one received a cord blood product. The primary GVHD prophylaxis regimen was cyclosporine and methotrexate (n=80). Seventy-seven patients developed grades II-IV acute GVHD at a median of 19 days after transplant. Fifty-seven patients developed extensive chronic GVHD at a median of 140 days after transplant. Only one patient failed to engraft and died early; no one experienced graft rejection. Chimerism studies were done using either unfractionated BM or fractionated (CD3⁺ and CD33⁺ cells) PB. Prior to June 2002, a panel of 10 Variable Number Tandem Repeat (VNTR) loci were amplified and analyzed for same sex donor/recipient pairs. Subsequently, PCR amplification and analyses of Short Tandem Repeat (STR) loci were compared for same sex donor/recipient pairs. FISH studies using X and Y chromosome-specific probes were used for sex-mismatched donor/recipient pairs. Forty-seven patients had chimerism studies performed on unfractionated BM specimens and 58 had studies of fractionated PB samples (20 patients had both BM and PB studies). Only 2 patients who had unfractionated BM chimerism analyses had <95% donor engraftment. Only 1 patient who had a fractionated PB chimerism study had <95% donor engraftment in the CD33⁺ fraction. Eighteen patients had <95% donor engraftment (range = 45–94%) in the CD3⁺ fraction. Lower percentages of CD3⁺ engraftment did not correlate with survival, relapse, or incidence and severity of acute or chronic GVHD. The laboratory fees for one chimerism study range from $750–$1,000. Given the high percentage of complete donor engraftment on day 80 after myeloablative transplant in this patient population, the lack of correlation of incomplete CD3⁺ donor engraftment with transplant outcome, and the cost of chimerism analysis, these studies are not indicated in patients with ALL undergoing myeloablative transplants in the absence of clinical evidence of graft failure or graft rejection.