Enough information has been gained from clinical trials to allow the conclusion that human gene transfer is feasible, can evoke biologic responses that are relevant to human disease, and can provide important insights into human biology. Adverse events have been uncommon and have been related to the gene delivery strategies, not to the genetic material being transferred. Human gene transfer still faces significant hurdles before it becomes an established therapeutic strategy. However, its accomplishments to date are impressive, and the logic of the potential usefulness of this clinical paradigm continues to be compelling.

Transfer of Genes to Humans: Early Lessons and Obstacles to Success

Flow cytometry, as the name suggests, is the analysis of cells (which carry one or more fluorescent labels) moving in a fluid flow (1,2). This technique has become widely used because of the enormous increase in the number and range of specificities of antibodies to cell determinants. Monoclonal and polyclonal antibodies to both murine and human antigens, indeed antibodies that have a fluorochrome covalently attached (and which have already been tested in various assay systems), are readily commercially available.

Flow cytometric analysis.

Thirty-eight patients with hematological malignancies, received T cell-depleted marrow transplants (BMT) and cyclosporine to prevent acute graft-versus-host disease (aGVHD), followed by delayed add-back of donor lymphocytes to prevent leukemia relapse. In 26 patients scheduled for donor T cell add-back of 2 x 10(6) cells/kg on day 30 and 5 x 10(7) cells/kg on day 45 (schedule 1), the overall probability of grade > or = II aGVHD developing was 31.5%, with a 15.5% probability of aGVHD occurring after T cell add-back. In 12 patients receiving 10(7) donor T cells/kg on day 30 (schedule 2), the probability of grade > or = II aGVHD was 100%. The incidence of grade III-IV aGVHD was higher in schedule 2 than in schedule 1 (P=0.02). Of 24 evaluable patients, 10 (46%) developed chronic GVHD which was limited in eight and extensive in two. Current disease-free survival for 18 patients at standard risk for relapse (chronic myeloid leukemia (CML) in chronic or accelerated phase, acute myeloid leukemia in remission) vs 20 patients with more advanced leukemia or multiple myeloma were respectively 72% vs 12% (P < 0.01) with a 29% vs 69% probability of relapse (P=0.08). In 12 CML patients surviving more than 3 months, PCR analysis of the BCR/ABL transcript showed that minimal residual disease after T cell add-back was transient except in two patients who developed hematological relapse. Results indicate that the risk of acute GVHD is low following substantial T cell doses, transfused 45 days after transplant, using cyclosporine prophylaxis. Furthermore a graft-versus-leukemia effect was conserved.

T cell-depleted bone marrow transplantation and delayed T cell add- back to control acute GVHD and conserve a graft-versus-leukemia effect

Bone marrow malignancies are clonal disorders resulting from neoplastic transformation of hematopoietic stem or progenitor cells. Similar to their normal counterparts, transformed blood-forming cells remain dependent on signals from the hematopoiesis-regulating stromal environment for survival and proliferation. There is increasing evidence that the microenvironment may also take a more active part in the disease process. A review of the literature on stromal abnormalities in the leukemias, the myelodysplastic syndromes, and multiple myeloma reveals three principal mechanisms by which stromal derangements can contribute to the evolution of a neoplastic disease. In the simplest case, neoplastic blood-forming cells induce reversible changes in stroma function or composition which result in improved growth conditions for the malignant cells ('malignancy-induced microenvironment'). In the second setting, functionally abnormal end cells derived from the malignant clone become an integral part of the stroma system, selectively stimulating the neoplastic cells and inhibiting normal blood cell formation ('malignant microenvironment'). In the third condition, the emergence of a neoplastic cell population is the consequence of a primary stroma lesion characterized by inability to control regular blood cell formation ('malignancy-inducing microenvironment'). The perception of different stroma-related disease mechanisms may eventually lead to the development of alternative therapeutic approaches.

Stromal abnormalities in neoplastic bone marrow diseases

Donor lymphocyte infusions (DLI) have been the mainstay of treatment for chronic myeloid leukemia (CML) relapsing after allogeneic stem cell transplantation (allo-SCT). Imatinib mesylate (IM) is also effective in these patients. However, advanced phase relapse (APRel) responds poorly with either treatment. To test the possibility that combinations of DLI and IM might be more effective, 37 patients with CML relapsing after allo-SCT between August 1994 and May 2004 were studied. Ten had molecular relapse (MRel), 14 hematological relapse (HRel) and 13 APRel. Thirteen received DLI, 9 IM and 11 DLI+IM. Four patients received DLI+IM but not concurrently. Thirty (81%) patients responded (actuarial survival and current leukemia-free survival of 80.6 +/- 6.7% and 69.1 +/- 7.7%). Of 30 patients, 26 are in molecular remission (MR), median follow-up of 1,226 days (range 249-3257) since relapse. Ten of 11 patients (including four with APRel) treated with DLI+IM achieved MR in 3 months and all are alive in MR. In contrast, only two of 22 treated with either modality (1/13 DLI and 1/9 IM) achieved MR at 3 months, 15 are alive, 11 in MR. Four patients receiving nonconcurrent DLI+IM are also alive in MR. In conclusion, DLI appears to synergize with IM to induce rapid and durable MR.

Imatinib synergizes with donor lymphocyte infusions to achieve rapid molecular remission of CML relapsing after allogeneic stem cell transplantation.

Long-term culture of chronic myelogenous leukemia marrow cells on stem cell factor-deficient stroma favors benign progenitors

Long-term culture of CML marrow on stem cell factor-deficient stroma favors-benign progenitors

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Long-term culture of chronic myelogenous leukemia marrow cells on stem cell factor-deficient stroma favors benign progenitors

Long-term culture of CML marrow on stem cell factor-deficient stroma favors-benign progenitors