Low-intensity conditioning is sufficient to ensure engraftment in matched unrelated bone marrow transplantation

OBJECTIVE

Matched unrelated bone marrow transplantation (BMT) for patients with hematological malignancies is associated with a high incidence of transplant-related complications due to high doses of chemoradiotherapy administered pre-BMT to ensure engraftment. The aim of this study was to investigate the feasibility of low-intensity conditioning for BMT from matched unrelated donors.

MATERIALS AND METHODS

Sixteen patients with hematologic malignancies underwent non-T-cell-depleted BMT following a low-intensity conditioning regimen consisting of fludarabine monophosphate 30 mg/m(2)/day for 6 days, busulfan 4 mg/kg/day for 2 days, anti-T lymphocyte globulin 10 mg/kg/day for 4 days. Seven of the patients suffered from chronic myelogenous leukemia, four from acute lymphoblastic leukemia, four from acute myelogenous leukemia, and one from Ki-1 non-Hodgkin's lymphoma. Three of the patients had secondary leukemia and two were post-autologous BMT (ABMT). All patients were transplanted from fully matched unrelated donors.

RESULTS

Fifteen of the 16 patients had 100% donor chimerism; no graft rejection was observed. None of the patients developed >Grade II veno-occlusive disease, sepsis, multiorgan failure, or renal or pulmonary toxicity. Four patients died posttransplant; one of thrombocytopenia and severe hemorrhagic cystitis, one of central nervous system toxicity, one of Grade IV graft-vs-host disease, and one following relapse (9 months post-BMT). Survival and disease-free survival at 36 months are 75% (95% confidence interval 46-90%) and 60% (95% confidence interval 30-80%), respectively.

CONCLUSION

These results indicate that low-intensity conditioning is sufficient to ensure stable engraftment of bone marrow grafts in a matched unrelated setting.

Cell therapy with preimmunized effector cells mismatched for minor histocompatible antigens in the treatment of a murine mammary carcinoma

Cell therapy with allogeneic donor cells mismatched for minor histocompatible (MiHC) antigens was applied to a murine mammary carcinoma (4T1) model to test the feasibility of graft versus tumor (GVT) effect against metastatic epithelial tumor cells. BALB/c mice bearing a 4T1 tumor of BALB/c origin were given syngeneic or MiHC-mismatched splenocytes. GVT effects were determined in secondary recipients of adoptively transferred lung cells derived from primary hosts who had previously been inoculated intravenously with 4T1 cells, and injected with one of the following: 1) naive BALB/c splenocytes, 2) naive DBA/2 splenocytes, 3) 4T1-immune DBA/2 splenocytes, or 4) DBA/2 splenocytes immunized with host-derived BABL/c spleen cells. Naive DBA/2 splenocytes inhibited tumor growth only slightly and only slightly prolonged the survival of secondary recipients, in comparison with fully matched tumor/host BALB/c spleen cells. An efficient GVT reaction was demonstrated in vitro and in vivo with MiHC-mismatched DBA/2 splenocytes from mice presensitized by multiple injections of irradiated tumor or BALB/c-derived spleen cells. All 30 mice adoptively inoculated with lung cells from primary hosts that had previously been treated with these presensitized effector cells were tumor free for >250 days. Secondary recipients inoculated with lung cells from mice given naive BALB/c or DBA/2 spleen cells died of metastatic tumors within 33 to 46 days. These results suggest that preimmunized donor cells represent an effective tool against metastatic disease; hence, the next goal should be to control graft-versus-host disease while exploiting the GVT potential.

Herpesvirus saimiri pathogenicity enhanced by thymidine kinase of herpes simplex virus

Herpesvirus saimiri can be used as an efficient gene expression vector for human T lymphocytes and thus may allow applications in experimental leukemia therapy. We constructed recombinant viruses for the functional expression of the thymidine kinase (TK) of herpes simplex virus type 1 (HSV) as a suicide gene. These viruses reliably allowed the targeted elimination of transduced nonpermissive human T cells in vitro after the administration of ganciclovir. To test the reliability of this function under the most stringent permissive conditions, in this study we analyzed the influence of the prodrugs ganciclovir and acyclovir in common marmosets on the acute leukemogenesis induced by either wild-type herpesvirus saimiri C488 or by a recombinant derivative expressing TK of HSV. Antiviral drug treatment did not influence the rapid development of acute disease. In contrast, the presence of the HSV tk gene resulted in a faster disease progression. In addition, HSV TK-expressing viruses showed faster replication than wild-type virus in culture at low serum concentrations. Thus, HSV TK accelerates the replication of herpesvirus saimiri and enhances its pathogenicity. This should be generally considered when HSV TK is applied as a transgene in replication-competent DNA virus vectors for gene therapy.

Planning for the Evaluation of a Pediatric End-of-Life Curriculum

BACKGROUND

Decision making at the end of life can be complex and emotionally challenging for healthcare providers, particularly in pediatrics. Unfortunately, few undergraduate and graduate medical education curricula adequately address these issues. In this article, we describe the plan and progress to date of the design, implementation, and evaluation of an end-of- life curriculum for pediatric residents.

NEEDS ASSESSMENT

Prior to the development of a formal end-of-life curriculum, a survey was given to a single cohort of residents four times over the course of their training to assess their attitudes toward end-of-life issues and their experience with the informal curriculum in residency. Entering pediatric residents felt relatively uncomfortable dealing with death and dying, but by the end of training, residents felt more comfortable dealing with these issues. Residents were relatively ambivalent about the degree to which their education helped them to deal with end-of-life issues.

CURRICULUM DEVELOPMENT AND EVALUATION PLAN

A number of curricular interventions were developed including a noon conference series, grand rounds presentations, a 3-hour seminar on giving bad news, and written information for the housestaff manual. The curriculum was implemented in the fall of 1999. The impact of the curriculum will be assessed using a single interventional group with historical control study design. The evaluation instruments will include the previously used survey and an objective written examination. The 3-hour seminar will be assessed with a pre-test post-test crossover design using standardized patients.

DISCUSSION

This rigorous, feasible, and cost-effective approach to curriculum development is intended to serve as a model for end-of-life education in pediatric residencies.

Adoptive immunotherapy with haploidentical allogeneic peripheral blood lymphocytes following autologous bone marrow transplantation

Patients who undergo autologous bone marrow transplantation for acute leukemia are at high risk for relapse. We have evaluated the feasibility of administering cell-mediated immunotherapy with family-related haploidentical lymphocytes following autologous bone marrow transplantation in order to evoke a graft-vs-leukemia effect in the autologous setting.Twenty-six patients aged 1.5-48 years were enrolled in this study. Eighteen suffered from acute myeloid leukemia, seven from acute lymphoblastic leukemia, and one from myelodysplastic syndrome. Eleven patients were transplanted in first remission, six in second remission, one in fourth remission, and eight in relapse. Conditioning consisted of Busulfan/Cyclophosphamide or Busulfan/Thiotepa/Cyclophosphamide. Nineteen patients (Group A) were treated with gradual increments of haploidentical donor T cells, starting on day +1, with an additional course of T cells plus intravenous recombinant human interleukin-2 one month later if no signs of graft-vs-host disease developed in the interim. Seven patients (Group B) were treated with high-dose haploidentical T cells on day +1 in conjunction with intravenous recombinant human interleukin-2. Donor cells were detected in the peripheral blood of both groups 12-48 hours post-cell-mediated immunotherapy, peaking at 48 hours. Three patients in Group A developed transient Grade I graft-vs-host disease. One patient in Group B developed Grade I, and three Grade IV, graft-vs-host disease. Group A patients engrafted normally, but the Group B patients with Grade IV graft-vs-host disease showed no signs of engraftment. Our results show that it is feasible to induce graft-vs-host disease in the autologous stem cell transplantation setting. However, the high-dose regimen of haploidentical T cells in conjunction with interleukin-2 results in severe toxicity and nonengraftment.

New strategies for bone marrow transplantation

Adoptive immunotherapy of hematologic malignancies and metastatic solid tumors by donor lymphocyte infusion following induction of host-versus-graft transplantation tolerance against can best be achieved following nonmyeloablative stem-cell transplantation (NST). Induction of mixed chimerism may represent the best approach for induction of transplantation tolerance to donor alloantigens. Thus NST may become the optimal approach for the treatment of nonmalignant diseases, where replacement of host with donor hematopoietic cells is indicated: for correction of genetic or stem cell deficiency diseases; as a platform for immunotherapy of autoimmune or infectious diseases; or for induction of tolerance to organ allografts.

Second allogeneic stem cell transplantation using nonmyeloablative conditioning for patients who relapsed or developed secondary malignancies following autologous transplantation

OBJECTIVE

Second allogeneic stem cell transplants for hematological malignancies are associated with a high incidence of transplant-related mortality due to the cumulative incidence of toxicity of the high-dose chemoradiotherapy traditionally used as an essential component of the conditioning. We have demonstrated previously that nonmyeloablative conditioning for primary allogeneic transplants from both sibling and unrelated donors results in minimal transplant-related toxicity and excellent stem cell engraftment. This study explores the possibility of using nonmyeloablative conditioning to minimize transplant-related toxicity in patients who have undergone second allogeneic transplants.

PATIENTS AND METHODS

Twelve high-risk, heavily treated patients-five with acute myelogenous leukemia (AML); five with non-Hodgkin's lymphoma (NHL); one with Burkitt's lymphoma, and one with acute lymphoblastic leukemia (ALL)-underwent second allogeneic nonmyeloablative stem cell transplantation (NST) from human leukocyte antigen (HLA)-matched donors, 29 (median) (range 3-57) months following their first transplantation procedure. The conditioning consisted of fludarabine 30 mg/m(2) daily for 6 days, busulfan 4 mg/kg daily for 2 days, and anti-T-lymphocyte globulin 10 mg/kg daily for 4 days. Anti-graft-vs-host disease (anti-GVHD) prophylaxis consisted of cyclosporine A alone, 3 mg/kg.

RESULTS

Engraftment was observed in all recipients, with complete and stable chimerism. None of the patients developed veno-occlusive disease of the liver or multi-organ failure. Five very high-risk patients with NHL (n = 3), Burkitt's lymphoma (n = 1), and AML (n = 1) relapsed 2 to 6 months post-transplant, and four of them died. Six patients appear to be disease-free after median follow-up of 23 months. One additional patient died from grade IV hemorrhagic cystitis. Actuarial survival and disease-free survival at 34 months are 56% and 50% respectively, with 95% confidence interval (25-78%).

CONCLUSION

These results suggest that nonmyeloablative conditioning significantly reduces transplant-related toxicity, thus making a second transplant feasible.

Maintenance of immune memory to the hepatitis B envelope protein following adoptive transfer of immunity in bone marrow transplant recipients

Adoptive transfer of immunity against hepatitis B surface antigen (HBsAg) has been documented in mice and humans. In the present study, we report long-term follow-up of antibodies to HBsAg in humans who received allogeneic bone marrow transplantation (BMT) from donors immunized with HBsAg. BM donors were immunized with recombinant HBsAg. BM or PB cells were transplanted to HLA matched recipients. Recipients were followed for anti-HBs seroconversion. Control groups included non-immunized or rHBsAg immunized healthy adults as well as individuals that had had hepatitis B and recovered spontaneously. PBLs were stimulated in vitro with rHBsAg and stimulation was expressed as stimulation index. Adoptive transfer of immunity to HBsAg was initially documented in 12 recipients of BM from anti-HBc+/anti-HBs+ donors. An almost 4 year follow-up showed detectable protective anti-HBs levels (>10 mIU/ml) in 50% of patients. Immunity to HBV was also documented in 22/35 BMT recipients (62%), who received their bone marrow from actively immunized donors. In 7/9 of these BMT recipients, anti-HBs antibodies levels were documented 25 months following BMT. In 6/8 (75%) of patients who received only PBLs from HBV immune donors, adoptive transfer of immunity to HBV, and seroconversion to HBsAg+, were documented within 2 months of i.v. injection. Evidence for specific cellular immune response with increased SIs was documented for healthy vaccinees, and BMT recipients, and in none of the healthy non-vaccinated controls. These results suggest that adoptive transfer of immunity to HBV is a useful method for providing long-lasting protection for BM recipients.

Correlation between enhancement of graft-versus-leukemia effects following allogeneic bone marrow transplantation by rIL-2 and increased frequency of cytotoxic T-lymphocyte precursors in murine myeloid leukemia

A model of mouse acute myeloid leukemia (mAML) was used to study the effector mechanism mediating the graft-versus-leukemia (GVL) effects in recipients of allogeneic bone marrow cells (BMC). mAML-bearing SJL/J (H-2s) mice were lethally irradiated and then transplanted with a mixture of BMC and spleen cells (SC) derived from normal syngeneic or allogeneic mice. To augment the GVL effect, recipients were injected intraperitoneally with recombinant human interleukin-2 (rIL-2) (1.2 x 10(5) IU) for 3 consecutive days, starting one day post BMC + SC transplantation. Spleen cells from treated recipients were adoptively transferred to untreated secondary SJL/J mice to test for the existence of residual tumor cells. All the secondary recipients of SC from mAML-bearing SJL/J mice rescued with syngeneic (SJL/J) or allogeneic (B10.S) BMC+SC (H-2s) differing at minor antigens of the histocompatibility complex (MiHC) developed leukemia and died. In sharp contrast, none of the secondary recipients of SC obtained from identical mAML-bearing mice rescued with B10.S BMC + SC but activated in vivo with IL-2 developed leukemia. Adoptive recipients of SC obtained from mAML-bearing recipients of major histocompatibility complex (MHC)-disparate (C57BL/6, H-2b) cells remained free of leukemia regardless of the use of rIL-2. In parallel with the in vivo findings, a 4-day in vitro exposure of splenocytes to 6 x 10(3) IU/ml rIL-2 resulted in a 5- to 20-fold increase in the frequency of alloreactive cytotoxic T-lymphocyte (CTL) precursors (CTLp) across MiHC and MHC barriers and a 2- to 6-fold increase in their cytotoxic activity. Our data suggest that augmentation of GVL effects by rIL-2 may be due to CTL activation by rIL-2, not excluding the potential beneficial role of rIL-2-activated allogeneic natural killer cells and MHC non-restricted killer cells. Cumulatively, our results suggest potentially beneficial effects of rIL-2, when used jointly with bone marrow transplantation or allogeneic cell therapy, on eradication of leukemia.

Partial protection of rat parotid glands from irradiation-induced hyposalivation by manganese superoxide dismutase

Head-and-neck irradiation in rats often results in reduction of water and food intake, weight loss, hyposalivation, and suppression of the white blood cell (WBC) count. Oxygen free radicals are believed to be involved in this deleterious process. Superoxide dismutase (SOD) is known to act as a first line of antioxidant defence against oxygen free radicals. Here, the protective effect of manganese SOD (MnSOD) and copper/zinc SOD (Cu/ZnSOD) against irradiation-induced injuries to the head and neck in rats was investigated. Wistar rats were irradiated with 15 Gy X-rays delivered to the head-and-neck region. MnSOD (50 mg/kg) or Cu/ZnSOD (100 mg/kg) were administered before and after irradiation. Body weight, food and water intake, WBC counts, and parotid and submandibular salivary functions were examined. Irradiation of 15 Gy resulted in a significant reduction of the parotid flow rate by 73% compared with non-irradiated controls (p<0.05). MnSOD but not Cu/ZnSOD partially reduced this effect on the parotid gland by 25% (p<0.05). Both MnSOD and Cu/ZnSOD demonstrated a protective effect against irradiation-induced WBC suppression, by 35% and 25%, respectively (p<0.05). Treatment with SOD did not protect the animals against irradiation-induced reduction in oral intake and weight loss, or against submandibular hypofunction. These results suggest that SOD partially protects against head-and-neck irradiation-induced injury. Both MnSOD and Cu/ZnSOD partially protect against irradiation-induced WBC loss. The parotid gland is partially protected by MnSOD but not Cu/ZnSOD, while the submandibular gland is not protected by either MnSOD or Cu/ZnSOD.

Continuous interleukin-2 infusion combined with cyclophosphamide- based combination chemotherapy in the treatment of hemato-oncological malignancies. Results of a phase I-II study

The combination of a cyclophosphamide (CTX)-based chemotherapy regimen and interleukin-2 (IL-2) has been shown to provide synergistic effects against malignancy in animal models. We therefore conducted a phase I-II trial combining CTX-based combination chemotherapy or CTX alone with high-dose IL-2 in patients with advanced and refractory malignant disease. Fifteen patients with hemato-oncological malignancies (malignant lymphoma 8, multiple myeloma 3, solid tumor 2, leukemia 2) were enrolled in the study. Continuous high-dose IL-2 infusion was shown to be safely administered, starting as soon as recovery of white blood cell count. All patients developed rebound lymphocytosis 24-48 h after termination of IL-2 infusion. Although grade IV toxicity was observed in 5 patients (7 episodes), all side effects completely subsided. Triple chemotherapy (CTX, etoposide and Ara-C) seemed rather toxic (in this group of heavily treated patients) while CTX alone was well tolerated. Four out of 13 (31%) evaluable patients had partial response and another patient (7%) had stabilization of disease progression lasting 2-8 months. Our conclusion is that the combination of CTX and continuous infusion of IL-2 is feasible and should be investigated in patients with various malignant neoplasms.

Graft vs autoimmunity following allogeneic non-myeloablative blood stem cell transplantation in a patient with chronic myelogenous leukemia and severe systemic psoriasis and psoriatic polyarthritis

OBJECTIVE

No specific therapy exists for autoimmune diseases caused by self-reactive lymphocytes. As shown in experimental animals, which led to pilot clinical studies, elimination of self-reactive lymphocytes can be accomplished with high-dose chemoradiotherapy, followed by autologous stem cell transplantation, by re-establishment of unresponsiveness to self antigens of newly generated lymphocytes, due to a mechanism of central clonal deletion. We hypothesized that self-reactive lymphocytes causing autoimmune disease may be successfully eliminated by highly immunosuppressive yet not necessarily myeloablative conditioning in conjunction with allogeneic blood stem cell transplantation, since immunocompetent alloreactive lymphocytes of donor origin can effectively eliminate residual host-type hematopoietic cells, self-reactive lymphocytes included, by a mechanism that resembles graft-vs-leukemia (GVL) effects. The present report is an attempt to confirm the existence of graft-vs-autoimmunity (GVA) effects in parallel with amplification of the alloreactive potential of donor lymphocytes following allogeneic non-myeloablative stem cell transplantation (NST).

METHODS

We identified a patient with severe psoriatic arthritis who also had Philadelphia (bcr/abl) positive chronic myelogenous leukemia and therefore was fully eligible for NST. Both diseases responded initially to non-myeloablative conditioning involving fludarabine 30 mg/m2 x 6, anti-T-lymphocyte globulin 10 mg/kg X 4, and busulfan 4 mg/kg x 2.

RESULTS

The initial NST procedure was uneventful and resulted in elimination of all signs of autoimmunity (psoriasis and arthritis). Recurrence of polyarthritis and exacerbation of psoriasis were observed in parallel with a significant increase in the proportion of male (host) DNA, and 5% of the mitoses were bcr/abl positive, indicating an increase in the clone of CML. Both bcr/abl-positive cells identified by RT-PCR and psoriatic arthritis were successfully eliminated following discontinuation of anti-GVHD prophylaxis with cyclosporine A (CSA), which resulted in activation of the alloreactive potential of donor T cells, accompanied by graft-vs-host disease (GVHD), suggesting the existence of GVA effects. RT-PCR for bcr/abl remains consistently negative for nearly 3 years, and all DNA remains donor type.

CONCLUSIONS

The response of autoimmune disease manifestations to GVA effects in parallel with elimination of all host-derived hematopoietic cells supports our working hypothesis that autoimmune diseases caused by self-reactive lymphocytes may be effectively treated by elimination of alloreactive self-reactive lymphocytes following induction of host-vs-graft tolerance, in analogy with replacement of malignant or genetically abnormal host cells following DLI. It is therefore suggested that intentional GVA effects may be inducible by DLI following a conventional or preferably safer non-myeloablative regimen in recipients with life-threatening autoimmune diseases resistant to conventional modalities. Adoptive immunotherapy of autoimmunity may thus involve a two-step procedure: first, inducing host-vs-graft and graft-vs-host transplantation tolerance through a transient stage of mixed chimerism; second, inducing controlled GVA effects, initially by discontinuation of CSA and then, if indicated, by late outpatient DLI to eradicate residual hematopoietic cells of host origin.

T-cell depletion of bone marrow transplants for leukemia from donors other than HLA-identical siblings: advantage of T-cell antibodies with narrow specificities

T-cell depletion of donor marrow decreases graft-versus-host disease resulting from transplants from unrelated and human leukocyte antigen (HLA)-mismatched related donors. However, there are diverse strategies for T-cell-depleted transplantation, and it is uncertain whether any improve leukemia-free survival (LFS). To compare strategies for T-cell-depleted alternative donor transplants and to compare T-cell depleted with non-T-cell-depleted transplants, we studied 870 patients with leukemia who received T-cell-depleted transplants from unrelated or HLA-mismatched related donors from 1982 to 1994. Outcomes were compared with those of 998 non-T-cell-depleted transplants. We compared LFS using different strategies for T-cell-depleted transplantation considering T-cell depletion technique, intensity of pretransplant conditioning, and posttransplant immune suppression using proportional hazards regression to adjust for other prognostic variables. Five categories of T-cell depletion techniques were considered: narrow-specificity antibodies, broad-specificity antibodies, Campath antibodies, elutriation, and lectins. Strategies resulting in similar LFS were pooled to compare T-cell-depleted with non-T-cell-depleted transplants. Recipients of transplants T-cell depleted by narrow-specificity antibodies had lower treatment failure risk (higher LFS) than recipients of transplants T-cell depleted by other techniques. Compared with non-T-cell-depleted transplants (5-year probability +/- 95% confidence interval [CI] of LFS, 31% +/- 4%), 5-year LFS was 29% +/- 5% (P = NS) after transplants T-cell depleted by narrow-specificity antibodies and 16% +/- 4% (P <.0001) after transplants T-cell depleted by other techniques. After alternative donor transplantation, T-cell depletion of donor marrow by narrow-specificity antibodies resulted in LFS rates that were higher than those for transplants T-cell depleted using other techniques but similar to those for non-T-cell-depleted transplants. (Blood. 2000;95:3996-4003)

Immunotherapy of hematologic malignancies and metastatic solid tumors in experimental animals and man

Following engraftment of donor hematopoietic cells and induction of host-versus-graft tolerance, immunocompetent lymphocytes of donor origin can induce graft-versus-leukemia (GVL) and graft-versus-tumor (GVT) effects. Engraftment of allogeneic bone marrow cells can be accomplished following non-myeloablative conditioning while possibly controlling graft-versus-host disease (GVHD). GVL and GVT effects may thus be successfully accomplished following non-myeloablative stem cell transplantation (NST) as shown by data derived from experimental animals and man.

Allogeneic peripheral blood stem cell transplantation using a fludarabine-based low intensity conditioning regimen for malignant lymphoma

Relapse is a serious complication following high-dose therapy and autologous bone marrow transplantation (ABMT) for malignant lymphoma (ML). Allogeneic transplantation (alloSCT) is a therapeutic option. However, it is associated with a high incidence of transplant-related organ toxicity and mortality. We recently reported fast engraftment and minimal transplant-related toxicity, using fludarabine-based conditioning with reduced amounts of chemotoxic drugs prior to alloSCT. We now present our experience with 23 heavily treated high risk ML patients who underwent matched alloSCT following the same low intensity conditioning. The patients (20 male, three female) were aged 13-63 years. Nineteen had NHL and four HD (resistant disease 12, partial remission 11). Five were post ABMT. Twenty-two patients had fully matched sibling donors, and one a fully matched unrelated donor. Engraftment was fast. There was no rejection or non-engraftment. Organ toxicity was moderate with no liver or renal toxicity >grade II. Four patients developed >grade II graft-versus-host disease (GVHD). Seven patients died - four of grade III-IV GVHD and severe infections, two of bacterial sepsis, one of pulmonary failure. Ten patients are alive after 22.5 (15-37) months. Survival and disease-free survival at 37 months are both 40%. Probability of relapse is 26%. These encouraging results suggest that alloSCT following fludarabine-based low intensity conditioning in high-risk patients merits further evaluation. Bone Marrow Transplantation (2000).

Functional long-term thymidine kinase suicide gene expression in human T cells using a herpesvirus saimiri vector

Herpesvirus saimiri transforms human T lymphocytes to stable growth and persists episomally without genomic integration and without virus production. The transformed T cells retain essential features of their parental cells including the MHC-restricted antigen specificity which may be useful for applications in adoptive immunotherapy. In order to improve the biological safety of such vectors, the prodrug activating gene thymidine kinase of herpes simplex virus was inserted into the genome of herpesvirus saimiri by homologous recombination. After infection with wild-type or cloned recombinant viruses, T cells from tamarin monkeys and from humans were transformed to stable growth. Thymidine kinase-expressing transformed T cells were efficiently eliminated in the presence of low concentrations of ganciclovir. This elimination mechanism remained fully functional over an observation period of 12 months. The potentially immunogenic neomycin resistance gene expression cassette was deleted from the genome of established mutant viruses by using the prokaryotic Cre/LoxP recombination system. At any time during the course of a therapeutic application, thymidine kinase-expressing transformed human T cells might be eliminated after administration of ganciclovir. In principle, this function could be useful for the T cell-dependent immunotherapy of resistant blood cancer while avoiding the risk of uncontrolled graft-versus-host disease.

Low intensity regimens with allogeneic hematopoietic stem cell transplantation as treatment of hematologic neoplasia

Conventional myeloablative conditioning regimens for allografting rely on the use of toxic myeloablative and immunosuppressive therapies to achieve engraftment and control of hematologic neoplasias. Unfortunately, these regimens have resulted in substantial morbidity and mortality. Preclinical and pilot clinical studies have shown that conditioning regimens can be reduced in intensity (resulting in reduced morbidity and mortality) since stem cell allografts can create their own space in the host's bone marrow. Initial promising results with these attenuated conditioning regimens confirm that such an approach is feasible in patients with hematologic neoplasias and genetic diseases ineligible for conventional allografting because of age and/or organ toxicity. The combination of high-dose therapy/autografting followed by a low intensity conditioning regimen (Flu-Cy protocol) and donor mobilized hematopoietic stem cell infusion (mini-allografting) may ultimately be useful in advanced resistant hematologic neoplasia. Finally, these initial promising results with attenuated conditioning regimens have been achieved in transplants with HLA-identical siblings. In the future the main goal will be to explore non-toxic conditioning regimens in the context of transplants from related MHC-mismatched or unrelated MHC-matched donors by increasing the patient's immunosuppression.