Summary. Chronic myeloid leukaemia (CML) dendritic cells (DC) are possible candidates for inducing antileukaemic immunity. This study aimed to investigate the frequency, phenotype and function of blood‐derived leukaemic DC in comparison with DC from healthy donors using flow cytometric assays and mixed leucocyte reaction (MLR). Immature leukaemic DC displayed a reduced endocytotic capacity as compared with healthy controls. Moreover, in vitro maturation of leukaemic DC was found to be deficient. Expression of CD80, CD83, CD86, and major histocompatibility complex class I and class II antigens were reduced on lipopolysaccharide (LPS)‐matured leukaemic DC but were enhanced by a mixture of interleukin 1β (IL‐1β), IL‐6, tumour necrosis factor‐α (TNF‐α) and prostaglandin E2 (PGE2). Upon stimulation with bacterial LPS, intracellular TNF‐α and IL‐8 production was diminished in maturing DC from CML patients. This distinct cytokine deficiency was overcome when leukaemic DC were stimulated with cytokines/PGE2. MLR showed fully functional leukaemic DC after TNF‐α‐induced maturation, but a reduced proliferative alloresponse of leukaemic peripheral blood mononuclear cells. Further, intracellular production of cytokines in CML‐derived T cells was markedly reduced. These data indicated that, in CML, the maturation response of leukaemic monocyte‐derived DC to a natural stimulus like LPS is abnormal and may be caused by an aberrant TNF‐α response in these cells. Thus, TNF‐α alone or in combination with pro‐inflammatory and T‐cell stimulatory cytokines should be considered as an adjuvant for DC‐based immunotherapy in CML.

Stem cell transplantation from unrelated donors is associated with an increased risk of graft failure and graft-versus-host disease (GVHD). Addition of pretransplant antithymocyte globulin (ATG), although reducing the risk of graft rejection and GVHD, bears the risk of overimmunosuppression, resulting in an increased relapse rate and transplant-related mortality. Therefore, we evaluated in 21 consecutive patients receiving unrelated stem cell grafts from either HLA-matched (38%) or -mismatched (62%) donors whether low-dose rabbit ATG added to cyclosporin A and methotrexate at a total dose of 3.5 mg/kg for HLA-identical and 5.0 mg/kg for HLA-mismatched transplants given in two divided doses on days -2 and -1 provides sufficient immunosuppression for prevention of GVHD and graft rejection but is associated with an acceptable risk of relapse and transplant-related mortality. Stable leukocyte engraftment was achieved in all patients (100%). Overall survival after a median follow-up of 26 (median, range 14-42) months was 56 +/- 26% (95% confidence interval, CI) and the overall relapse rate at 3 years was 24 +/- 21%. Three-year survival for standard-risk patients, i.e., chronic myeloid leukemia (CML) in first chronic phase or acute leukemia in first complete remission, was 87% +/- 13% versus 40% +/- 31% for patients with more advanced disease. The incidence of acute GVHD II-IVdegrees was 55 +/- 22%; that of severe acute GVHD III-IVdegrees was 21 +/- 19%. Chronic GVHD was observed in 5/17 (29%) patients surviving more than 100 days post stem cell transplantation. Transplant-related mortality was 16 +/- 15% (95% CI) at day + 100 and 25 +/- 19% (95% CI) at 1 year after the transplant. The data presented show that pretransplant in vivo T cell depletion with low-dose rabbit ATG results in a low transplant-related mortality due to a low incidence of severe acute and chronic GVHD and a low relapse rate. To find out the optimal rabbit ATG dose in the unrelated stem cell transplantation setting, further dose-finding studies comparing high- and low-dose regimens are necessary.

HLA-A2-restricted T cells show peptide-specific activity against cytomegalovirus and leukaemia cells. We retrospectively analysed the influence of donor cytomegalovirus serostatus on the outcome of 103 consecutive patients who had leukaemia and who received bone-marrow transplants from HLA-identical sibling donors. We found that donor cytomegalovirus seropositivity significantly improved overall survival (p=0.02) as a result of lower relapse incidence (p=0.035) in HLA-A2-positive but not HLA-A2-negative recipients. In HLA-A2-positive recipients donor cytomegalovirus seropositivity was associated with chronic graft-versus-host disease (GVHD), but even in patients without chronic GVHD donor cytomegalovirus seropositivity significantly improved survival (p=0.0483). These preliminary data provide evidence that at least in HLA-A2-positive recipients, transplantation of bone marrow from cytomegalovirus positive, HLA-identical sibling donors seems to be associated with substantial graft-versus-leukaemia activity, and suggests a cross-reactivity of cytomegalovirus-specific donor-derived cytotoxic T cells with HLA-A2-restricted recipient minor histocompatibility antigens.

The gene of the leukocyte-specific transcript (LST1) is encoded within the TNF region of the human MHC. The LST1 gene is constitutively expressed in leukocytes and dendritic cells, and it is characterized by extensive alternative splicing. We identified 7 different LST1 splice variants in PBMC; thus, 14 LST1 splice variants (LST1/A-LST1/N) have been detected in various cell types. These isoforms code for transmembrane as well as soluble LST1 proteins characterized by two alternative open reading frames at their 3' end. We demonstrate the presence of the transmembrane variant LST1/C on the cell surface of the monocytic cell lines U937 and THP1. Recombinant expression of LST1/C permitted its profound inhibitory effect on lymphocyte proliferation to be observed. In contrast, the alternative transmembrane variant LST1/A, the extracellular domain of which shows no amino acid sequence homology to LST1/C exerted a weaker but similar inhibitory effect on PBMC. These data demonstrate the protein expression of LST1 on the cell surface of mononuclear cells, and they show an inhibitory effect on lymphocyte proliferation of two LST1 proteins although they have only a very short amino acid homology.

The gene of the leukocyte-specific transcript (LST1) is encoded within the TNF region of the human MHC. The LST1 gene is constitutively expressed in leukocytes and dendritic cells, and it is characterized by extensive alternative splicing. We identified 7 different LST1 splice variants in PBMC; thus, 14 LST1 splice variants (LST1/A-LST1/N) have been detected in various cell types. These isoforms code for transmembrane as well as soluble LST1 proteins characterized by two alternative open reading frames at their 3′ end. We demonstrate the presence of the transmembrane variant LST1/C on the cell surface of the monocytic cell lines U937 and THP1. Recombinant expression of LST1/C permitted its profound inhibitory effect on lymphocyte proliferation to be observed. In contrast, the alternative transmembrane variant LST1/A, the extracellular domain of which shows no amino acid sequence homology to LST1/C exerted a weaker but similar inhibitory effect on PBMC. These data demonstrate the protein expression of LST1 on the cell surface of mononuclear cells, and they show an inhibitory effect on lymphocyte proliferation of two LST1 proteins although they have only a very short amino acid homology.

In Misiones, in the northeast of Argentina, agroforestry systems of timber trees and perennial cash crops are becoming increasingly common. We evaluated the productivity of Ilex paraguariensis St Hill (South American holly or yerba mate, Aquifoliaceae) in association with indigenous trees: Enterolobium contortisiliquum (Vellozo) Morong. (timbó, Leguminosae, a N2-fixing tree), and two timber species, Balfourodendron riedelianum (Engler) Engler (guatambú, Rutaceae) and Tabebuia heptaphylla (Vellozo) Toledo (lapacho negro, Bignoniaceae). Five years after planting, the tree species were 2.7 to 5.0 m high and 3 to 7 cm in diameter at breast height, and the yerba mate produced its first harvest. Additionally, the production of associated crops of subsistence covered the annual needs of the farmer. These systems are promising for sustainable use of deforested lands in the region.