Minor histocompatibility antigen DDX3Y induces HLA-DQ5-restricted T cell responses with limited TCR-Vbeta usage both in vivo and in vitro.

In vitro stimulation of human female T cells with male HLA-identical dendritic cells resulted in the generation of HLA-DQB1*0501/0502-restricted minor histocompatibility H-Y antigen-specific CD4(+) T cell clones. Two clones generated from different HLA-identical pairs were analyzed. Use of HLA-DQ5-expressing female Epstein-Barr virus transformed B lymphoblastoid cell lines transfected with various H-Y genes and loaded with overlapping peptides demonstrated that both T cell clones are specific for a peptide encoded by DDX3Y. Previously, an HLA-DQ5-restricted T cell clone specific for the same peptide was isolated from a patient with graft-versus-host disease. Thus, we compared the T cell receptor (TCR) rearrangements of the 2 in vitro generated T cell clones and the ex vivo isolated T cell clone. All 3 clones shared the same TCRBV5-4* gene segment and 2 of 3 clones also used similar TCR-Valpha segments. Our results suggest that T cells recognizing the HLA-DQ5/DDX3Y T cell epitope might be characterized by a relatively limited TCR-beta repertoire. The differences in the junctional TCR-beta region had no effect on the antigen specificity, but altered the capacity of the TCR to distinguish the HLA-DQ5/DDX3Y complex from its allelic counterpart. The results also demonstrate that in vitro stimulation of T cells with allogeneic HLA-identical dendritic cells may facilitate the characterization of in vivo, potentially relevant HLA class II-restricted minor H epitopes.     

A novel approach to identify antigens recognized by CD4 T cells using complement-opsonized bacteria expressing a cDNA library.

In patients with hematological malignancies receiving HLA-matched stem cell transplantation, T cells specific for minor histocompatibility antigens play a major role in graft rejection, induction of graft-versus-host disease and beneficial graft-versus-leukemia reactivity. Several human minor histocompatibility antigens recognized by T cells have been identified, but only two are presented by HLA class II molecules. In search of an efficient approach to identify antigenic peptides processed through the HLA class II pathway, we constructed a cDNA library in bacteria that were induced to express proteins. Bacteria were opsonized with complement to enforce receptor-mediated uptake by Epstein-Barr virus immortalized B cells that were subsequently used as antigen-presenting cells. This approach was validated with an HLA class II-restricted antigen encoded by gene DBY. We were able to identify bacteria expressing DBY diluted into a 300-fold excess of bacteria expressing a nonrelevant gene. Screening of a bacterial library using a DBY-specific CD4 T cell clone resulted in the isolation of several DBY cDNAs. We propose this strategy for a rapid identification of HLA class II-restricted antigenic peptides recognized by CD4 T cells.     

An animal model for human cellular immunotherapy: specific eradication of human acute lymphoblastic leukemia by cytotoxic T lymphocytes in NOD/scid mice

Adoptive immunotherapy using in vitro-generated donor-derived cytotoxic T lymphocytes (CTLs) can be effective in the treatment of relapsed leukemia after allogeneic transplantation. To determine effector cell characteristics that result in optimal in vivo antileukemic efficacy, we developed an animal model for human CTL therapy. Nonobese diabetic/severe combined immunodeficiency (NOD/scid) mice were inoculated with either of 2 primary human acute lymphoblastic leukemia (ALL), denoted as SK and OF. Anti-SK and anti-OF CTLs were generated in vitro by repeated stimulation of donor peripheral blood mononuclear cells with either SK or OF cells. Both CTL lines displayed HLA-restricted reactivity against the original targets and non-major histocompatibility class (MHC)-restricted cross-reactivity in vitro. The CTLs were administered intravenously weekly for 3 consecutive weeks to mice engrafted with either SK or OF leukemia. In 3 of 8 SK-engrafted and anti-SK-treated mice, complete remissions were achieved in blood, spleen, and bone marrow. In the remaining 5 animals partial remissions were observed. In 4 of 4 OF-engrafted anti-OF-treated mice partial remissions were observed. The antileukemic effect of specific CTLs was exerted immediately after administration and correlated with the degree of HLA disparity of the donor-patient combination. In cross-combination-treated animals, no effect on leukemic progression was observed indicating that in vivo antileukemic reactivity is mediated by MHC-restricted effector cells. The CTLs, however, displayed an impaired in vivo proliferative capacity. Ex vivo analysis showed decreased reactivity as compared to the moment of infusion. We therefore conclude that the model can be used to explore the requirements for optimal in vivo efficacy of in vitro- generated CTLs.     

New CFSE-based assay to determine susceptibility to lysis by cytotoxic T cells of leukemic precursor cells within a heterogeneous target cell population

For the clinical evaluation of the efficacy of cellular immunotherapy it is necessary to analyze the effector functions of T cells against primary leukemic target cell populations which are usually considerably heterogeneous caused by differential maturation stages of the leukemic cells. An appropriate assay should not only allow the quantitative analysis of rapid cell death induction as measured by the conventional 51Cr release assay but also of the more slowly executing pathways of T-cell-induced apoptosis occurring within days instead of hours which cannot be measured using this method. Furthermore, it should dissect the differential susceptibility to T-cell-induced cell death of various target cell subpopulations and characterize the malignant precursor cells capable of producing malignant progeny. To fulfill these requirements we developed a new assay based on carboxyfluorescein diacetate succinimidyl ester (CFSE) labeling of the target cell population combined with antibody staining of specific cell populations and addition of fluorescent microbeads to quantitatively monitor target cell death occurring within a longer time frame up to at least 5 days. This new assay facilitates the analysis of differential recognition of distinct cell types within a heterogeneous target cell population and allows simultaneously evaluation of the proliferative status of surviving target cells in response to relevant cytokines.     

Effect of mast cell growth factor (c-kit ligand) on clonogenic leukemic precursor cells.

Mast cell growth factor (MGF), the ligand for the c-kit receptor, has been shown to be a hematopoietic growth factor that preferentially stimulates the proliferation of immature hematopoietic progenitor cells (HPC). We studied the effect of MGF on the in vitro growth of clonogenic leukemic precursor cells in the presence or absence of interleukin-3 (IL-3), granulocyte-macrophage colony-stimulating factor (GM-CSF), and/or erythropoietin (EPO). Leukemic blood and bone marrow cells from patients with various types of acute myeloid leukemia (AML), chronic myeloid leukemia (CML) in chronic phase, as well as bone marrow samples from patients with myelodysplastic syndromes (MDS) were studied. MGF as a single factor did not induce significant colony formation by clonogenic leukemic precursor cells. In the presence of IL-3 and/or GM-CSF, MGF weakly stimulated the colony formation by clonogenic precursor cells from patients with AML. In contrast, in the presence of IL-3 and/or GM-CSF, MGF strongly induced both size and number of leukemic colonies from patients with CML in chronic phase. Furthermore, in the presence of EPO, MGF strongly stimulated erythroid colony formation by CML precursor cells. Cytogenetic analysis of the colonies showed that all metaphases after 1 week of culture were derived from the leukemic clone. In patients with MDS, MGF strongly stimulated myeloid colony formation in the presence of IL-3 and/or GM-CSF (up to fourfold), and erythroid colony formation in the presence of EPO (up to eightfold). Not only the number, but also the size of the colonies increased. In the presence of MGF, the percentage of normal metaphases increased in three patients tested after 1 week of culture compared with the initial suspension, suggesting that the normal HPC were preferentially stimulated compared with the preleukemic precursor cells. In the absence of exogenous EPO and in the presence of 10% human AB serum, MGF in the presence of IL-3 and/or GM-CSF induced erythroid colony formation from normal bone marrow and patients with MDS or CML, illustrating that MGF greatly diminished the EPO requirement for erythroid differentiation. These results indicate that MGF may be a candidate as a hematopoietic growth factor to stimulate normal hematopoiesis in patients with acute myeloid leukemia, or with myelodysplastic syndromes.     

Influence of T-lymphocytes and lactoferrin on the survival-promoting effects of IL-1 and IL-6 on human bone marrow granulocyte-macrophage and erythroid progenitor cells

Purified recombinant human (rhu) interleukin (IL)-1 alpha, rhuIL-6, iron saturated lactoferrin (LF), and T-lymphocytes were assessed for their effects on the survival of granulocyte-macrophage (granulocyte-macrophage colony-forming units, CFU-GM) and erythroid (erythroid burst-forming units, BFU-E) progenitor cells from human low-density (LD) and nonadherent LD T-lymphocyte-depleted (NALT-) bone marrow (BM) cells. Colony-stimulating factor (CSF) deprivation studies showed that 10 ng/ml IL-1 alpha could promote the survival of CFU-GM and BFU-E from NALT- BM cells. Concentrations of 1 ng/ml IL-1 alpha and 1-100 ng/ml IL-6 alone could not promote progenitor cell survival from NALT- BM cells; however, concentrations of 1 ng/ml each of IL-1 alpha and IL-6 could synergize to promote the survival of CFU-GM but not of BFU-E. The combination of these low concentrations of IL-1 alpha and IL-6 could, however, support the survival of BFU-E in the presence of purified T-lymphocytes. LF could decrease the survival of CFU-GM and BFU-E from LD but not from NALT- BM cells, apparently due to the inhibition of IL-1 release from monocytes in this cell population. The suppressive effect of LF on the survival of those progenitor cells was abolished by concentrations of 10 ng/ml IL-1 alpha or 1 ng/ml each of IL-1 alpha and IL-6. These results demonstrate that the survival of human marrow CFU-GM and BFU-E can be influenced by IL-1, IL-6, LF, and T-lymphocytes.     

Bone marrow transplantation or chemotherapy as post-remission treatment of adult acute myelogenous leukemia

Summary We compared three consolidation regimens in patients with acute myelogenous leukemia in first remission. Thirty-four patients received only intensive consolidation chemotherapy (SIC); 28 patients were scheduled to undergo an autologous bone marrow transplant (auto-BMT) and 44 patients an allogeneic BMT (allo-BMT). Twenty-seven of them were referred in first remission for allo-BMT. Nineteen patients achieved a complete remission after salvage treatment. All other patients obtained a remission after one or two courses of a standard combination of cytosine arabinoside and daunorubicin. Except for the patients who were referred in remission, all patients received intermediate dose cytosine arabinoside and amsacrine as a first consolidation treatment. The median ages of the three groups were 48 (SIC), 39 (auto-BMT) and 33 years (allo-BMT). Two patients relapsed before auto-BMT and 1 before allo-BMT. The median interval from the date of complete remission to the auto- or allo-BMT was 3 months. In total, 80% of the patients of the SIC group relapsed, compared to 50% of the patients belonging to the auto-BMT group and 35% of the 44 patients who were scheduled to receive an allo-BMT. The overall median disease-free survival was 14 months, 30% of the patients being alive and disease-free at 3 years. The disease-free survival rate at three years was 25% for the SIC group, 30% for the allo-BMT group and 40% for the ABMT group (P=0.45). Our study shows no benefit for bone marrow transplantation over intensive consolidation treatment. However, large randomized trials are required to define the real value of these treatment modalities.     

Mixed functional characteristics correlating with TCR‐ligand koff‐rate of MHC‐tetramer reactive T cells within the naive T‐cell repertoire

The low frequency of antigen‐specific naïve T cells has challenged numerous laboratories to develop various techniques to study the naïve T‐cell repertoire. Here, we combine the generation of naïve repertoire‐derived antigen‐specific T‐cell lines based on MHC‐tetramer staining and magnetic‐bead enrichment with in‐depth functional assessment of the isolated T cells. Cytomegalovirus (CMV) specific T‐cell lines were generated from seronegative individuals. Generated T‐cell lines consisted of a variety of immunodominant CMV‐epitope‐specific oligoclonal T‐cell populations restricted to various HLA‐molecules (HLA‐A1, A2, B7, B8, and B40), and the functional and structural avidity of the CMV‐specific T cells was studied. Although all CMV‐specific T cells were isolated based on their reactivity toward a specific peptide‐MHC complex, we observed a large variation in the functional avidity of the MHC‐tetramer positive T‐cell populations, which correlated with the structural avidity measured by the recently developed Streptamer k_off‐rate assay. Our data demonstrate that MHC‐tetramer staining is not always predictive for specific T‐cell reactivity, and challenge the sole use of MHC‐tetramers as an indication of the peripheral T‐cell repertoire, independent of the analysis of functional activity or structural avidity parameters.     

Minor histocompatibility antigens HA-1-, -2-, and -4-, and HY-specific cytotoxic T-cell clones inhibit human hematopoietic progenitor cell growth by a mechanism that is dependent on direct cell-cell contact

HLA-identical bone marrow transplantation (BMT) may be complicated by graft-versus-host disease or graft rejection. Both complications are thought to be initiated by recognition of minor histocompatibility (mH) antigens by HLA-restricted mH-antigen-specific T lymphocytes. Using HLA- A2-restricted mH antigens HA-1-, -2-, and -4-, and HY-specific cytotoxic T lymphocyte (CTL) clones, we studied the recognition by these CTL clones of interleukin-2 (IL-2)-stimulated T cells (IL-2 blasts), BM mononuclear cells (BMMNCs), and hematopoietic progenitor cells (HPCs). We showed that, when IL-2 blasts from the BM donors who were investigated were recognized by the HA-1-, -2-, and -4-, and HY- specific CTL clones, their BMMNCs and HPCs were recognized as well by these CTL clones, resulting in antigen-specific growth inhibition of erythrocyte burst-forming units (BFU-E), colony-forming units- granulocyte (CFU-G), and CFU-macrophage (CFU-M). the HA-2-specific CTL clone, however, inhibited BFU-E and CFU-G growth from four donors to a lesser extent than from two other donors. We further investigated whether inhibitory cytokines released into the culture medium by the antigen-specific stimulated CTLs or by stimulated BMMNCs were responsible for suppression of HPC growth or whether this effect was caused by direct cell-cell contact between CTLs and HPCs. HPC growth inhibition was only observed after preincubation of BMMNCs and CTLs together for 4 hours before plating the cells in semisolid HPC culture medium. When no cell-cell contact was permitted before plating, neither antigen-stimulated CTL nor antigen-nonstimulated CTLs provoked HPC growth inhibition. Culturing BMMNCs in the presence of supernatants harvested after incubation of BMMNCs and CTL clones together for 4 or 72 hours did also not result in HPC growth inhibition. Both suppression of HPC growth and lysis of IL-2 blasts and BMMNCs in the 51Cr-release assay appeared to be dependent on direct cell-cell contact between target cells and CTLs and were not caused by the release of inhibitory cytokines into the culture medium by antigen-specific stimulated CTLs or by stimulated BMMNCs. Our results show that mH-antigen-specific CTLs can inhibit HPC growth by a direct cytolytic effect and may therefore be responsible for BM graft rejection after HLA-identical BMT.