Specific depletion of alloreactive T cells in HLA-identical siblings: a method for separating graft-versus-host and graft-versus-leukaemia reactions

Accumulating evidence indicates that alloreactive donor T cells confer both graft-versus-host (GVH) and graft-versus-leukaemia (GVL) reactivity following allogeneic bone marrow transplantation. We have developed a method to deplete alloreactive donor T cells with an immunotoxin targeting the alpha chain of the IL-2 receptor. In patients with chronic myeloid leukaemia and their HLA-identical sibling donors, we measured donor helper T-lymphocyte precursor frequencies (HTLPf) against recipient peripheral blood mononuclear cells (PBMNC; donor versus host), recipient leukaemia cells (donor versus leukaemia) and third-party PBMNC, before and after the depletion. In seven pairs there was a 4.3-fold reduction of donor-versus-host HTLPf (P=0.017), without a significant change in the donor frequencies against third party (P=0.96). In eight further donor-recipient pairs, immunotoxin-depleted donor versus patient PBMNC HTLPf 4.5-fold (mean 1/155,000 before and 1/839,000 after depletion, P=0.007). There was a smaller non-significant 1.8-fold reduction in donor-versus-leukaemia HTLPf from 1/192,000 to 1/334,000 (P=0.19). These results suggest that selective T-cell depletion can significantly deplete donor anti-host reactivity while conserving anti-leukaemia reactivity in HLA-matched donor-recipient pairs.

HLA binding characteristics and generation of cytotoxic lymphocytes against peptides derived from oncogenic proteins

AIMS AND BACKGROUND

Structurally altered proteins (derived from chromosomal translocations or gene mutations) can be considered tumor specific antigens and represent an attractive target for a T-cell mediated response. T lymphocytes recognize antigens in the form of peptides bound to HLA-molecules.

MATERIALS AND METHODS

Peptides derived from oncogenic proteins were screened for the presence of HLA binding motifs; actual binding were evaluated by HLA stabilization experiments using transfectants and specific anti-HLA antibodies. Specific lymphocytes were induced by in vitro peptide sensitization and screened by thymidine uptake or cellular cytotoxic assays.

RESULTS

We identified peptides derived from EWS/FLI-1 fusion protein and from mutated K-RAS protein (encompassing respectively the fusion point and the mutation at position 12) that showed binding motif for HLA-Cw*0702 and HLA-A3 respectively. The actual binding of these peptides was analysed in a stabilization assay. We detected binding for the EWS/FLI-1 peptide and for 5 RAS peptides (1 wild type and 4 mutated). The effect of temperature, beta 2-microglobulin (beta 2-m) and fetal calf serum (FCS) on the binding and the stability of the HLA/peptide complex was studied. A low temperature (26 degrees C) increased the binding both in HLA-A3 and HLA-Cw*0702, while FCS reduced it. beta 2-m increased the binding to the HLA-A3 molecule but did not influence the binding to the HLA-Cw*0702. The stability of already formed complexed was somewhat different in the HLA-A3 and HLA-Cw*0702 system: both were more stable at 26 degrees C than at 37 degrees C but while the beta 2-m and FCS did not influence the stability of the HLA-A3/peptide complex, they seemed to cause opposite effects in the HLA-Cw*0702 system (beta 2-m stabilized and FCS destabilized the complex). Finally, we were able to generate a specific CD8+ CTL line against a K-RAS mutated peptide.

CONCLUSIONS

Although binding motifs and actual HLA binding can be detected in several cases, the generation of a cellular response is infrequent, confirming that HLA binding is necessary but not sufficient to obtain an in vitro response. Further optimization of culture conditions, type of Antigen Presenting Cells (APC), peptides, use of stabilizers like beta 2-m are still needed.

Preferential usage of T cell receptor (TCR) V beta by allogeneic T cells recognizing myeloid leukemia cells: implications for separating graft-versus-leukemia effect from graft-versus-host disease

New understanding of the alloresponse following bone marrow transplantation supports the possibility that the graft-versus-host disease (GVHD) response can be separated from a favorable graft-versus-leukemia (GVL) effect. We used chronic myeloid leukemia (CML) cells to generate 122 recipient-reactive T cell clones from a closely HLA-matched sibling responder. Clones were tested for their proliferative response to stimulator CML cells or PHA-transformed (non-leukemic) lymphoblasts. Of 78 clones tested, 32 recognized both leukemia cells and PHA blasts, 19 only CML and four only PHA blasts. The remainder were non-specific responders. This functional specificity corresponded to distinct patterns of T cell receptor (TCR) V beta usage: clones recognizing CML cells preferentially used V beta 5, V beta 6/7 while clones recognizing both CML and PHA blasts or only PHA blasts preferentially used V beta 3 and V beta 8. It may therefore be possible to identify in vitro-generated myeloid leukemia-restricted donor T cells by their pattern of V beta usage. TCR V beta antibodies could thus be used to select and expand leukemia-restricted donor T cells for transfusion after BMT to specifically enhance the GVL response.

Mapping of HLA class I binding motifs in forty-four fusion proteins involved in human cancers

Chromosomal translocations coding for abnormal proteins are present in several human cancers. The junctional region of fusion proteins represents a potential target for a T cell-mediated antitumor response. T lymphocytes recognize antigens in the form of short peptides that must bind to HLA molecules. Different HLA specificities can bind different peptides, thus depicting different "peptide binding motifs." It would be useful to know whether a certain fusion protein presents, within its fusion region, the binding motif(s) for a certain HLA molecule. This information would allow a more focused immunological analysis. Here we present data obtained from the screening of the fusion regions of 44 different fusion proteins for the presence of binding motifs to 34 class I HLA molecules, including all of the most frequently encountered specificities. A total of 201 independent peptides was identified (range, 0-11 peptides/fusion protein). A marked heterogeneity among the 44 different fusion proteins analyzed is evident. For example, the pml/RARalpha fusion protein present in acute promyelocytic leukemia presents no binding motif (BCR 3) at all or to a single HLA molecule (Cw*0301, BCR 1). Alternatively, the fusion proteins BCR/ABL, ALL1/AF-6, EWS/ATF-1, or NPM/ALK exhibit motifs for several common HLA specificities. Heterogeneity is also present inside a single translocation (in ALL1/ENL, for example, different subtypes match motifs with cumulative frequencies in the population from 108 to 0%). In two cases where the relative frequency of different fusion protein subtypes was available, a tendency toward an inverse relationship between frequency and the percentage of population covered by the identified binding motifs was observed. Peptides with motifs for HLA A*0201, A3, and Cw*0702 were also tested for actual binding using a stabilization assay; 13-40% showed significant HLA binding, using this assay. However, fewer fusion protein-derived peptides bound to HLA A*0201 and A3 than non-fusion protein-derived peptides. These data provide the first list of peptides derived from fusion proteins that may be assessed as potential tumor-specific antigens.

Immune escape from a graft-versus-leukemia effect may play a role in the relapse of myeloid leukemias following allogeneic bone marrow transplantation

We studied patients relapsing with myeloid leukemias following allogeneic bone marrow transplantation (BMT) for evidence of immune escape by clonal evolution of the leukemia. Relapsed cells from four out of five patients had a reduced ability to stimulate proliferation of lymphocytes from an HLA-mismatched responder. There was decreased susceptibility to lysis by CTL in three and reduced susceptibility to NK-mediated lysis in one. Relapsed leukemias had marked alterations in expression of critical surface molecules involved in immune responsiveness. Three had decreased expression of MHC class I and II, with no change or increase in CD54 (ICAM-1) or CD80 (B7.1). None of these responded to treatment with donor lymphocytes. Three patients showed no change, or increased expression of MHC with no change or decrease in ICAM-1 or B7.1. Two achieved remission - one in response to donor lymphocytes and one following withdrawal of cyclosporine. In one patient transplanted with myelodysplastic syndrome in transformation, interferon-gamma upregulated expression of MHC molecules in relapsed cells and increased their stimulatory capacity and target susceptibility to unmatched responder lymphocytes. These results suggest that immune escape through clonal evolution of the leukemia is a common occurrence in patients who relapse with myelogenous leukemias after BMT.

Targeted T-cell therapy for human leukemia: cytotoxic T lymphocytes specific for a peptide derived from proteinase 3 preferentially lyse human myeloid leukemia cells

Proteinase 3 is present in high concentration in the primary granules of acute and chronic myeloid leukemia blasts, and may represent a potential T-cell target antigen. We screened proteinase 3 against the binding motif of HLA-A2.1. Based on its high predicted binding, a 9-mer peptide, "PR-1," was synthesized and tested for binding to HLA-A2.1 using the T2 cell line. PR-1 at 100 micrograms/mL significantly increased expression of HLA-A2.1, with median channel of fluorescence increasing from 22 to 294. Binding half-life was determined to be 1,460 minutes by I125-labeled beta 2-microglobulin incorporation. HLA-A2.1+ peripheral blood mononuclear cells from a normal donor were used to generate a T-cell line specific for PR-1. The line demonstrated 85% PR-1-specific lysis at an E:T ratio of 50:1, compared with 20% lysis without PR-1, using T2 cells as targets. It also showed 79% specific lysis to fresh chronic myelogenous leukemia blasts, 54% to fresh acute myelogenous leukemia blasts, and only background lysis (< 20%) to HLA-A2.1+ normal allogeneic marrow cells. The amount of lysis of HLA-A2.1+ myeloid cells was proportional to cytoplasmic proteinase 3 expression. Thus, HLA-A2.1-restricted cytotoxic T cells, raised against a peptide contained in proteinase 3, preferentially lysed fresh human leukemic cells.

Alloreactive CD4+ T lymphocytes can exert cytotoxicity to chronic myeloid leukaemia cells processing and presenting exogenous antigen

Existing evidence supports that CD4+ T lymphocytes play a role in the graft-versus-leukaemia (GVL) reaction after allogeneic bone marrow transplantation (BMT) for chronic myeloid leukaemia (CML), not only as initiators of the immune response but also as effectors of GVL. In BMT between HLA-identical pairs this CD4-mediated GVL would require CML cells to process and present antigens through MHC class II molecules. To investigate whether CML cells are capable of processing and presenting antigens, and suitable targets for CD4+ T-cell-mediated cytotoxicity, we generated HLA-DR1-restricted CD4+ cytotoxic T-cell clones that specifically recognized tuberculous purified protein derivative (PPD). We have shown that CML cells and B lymphoblastoid cell line (B-LCL) cells but not PHA-blasts from patients with CML processed exogenous antigen, PPD, and induced proliferative and cytotoxic CD4+ T-cell responses. Antigen presentation was blocked by antibodies to HLA-DR but not to MHC class I and by treatment with chloroquine and brefeldin. This indicates that CML cells use a classic MHC class II antigen processing pathway to present PPD antigens to CD4+ T cells. Cytotoxicity to CML was shown by antibody blocking studies to be mediated mainly through fas antigen. These findings indicate that donor CD4+ T cells alone are sufficient to mediate GVL effects following allogeneic BMT for CML.

Interaction of natural killer cells with MHC class II: reversal of HLA-DR1-mediated protection of K562 transfectant from natural killer cell-mediated cytolysis by brefeldin-A

Major histocompatibility complex (MHC) class I antigens on tumour cell surfaces have been shown to modulate target susceptibility to natural killer (NK) cell-mediated lysis in some, although not all, systems investigated. MHC class II expression may also affect NK cell function, but the mechanism by which MHC class II antigen regulates NK cell activity has not been fully examined. In this study we induced HLA-DR1 expression by gene transfection into the classic NK-sensitive K562 cell line to study the interaction of NK cells with MHC class II molecules and the effect of brefeldin-A (BFA), an endogenous antigen-processing pathway blocker, on NK-target cell interaction. We demonstrated that the expression of HLA-DR1 on the cell surface reduced K562 cell susceptibility to NK lysis by peripheral blood monuclear cells and a NK cell line. The effect was demonstrable in prolonged (8 hr) cytotoxicity assays and was blocked by pretreatment of target cells with anti-HLA-DR antibody. Treatment of K562 DR transfectant with BFA abrogated the resistance of K562 transfectant to NK-mediated cytolysis. These findings indicate that HLA class II molecules regulate NK cell function and target recognition, and suggest that endogenous peptides presented through MHC molecules are responsible for regulating NK cytolysis.

Lack of T-cell-mediated recognition of the fusion region of the pml/RAR-alpha hybrid protein by lymphocytes of acute promyelocytic leukemia patients

In previous studies, it was shown that the fusion region of the pml/RAR-alpha protein, expressed by acute promyelocytic leukemia (APL) cells, can be specifically recognized in vitro by donor (D. E. ) CD4 T cells in a HLA class II DR11-restricted fashion. We present here the results on the recognition of several pml/RAR-alpha peptides by APL patients expressing HLA DR11. The in vitro immunization of peripheral blood lymphocytes from four patients in remission (S. R., F. R., M. M., P. G.) with BCR1/25, a 25-mer pml/RAR-alpha, did not elicit either a polyclonal or a clonal immune response specific to the peptide. We then generated new donor anti-pml/RAR-alpha CD4(+) T-cell clones. These clones were tested for their recognition of BCR1/25. One clone (C3/5, CD3(+), CD4(+), CD8(-)) was selected for further analysis. Clone C3/5 showed specific proliferation, cytotoxicity, and cytokine (tumor necrosis factor alpha, granulocyte-macrophage colony-stimulating factor) production when challenged with autologous lymphoblastic cell lines pulsed with peptide BCR1/25. C3/5 cells developed specific proliferation and cytotoxicity when challenged with peptide-pulsed lymphoblastic cell lines and peripheral blood lymphocytes from the four DR11(+) APL patients. APL blasts, available only from patients F. R. and P. G., were not lysed by C3/5 and were unable to present peptide BCR1/25. Incubation of APL cells with IFN-gamma failed to induce HLA class II molecules and recognition by the C3/5 clone. Since APL cells do not express HLA class II molecules, we tested in two donors (D. E. and C. H. R.) and in patients S. R. and P. G. whether the use of 9-mer peptides (BCR1/9) would generate a CD8/HLA class I-restricted response. No peptide-specific T-cell line or clone could be generated from both donors and patients. These findings are discussed in relation to possible therapeutic approaches to the immunotherapy of APL.

The role of the immune system in anti-tumour responses. Potential for drug therapy

In the last 5 years significant progress has been made in our understanding of the molecular nature of anti-tumour T cell-mediated responses. This review describes the involvement of the cellular immune system in the recognition and destruction of cancer cells. Four aspects are discussed: (i) the generalized immune activation induced by the systemic administration of cytokines, in particular, interleukin-2; (ii) the specific T cell-mediated reactions against tumour cells through the recognition of tumour-associated molecules, 1) and tyrosinase proteins described in melanomas, and minor histocompatibility antigens in the setting of allogenic bone marrow transplantation for leukaemia; (iii) the potentially significant but still hypothetical immune-mediated recognition of molecules either tumour-associated or transformation-related (including altered oncogenic proteins); and (iv) the role of co-stimulatory molecules in the induction of tumour-specific immunity. The current and future therapeutic applications in cancer treatment and potential limitations in this approach are discussed.

Acute promyelocytic leukaemia cells resistant to retinoic acid show further perturbation of the RAR alpha signal transduction system

Acute promyelocytic leukaemia (APL) cell lines resistant to all-trans retinoic acid (ATRA) have been previously derived from the NB4 cell line, and characterized as having lost the expression of the intact pml/RAR alpha fusion protein. To confirm the association between ATRA-resistance and alteration in the fusion protein at the clonal level, 16 clones were generated from ATRA-resistant APL cell lines. All clones show immunological (HLA class I and II, CD11b and c, CD13 and 33), molecular and growth features similar to the parental cell lines. To investigate whether the irradiation protocol used to generate the previously reported retinoic acid-resistant NB4.306 cell line induced additional alterations that could render these cells able to escape the anti-proliferative effect of retinoic acid (ATRA), an additional ATRA-resistant APL cell line, [NB4.007/6], was generated, under the selective pressure of ATRA, from the NB4 cell line without previous radiation. This cell line shows resistance to the anti-proliferative and differentiating action of ATRA. The NB4.007/6 cell line contains the t(15;17) chromosome translocation, shows the usual pml/RAR alpha hybrid DNA but expresses no detectable amount of the usual pml/RAR alpha protein in Western blot analysis, similarly to the NB4.306 cell line. Finally, the relative resistance to ATRA of NB4.306 and NB4.007/6 was evaluated by comparing the phenotypic (CD11b) changes induced by ATRA in these two lines with those induced in the parental, ATRA-sensitive, NB4 cell line. It is estimated that NB4.306 and NB4.007/6 are about 300 and 70 times less sensitive to ATRA than the original NB4 cell line.

Occurrence of resistance to retinoic acid in the acute promyelocytic leukemia cell line NB4 is associated with altered expression of the pml/RAR alpha protein

The mechanism(s) by which acute promyelocytic leukemia (APL) cells acquire resistance to all-trans retinoic acid (ATRA) is poorly understood. We describe here an APL cell line, named NB4.306, that shows resistance to the anti-proliferative action of ATRA. This cell line is also operationally resistant to most ATRA-induced phenotypic modifications (CD11b, CD11c, CD13, and CD33). No significant differences in ATRA intracellular accumulation, efflux, or metabolism were found between NB4.306 and the parent NB4 cell line that could explain the observed resistance of the NB4.306 line. The NB4.306 cell line was found to be positive for the t15;17 translocation and showed the usual pml/RAR alpha fusion bands in both Southern and Northern blot assays, but expressed no detectable amount of the usual pml/RAR alpha protein, as assayed by Western blot analysis using an anti-RAR alpha antibody. These results were confirmed in 14 of 14 clones obtained from the NB4.306 cell line, while 30 of 30 clones obtained from the parental NB4 line expressed the usual 110-Kd fusion polypeptide. It is concluded that the occurrence of resistance to ATRA in the NB4.306 cell line is closely associated to the loss of expression of the intact pml/RAR alpha protein.