PR1 peptide vaccine induces specific immunity with clinical responses in myeloid malignancies

PR1, an HLA-A2-restricted peptide derived from both proteinase 3 and neutrophil elastase, is recognized on myeloid leukemia cells by cytotoxic T lymphocytes (CTL) that preferentially kill leukemia and contribute to cytogenetic remission. To evaluate safety, immunogenicity and clinical activity of PR1 vaccination, a phase I/II trial was conducted. Sixty-six HLA-A2+ patients with acute myeloid leukemia (AML: 42), chronic myeloid leukemia (CML: 13) or myelodysplastic syndrome (MDS: 11) received three to six PR1 peptide vaccinations, administered subcutaneously every 3 weeks at dose levels of 0.25, 0.5 or 1.0 mg. Patients were randomized to the 3 dose levels after establishing the safety of the highest dose level. Primary endpoints were safety and immune response, assessed by doubling of PR1/HLA-A2 tetramer-specific CTL, and the secondary endpoint was clinical response. Immune responses were noted in 35 of 66 (53%) patients. Of the 53 evaluable patients with active disease, 12 (24%) had objective clinical responses (complete: 8, partial: 1 and hematological improvement: 3). PR1-specific immune response was seen in 9 of 25 clinical responders vs. 3 of 28 clinical non-responders (p=0.03). In conclusion, PR1 peptide vaccine induces specific immunity that correlates with clinical responses, including molecular remission, in AML, CML and MDS patients.

Activity of 8F4, a T-cell receptor-like anti-PR1/HLA-A2 antibody, against primary human AML in vivo

The PR1 peptide, derived from the leukemia-associated antigens proteinase 3 and neutrophil elastase, is overexpressed on HLA-A2 in acute myeloid leukemia (AML). We developed a high affinity T cell receptor-like murine monoclonal antibody, 8F4, which binds to the PR1/HLA-A2 complex, mediates lysis of AML, and inhibits leukemia colony formation. Here, we explored whether 8F4 was active in vivo against chemotherapy-resistant AML, including secondary AML. In a screening model, co-incubation of AML with 8F4 ex vivo prevented engraftment of all tested AML subtypes in immunodeficient NSG mice. In a treatment model of established human AML, administration of 8F4 significantly reduced or eliminated AML xenografts and extended survival compared with isotype antibody-treated mice. Moreover, in secondary transfer experiments, mice inoculated with bone marrow from 8F4-treated mice showed no evidence of AML engraftment, supporting possible activity of 8F4 against the subset of AML with self-renewing potential. Our data provide evidence that 8F4 antibody is highly active in AML, including chemotherapy-resistant disease, supporting its potential use as a therapeutic agent in patients with AML.

PR1 peptide vaccination for patients with myeloid leukemias

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Background: PR1 is a nanomeric HLA-A2-restricted peptide derived from the myeloid leukemia-associated antigens proteinase 3 and neutrophil elastase. Methods: Sixty-six HLA-A2+ patients with acute myeloid leukemia (42), chronic myeloid leukemia (13) or myelodysplastic syndrome (11) were treated with PR1 peptide vaccine. The first 54 patient received three vaccinations, and the last 12 patients were given six vaccinations. The vaccine was injected subcutaneously, at 3 week intervals at one of three dose levels: 0.25, 0.5 or 1.0 mg per vaccination. Immune response to the vaccine was defined as a ≥ 2-fold increase in PR1-specific cytotoxic T lymphocytes. Results: Fifty-three patients had measurable disease (MD) and 13 were in complete remission. The vaccine was well tolerated, with toxicity limited to grade I and II injection site reactions. Forty-four of the 53 patients with MD were evaluable for both immune and clinical responses. PR1-specific immune response was observed in 35/44 (57%) of the evaluable patients. Clinical responses were observed in 10 of the 25 immune responders versus 2 of the 19 immune non-responders (p=0.04). PR1 vaccine-induced immune response was associated with a longer event-free survival, 8.7 months vs. 4.1 months in immune non-responders (p = 0.17). Older age and high blast count were associated with short event-free survival (p=0.01 and <0.001). Conclusion: PR1 peptide vaccine-induced immune response is associated with a superior overall clinical response and a trend towards longer event-free survival in patients with persistent myeloid leukemia.

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Risk factors associated with late cytomegalovirus reactivation after allogeneic stem cell transplantation for hematological malignancies

We analyzed the clinical factors associated with late cytomegalovirus (CMV) reactivation in a group of 269 consecutive recipients of allogeneic stem cell transplant (SCT) for hematological malignancies. Eighty-four subjects (31%) experienced late CMV reactivation, including 64 with prior early reactivation and 20 with isolated late reactivation. Multivariate analyses were conducted in patients with early CMV reactivation to identify factors associated with late recurrence. Important risk factors included lymphoid diagnosis, occurrence of graft-versus-host disease (GVHD), greater number of episodes of early reactivation, persistent day 100 lymphopenia and the use of a CMV-seronegative donor graft. We combined these risk factors in a predictive model to identify those at relatively low, intermediate and high risk. The low-risk group (15% cumulative incidence, CI) encompassed patients without early CMV reactivation, and subjects transplanted for a myeloid malignancy from a matched-related (MR) donor without subsequent acute GVHD. The high-risk patients (73% CI) met all of the following criteria: (1) received an MR graft but developed GVHD, or received a non-MR graft irrespective of GVHD; (2) had more than two episodes of early reactivation; and (3) received a CMV-seronegative graft and/or remained persistently lymphopenic at day 100 after SCT. The remaining patients had an intermediate incidence of 32%.

Leukemia vaccines

Leukemia is susceptible to immune-mediated therapies such as allogeneic stem-cell transplantation, donor lymphocyte infusion, and interferon. The clinical effectiveness of these immune-based modalities has encouraged interest in vaccine therapies for leukemia. Substantial progress has recently been made in basic immunology, allowing scientifically based vaccination strategies to be developed. The discovery of leukemia- specific and leukemia-associated antigens will allow antigen-specific therapeutic strategies to be developed. Vaccination with genetically modified leukemia cells and the use of dendritic cells in various vaccination approaches are all promising avenues of study for development of effective leukemia vaccines.

Evidence that specific T lymphocytes may participate in the elimination of chronic myelogenous leukemia

Although the immune system has long been implicated in the control of cancer, evidence for specific and efficacious immune responses in human cancer has been lacking. In the case of chronic myelogenous leukemia (CML), either allogeneic bone marrow transplant (BMT) or interferon-alpha2b (IFN-alpha2b) therapy can result in complete remission, but the mechanism for prolonged disease control is unknown and may involve immune anti-leukemic responses. We previously demonstrated that PR1, a peptide derived from proteinase 3, is a potential target for CML-specific T cells. Here we studied 38 CML patients treated with allogeneic BMT, IFN- alpha2b or chemotherapy to look for PR1-specific T cells using PR1/HLA-A*0201 tetrameric complexes. There was a strong correlation between the presence of PR1-specific T cells and clinical responses after IFN-alpha and allogeneic BMT. This provides for the first time direct evidence of a role for T-cell immunity in clearing malignant cells.

A PR1-human leukocyte antigen-A2 tetramer can be used to isolate low-frequency cytotoxic T lymphocytes from healthy donors that selectively lyse chronic myelogenous leukemia

We previously showed (E. Clave et al., J. Immunother., 22: 1-6, 1999; J. Molldrem et al., Blood, 88: 2450-2457, 1996) that PR1, a human-lymphocyte-antigen (HLA)-A2.1-restricted peptide from proteinase 3, could be used to elicit CTLs from normal individuals. These CTLs showed HLA-restricted cytotoxicity and colony inhibition of myeloid leukemia cells that overexpress proteinase 3. In this study, we constructed a phycoerythrin-labeled PR1-HLA-A2 tetramer to identify PR1-specific CTLs by flow cytometry. No peripheral blood lymphocytes from three HLA-2.1+ donors stained with the tetramer, but, after 20 days in culture with weekly PR1 stimulation, 2-8% became tetramer+. Tetramer staining identified up to 40-fold more PR1-specific CTLs than were identified by limiting dilution analysis and correlated better with lysis of PR1-coated T2 cells (R2 = 0.95 versus R2 = 0.76). Tetramer+ CTLs were memory phenotype (91% CD45RO+), and most (58% CD95+) were activated. Tetramer-sorted allogeneic CTLs produced 83% lysis of HLA-A2.1+ chronic myelogenous leukemia (CML) blasts at an E:T ratio of 2.5:1, compared with 23% lysis by nonsorted CTLs, with no background lysis of HLA-A2.1+ normal cells. Cytoplasmic proteinase-3 expression was one log greater in CML blasts than in normal granulocytes. These results show that a PR1-HLA-A2 tetramer can be used to identify and select CTLs from normal donors that preferentially lyse CML cells, which could be used for leukemia-specific adoptive immunotherapy.

Haematological response of patients with myelodysplastic syndrome to antithymocyte globulin is associated with a loss of lymphocyte-mediated inhibition of CFU-GM and alterations in T-cell receptor Vbeta profiles

We have demonstrated that 44% of myelodysplastic syndrome (MDS) patients with cytopenia have a haematological response to antithymocyte globulin (ATG). Three ATG responders and two non-responders with refractory anaemia were further studied for lymphocyte-mediated inhibition of bone marrow using a standard CFU-GM assay. In responders, peripheral blood lymphocytes (PBL) added at a 5:1 ratio suppressed CFU-GM by 54+/-9% (P=0.04) and was reversed by ATG treatment. Pre-treatment marrow depleted of CD3 lymphocytes, increased CFU-GM by 32% (P=0.02) in an ATG responder, but not in a non-responder. CD3 lymphocytes from 6-month post-treatment marrow did not inhibit pre-treatment CFU-GM, indicating ATG had affected the T cells. Pre-treatment marrow depleted of CD8 lymphocytes, increased CFU-GM by 60% (P=0.01) and 49% (P=0.03) in two ATG responders, but not in a non-responder. Inhibition required cell-cell interaction through MHCI. TCRVbeta families, analysed by SSCP, changed from clonal to polyclonal in one ATG responder after 6 months, but clones persisted in a non-responder. These results indicate patients with refractory anaemia who respond to ATG have CD8 T-cell clones that mediate MHCI-restricted suppression of CFU-GM which are replaced by polyclonal T cells that do not suppress CFU-GM after ATG treatment.

Antithymocyte globulin for patients with myelodysplastic syndrome

Twenty-five transfusion-dependent myelodysplastic syndrome (MDS) patients (with < 20% blasts) were treated in a phase II study with antithymocyte globulin (ATG) at 40 mg/kg/d for four doses and then followed with blood counts every 2 weeks and clinic visits every 3 months, for a median of 14 months (range 1-38 months). 11 (44%) patients responded and became transfusion-independent after ATG, including three complete responses, six partial responses, and two minimal responses. Responses were observed in 9/14 patients (64%) with refractory anaemia (RA) and 2/6 patients (33%) with refractory anaemia with excess blasts (RAEB). Median response duration was 10 months (range 3-38 months). The Kaplan-Meier estimate of overall survival was 84% at 38 months, with one early death due to pneumonia and two deaths from disease progression to leukaemia. Side-effects consisted mainly of mild serum sickness in all patients. A single course of ATG restored haemopoiesis in some patients with MDS and was well tolerated.

Cytotoxic T lymphocytes specific for a nonpolymorphic proteinase 3 peptide preferentially inhibit chronic myeloid leukemia colony-forming units

We previously showed that a peptide (PR1) derived from the primary granule enzyme proteinase 3 induced peptide specific cytotoxic T lymphocytes (CTL) in a normal HLA-A2.1+ individual. These CTL showed HLA-restricted cytotoxicity to myeloid leukemias (which overexpress proteinase 3). To further investigate their antileukemic potential, we studied the ability of PR1-specific CTL, derived from two HLA-A2.1+ normal individuals, to inhibit colony-forming unit granulocyte-macrophage (CFU-GM) from normal and leukemic individuals. CTL from 20 day PR1 peptide-pulsed lymphocyte cultures showed 89% to 98% HLA-A2.1-restricted colony inhibition of chronic myeloid leukemia targets. Colony formation in normal HLA-A2.1+ bone marrow or HLA-A2.1- CML cells was not inhibited. Sequencing of the exon encoding PR1 showed that colony inhibition was not caused by polymorphic differences in proteinase 3 between effectors and targets. Analysis by flow cytometry showed that proteinase 3 was overexpressed in the leukemia targets compared with normal marrow targets (median channel fluorescence 1,399 v 298, P = .009). These results show that PR1-specific allogeneic T cells preferentially inhibit leukemic CFU-GM based on overexpression of proteinase 3, and that proteinase 3-specific CTL could be used for leukemia-specific adoptive immunotherapy.