Gheath Alatrash

PD-L1 Expression in Triple-Negative Breast Cancer

Using tissue microarrays containing 105 triple-negative breast cancer (TNBC) specimens, Mittendorf and colleagues show that 20% of the TNBC specimens express PD-L1, half have lost PTEN, and inhibitors of PI3K pathway decrease PD-L1 expression, providing a rationale for therapeutic targeting of PD-L1 for TNBC. Early-phase trials targeting the T-cell inhibitory molecule programmed cell death ligand 1 (PD-L1) have shown clinical efficacy in cancer. This study was undertaken to determine whether PD-L1 is overexpressed in triple-negative breast cancer (TNBC) and to investigate the loss of PTEN as a mechanism of PD-L1 regulation. The Cancer Genome Atlas (TCGA) RNA sequencing data showed significantly greater expression of the PD-L1 gene in TNBC (n = 120) compared with non-TNBC (n = 716; P < 0.001). Breast tumor tissue microarrays were evaluated for PD-L1 expression, which was present in 19% (20 of 105) of TNBC specimens. PD-L1+ tumors had greater CD8+ T-cell infiltrate than PD-L1− tumors (688 cells/mm vs. 263 cells/mm; P < 0.0001). To determine the effect of PTEN loss on PD-L1 expression, stable cell lines were generated using PTEN short hairpin RNA (shRNA). PTEN knockdown led to significantly higher cell-surface PD-L1 expression and PD-L1 transcripts, suggesting transcriptional regulation. Moreover, phosphoinositide 3-kinase (PI3K) pathway inhibition using the AKT inhibitor MK-2206 or rapamycin resulted in decreased PD-L1 expression, further linking PTEN and PI3K signaling to PD-L1 regulation. Coculture experiments were performed to determine the functional effect of altered PD-L1 expression. Increased PD-L1 cell surface expression by tumor cells induced by PTEN loss led to decreased T-cell proliferation and increased apoptosis. PD-L1 is expressed in 20% of TNBCs, suggesting PD-L1 as a therapeutic target in TNBCs. Because PTEN loss is one mechanism regulating PD-L1 expression, agents targeting the PI3K pathway may increase the antitumor adaptive immune responses. Cancer Immunol Res; 2(4); 361–70. ©2014 AACR.

Improved Early Outcomes Using a T Cell Replete Graft Compared with T Cell Depleted Haploidentical Hematopoietic Stem Cell Transplantation

Haploidentical stem cell transplantation (SCT) has been generally performed using a T cell depleted (TCD) graft; however, a high rate of nonrelapse mortality (NRM) has been reported, particularly in adult patients. We hypothesized that using a T cell replete (TCR) graft followed by effective posttransplantation immunosuppressive therapy would reduce NRM and improve outcomes. We analyzed 65 consecutive adult patients with hematologic malignancies who received TCR (N = 32) or TCD (N = 33) haploidentical transplants. All patients received a preparative regimen consisting of melphalan, fludarabine, and thiotepa. The TCR group received posttransplantation treatment with cyclophosphamide (Cy), tacrolimus (Tac), and mycophenolate mofetil (MMF). Patients with TCD received antithymocyte globulin followed by infusion of CD34+ selected cells with no posttransplantation immunosuppression. The majority of patients in each group had active disease at the time of transplantation. Outcomes are reported for the TCR and TCD recipients, respectively. Engraftment was achieved in 94% versus 81% (P = NS). NRM at 1 year was 16% versus 42% (P = .02). Actuarial overall survival (OS) and progression-free survival (PFS) rates at 1 year posttransplantation were 64% versus 30% (P = .02) and 50% versus 21% (P = .02). The cumulative incidence of grade II-IV acute graft-versus-host disease (aGVHD) was 20% versus 11% (P = .20), and chronic GVHD (cGVHD) 7% versus 18% (P = .03). Improved reconstitution of T cell subsets and a lower rate of infection were observed in the TCR group. These results indicate that a TCR graft followed by effective control of GVHD posttransplantation may lower NRM and improve survival after haploidentical SCT.

Myeloablative Reduced-Toxicity i.v. Busulfan-Fludarabine and Allogeneic Hematopoietic Stem Cell Transplant for Patients with Acute Myeloid Leukemia or Myelodysplastic Syndrome in the Sixth through Eighth Decades of Life

The optimal pretransplant regimen for acute myeloid leukemia (AML) or myelodysplastic syndrome (MDS) in patients ≥ 55 years of age remains to be determined. The myeloablative reduced-toxicity 4-day regimen i.v. busulfan (Bu) (130 mg/m(2)) and i.v. fludarabine (Flu) (40 mg/m(2)) is associated with low morbidity and mortality. We analyzed 79 patients ≥ 55 years of age (median, 58 years) with AML (n = 63) or MDS (n = 16) treated with i.v. Bu-Flu conditioning regimens between 2001 and 2009 (median follow-up, 24 months). The patients who received this regimen had a good performance status. The 2-year overall survival (OS) rates for patients in first complete remission (CR1), second CR (CR2), or refractory disease and for all patients at time of transplantation were 71%, 44%, 32%, and 46%, respectively; 2-year event-free survival (EFS) rates for patients in CR1, CR2, or refractory disease at time of transplantation and for all patients were 68%, 42%, 30%, and 44%, respectively. One-year transplant-related mortality (TRM) rates for patients who were in CR or who had active disease at the time of transplantation were 19% and 20%, respectively. Grade II-IV acute graft-versus-host (aGVHD) disease was diagnosed in 40% of the patients. Our results suggest that age alone should not be the primary reason for exclusion from receiving myeloablative reduced-toxicity conditioning with i.v. Bu-Flu preceding transplantation in patients with AML/MDS.

An anti–PR1/HLA-A2 T-cell receptor–like antibody mediates complement-dependent cytotoxicity against acute myeloid leukemia progenitor cells

PR1 (VLQELNVTV) is a human leukocyte antigen-A2 (HLA-A2)-restricted leukemia-associated peptide from proteinase 3 (P3) and neutrophil elastase (NE) that is recognized by PR1-specific cytotoxic T lymphocytes that contribute to cytogenetic remission of acute myeloid leukemia (AML). We report a novel T-cell receptor (TCR)-like immunoglobulin G2a (IgG2a) antibody (8F4) with high specific binding affinity (dissociation constant [K(D)] = 9.9nM) for a combined epitope of the PR1/HLA-A2 complex. Flow cytometry and confocal microscopy of 8F4-labeled cells showed significantly higher PR1/HLA-A2 expression on AML blasts compared with normal leukocytes (P = .046). 8F4 mediated complement-dependent cytolysis of AML blasts and Lin(-)CD34(+)CD38(-) leukemia stem cells (LSCs) but not normal leukocytes (P < .005). Although PR1 expression was similar on LSCs and hematopoietic stem cells, 8F4 inhibited AML progenitor cell growth, but not normal colony-forming units from healthy donors (P < .05). This study shows that 8F4, a novel TCR-like antibody, binds to a conformational epitope of the PR1/HLA-A2 complex on the cell surface and mediates specific lysis of AML, including LSCs. Therefore, this antibody warrants further study as a novel approach to targeting leukemia-initiating cells in patients with AML.

Breast Cancer Cell Uptake of the Inflammatory Mediator Neutrophil Elastase Triggers an Anticancer Adaptive Immune Response

There is little understanding of the impact of tumor-associated neutrophils (TAN) on adaptive immunity to tumors. In this study, we report the results of an investigation of the pathobiologic basis for the prognostic significance of neutrophil elastase, a serine protease found in neutrophil granules, in a model of cyclin E (CCNE)-overexpressing breast cancer. We established that neutrophil elastase was expressed by TAN within breast cancer tissues but not by breast cancer cells. Neutrophil elastase modulated killing of breast cancer cells by CTLs specific for CCNE-derived HLA-A2-restricted peptide (ILLDWLMEV). Breast cancer cells exhibited striking antigen-specific uptake of neutrophil elastase from the microenvironment that was independent of neutrophil elastase enzymatic activity. Furthermore, neutrophil elastase uptake increased expression of low molecular weight forms of CCNE and enhanced susceptibility to peptide-specific CTL lysis, suggesting that CCNE peptides are naturally presented on breast cancer cells. Taken together, our findings reveal a previously unknown mechanism of antitumor adaptive immunity that links cancer cell uptake of an inflammatory mediator to an effective cytolytic response against an important breast cancer antigen.

PR1-Specific T Cells Are Associated with Unmaintained Cytogenetic Remission of Chronic Myelogenous Leukemia After Interferon Withdrawal

Background Interferon-α (IFN) induces complete cytogenetic remission (CCR) in 20–25% CML patients and in a small minority of patients; CCR persists after IFN is stopped. IFN induces CCR in part by increasing cytotoxic T lymphocytes (CTL) specific for PR1, the HLA-A2-restricted 9-mer peptide from proteinase 3 and neutrophil elastase, but it is unknown how CCR persists after IFN is stopped. Principal Findings We reasoned that PR1-CTL persist and mediate CML-specific immunity in patients that maintain CCR after IFN withdrawal. We found that PR1-CTL were increased in peripheral blood of 7/7 HLA-A2+ patients during unmaintained CCR from 3 to 88 months after IFN withdrawal, as compared to no detectable PR1-CTL in 2/2 IFN-treated CML patients not in CCR. Unprimed PR1-CTL secreted IFNγ and were predominantly CD45RA±CD28+CCR7+CD57-, consistent with functional naïve and central memory (CM) T cells. Similarly, following stimulation, proliferation occurred predominantly in CM PR1-CTL, consistent with long-term immunity sustained by self-renewing CM T cells. PR1-CTL were functionally anergic in one patient 6 months prior to cytogenetic relapse at 26 months after IFN withdrawal, and in three relapsed patients PR1-CTL were undetectable but re-emerged 3–6 months after starting imatinib. Conclusion These data support the hypothesis that IFN elicits CML-specific CM CTL that may contribute to continuous CCR after IFN withdrawal and suggest a role for T cell immune therapy with or without tyrosine kinase inhibitors as a strategy to prolong CR in CML.

Cancer immunotherapies, their safety and toxicity

Introduction: Cancer immunotherapy encompasses a wide range of treatment modalities that harness the anti-tumor effects of the immune system. Some immunotherapies broadly activate the immune system while others precisely target distinct tumor antigens. Because of this heterogeneity, the side effects associated with immunotherapy can be mild and localized or more severe and systemic. Areas covered: Cytokines, adoptive cellular therapies and vaccines are the most commonly used immunotherapies for the treatment of a number of malignancies and have been used for many decades. Checkpoint blockade has recently emerged as a promising immunotherapy. The biggest benefits of immunotherapy have been demonstrated in melanoma, renal cell carcinoma and hematologic malignancies. Emerging data are highlighting the potential for broad applicability of immunotherapy in a number of solid and hematologic malignancies. Expert opinion: Immunotherapies are slowly becoming integrated into the standard of care in cancer treatment. Promising results using immunotherapy have been reported demonstrating complete remissions and cures in many patients with aggressive malignancies. The complexity and cost of engineering and administering of some forms of immunotherapy limit their use to distinct patient populations. High-throughput and cost-effective techniques are being used to broaden the applications of immunotherapy to treat cancer patients.

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 (CTLs) 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 three dose levels after establishing the safety of the highest dose level. Primary end points were safety and immune response, assessed by doubling of PR1/HLA-A2 tetramer-specific CTL, and the secondary end point 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 versus 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.

Adoptive transfer of PR1 cytotoxic T lymphocytes associated with reduced leukemia burden in a mouse acute myeloid leukemia xenograft model

BACKGROUND AIMS Tumor antigen-specific cytotoxic T lymphocytes (CTL) have been used in the treatment of human cancer, including leukemia. Several studies have established PR1 peptide, an HLA-A2.1-restricted peptide derived from proteinase 3 (P3), as a human leukemia-associated antigen. PR1-specific CTL elicited in vitro from healthy donors have been shown to lyse P3-expressing AML cells from patients. We investigated whether PR1-CTL can be adoptively transferred into NOD/SCID mice to eliminate human leukemia cells. METHODS PR1-CTL were generated in bulk culture from peripheral blood mononuclear cells (PBMC) stimulated with autologous dendritic cells. Human acute myeloid leukemia (AML) patient samples were injected and engrafted in murine bone marrow at 2 weeks post-transfer. RESULTS Following adoptive transfer, bone marrow aspirate from mice that received AML alone had 72-88% blasts in a hypercellular marrow, whereas mice that received AML plus PR1-CTL co-infusion had normal hematopoietic elements and only 3-18% blasts in a hypocellular marrow. The PR1-CTL persisted in the bone marrow and liver and maintained a CD45RA⁻CD28+ effector phenotype. CONCLUSIONS We found that adoptive transfer of PR1-CTL generated in vitro is associated with reduced AML cells in NOD/SCID mice. PR1-CTL can migrate to the sites of disease and maintain their capacity to kill the AML cells. The surface phenotype of PR1-CTL was consistent with their trafficking pattern in both vascular and end-organ tissues.

Results of a 2-arm, phase 2 clinical trial using post-transplantation cyclophosphamide for the prevention of graft-versus-host disease in haploidentical donor and mismatched unrelated donor hematopoietic stem cell transplantation

High‐dose, post‐transplantation cyclophosphamide (PTCy) to prevent graft‐versus‐host disease (GVHD) has improved outcomes in haploidentical (HAPLO) stem cell transplantation (SCT). However, it remains unclear whether this strategy is effective in SCT from 1‐antigen human leukocyte antigen (HLA)‐mismatched unrelated donors (9/10 MUD) and how the outcomes of these patients compare with those of haploidentical transplantation recipients.