CML28 is a broadly immunogenic antigen,which is overexpressed in tumor cells

Donor lymphocyte infusion (DLI) reliably induces durable remission in 75-80% of patients with relapsed chronic myelogenous leukemia (CML) after allogeneic hematopoietic stem cell transplantation. To identify immunological targets of the graft-versus-leukemia response (GVL) after DLI, we used CML post-DLI responder sera to screen a CML cDNA expression library. One of the antigens identified in this screen is a M(r) 28,000 protein, termed CML28. CML28 is identical to hRrp46p, a component of the human exosome, a multiprotein complex involved in the 3' processing of RNA. Components of the human exosome include known autoantigens, such as PMScl-100, an autoantibody target in patients with polymyositis, scleroderma, or polymyositis-scleroderma overlap syndrome. Recombinant CML28-GST fusion protein was purified, and used in Western blot and ELISA to demonstrate the development of a high-titer CML28-specific IgG antibody response in a patient with relapsed CML who responded to DLI. Northern blotting demonstrated that CML28 is highly expressed in a variety of hematopoietic and epithelial tumor cell lines, but not in normal hematopoietic tissues or other normal tissue, with the exception of testis. Purified recombinant CML28 was used to generate a CML28-specific murine monoclonal antibody. Western blotting with CML28 monoclonal antibody against whole-cell lysates derived from blood and marrow of normal donors and patients with leukemia revealed high expression of this antigen in tumor but not in normal samples. Because CML28 was highly expressed in epithelial tumor cell lines, anti-CML28 responses were also examined in patients with solid tumors. By ELISA, we found specific serological responses in 10-33% of patients with lung cancer, melanoma, and prostate cancer. Our studies suggest that immunogenicity of CML28 is likely because of overexpression of this antigen in tumor cells. Moreover, given its expression and immunogenicity in a wide variety of malignancies, CML28 merits additional evaluation as a target for antigen-specific immunotherapy.     

A CD4+ T cell clone selected from a CML patient after donor lymphocyte infusion recognizes BCR-ABL breakpoint peptides but not tumor cells

BACKGROUND: In patients with chronic myelocytic leukemia (CML), the breakpoint cluster region and fusion between the BCR and the c-ABL genes (BCR-ABL) oncogen product is a potential tumor-specific antigen. Previous studies have shown that T cells specific for the junctional region peptides of the BCR-ABL oncoprotein can be detected in healthy individuals as well as in patients with CML in chronic phase. We assessed whether BCR-ABL- specific T cells could be found in a patient achieving a complete cytogenetic remission after CD4+ donor lymphocyte infusion. METHODS: Using dendritic cells pulsed with BCR-ABL breakpoint peptides as antigen-presenting cells, we stimulated patient peripheral blood lymphocytes to isolate peptide-specific T cell clones present at the time of the cytogenetic response. T cell clones were isolated and the cellular specificity of these cells was examined. RESULTS: A CD3+ CD4+ T cell clone (1F7) that recognizes overlapping p210 junctional peptides presented by HLA-DR molecules was identified and expanded in vitro. Clone 1F7 failed to recognize autologous tumor cells as well as dendritic cells derived from patient CML cells. Clone 1F7 did not inhibit the growth and differentiation of CML precursor cells in a standard colony formation assay. Finally, using a clone-specific probe, 1F7 cells could not be detected in patient peripheral blood at the time of the donor lymphocyte infusion response. CONCLUSIONS: These results suggest that clone 1F7 was selected in vitro using highly potent peptide pulsed dendritic cells but was not representative of the anti-leukemia immune response in vivo. Based on these findings, CD4+ T cells with BCR-ABL specificity do not appear to be mediators of the anti-leukemia response in vivo after donor lymphocyte infusion.     

White blood cell recovery after allogeneic hematopoietic cell transplantation predicts clinical outcome

To determine whether outcome after allogeneic hematopoietic cell transplantation (HCT) could be estimated by using peripheral white blood cell count (WBC) as a metric that integrates several aspects of HCT recovery, we conducted a retrospective study of 1,109 adult patients who underwent first allogeneic HCT from 2003 through 2009. WBC at 1–3 months after HCT was categorized as low (<2), normal (2–10), and high (>10 × 10⁹ cells/L). Overall survival (OS) and progression‐free survival (PFS) were lower for patients with low or high WBC at 1–3 months after HCT (P < 0.0001). We developed a predictive three‐group risk model based on the pattern of WBC recovery early after HCT. Five‐year OS was 47, 30, and 15% (P < 0.0001) and 5‐year PFS was 39, 22, and 14% for patients in the three different risk groups (P < 0.0001). The pattern of WBC recovery early after HCT provides prognostic information for relapse, nonrelapse mortality, progression‐free survival, and overall survival. A scoring system based on the trajectory of the WBC in the first 3 months after HCT can effectively stratify patients into three groups with different PFS and OS. If validated, this system could be useful in the clinical management of patients after HCT, and to stratify patients enrolled on HCT clinical trials. Am. J. Hematol. 89:591–597, 2014. © 2014 Wiley Periodicals, Inc.