Humoral Immune Responses Against the Oncofetal-Antigen/Immature Laminin Receptor (OFA/iLR) in Patients with Chronic Lymphocytic Leukemia.

The 37 kD oncofetal antigen/immature laminin receptor (OFA/iLR) is a strongly overexpressed tumor antigen on malignant cells of numerous tumor entities including several hematological malignancies but it is not present on the cell surface of normal differentiated tissues. OFA/iLR is widely expressed on chronic lymphocytic leukemia (CLL) cells while absent on different normal B-cell subsets. The aim of this study was to evaluate and characterize humoral immune responses towards OFA/iLR in patients with CLL. 38 healthy individuals and 68 untreated patients with chronic lymphocytic leukemia were analysed for the presence of anti-OFA/iLR-antibodies. Sera were screened in an enzyme-linked immunosorbent assay (ELISA) for immunoglobulin G (IgG) and IgM anti-OFA/iLR-antibodies. Detectable IgG or IgM responses to OFA protein were present in 32 of 68 patients (47,0%) but only in 4 of 38 (10,5%) healthy donors. IgG subtype analysis revealed a predominant IgG1 and IgG3 response. Utilizing 42 peptides deduced from the complete OFA/iLR amino acid sequence, 24 (35,3%) samples with significant anti-OFA/iLR IgG and/or IgM titers were also reactive with at least one OFA/iLR epitope. Patient-derived anti-OFA/iLR antibodies were capable of recognizing and selectively killing OFA/iLR expressing CLL cells in complement-mediated and antibody-dependent cellular cytotoxicity (ADCC) assays. Kaplan-Meier plots for progression-free survival (PFS) revealed a tendendy for longer PFS in patients with detectable humoral responses compared patients with negative ELISA (p=0,0165).

In addition, sera from eight CLL patients who had undergone allogeneic hematopoetic stem cell transplantion (allo-HSCT) were analysed. Six out of eight patients showed high values for IgG or IgM anti-OFA/iLR-antibodies after allo-HSCT as long as remaining in complete remission suggesting a potential role of anti-OFA/iLR-directed Graft-versus-Leukemia effects. For the first time, these data suggest that anti-OFA/iLR antibodies might be involved in the immunological control of OFA/iLR expressing CLL cells in vivo.