Therapeutic antibodies are generally partially to fully humanized, yet they can show unwanted immunogenicity and lead to antibody response and adverse effects when administered to humans. As immunogenicity relies on a T-cell-dependent mechanism, we have evaluated in vitro the size of the preexisting CD4 T-cell repertoire specific to therapeutic antibodies in healthy donors. Specific CD4 T cells of individuals with different HLA-DR allotypes were amplified by in vitro stimulation and quantified. Well-known immunogenic proteins, KLH and a murine antibody, exhibited a strong in vitro T-cell response characterized by a mean of preexisting T cells >1 cell/10(6) cells. In contrast, the preexisting CD4 T-cell repertoires specific to 2 chimeric, 2 humanized, and 2 fully human antibodies remained generally inferior to this value, confirming the role of species-specific sequences in their shaping. Mean values ranged from 0.01 to 0.3 cell/10(6) cells and varied not necessarily in relationship with the humanization level of the therapeutic antibodies. Relationship with their known immunogenicity is discussed. These results contribute to a better understanding and prediction of immunogenicity of therapeutic antibodies in humans.

04). In multivariate analysis, FADD؊/low protein expression was independently associated with a poor EFS and overall survival (P ‫؍‬ 0.002 and P ‫؍‬ 0.026, respectively). Importantly, FADD ؊/low protein expression predicted poor EFS even in patients with standard-or good-risk AML (P ‫؍‬ 0.009). Thus, we identified low or absent expression of the FADD protein in leukemic cells at diagnosis as a poor independent prognostic factor that can predict worse clinical outcome even for patients with standard-or good-risk AML.

Identification of tumor-associated Ags is a prerequisite for vaccine-based and adoptive immune therapies. Some tumor-associated Ags elicit specific CD8 T cells in patients with chronic myeloid leukemia (CML). Here, we characterized ex vivo responses of CD8 T cells from CML patients to extrajunction bcr-abl peptides and telomerase 540–548 hTert, PR1, and WT1 peptides. CML-specific CD8 T cells were present in most treated patients and were usually multiepitopic: WT1, hTert, PR1, and bcr74 tetramer+ cells were detected in 85, 82, 67, and 61% of patients, respectively. The breadth and magnitude of these responses did not differ significantly according to treatment or disease status. CML-specific tetramer+ CD8 T cells had a predominantly memory phenotype, an intermediate perforin content, and low intracellular IFN-γ accumulation in the presence of the relevant peptide. However, in short-term culture with HLA-matched leukemia cells, the patients’ memory T cells were specifically reactivated to become IFN-γ-producing effector cells, suggesting that CD8 T cell precursors with lytic potential are present in vivo and can be activated by appropriate stimulation. In conclusion, this study shows that multiepitopic tumor-specific CD8 T cell responses occur naturally in most CML patients, opening the way to new strategies for enhancing anti-CML immunity, in particular in patients with minimal residual disease.