The number of monoclonal antibodies used as drug or under clinical investigation increases rapidly. The first murine monoclonal antibodies (mAbs) used in therapy induces human anti-mouse antibodies (HAMAs) when administered to patients. Such HAMAs hamper the therapeutic efficacy of mAbs and induce side effects. To limit these effects, new antibodies were developed during the, last 30 years. Chimeric, humanized and fully human antibodies were engineered. The use of human monoclonal antibodies (hAbs) appears ideal to solve the problem of HAMAs. Nowadays 9 fully human antibodies are available and others are evaluated in clinical trials or currently investigated in research labs. Three methods exist to produce fully human antibodies: the phage display, the transgenic mice and the use of human B lymphocytes. The majority of fully human antibodies resulted from the phage display and the transgenic mice methods. The use of human B lymphocytes is less investigated due to a poor yield and stability problems. These last years, the immortalization process, thanks to the involvement of the Epstein-Barr virus and human myeloma, induced a rise of interest for human B lymphocytes. In this context we decided to develop fully human monoclonal antibodies using human B lymphocytes through immortalization using the Epstein-Barr virus followed or not by an immortalization with a human/mouse heteromyeloma HM. The first approach is based on hAbs production from peripheral blood memory B lymphocytes isolated from infected or vaccinated donors. The Staphylococcus aureus enterotoxine B (SEB) was used as a model. Memory B lymphocytes were purified and cultured in the presence of Epstein-Barr virus (EBV). The transformation of memory B lymphocytes by EBV allowed the generation of immortalized B lymphocytes lines producing IgGs antibodies directed against SEB. We succeeded in isolating 6 EBV-immortalized memory B lymphocytes lines secreting anti-SEB IgGs antibodies. After many attempts to immortalize EBV immortalized memory B lymphocytes lines secreting anti-SEB antibodies with myeloma, the fusion of a EBV immortalized memory B lymphocytes with the human/mouse heteromyeloma HM led to an hybridoma. Unfortunately this hybridoma has rapidly lost its capacity to secrete d’IgGs anti-SEB. In the second approach the hAbs production implies the in vitro immunization of peripheral blood naïve lymphocytes. This strategy could allow the hAbs production against antigens for which no infected or vaccinated donors may be available. The Clostridium Botulinum neurotoxin A (BoNT/A), the most powerful toxin, and its N-terminal peptide (TBA-Nter) or the fusion protein ZZTat101 were used as models. ZZTat101 is a fusion between the ZZ domain of Staphylococcus aureus and the Tat protein of the human immunodeficiency virus HIV-1. Monocytes, B lymphocytes and T lymphocytes were isolated from human PBMC depleted of Natural killer. These cells were tools to develop efficient in vitro immunization protocols. IgMs directed against TBA-Nter and also IgMs (and possibly IgGs) directed against Tat were obtained. The use of the Epstein-Barr virus induced 7 EBV immortalized lines secreting anti-TBA-Nter IgMs antibodies. Unfortunately, after fusion with the heteromyeloma HM no hybridoma was isolated against TBA-Nter and Tat. The ZZTat101 mechanism involved on humoral response was studied, showing that the 7 cysteines, the region 22-57 and the ability of Tat to bind heparane sulfate are necessary to trigger the humoral response.
