Focussing human B cell specificity by immunoselection via antigen-presenting cells in vitro

We present a protocol for in vitro immunization of B cells using monocyte-derived accessory cells (MoAC). MoAC are developed from human peripheral blood monocytes in culture and represent functionally competent inducers of antigen-specific immune responses. Using MoAC, we attempted to immunoselect TT-specific lymphocytes by rosetting. Adherent human MoAC were pulsed with tetanus toxoid (TT) and allowed to form clusters with autologous lymphocytes, followed by removal of non-adherent cells. After one week of culture, a specific anti-TT antibody response emerged on a low background of unspecific Ig. In comparison, cultures which had not been selected for adherent cells produced a high polyclonal background. Our results demonstrate that from peripheral blood cells, previously not a favourable source for in vitro immunization, in a majority of tests antigen-specific B cells could efficiently be immunoselected via adherence to autologous antigen-presenting cells, leading to a high-titre in vitro immunization.