Long term cultures (LTC) producing dendritic cells (DC) have been established from spleen. A well developed stromal cell layer supported production of DC in numbers suitable for experimentation. Cells had obvious membrane pseudopodia and could be collected from culture every 2-3 days. Large cells produced in LTC stained with fluorescently labelled monoclonal antibodies specific for DC such as 33D1, and M1/70 which is specific for DC and myeloid cells. These staining patterns confirmed the presence of DC within the LTC population.
LTC-DC were tested and shown capable of migration in vivo in B10.A(2R) mice following footpad inoculation. Most cells entered the spleen and a small number entered popliteal lymph node. LTC-DC have migratory capacity comparable with control spleen lymphocytes. LTC-DC were tested for capacity to induce an anti-tumour immune response after exposing cells to tumour cell membranes. LTC-DC pulsed with BL/VL3 tumour antigens were able to induce a BL/VL3-specific primary cytotoxic T lymphocyte (CTL) response detectable in popliteal lymph nodes and spleen of C57BL/6J mice within 6 days of priming. BL/VL3 tumour cells grew in sublethally irradiated C57BL/6J mice giving 100% mortality. Adoptive transfer of spleen cells from mice given BL/VL3 antigen-pulsed LTC-DC, two weeks previously, significantly slowed the growth of BL/VL3 tumour cells in mice.
DC produced in LTC can function as antigen presenting cells (APC) when adoptively transferred into animals. Their capacity to migrate effectively, to induce a CTL response and to reduce tumour load suggests that DC grown using this in vitro system may have valuable clinical potential in humans.