The augmenting effect of OK432-stimulated B cells on the in vitro generation of anti-tumor cytotoxic T lymphocytes from tumor-draining lymph node cells: the possible role of interleukin-12

Effect of a local injection with a streptococcal preparation OK432 on the in vitro generation of anti-tumor cytotoxic T lymphocytes (CTLs) from tumor-draining lymph nodes (LN) was investigated. A peritumoral injection with OK432 on days 2, 4, 6 and 8 significantly increased both the total cell number and the proportion of B cells in the draining LN cells on day 10 after a subcutaneous inoculation with B16 melanoma. In an in vitro proliferative assay, OK432 showed a stimulatory effect on both normal splenic T and B cells. In a cytolytic assay, the OK432-injected B16-draining LN cells showed a higher level of anti-B16 CTL activity than the B16-draining LN cells after in vitro restimulation. This augmenting effect of OK432 was dependent on the B cells. Moreover, nonadherent cells from the OK432-injected B16-draining LN cells showed a low but significantly higher level of anti-B16 CTL activity than those from the B 16-draining LN cells after in vitro restimulation, whereas this augmenting effect of OK432 was abolished by the in vitro addition of anti-interleukin (IL)-12 monoclonal antibody. Collectively, these findings suggest that the augmenting effect of a local injection with OK432 on the potential of tumor-draining LN cells to turn into anti-tumor CTLs after in vitro restimulation was at least in part due to IL-12 derived from the OK432-stimulated B cells.