Immune response against cell-wall skeleton of Mycobacterium bovis BCG at the inoculation site and peripheral lymphoid...

We reported in the previous paper that highly purified cell-wall skeleton of M. bovis BCG (SMP-105) eliminated lymph node metastases and primary implanted tumor, presumably by generating tumor immunity, employing guinea pigs. In this paper, we investigated the immune reactions to elucidate the mechanisms of antitumor activity. Twenty-four hours after intradermal injection, inflammatory cells were seen migrating to the inoculation site. Massive infiltrations of lymphocytes were observed on day 7, when a large amount of SMP-105 was still observed in the dermis. Several chemokines attracting neutrophils and monocytes, detected by TaqMan RT-PCR, were induced rapidly and declined 72 h post-injection, but most increased again on day 7, consistent with the pathological findings of lymphocyte infiltration. Activation of lymph node cells was investigated using mice. Upon stimulation by SMP-105 in vitro, the draining lymph node cells collected from mice treated with SMP-105 produced interferon-γ (IFN-γ), whereas, lymph node cells did not release IFN-γ when prepared from mice treated with OK-432. This evidence prompted us to assume that SMP-105 functioned as T cell antigens. Intracellular cytokine analysis demonstrated that IFN-γ was mainly attributable to CD4-CD8+αβT and CD4-CD8-αβT cells. In conclusion, oil-in-water emulsion of SMP-105 resided for a long time at the inoculation site and activated T cells, probably recognizing SMP-105 itself. The strong tumor eliminating activity of SMP-105 may be explained by the boost of generating tumor immunity via positive feed-back from T cells reacting to it, and CD4-CD8+αβT and CD4-CD8-αβT cells may distinguish SMP-105 from other synthetic adjuvants.