Immune Adjuvant Activity Of Barrogen, A Novel Immunomodulatory Protein

3883 The recombinant immunomodulatory Eimeria antigen (EA) protein (Barrogen) has demonstrated remarkable immunotherapeutic activity against experimental transplantable tumors and appears to be a potent stimulator of the innate immune system (Rosenberg et. al., Int. J. Cancer 114:756-765, 2005). Nearly 100% cure rates are observed in mice treated with ng doses of Barrogen immediately following tumor transplantation. In addition, elevated systemic levels of IL-12p70 and other pro-inflammatory cytokines are associated with Barrogen treatment both in vivo and in vitro. The cellular mechanism of action of Barrogen is thought to be mediated through the activation of dendritic cells, which are central to the induction of both innate and adaptive immune responses. To examine the activity of Barrogen in the induction of adaptive immune responses in vivo we examined the effect of Barrogen treatment in conjunction with a tumor vaccine prior to the transplantation of a lethal dose of tumor (S180) cells. Male Balb/c mice were treated as follows: (1) Sham injected with vehicle controls; (2) Injected (ip) with an S180 tumor vaccine in the form of a whole tumor cell homogenate (TuAg) 19 days prior to S180 tumor cell transplantation; (3) Injected (ip) with Barrogen alone (10ng per mouse) 19, 16, 12 and 9 days prior to S180 tumor cell transplantation; (4) Injected with both TuAg 19 days prior to and Barrogen (10 ng per mouse) 19, 16, 12 and 9 days prior to S180 tumor cell transplantation. Survival rates were observed for 90 days following tumor cell transplantation. Sham injected mice or mice treated with Barrogen alone had 0% survival. 25% of the mice treated with the TuAg alone survived. However, 75% of the mice treated with both TuAg and Barrogen survived suggesting that Barrogen in conjunction with a tumor vaccine can result in effective protection against a lethal tumor challenge by enhancement of the adaptive immune system. There was a 2-fold increase in spleen weights in mice treated with both TuAg and Barrogen when compared with mice treated with TuAg or Barrogen alone. In a separate experiment, large granular lymphocytes (LGLs) were isolated from the spleens of mice treated as described above. LGLs were co-cultured with S180 tumor cells in an in vitro assay to assess cell-mediated cytotoxicity against S180 cells. A significant increase in the number and percentage of S180-specific cytolytic lymphocytes was observed in LGLs isolated from the spleens of mice treated with the combination of Barrogen and TuAg compared with mice treated with TuAg or Barrogen alone. These results indicated that in addition to previous reports describing Barrogen-induced activation of the innate immune system, Barrogen can also stimulate adaptive immune responses, suggesting that Barrogen may be useful as an effective adjuvant to stimulate adaptive immune responses against cancer cells.