Tumor associated release of interleukin-10 alters the prolactin receptor and down-regulates prolactin responsiveness of immature cortical thymocytes.

The soluble factors produced either by Ehrlich's ascites carcinoma (EAC) or thymic adherent cells (TAC) of tumor-bearing mice comprising of CD11b(+) and CD11c(+) antigen-presenting cells caused a sharp decrease in prolactin (PRL)-induced ConA-mediated effect on survival of PNA(+) thymocytes. Similar suppression of PRL-induced effect was observed when the cells were cocultured with TAC of EAC-bearing mice. Anti-IL-10 antibody could reverse the PRL inability to induce ConA-mediated effect on PNA(+) thymocyte survival, indicating the presence of IL-10 in EAC culture supernatant (EAC sup) and thymic microenvironment. IL-10 could block PRL-induced proliferation of PNA(+) thymocytes without affecting spontaneous apoptosis. IL-10 altered the expression of the long-form (LF) of PRL-R and reduced the PRL binding of the cells, suggesting down-regulation of the PRL effect on PNA(+) thymocyte by the cytokine. Induction of tumor, which was found to increase the IL-10 secretion by TAC, also modified the PRL-R (LF) to PRL-R (SF). Since PRL plays a role in survival, proliferation and differentiation of lymphoid progenitor cells, the tuning of PRL action by IL-10 may be a possible mechanism of depletion of immature cortical thymocytes and thymic atrophy in tumor-bearing mice.

CpG oligonucleotides enhance the tumor antigen-specific immune response of an anti-idiotype antibody-based vaccine strategy in CEA transgenic mice.

A murine monoclonal anti-idiotype (Id) antibody, 3H1 has been developed and characterized previously. Anti-Id 3H1 mimics a specific epitope of carcinoembryonic antigen (CEA) and can be used as a surrogate antigen for CEA. 3H1 induced anti-CEA immunity in different species of animals as well as humans and showed promise as a potential vaccine candidate in phase I/II clinical trials for colon cancer patients. One area of interest to us has been the development of new immune adjuvants that may augment the potency of 3H1 as a tumor vaccine. Oligodeoxynucleotides containing unmethylated CpG motifs (CpG ODN) are potent immunostimulatory agents capable of enhancing the Ag-specific Th1 response when used as immune adjuvants. In this study, we have evaluated the efficacy of 3H1 as a tumor vaccine when admixed with a select CpG ODN 1826 in transgenic mice that express human CEA. The vaccine potential of 3H1 was also assessed in the presence of another widely used adjuvant, QS-21. 3H1 coupled to keyhole limpet hemocyanin (KLH) and mixed with Freund's adjuvant (FA) was used as a gold standard in this system. 3H1 vaccination with different adjuvants induced both humoral and cellular anti-3H1, as well as anti-CEA immunity in CEA transgenic mice. The immune sera could lyse CEA-transfected murine colon carcinoma cells, C15 effectively in an antibody-dependent cellular cytotoxicity assay. The anti-CEA antibody responses were somewhat comparable in each adjuvant-treated group of mice, whereas cellular immune responses were significantly greater when CpG was used as an adjuvant. Splenocytes obtained from 3H1-CpG-immunized mice showed an increased proliferative CD4(+) Th1-type T-cell response when stimulated in vitro with 3H1 or CEA and secreted elevated levels of Th1 cytokines (IL-2, IFN-gamma). This vaccine also induced MHC class I antigen-restricted CD8(+) T-cell responses. In a solid tumor model, C15 tumor growth was significantly inhibited by 3H1 vaccinations. In 3H1-CpG-vaccinated mice, the duration of survival was, however, longer compared to the 3H1-QS21-vaccinated mice. These findings suggest that 3H1-CpG vaccinations can break peripheral tolerance to CEA and induce protective antitumor immunity in this murine model transgenic for human CEA.

Immunostimulatory CpG oligonucleotides enhance the immune response of anti-idiotype vaccine that mimics carcinoembryonic antigen.

We have developed and characterized a monoclonal anti-idiotype (Id) antibody, designated 3H1, which mimics a specific epitope of carcinoembryonic antigen (CEA) and can be used as a surrogate for CEA. Anti-Id 3H1 induced anti-CEA immunity in different species of animals as well as humans and showed promise as a potential vaccine candidate in phase I/II clinical trials for colorectal cancer patients. One area of interest to us has been the development of new immune adjuvants that may augment the potency of 3H1 as a tumor vaccine. Immunostimulatory oliogonucleotides containing the unmethylated CpG motif (CpG ODN) are potent inducers of both innate and adaptive immunity and can serve as suitable vaccine adjuvants. In this study, using the CEA-transduced MC-38 murine colon carcinoma model in syngeneic C57BL/6 mice, we assessed whether a select CpG ODN (1826) can function as immune adjuvant in immunization of mice with anti-Id 3H1. Complete Freund's adjuvant (FA) was used as a gold standard in this system. A single immunization of 3H1 mixed with CpG ODN 1826 was sufficient to induce measurable anti-CEA immunity in naïve mice. However, 3 immunizations every other week were necessary to obtain and sustain peak immune reactivity over a long period of time. With FA and 3H1, single immunization was ineffective and multiple immunizations (5 to 6) were needed to achieve and sustain peak immunity. Anti-CEA antibody reactivity was comparable in both groups, but cellular immune reactivity as measured by immune splenic lymphocyte T cell proliferation and cytoxicity assay was slightly higher in the CpG ODN group. Mice immunized with 3H1 and either CpG ODN or FA were protected from challenge by lethal doses of MC-38-CEA cells. However, the degree of protection was slightly higher and the duration of survival was somewhat longer in the group of mice treated with 3H1 plus CpG ODN. Thus, CpG ODN 1826 was faster than FA in increasing anti-tumor immunity induced by anti-Id 3H1 immunization in this prophylactic model.