Immunogene therapy against mouse leukemia using B7 molecules

Whole leukemia cell vaccines: Past progress and future directions

It has long been recognized that allogeneic hematopoietic stem cell transplantation can reduce the risk of leukemia relapse by inducing the graft-versus-leukemia effect. However, allogeneic stem cell transplantation is also known to be able to cause graft-versus-host disease, which can cause considerable morbidity and even mortality in patients receiving allogeneic hematopoietic stem cell transplantation. Therefore, to elicit leukemia-specific immune responses without alloimmune reaction, the possibilities of active immunotherapy methods such as leukemia vaccines have been studied for decades. Among various types of leukemia vaccines, whole leukemia cell vaccines are known to be able to induce immune responses against multiple unknown antigens without the need for adoptive transfer of dendritic cells. In this review, we will discuss the past progress of whole leukemia cell vaccines, with a focus on strategies to enhance their immunogenicity. We will also present the future directions of whole leukemia cell vaccines along with addressing newly emerging concepts, such as immunogenic cell death and necroptosis. We will not discuss in detail other factors that can reduce the therapeutic efficacy of whole leukemia cell vaccines such as various immunosuppressive mechanisms of leukemia.

Interferon type I responses in primary and secondary infections

The mammalian host responds to a microbial infection with a rapid innate immune reaction that is dominated by type I interferon (IFN-I) release. Most cells of vertebrates can respond to microbial attack with IFN-I production, but the cell type responsible for most of the systemic IFN-I release is thought to be plasmacytoid dendritic cells (pDCs). Besides its anti-microbial and especially anti-viral properties IFN-I also exerts a regulatory role on many facets of the sequential adaptive immune response. One of these is being the recently described partial, systemic activation of the vast majority of B and T lymphocytes in mice, irrespective of antigen reactivity. The biological significance of this partial activation of lymphocytes is at present speculative. Secondary infections occurring within a short time span of a primary infection fail to elicit a similar lymphocyte activation response due to a refractory period in systemic IFN-I production. This period of exhaustion in IFN-I responses is associated with an increased susceptibility of the host to secondary infections. The latter correlates with well-established clinical observations of heightened susceptibility of patients to secondary microbial infections after viral episodes.

Therapeutic Effect of pEgr-IL18-B7.2 Gene Radiotherapy in B16 Melanoma-Bearing Mice

To evaluate the antitumor role of genes B7.2 and IL18, the radiation-inducible dual-gene coexpression plasmid pEgr-IL18-B7.2 was constructed and its effects on tumor were detected both in vitro and in vivo. After the introduction of pEgr-IL18-B7.2 into B16 melanoma cells, followed by X-ray irradiation, higher expression levels of B7.2 and IL18 compared with control were found both by flow cytometry and enzyme-linked immunosorbent assay. It was shown that even low-dose irradiation was able to induce their expression, which could be tightly regulated either by giving cells different doses of radiation or the same dose at different time points. pEgr-IL18-B7.2 was then packaged with liposome and injected into melanoma tumor-bearing mice. The tumors received 5 Gy of local X-ray irradiation every other day for a total of five treatments. B16 tumor growth slowed significantly when treated with pEgr-IL18-B7.2 plus X-radiation versus either treatment separately. Both 1 and 3 days after the last irradiation the group of mice with combined gene and radiation therapy showed significantly higher tumor necrosis factor (TNF)-alpha secretion in peritoneal macrophages, upregulated splenic cytotoxic T lymphocytes (CTLs) and natural killer (NK) cells, and higher interferon (IFN)-gamma secretion than those in either individual treatment group or the control group. The stimulation of host anticancer immunity by increased secretion of IL-18 and upregulated immunogenicity of the tumor cells by increased expression of B7.2 on their surface, in addition to the direct effect of local X-irradiation on the tumor cells, may contribute to the novel effect of the combined therapy.

Autologous control of a highly malignant syngeneic CRNK-16 leukemia in the rat: a role for NK cells

It is unclear whether autologous immunity could be recruited to restrict the progression of leukemia. Patients harboring leukemia commonly display suppressed cell mediated immunity, which may contribute to their inability to control the disease. Immune response against leukemia is evident in allogeneic HLA-mismatched bone marrow transplantation, implicating the involvement of NK cells. This graft-versus-leukemia (GVL) activity suggests that, if not suppressed, an autologous NK cell response could potentially control acute leukemia that had down-regulated HLA expression. In the current study we assessed the role of non-suppressed autologous NK cells in controlling a syngeneic highly malignant leukemia, the CRNK-16 line, that constitute a major cause of natural death in aged F344 rats. A minuscule dose of 60 CRNK-16 leukemia cells per rat was sufficient to induce 50% mortality rates, and animals that survived this challenge did not show improved survival upon a second challenge. The CRNK-16 line was found to exhibit low levels of MHC-I, and selective in vivo depletion of NK cells nullified in vitro NK activity against the CRNK-16 line and reduced survival rates from this leukemia. In vivo activation of NK cells, employing low doses of poly I-C or IL-12, increased in vitro NK activity against the leukemia and dramatically improved survival rates when treatment was initiated before, but not after leukemia inoculation. These results indicate the ability of competent autologous NK cells to restrict highly malignant non-immunogenic leukemia. Thereby, this model presents an opportunity to study specific in vivo NK-leukemia interactions.

Challenge with mammary tumor cells expressing MHC class II and CD80 prevents the development of spontaneously arising tumors in MMTV-neu transgenic mice

The HER-2/Neu oncogene has been implicated in human and mouse breast cancer. Indeed, transgenic MMTV-neu mice expressing this oncogene from the mammary tumor virus long terminal repeat develop spontaneous mammary tumors and die within 1 year of life. We have expressed the class II transactivator (CIITA) and/or the costimulatory molecule CD80 (B7.1) in a mammary carcinoma cell line (MCNeuA) derived from these mice. Class II transactivator directs the expression of MHC class II and the machinery for antigen processing and presentation by this pathway. When injected into MMTV-neu mice, tumor cells expressing CD80 or CD80 and CIITA, were rejected completely. In addition, following the rejection of dual expressing cells, 75% of the mice were protected against the development of subsequent spontaneous tumors. Cells expressing only CD80 or CIITA were not as effective as antitumor vaccines in preventing the development of spontaneous tumors. Thus, converting cancer cells into antigen presenting cells could represent an effective immunotherapy for breast cancer.

Gene transfer of pro-IL-18 and IL-1β converting enzyme cDNA induces potent antitumor effects in L1210 cells

We report in a murine model of acute lymphoid leukemia L1210 the potent antitumor efficiency of a combinatorial delivery of pro-IL-18 gene modified L1210 (Lp18) and IL-1beta converting enzyme (ICE) gene modified L1210 (LpICE). Live leukemia cells Lp18 or Lp18 plus LpICE showed apparently reduced leukemogenicity with a survival rate of 40 or 50% at 50 days after intraperitoneal (i.p.) inoculation of a lethal dose of cells, respectively. Combination of Lp18 and LpICE was capable of inhibiting accumulation of bloody ascites, synergistically superior to Lp18 or LpICE alone. All surviving mice were rechallenged with parental L1210 cells at day 50, and all survived up to day 80, suggesting that gene-modified cells induced immune protection. Moreover, NK cytotoxicity and CTL activity were both enhanced in mice injected with Lp18, especially Lp18 plus LpICE. Levels of IFN-gamma were not altered significantly by inoculation of Lp18 or Lp18 plus LpICE. Our results demonstrate that IL-18 is a useful candidate gene in gene therapy of lymphoma or lymphoid leukemia, and ex vivo combinatorial delivery of Lp18 plus LpICE either as a single approach or as an adjunct to concomitant radiotherapy or chemotherapy, may be more efficient in a situation of minimal residual disease.

Prevention of hepatocellular carcinoma in mice by IL-2 and B7-1 genes co-transfected liver cancer cell vaccines

AIM: To study the immunoprotective effect of liver cancer vaccine with co-transfected IL-2 and B7-1 genes on hepatocarcinogenesis in mice.

METHODS: The murine liver cancer cell line Hepal-6 was transfected with IL-2 and/or B7-1 gene via recombinant adenoviral vectors and the liver cancer vaccines were prepared. C57BL/6 mice were immunized with these vaccines and challenged with the parental Hepal-6 cells afterwards. The immunoprotection was investigated and the reactive T cell line was assayed.

RESULTS: The immunoprotection of the tumor vaccine was demonstrated. The effect of IL-2 and B7-1 genes co-transfected Hepal-6 liver cancer vaccine (Hep6-IL2/B7 vaccine) on the onset of tumor formation was the strongest. When attacked with wild Hepal-6 cells, the median survival period of the mice immunized with Hep6-IL2/B7 vaccine was the longest (68 d, χ² = 7.70-11.69, P < 0.05) and the implanted tumor was the smallest (z = 3.20-44.10, P < 0.05). The effect of single IL-2 or B7-1 gene-transfected vaccine was next to the IL2/B7 gene co-transfected group, and the mean survival periods were 59 and 54 d, respectively. The mean survival periods of wild or enhanced green fluorescence protein gene modified vaccine immunized group were 51 and 48 d, respectively. The mice in control group all died within 38 d and the implanted tumor was the largest (z = 3.20-40.21, P < 0.05). The cellular immunofunction test and cytotoxicity study showed that the natural killer (NK) cell, lymphokine activated killer (LAK) cell and cytotoxic T lymphocyte (CTL) activities were significantly increased in mice immunized with the Hep6-IL2/B7 vaccine, (29.5% ± 2.5%, 65.0% ± 2.9%, 83.1% ± 1.5% respectively, compared with other groups, P < 0.05).

CONCLUSION: The Hep6-IL2/B7 liver cancer vaccines can induce the mice to produce activated and specific CTL against the parental tumor cells, and demonstrate stronger effect on the hepatocarcinogenesis than single gene modified or the regular tumor vaccine. Therefore, the vaccines may become a novel potential therapy for recurrence and metastasis of HCC.

Synergetic anticancer effect of combined quercetin and recombinant adenoviral vector expressing human wild-type p53, GM-CSF and B7-1 genes on hepatocellular carcinoma cells in vitro

AIM: This study investigated the anti-cancer effect of combined quercetin and a recombinant adenovirus vector expressing the human p53, GM-CSF and B7-1 genes (designated BB-102) on human hepatocellular carcinoma (HCC) cell lines in vitro.

METHODS: The sensitivity of HCC cells to anticancer agents was evaluated by 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) assay. The viability of cells infected with BB-102 was determined by trypan blue exclusion. The expression levels of human wild-type p53, GM-CSF and B7-1 genes were determined by Western blot, enzyme-linked immunosorbent assay (ELISA) and flow cytometric analysis, respectively. The apoptosis of BB-102-infected or quercetin-treated HCC cells was detected by terminal deoxynucleotidyl transferase (TdT) assay or DNA ladder electrophoresis.

RESULTS: Quercetin was found to suppress proliferation of human HCC cell lines BEL-7402, HuH-7 and HLE, with peak suppression at 50 μmol/L quercetin. BB-102 infection was also found to significantly suppress proliferation of HCC cell lines. The apoptosis of BB-102-infected HCC cells was greater in HLE and HuH-7 cells than in BEL-7402 cells. Quercetin did not affect the expression of the three exogenous genes in BB-102-infected HCC cells (P > 0.05), but it was found to further decrease proliferation and promote apoptosis of BB-102-infected HCC cells.

CONCLUSION: BB-102 and quercetin synergetically suppress HCC cell proliferation and induce HCC cell apoptosis, suggesting a possible use as a combined anti-cancer agent.

Negative effect of CTLA-4 on induction of T-cell immunity in vivo to B7-1+, but not B7-2+, murine myelogenous leukemia

B7 molecules provide important costimulatory signals to T cells, and B7 genes have been introduced into B7-negative tumor cells to enhance their immunogenicity. However, the role of B7 molecules in inducing tumor immunity is controversial because of conflicting results and reports of differential signaling through the B7 molecules and their ligands CD28 and CTLA-4. In this study, we compared the effect of B7-1 (CD80) and B7-2 (CD86) on the induction of T-cell immunity to C1498, a murine myelogenous leukemia. When cultured with exogenous cytokines in vitro, C1498/B7-1 and C1498/B7-2 induced syngeneic CD8+ T cells to kill parental C1498. In vivo, C1498/B7-1 grew progressively after subcutaneous injection, whereas C1498/B7-2 completely regressed after transient growth in naive mice. Spontaneous rejection of C1498/B7-2 resulted in immunity to challenge doses of C1498 and C1498/B7-1. Antibody-depletion studies in vivo showed that CD8+ T cells rejected C1498/B7-2, whereas only natural killer cells affected the growth of C1498/B7-1. Two approaches were used to determine whether preferential interaction of B7-1 with CTLA-4 contributed to the failure of C1498/B7-1 to activate CD8+ T cells in vivo. First, CTLA-4 specific monoclonal antibody was used to block B7-1-CTLA-4 interaction. Second, CTLA-4 deletional mutant (-/-) bone marrow chimeras were used as tumor hosts. In both systems, there was a significant increase in the rate of rejection of C1498/B7-1 tumors. Resistance to C1498/B7-1 in CTLA-4(minus sign/minus sign) hosts was mediated by CD8+ T cells. Blocking or deletion of CTLA-4 did not affect the growth of parental C1498, indicating that B7-1 was important for the induction of CD8+ T-cell immunity in the absence of CTLA-4.