Heterogeneous effects of B7-1 and B7-2 in the induction of both protective and therapeutic anti-tumor immunity against different mouse tumors

IDO-1 inhibitor INCB24360 elicits distant metastasis of basal extruded cancer cells in pancreatic ductal adenocarcinoma

Neoplastic cells of non-immunogenic pancreatic ductal adenocarcinoma (PDAC) express indoleamine 2,3-dioxygenase 1 (IDO-1), an immunosuppressive enzyme. The metabolites of IDO-1 in cancers provide one-carbon units that annihilate effector T cells, and recruit immunosuppressive cells. In this study we investigated how IDO-1 affected the neoplastic cell behaviors in PDACs. Using multiple markers co-labeling method in 45-µm-thick tissue sections, we showed that IDO-1 expression was uniquely increased in the neoplastic cells extruded from ducts’ apical or basal domain, but decreased in lymph metastatic cells. IDO-1+ extruding neoplastic cells displayed increased vimentin expression and decreased cytokeratin expression in PDACs, characteristics of epithelial-mesenchymal transition (EMT). However, IDO-1 expression was uncorrelated with immunosuppressive infiltrates and clinicopathological characteristics of grim outcome. We replicated basal extrusion with EMT in murine KPIC PDAC organoids by long-term IFN-γ induction; application of IDO-1 inhibitor INCB24360 or 1-MT partially reversed basal extrusion coupled EMT. Ido-1 deletion in KPIC cells deprived its tumorigenicity in immunocompetent mice, decreased cellular proliferation and macropinocytic ability, and increased immunogenicity. KPIC organoids with IFN-γ-induced basal extrusion did not accelerate distant metastasis, whereas inhibition IFN-γ-induced IDO-1 with INB24360 but not 1-MT in KPIC organoids elicited liver metastasis of subcutaneous KPIC organoid tumors, suggesting that lower IDO-1 activity accelerated distant metastasis, whereas IDO-1 was indispensable for tumorigenicity of PDAC cells and supports the survival of extruding cells.

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.

Bioprofiling TS/A Murine Mammary Cancer for a Functional Precision Experimental Model

The TS/A cell line was established in 1983 from a spontaneous mammary tumor arisen in an inbred BALB/c female mouse. Its features (heterogeneity, low immunogenicity and metastatic ability) rendered the TS/A cell line suitable as a preclinical model for studies on tumor-host interactions and for gene therapy approaches. The integrated biological profile of TS/A resulting from the review of the literature could be a path towards the description of a precision experimental model of mammary cancer.

Anti-tumor immunity in a model of acute myeloid leukemia

Whole-cell vaccines allow the induction of anti-tumor immune responses without the need to define tumor antigens. We wished to directly compare, for the first time, the capacity of B7-1, B7-2 and 4-1BB ligand (4-1BBL) costimulatory molecules to convert murine and human acute myeloid leukemia (AML) cells into whole vaccines. 32Dc-kit is a murine myeloid cell line, which develops an AML-like disease over a protracted period, emulating human AML disease development. 32Dc-kit cells were modified to express elevated levels of B7-1, B7-2 or 4-1BBL, and each led to tumor rejection, although only mice injected with 32Dc-kit/B7-2 cells were able to reject subsequent parental tumor cell challenge. T-cell deficient nude mice were able to reject the 32Dc-kit variants, but they could not reject parental cell challenge; however, we found no evidence of cytotoxic T lymphocyte or natural killer (NK) activity ex vivo suggesting that tumor cell killing was mediated by an immune response that could not be recapitulated using purified NK or T cells as lone effectors. In human allogeneic mixed lymphocyte reactions (MLRs), we found no single costimulatory molecule was more effective, suggesting that the induction of a universal anti-tumor response will require a combination of costimulatory molecules.

B7-1 and B7-2: Similar costimulatory ligands with different biochemical, oligomeric and signaling properties

B7-1 and B7-2 are homologous costimulatory ligands expressed on the surface of antigen presenting cells (APCs). Binding of these molecules to the T cell costimulatory receptors, CD28 and CTLA-4, is essential for the activation and regulation of T cell immunity. Despite strong structural similarities, B7-1 and B7-2 exhibit different biochemical features, and their binding to the costimulatory receptors results in distinct T cell functional outcomes. Using photobleaching based fluorescence resonance energy transfer (FRET), our previous studies have demonstrated that B7-1 and B7-2 have different cell surface oligomeric states. While B7-1 is present as a dimer, B7-2 exists as a monomer on the cell surface suggesting that the unique cell surface oligomeric states of the costimulatory ligands may play a key role in the regulation of T cell responses. Moreover, signaling via B7-1 and B7-2 in dendritic cells has been reported to be dependent on their simultaneous expression, raising the possibility that their direct interaction or their involvement in synergistic signaling pathways may play a role in the function of antigen presenting cells. We discuss physiological relevance of distinct oligomeric states of B7-1 and B7-2 and address whether these molecules can associate with one another on the cell surface to form hetero-oligomers. Our findings suggest that B7-1 and B7-2 do not form hetero-oligomers, underscoring the biological relevance of dimeric and monomeric state of B7-1 and B7-2, respectively.

Anti-tumor immune responses following neoadjuvant immunotherapy with a recombinant adenovirus expressing HSP72 to rodent tumors

Gene modification of tumor cells is commonly utilized in various strategies of immunotherapy preventive both as treatment and a means to modify tumor growth. Gene transfer prior to surgery as neoadjuvant therapy has not been studied systematically. We addressed, whether direct intra-tumoral injection of a recombinant adenovirus expressing the immunomodulatory molecule, heat shock protein 72 (ADHSP72), administered prior to surgery could result in sustainable anti-tumor immune responses capable of affecting tumor progression and survival in a number of different murine and rat tumor models. Using intra-dermal murine models of melanoma (B16), colorectal carcinoma (CT26), prostate cancer (TrampC2) and a rat model of glioblastoma (9L), tumors were treated with vehicle or GFP expressing adenovirus (ADGFP) or ADHSP72. Tumors were surgically excised after 72 h. Approximately 25-50% of animals in the ADHSP72 treatment group but not in control groups showed sustained resistance to subsequent tumor challenge. Tumor resistance was associated with development of anti-tumor cellular immune responses. Efficacy of ADHSP72 as neoadjuvant therapy was dependent on the size of the initial tumor with greater likelihood of immune response generation and tumor resistance associated with smaller tumor size at initial treatment. ADHSP72 neoadjuvant therapy resulted in prolonged survival of animals upon re-challenge with autologous tumor cells compared to ADGFP or vehicle control groups. To study the effects on tumor progression of distant metastases, a single tumor focus of animals with multifocal intra-dermal tumors was treated. ADHSP72 diminished progression of the secondary tumor focus and prolonged survival, but only when the secondary tumor focus was <50 mm3 . Our results indicate that gene modification of tumors prior to surgical intervention may be beneficial to prevent recurrence in specific circumstances.

Aged mice develop protective antitumor immune responses with appropriate costimulation

There is a clear decrease in CD8(+) T cell effector function with aging, a loss once thought to be intrinsic to the CD8(+) T cells. Recent studies suggest, however, that this decline may be a consequence of altered stimulatory signals within the aged lymphoid microenvironment. In this study, we compared the immune responses of young and old mice against the BM-185 pre-B cell lymphoma expressing enhanced GFP (EGFP) as a surrogate tumor Ag. Young animals develop protective immune responses when immunized with BM-185-EGFP, but aged mice do not and ultimately succumb to the tumor. However, expression of CD80 (B7.1) on the BM-185-EGFP (BM-185-EGFP-CD80) results in rejection of the tumor by both young and old animals. Additionally, injection of BM-185-EGFP-CD80 cells in young mice promotes the development of long-lasting memory responses capable of rejecting BM-185 wild-type tumors. Aged animals similarly injected did not develop antitumor memory responses. Interestingly, old animals immunized with the BM-185-EGFP-CD80 cells plus injections of the agonist anti-OX40 mAb did develop long-lasting memory responses capable of rejecting the BM-185 wild-type tumors with the same vigor as the young animals. We show that old mice have the capacity to develop strong antitumor responses and protective memory responses as long as they are provided with efficient costimulation. These results have important implications for the development of vaccination strategies in the elderly, indicating that the aged T cell repertoire can be exploited for the induction of tumor immunity.

Ionizing radiation inhibition of distant untreated tumors (abscopal effect) is immune mediated

PURPOSE

Ionizing radiation can reduce tumor growth outside the field of radiation, known as the abscopal effect. Although it has been reported in multiple malignancies, the abscopal effect remains a rare and poorly understood event. Ionizing radiation generates inflammatory signals and, in principle, could provide both tumor-specific antigens from dying cells and maturation stimuli that are necessary for dendritic cells' activation of tumor-specific T cells. We therefore tested the hypothesis that the abscopal effect elicited by radiation is immune mediated. This was directly tested by enhancing the number of available dendritic cells using the growth factor Flt3-Ligand (Flt3-L).

METHODS AND MATERIALS

Mice bearing a syngeneic mammary carcinoma, 67NR, in both flanks were treated with Flt3-L daily for 10 days after local radiation therapy (RT) to only 1 of the 2 tumors at a single dose of 2 or 6 Gy. The second nonirradiated tumor was used as indicator of the abscopal effect. Data were analyzed using repeated measures regression.

RESULTS

RT alone led to growth delay exclusively of the irradiated 67NR tumor, as expected. Surprisingly, growth of the nonirradiated tumor was also impaired by the combination of RT and Flt3-L. As control, Flt3-L had no effect without RT. Importantly, the abscopal effect was shown to be tumor specific, because growth of a nonirradiated A20 lymphoma in the same mice containing a treated 67NR tumor was not affected. Moreover, no growth delay of nonirradiated 67NR tumors was observed when T cell deficient (nude) mice were treated with RT plus Flt3-L.

CONCLUSIONS

These results demonstrate that the abscopal effect is in part immune mediated and that T cells are required to mediate distant tumor inhibition induced by radiation.

Correction of defects responsible for impaired Qa-2 class Ib MHC expression on melanoma cells protects mice from tumor growth

One of the principal mechanisms of tumor immune evasion is alteration of class I MHC expression. We have identified defects contributing to down-regulation of class I MHC expression in the widely studied murine B16 melanoma and its variants B16F1, B16F10, BL6-2, BL6-8 and B78H1. Transcription of the nonclassical class I MHC genes Q8 and Q9 (Qa-2 Ags) has been switched off in the entire panel of melanoma lines, suggesting that this event occurred early during tumor progression. B78H1, unlike B16F1 and B16F10 sublines, is also selectively devoid of TAP2 and low molecular weight protein 7 as well as classical class I MHC K(b) and D(b) transcripts. Cotransfection of B78H1 with TAP2 and class I H chain genes is sufficient to reconstitute surface expression of exogenously delivered class I MHC without concomitant re-expression of endogenous beta(2)-microglobulin-associated class I. The serological absence of endogenous class Ia and Ib at the surface of TAP2-negative as well as TAP2-transfected B78H1 makes this system a suitable model for studying the properties of isolated class I proteins in tumors. We used this system to demonstrate that B78H1 cells genetically manipulated to re-express Q9 Ag have reduced tumor potential in syngeneic B6 mice compared with TAP2-transfected parental melanoma. Both NK cells and CTLs appear to collaborate in restraining growth of Q9-positive tumors. The results implicate Qa-2 in antitumor responses and illustrate the utility of the B78H1 system for identifying in vivo interactions between class I MHC molecules of interest and immune cells of innate and/or adaptive immunity.

On the biological relevance of MHC class II and B7 expression by tumour cells in melanoma metastases

A large number of studies have indicated that specific immune reactivity plays a crucial role in the control of malignant melanoma. In this context, expression of MHC I, MHC II and B7 molecules by melanoma cells is seen as relevant for the immune response against the tumour. For a better understanding of the biological relevance of MHC II and B7 expression by tumour cells in metastatic melanoma, we studied the expression of these molecules in melanoma metastases in relation to the inflammatory response, regression of the tumour and survival from 27 patients treated with biochemotherapy (30 mg m(-2) Cisplatin and 250 mg m(-2) decarbazine (dimethyl-triazene-imidazole-carboxamide, DTIC) on days 1-3 i.v., and 10(7) IU IFN-alpha 2b 3 days a week s.c., q. 28d). In 19 out of 27 lesions studied, we found expression of MHC II by the tumour cells, while only in one out of 11 tumour biopsies obtained from untreated metastatic melanoma patients, MHC II expression was detected. Expression of B7.1 and B7.2 by tumour cells was found in nine out of 24 and 19 out of 24 lesions, respectively. In all cases where B7.1 expression was found, expression of B7.2 by the tumour cells was also seen. In general, no or only few inflammatory cells positive for B7 were found. Expression of MHC II by tumour cells was positively correlated with the presence of tumour-infiltrating lymphocytes, regression of the lesion, and with time to progression (TTP) and overall survival (OS) of the patient. However, no significant correlation between B7.1 or B7.2 expression and regression of the tumour, TTP or OS was found. In light of other recent findings, these data altogether do support a role as biomarker for MHC II expression by tumour cells; however, its exact immunological pathomechanism(s) remain to be established.

Presentation of native TROP-2 tumor antigens to human cytotoxic T lymphocytes by engineered antigen-presenting cells

Professional antigen-presenting cells (APC), e.g. dendritic cells, express immuno-proteasome components and process proteins for MHC presentation differently from non-immune cells. Thus, they induce reactivities against sets of peptides that do not overlap with those generated by non-professional APC, i.e., tumor cells, and stimulate cytotoxic T lymphocytes (CTL) that may not recognize them. The goal of this work was to establish a system for antigen presentation and in vitro stimulation of human CTL using "tumor-cell-like" engineered APC. Murine fibroblasts were transfected with human HLA Class I alleles, together with the B7.1, ICAM-1 and germ-line TROP2 genes. The last encodes a cell surface glycoprotein widely expressed by human cancers. Unseparated peripheral blood mononuclear cells from HLA Class I-matched individuals were stimulated in vitro by the engineered APC. These efficiently induced the activation and proliferation of antigen-specific HLA-restricted CTL lines and clones. The Trop-2-specific CTL demonstrated high specific cytotoxicity against the appropriate transfected target cells. They also efficiently lysed MCF-7 human tumor cells expressing endogenous HLA-A2.1, Trop-2 together with ICAM-1. These results demonstrate that Trop-2 is a target molecule recognized by human CTL. Moreover, they demonstrate that non-immune engineered APC efficiently process and present native tumor-specific proteins in the context of human MHC Class I, and stimulate the growth and cytotoxicity of specific anti-tumor CTL.

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.

Expression of B7.1 (CD80) in a renal cell carcinoma line allows expansion of tumor-associated cytotoxic T lymphocytes in the presence of an alloresponse

We have selected a well-characterized human renal cell carcinoma (RCC) line as the basis for development of a genetically engineered tumor cell vaccine to be applied in an allogeneic setting. This cell line was genetically modified by retroviral transduction to express B7.1 costimulatory molecules. The unmodified tumor cells and B7.1-expressing tumor cells were compared for their ability to induce tumor-associated responses in allogeneic peripheral blood mononuclear cells (PBMC) of two normal control donors having single MHC class I allele matches with the tumor cells. PBMC primed using B7.1-modified tumor cells showed a preponderance of CD3+CD8+ cytotoxic T lymphocytes (CTL) that proliferated over extended periods of time in mixed lymphocyte tumor cell (MLTC) cultures. Strong cytolytic activity developed in the primed populations and included allospecific CTL with specificity for mismatched HLA-A, -B and -C molecules. Nevertheless, it was possible to isolate CTL clones that were able to lyse tumor cells but not lymphoblastoid cells that expressed all the corresponding allospecificities. Thus, induction of complex allospecific responses did not hinder the development of tumor-associated CTL in vitro. These results support the use of this genetically modified allogeneic tumor cell line for vaccination of partial-MHC matched RCC patients.

Transgenic expression of Ly49A on T cells impairs a specific antitumor response

Inhibitory MHC receptors determine the reactivity and specificity of NK cells. These receptors can also regulate T cells by modulating TCR-induced effector functions such as cytotoxicity, cytokine production, and proliferation. Here we have assessed the capacity of mouse T cells expressing the inhibitory MHC class I receptor Ly49A to respond to a well-defined tumor Ag in vivo using Ly49A transgenic mice. We find that the presence of Ly49A on the vast majority of lymphocytes prevents the development of a significant Ag-specific CD8+ T cell response and, consequently, the rejection of the tumor. Despite minor alterations in the TCR repertoire of CD8+ T cells in the transgenic lines, precursors of functional tumor-specific CD8+ T cells exist but could not be activated most likely due to a lack of appropriate CD4+ T cell help. Surprisingly, all of these effects are observed in the absence of a known ligand for the Ly49A receptor as defined by its ability to regulate NK cell function. Indeed, we found that the above effects on T cells may be based on a weak interaction of Ly49A with Kb or Db class I molecules. Thus, our data demonstrate that enforced expression of a Ly49A receptor on conventional T cells prevents a specific immune response in vivo and suggest that the functions of T and NK cells are differentially sensitive to the presence of inhibitory MHC class I receptors.

Induction of tumor-specific immunity in mice by immunization with reconstituted tumor membrane liposomes containing recombinant B7-2 (CD86)

There has been considerable interest in developing experimental vaccines using genetically modified tumor cells expressing cytokines or costimulatory molecules to enhance immunogenicity. The authors investigated an alternative approach of using protein transfer rather than gene transfer to introduce costimulatory molecules rapidly into tumor membranes. Immunization with a single dose of reconstituted tumor membrane liposomes containing purified recombinant B7-2 (CD86) induced tumor rejection in mice challenged with syngeneic tumors, including the poorly immunogenic AG104A fibrosarcoma. These findings support the possibility that cell-free vaccines composed of reconstituted tumor membrane liposomes containing additional immunostimulatory proteins may offer a practical and safe alternative to genetically modified tumor cells for treating human cancer.

Vaccination with mouse mammary adenocarcinoma cells coexpressing B7-1 (CD80) and B7-2 (CD86) discloses the dominant effect of B7-1 in the induction of antitumor immunity

Nonreplicating TS/A mammary adenocarcinoma cells expressing B7-2 (CD86) (TS/A-2) are more immunogenic than those expressing B7-1 (CD80) (TS/A-1), indicating that B7-1 and B7-2 display nonredundant costimulatory effects in inducing antitumor responses. Whereas transfection of B7-2 cDNA into TS/A-1 cells does not improve their immunogenicity, transfection of B7-1 cDNA into TS/A-2 cells (TS/A-2/1) decreases their immunogenicity in a manner that is directly related to the surface levels of B7-1. Ab blocking of B7-1 on TS/A-2/1 cells before their injection in vivo restores the higher immunogenicity characteristic of single B7-2 transfectants, indicating therefore that B7-1 actively modulates the B7-2-dependent costimulation. The expression of B7-1 also modifies quantitatively the balance of endogenous IFN-gamma and IL-4 induced in vivo by TS/A-2 vaccines. In fact, we find that vaccination with TS/A-2/1 cells results in the production of more IFN-gamma and less IL-4 than TS/A-2 vaccines, a pattern comparable to that induced by TS/A-1 cells. Thus, in the TS/A model of antitumor response, B7-1 modulates B7-2-dependent costimulatory effects in a dominant, noncompetitive way.

4-1BB Ligand, a Member of the TNF Family, Is Important for the Generation of Antiviral CD8 T Cell Responses

4-1BB (CD137) is a costimulatory molecule expressed on activated T cells and interacts with 4-1BB ligand (4-1BBL) on APCs. To investigate the role of 4-1BB costimulation for the development of primary immune responses, 4-1BBL-deficient (4-1BBL−/−) mice were infected with lymphocytic choriomeningitis virus (LCMV). 4-1BBL−/− mice were able to generate CTL and eliminate acute LCMV infection with normal kinetics, but CD8 T cell expansion was 2- to 3-fold lower than in wild-type (+/+) mice. In the same mice, virus-specific CD4 Th and B cell responses were minimally affected, indicating that 4-1BB costimulation preferentially affects CD8 T cell responses. This result contrasts with our earlier work with CD40L-deficient (CD40L−/−) mice, in which the CD8 T cell response was unaffected and the CD4 T cell response was markedly impaired. When both 4-1BBL- and B7-dependent signals were absent, CD8 T cell expansion was further reduced, resulting in lower CTL activity and impairing their ability to clear LCMV. Altogether, these results indicate that T cells have distinct costimulatory requirements: optimal CD8 responses require 4-1BBL-dependent interactions, whereas CD4 responses are minimally affected by 4-1BB costimulation, but require CD40-CD40L and B7-dependent interactions.

Human Fibroblasts Transduced with CD80 or CD86 Efficiently trans-Costimulate CD4+ and CD8+ T Lymphocytes in HLA-Restricted Reactions: Implications for Immune Augmentation Cancer Therapy and Autoimmunity

Augmenting immunogenicity by genetically modifying tumor cells to express costimulatory molecules has proven to be a promising therapeutic strategy in murine tumor models and is currently under investigation in human clinical trials for metastatic cancer. However, there are significant technical and logistic problems associated with implementing strategies requiring direct gene modification of primary tumor cells. In an effort to circumvent these problems, we are developing a strategy in which the costimulatory signal required for tumor-specific T lymphocyte activation is provided by a genetically modified human fibroblast (trans-costimulation). We have evaluated the efficiency of CD80- and CD86-mediated trans-costimulation in the activation of human CD8+ and CD4+ T lymphocytes in MHC class I- and class II-restricted lymphoproliferation reactions. Our studies demonstrate that the efficiency of CD80- or CD86-mediated trans-costimulation of purified human CD8+ and CD4+ T lymphocytes is comparable to cis-costimulation under defined conditions. Moreover, a dose-response relationship consistent with the predicted two-hit kinetics of the reaction was evident in trans-costimulation reactions in which the ratio of target cells expressing either signal 1 or signal 2 was varied incrementally from 1:10 to 10:1. Importantly, the level of cell-surface CD86 required for trans-costimulation is equivalent to that constitutively expressed by human peripheral blood monocytes. These results may have significant implications for the clinical implementation of this type of cancer immunotherapy and also raise questions about the possibility of trans-costimulating autoreactive T lymphocytes in vivo.

Immunogenicity of Apoptotic Cells In Vivo: Role of Antigen Load, Antigen-Presenting Cells, and Cytokines

Apoptosis allows the clearance of unwanted cells from living tissues without causing inflammation. Processing of phagocytosed apoptotic cells yields Ags that access the cytosol and the MHC class I pathway of engulfing cells and are recognized by Ag-specific CTL. We show here that injection of apoptotic RMA cells, a syngeneic T cell lymphoma, into C57BL/6 mice results in priming of a functional and long-lasting tumor-specific immune response. Cross-priming of CTLs by apoptotic cells requires CD4+ T cell help. Apoptotic cells, however, are at least 20-fold less immunogenic than nonreplicating live cells. Immunogenicity of apoptotic cells is proportional to the number of cells injected, correlates with the serum concentration of IL-10 and IL-1β cytokines, and is enhanced in IL-10 knockout mice. Moreover, immunization with dendritic cells (DCs), but not macrophages (Mφ), pulsed with apoptotic cells primes tumor-specific CTLs and confers protection against a tumor challenge. Our findings demonstrate that tumor cells undergoing apoptosis are, though scarcely, immunogenic in vivo, outline the different roles of Mφ and DCs in the physiologic clearance of unwanted cells, and have implications in designing immunomodulating vaccines.

Interaction between B.7 and CD28 costimulatory molecules is essential for the activation of effector function mediating spontaneous tumour regression

The spontaneous regression of a rat histiocytoma, AK-5, is mediated by activated natural killer cells through antibody-dependent cellular cytotoxicity. In addition to the Fc-FcR interaction between the target and the effector cells demonstrated previously, we show the participation of costimulatory molecules B7 and CD28 in the efficient killing of the tumour cell. Blockade of the costimulatory interaction in vivo using anti-CD28 led to increased tumour growth and a suppressed cytokine response. Anti-CD28 antibody administration in vivo also diminished the cytotoxic potential of NK cells against AK-5 cells in vitro. Our studies also demonstrate the expression of B7.1 and B7.2 antigen on AK-5 tumour cells. The cytotoxic activity of natural killer cells was significantly inhibited when the effector/target cells were cultured in the presence of antibodies raised against B7.1, B7.2 and CD28. Administration of anti-CD28 in vivo also affected the efficiency of the formation of effector/target conjugates in vitro. Similarly, anti-CD28 injections affected expression of the adhesion molecules LFA 1 and ICAM 1 by splenocytes. Administration of anti-B7.1 and B7. 2 antibodies in AK-5 tumour-bearing animals showed a differential response. The cytotoxicity of natural killer cells was significantly inhibited after anti-B7.2 administration, suggesting the preferential participation of B7.2 molecules in vivo. These observations suggest an important role for B7-CD28 interaction in AK-5 tumour regression.

Combination Gene Therapy with CD86 and the MHC Class II Transactivator in the Control of Lung Tumor Growth

Early reports suggest that the costimulatory molecule CD86 (B7-2) has sporadic efficacy in tumor immunity, whereas changes in cancer immunity mediated by the MHC class II transactivator (CIITA) have not been extensively investigated. CIITA activates MHC class II expression in most cells; however, in the Line 1 lung carcinoma model system, CIITA activates MHC class I and well as class II. Here we show that CD86 is very effective in inducing a primary immune response against Line 1. Tumor cells expressing CD86 grew in only 50% of the mice injected with live cells, and those mice that developed tumors did so with significantly delayed kinetics. Furthermore, irradiated CD86-expressing Line 1 cells served as an effective tumor vaccine, demonstrating that CD86 is effective in inducing tumor immunity in the Line 1 system. These data suggest that if CIITA and CD86 cooperate, enhanced tumor immunity could be achieved. CIITA alone was mildly beneficial in slowing primary tumor growth but only when expressed at low levels. Clones expressing high levels of class II MHC grew as fast as or faster than parental tumor, and CIITA expression in a tumor vaccine assay lacked efficacy. When CIITA and CD86 were coexpressed, there was no cooperative immune protection from tumor growth. Cells that coexpress both genes also failed as a cancer vaccine, suggesting a negative role for CIITA in this lung carcinoma. These data suggest that human cancer vaccine trials utilizing CIITA gene therapy alone or in combination with CD86 should be approached with caution.

Triggering of Murine NK Cells by CD40 and CD86 (B7-2)

NK cell-mediated cytotoxicity is regulated by both triggering and inhibitory signals. The interaction between MHC class I molecules expressed on target cells and specific MHC class I-binding receptors expressed by NK cells generally leads to inhibition of lysis. We have shown recently that CD80 (B7-1) in mice and CD40 in humans trigger NK cell-mediated cytotoxicity in vitro. In the present study, we show that murine CD40 and CD86 (B7-2) trigger murine NK cell-mediated cytotoxicity in vitro when expressed on tumor cells. Preincubation of the transfected cell lines with anti-CD40 F(ab′)2 fragments or cytolytic T lymphocyte-associated Ag-4-Ig (CTLA-4-Ig) before the cytotoxic assay abolished the triggering effect. Furthermore, radiolabeled CD40- and B7-2-expressing cells were rapidly eliminated in vivo in an NK cell-dependent manner. NK cells from CD40 ligand (CD40L)−/− or CD28−/− mice were triggered by tumor cells transfected with CD40 and B7-2, respectively, and these transfectants were rapidly eliminated in vivo when inoculated into CD40L−/− and CD28−/− mice. This suggests that the CD40 and B7-2 molecules can interact with receptors on NK cells other than CD40L and CD28, respectively, and that these may account for some of the reactivities observed in the present study. Collectively, these data demonstrate that 1) costimulatory molecules, other than B7-1, can modulate NK cell responses in vitro, 2) they can also affect NK cell-dependent responses in vivo, and 3) parts of these reactions are independent of CD28 and CD40L.

Interleukin-12-secreting human papillomavirus type 16-transformed cells provide a potent cancer vaccine that generates E7-directed immunity

The development of a vaccine that would be capable of preventing or curing the (pre)cancerous lesions induced by genital oncogenic human papillomaviruses (HPVs) is the focus of much research. Many studies are presently evaluating vaccines based on the viral E6 and E7 oncoproteins, both of which are continually expressed by tumor cells. The success of a cancer vaccine relies, in large part, on the induction of a tumor-specific Th1-type immunity. In this study, we have evaluated the ability of B7-related and/or interleukin-12 (IL-12)-expressing, non-immunogenic murine HPV16-transformed BMK-16/myc cells, to achieve this goal. BMK-16/myc cells engineered to express surface B7-1 or B7-2 molecules remain tumorigenic in syngeneic BALB/c mice, suggesting that expression of these molecules alone is not sufficient to induce tumor regression. In contrast, mice injected with tumor cells engineered to secrete IL-12 remained tumor-free, demonstrating that IL-12 expression is sufficient to induce tumor rejection. IL-12-secreting BMK-16/myc cells were further shown to induce potent and specific long-term tumor resistance, even after irradiation. B7-1 was found to slightly but systematically improve anti-tumor immunity elicited by IL-12-secreting BMK-16/myc cells. Injection of irradiated B7-1/IL-12+ BMK-16/myc cells generates long-lasting, Th1-type, BMK-16/myc-directed immunity in tumor-resistant mice. These mice display a memory-type, E7-specific, cell-mediated immune response, which is potentially significant for clinical applications.

4-1BBL Cooperates with B7-1 and B7-2 in Converting a B Cell Lymphoma Cell Line into a Long-Lasting Antitumor Vaccine

A20 is a B cell lymphoma that constitutively expresses the costimulatory molecule B7-2 yet grows readily as a tumor in syngeneic BALB/c mice. We have compared the tumorigenicity of A20 variants expressing either B7-1 (A20/B7-1) or B7-2 (A20/B7-2) with an A20 variant expressing B7-1 and B7-2 with 4-1BBL (A20/4-1BBL), a costimulatory member of the TNF family. Mice injected with tumors expressing the vector backbone (A20/CMV) or B7-1 developed tumors within 25 days of s.c. injection. In contrast, mice injected with A20/4-1BBL were tumor free for the 150-day follow-up period, while 25% of mice injected with A20/B7-2 developed tumors. Tumorigenicity experiments using nude mice indicated the requirement for T cells for variant rejection. Almost all mice that resisted the initial tumor challenge were resistant to further challenge with the parental tumor. Splenocytes from these mice showed high CTL lytic activity against the parental tumor, A20, as well as the syngeneic BALB/c lymphoma K46J, but showed background levels of lytic activity against the congenic SCID thymoma line ST-D2 or the allogeneic EL4 thymoma. In vitro blocking experiments with anti-B7-1 plus anti-B7-2 and/or soluble 4-1BB receptor showed B7-1, B7-2, and 4-1BBL all contributed to the CTL activity. Thus, the data show that neither B7-1 or B7-2 alone can confer full immunogenicity to the A20 lymphoma but that the addition of 4-1BBL results in a tumor that is highly immunogenic and can confer long-lasting protection against challenge with parental tumor in vivo.

Differential CD86/B7-2 expression and cytokine secretion induced by Toxoplasma gondii in macrophages from resistant or susceptible BALB H-2 congenic mice

The influence of the intracellular parasite Toxoplasma gondii on macrophage expression of co-stimulatory molecules was studied. Unlike surface expression of CD80/B7-1, that of CD86/B7-2 is increased in mouse peritoneal macrophages 24 h following exposure to live toxoplasma in vitro. Most CD86 molecules are found on infected cells bearing a maximum parasite load. Consistent with the elevated membrane expression, the quantity of CD86 gene transcript is increased in macrophages infected by T. gondii in vitro or in vivo. CD86 up-regulation contributes to the augmented capacity of parasitized macrophages to present antigen to tuberculin-specific CD4+ T cells as demonstrated by blocking CD86 ligand interaction. T. gondii triggers up-regulation of CD86 in macrophages from BALB/c mice which are resistant to the development of toxoplasmic encephalitis. Infection of macrophages from the susceptible strain BALB.B, however, results in a decreased surface expression of CD86, although the parasite load and intracellular proliferation proved comparable in both macrophages. This differential host cell reaction correlates with disparate profiles in T. gondii-induced cytokine secretion. Upon challenge with toxoplasma, IL-1alpha and tumor necrosis factor (TNF)-alpha are released to a significantly higher extent by BALB/c than by BALB.B macrophages, whereas the latter secrete more IL-12 and IL-10. In BALB.B macrophages, T. gondii-induced IL-10 down-regulates surface expression of CD86, thus indicating an interference of parasite-dependent cytokine release and modulation of CD86. The biased secretory response in macrophages from the two congenic strains implies an MHC-dependent and dichotomous monokine induction by T. gondii. Up-regulation of CD86 seems to occur along the IL-1/TNF-inducing pathway and experimental evidence indicates that this enhances T cell activation by parasitized macrophages.

Enhanced interleukin-2 gene transfer immunotherapy of breast cancer by coexpression of B7-1 and B7-2

The capability of B7-1 to augment the antitumor activity of some cytokines has been shown primarily for such cytokines as interleukin-12 (IL-12), IL-7, and to a lesser extent IL-2. In this study, we investigate the ability of B7-1 and B7-2 to augment the antitumor activity of IL-2. Considering the affinity of both molecules for CD28 (T cell receptor for B7-1 and B7-2), we postulated that their potential to augment IL-2 antitumor activity would be similar. Two murine transgenic adenocarcinoma models were chosen to investigate the activity of adenoviral vectors constructed to express either B7-1 and IL-2 or B7-2 and IL-2. Before administering the vector intratumorally to tumor-bearing mice, we determined the expression of B7-1, B7-2, MHC I, and MHC II on these tumor cells and demonstrated positive expression of only MHC I. Intratumoral injection of the vector expressing B7-1 and IL-2 resulted in complete regression of all tumors treated. In contrast, the vector expressing B7-2 and IL-2 was significantly less effective at regressing PyMT tumors, whereas both double recombinant vectors demonstrated similar levels of complete regression in the Neu (NDL 8142) model. Regressed mice were all protected for rechallenge in both models and demonstrated antigen-specific cytotoxic T lymphocytes (CTL) in the PyMT model. These findings indicate that the combination of IL-2 with B7-1 or B7-2 significantly enhances the antitumor activity of IL-2.

T Cell-Mediated, IFN-γ-Facilitated Rejection of Murine B16 Melanomas

The murine melanoma cell line B16.F10 (H-2b) was used to study specific T cell responses that reject tumors. Stable B16 transfectants were established that express viral Ags, either the hepatitis B surface Ag (HBsAg) or the large tumor Ag (T-Ag) of SV40. B16 cells and their transfected sublines were CD40+CD44+ but expressed no (or low levels of the) costimulator molecules CD154 (CD40L), CD48, CD54, CD80, and CD86. Surface expression of MHC class I (Kb, Db) and class II (I-Ab) molecules by B16 cells was low, but strikingly up-regulated by IFN-γ. CD95 (Fas) and CD95 ligand (CD95L (FasL)) were “spontaneously” expressed by B16 cells growing in vitro in serum-free medium; these markers were strikingly up-regulated by IFN-γ. B16 cells coexpressing CD95 and CD95L were irreversibly programed for apoptosis. In vitro, noninduced B16 transfectants stimulated a specific IFN-γ release response, but no cytolytic response (in a 4-h assay) in MHC class I-restricted CTL; in contrast, IFN-γ-induced B16 targets were efficiently and specifically lysed by CTL. In vivo, B16 transfectants were specifically rejected by DNA-vaccinated syngeneic hosts through a T-dependent immune effector mechanism. The tumors showed evidence of massive apoptosis in vivo during the rejection process. The data suggest that CTL-derived IFN-γ enhances an intrinsic suicide mechanism of these tumor cells in addition to facilitating lytic interactions of effectors with tumor targets.

Human melanoma cells transfected with the B7-2 co-stimulatory molecule induce tumor-specific CD8+ cytotoxic T lymphocytes in vitro

Neoplastic cells express tumor-associated antigens, but tumor rejection seldom occurs in vivo. The absence of an effective immune response may be explained by the inability of tumor cells to deliver co-stimulatory signals. Indeed, transfection of either B7-1 or B7-2 co-stimulatory molecules into mouse tumor cells enhances antitumor immune responses. In this study, we stably transfected human melanoma cells with the cDNA encoding the B7-2 molecule to evaluate in vitro: (i) the induction of anti-melanoma cytotoxic T lymphocytes (CTL) by stimulation of CD8+ T cells, purified from healthy donors and a melanoma patient, with B7-2 transfected allogeneic HLA-matched melanoma cells; (ii) the tumor specificity and the HLA restriction of the induced CTL; and (iii) the feasibility to propagate long-term antimelanoma CTL lines. We found that B7-2 transfected, but not untransfected or mock-transfected, melanoma cells activated MHC-class I-restricted, melanoma-specific CD8+ CTL from healthy donors. More importantly, CD8+ tumor-associated lymphocytes, purified from a tumor-invaded lymph node of a melanoma patient and stimulated with B7-2-transfected melanoma cells, acquired a strong reactivity toward the autologous tumor. CTL lines with specific cytolytic activity could be propagated in long-term culture. These results indicate that: (i) the expression of the B7-2 molecule into human melanoma cells makes them immunogenic and able to act as antigen-presenting cells and (ii) purified CD8+ cells, stimulated with B7-2+ allogeneic HLA-matched melanoma cells, preferentially recognize melanoma-specific rather than allogeneic antigens. This study may have clinical implications for passive and/or active immunotherapy in melanoma patients.

Gene therapy for breast cancer

Gene therapy for breast cancer is still in the very early stages of development. Many of the molecular strategies that have been proposed are also being developed for other cancers. Their application to breast cancer, however, needs to address several issues specific to this disease such as the widespread nature of metastases, the indolent growth of the tumor cells, and the production by the tumor of immunosuppressive agents. Nonetheless, these approaches appear promising, particularly those that employ a combination of strategies. Gene therapies that affect the biology of breast cancer cells or regulate host immune mechanisms have been most successful and may be paired with existing therapies for breast cancer.

Blockade of B7-2, not B7-1, inhibits purified protein derivative-primed T-lymphocyte responses but fails to influence the proportion of Th1 versus Th2 subsets

The ability to select for a cell-mediated response rather than antibody production following infection with intracellular mycobacteria, would be an advantage in preventing the occurrence of disease. Recent work suggests that the two members of the B7 family of costimulatory molecules, B7-1 and B7-2, may differentially influence the nature of primary immune responses but little is known of their role in this capacity in secondary responses. We have used an in vitro model to investigate whether blocking B7-1 and B7-2 affects changes in the cytokine profiles of Th lymphocytes previously primed to purified protein derivative (PPD) from Mycobacterium bovis. In C57BL/6 and BALB/c mice we found that the proliferative responses of a component of recently activated T lymphocytes, and those returning to the resting state, were inhibited by B7-2 blockade. B7-1 blockade had no distinguishable effect. However, in cultures containing anti-B7-2 antibody, the production of both interferon-gamma (IFN-gamma) and interleukin-4 (IL-4), indicative of cell-mediated and antibody responses, respectively, were reduced. This suggests that intervention in a recall response to mycobacterial antigen by blocking B7-1 or B7-2 molecules, is unlikely to alter the nature of the immune response.

Gene Immunotherapy in Murine Acute Myeloid Leukemia: Granulocyte-Macrophage Colony-Stimulating Factor Tumor Cell Vaccines Elicit More Potent Antitumor Immunity Compared With B7 Family and Other Cytokine Vaccines

In an attempt to explore novel treatment modalities in acute myeloid leukemia (AML), we studied the role of costimulatory and cytokine gene immunotherapy in murine AML. We have previously shown that leukemic mice can be cured with CD80 transfected leukemic cells (B7.1-AML vaccine) administered early in the course of the disease and that the failure B7.1-AML vaccines administered late cannot be attributed to immunosuppression induced by tumor growth. CD8+ T cells, which are necessary for tumor rejection, are activated rather than suppressed during the first half of the leukemic course in nonvaccinated mice. In this report, we question whether CD86 (B7.2) or the cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-4 (IL-4), or tumor necrosis factor-α (TNF-α) can improve the vaccination potential of AML cells. The choice of cytokines was based on their combined and alone as well ability to direct the differentiation of CD34+ cells into potent antigen-presenting dendritic cells in vitro. Our studies show that (1) mice vaccinated with a leukemogenic number of AML cells engineered to express B7.2 (B7.2-AML) or to secrete GM-CSF, IL-4, or TNF-α (GM-, IL-4–, TNF-α–AML) do not develop leukemia; (2) GM-AML cells are tumorigenic in sublethally irradiated SJL/J mice but not in Swiss nu/nu mice, indicating that killing of tumor cells is not T-cell–dependent; (3) vaccines with irradiated GM-AML, but not B7.2-, IL-4–, or TNF-α–AML cells, can elicit leukemia-specific protective and therapeutic immunity; and (4) in head-to-head comparison experiments, vaccination with irradiated GM-AML is more potent than B7.1-AML, curing 80% and providing 20% prolonged survival of the leukemic mice at week 2, as opposed to cures only up to 1 week with B7.1-AML vaccines. These preclinical data emphasize that GM-CSF gene immunotherapy deserves clinical evaluation in AML.

Gene Immunotherapy in Murine Acute Myeloid Leukemia: Granulocyte-Macrophage Colony-Stimulating Factor Tumor Cell Vaccines Elicit More Potent Antitumor Immunity Compared With B7 Family and Other Cytokine Vaccines

In an attempt to explore novel treatment modalities in acute myeloid leukemia (AML), we studied the role of costimulatory and cytokine gene immunotherapy in murine AML. We have previously shown that leukemic mice can be cured with CD80 transfected leukemic cells (B7.1-AML vaccine) administered early in the course of the disease and that the failure B7.1-AML vaccines administered late cannot be attributed to immunosuppression induced by tumor growth. CD8+ T cells, which are necessary for tumor rejection, are activated rather than suppressed during the first half of the leukemic course in nonvaccinated mice. In this report, we question whether CD86 (B7.2) or the cytokines granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin-4 (IL-4), or tumor necrosis factor-α (TNF-α) can improve the vaccination potential of AML cells. The choice of cytokines was based on their combined and alone as well ability to direct the differentiation of CD34+ cells into potent antigen-presenting dendritic cells in vitro. Our studies show that (1) mice vaccinated with a leukemogenic number of AML cells engineered to express B7.2 (B7.2-AML) or to secrete GM-CSF, IL-4, or TNF-α (GM-, IL-4–, TNF-α–AML) do not develop leukemia; (2) GM-AML cells are tumorigenic in sublethally irradiated SJL/J mice but not in Swiss nu/nu mice, indicating that killing of tumor cells is not T-cell–dependent; (3) vaccines with irradiated GM-AML, but not B7.2-, IL-4–, or TNF-α–AML cells, can elicit leukemia-specific protective and therapeutic immunity; and (4) in head-to-head comparison experiments, vaccination with irradiated GM-AML is more potent than B7.1-AML, curing 80% and providing 20% prolonged survival of the leukemic mice at week 2, as opposed to cures only up to 1 week with B7.1-AML vaccines. These preclinical data emphasize that GM-CSF gene immunotherapy deserves clinical evaluation in AML.

Nonreplicating recombinant vaccinia virus encoding human B-7 molecules elicits effective costimulation of naive and memory CD4+ T lymphocytes in vitro

We constructed recombinant vaccinia viruses (recVV) encoding the human T-cell costimulatory molecules B7-1 and B7-2. To abrogate the vaccinia virus transcription termination signal for early genes, the cDNA of B7-1 had to be modified by a T through C sense mutation at position 766. Upon infection with replication incompetent and noncytopathic recVV, several tumor cell lines as well as cultured human fibroblasts expressed the costimulatory molecules. All these cells were capable of providing effective costimulation for proliferation of resting CD4(+) T-cells after infection with recVV encoding B7 molecules. The costimulatory effect could be blocked with CTLA-4 IgG fusion protein, the soluble ligand for B7. RecVV-induced overexpression of B7 on syngeneic EBV-transformed lymphoblastoid B-cells was able to costimulate the proliferative response of CD4(+) memory cells against VV antigens. The possibility of easily engineering a variety of human cells using recVV encoding human B7 molecules holds implications for the future design of vaccination strategies.

Antitumor efficacy of adenocarcinoma cells engineered to produce interleukin 12 (IL-12) or other cytokines compared with exogenous IL-12

BACKGROUND

Numerous animal model studies have examined the ability of genetically engineered tumor cells to release cytokines and to elicit an immune memory against the parental tumor. Often only a single cytokine is studied, and few comparative studies have been conducted.

PURPOSE

We evaluated the antitumor efficacy of adenocarcinoma cells engineered to release interleukin (IL)-12 in a mouse model system. The efficacy of this cytokine was compared with that of other cytokines released by engineered adenocarcinoma cells and that of exogenous IL-12 administered both locally and intraperitoneally.

METHODS

BALB/cAnCr mice were inoculated with syngeneic parental mammary adenocarcinoma (TSA) cells in quantities sufficient to lead to tumors in all inoculated mice. TSA cells engineered to release IL-12 (TSA-IL12) were also injected into normal and selectively immunosuppressed BALB/cAnCr mice. Tumor incidence, growth, and rejection patterns were evaluated by the measurement of neoplastic masses and by the study of the histologic and ultrastructural features of the tumor site. The effects of local or intraperitoneal administration of recombinant IL-12 (rIL-12) on tumor-bearing animals were also studied.

RESULTS

Most mice rejected TSA-IL12 cells through a CD8-positive, T-lymphocyte-dependent reaction associated with macrophage infiltration, vessel damage, and necrosis. The systemic immunity of mice that had rejected TSA-IL12 cells to a subsequent challenge with parental TSA cells was less efficient than that elicited by TSA cells engineered to release IL-4 or IL-10 but equivalent to that elicited by TSA cells engineered to release IL-2, IL-7, and interferon alfa. Compared with TSA cells engineered to produce other cytokines, TSA-IL12 cells were the most efficient in curing mice with established TSA tumors; injection of 0.1 million proliferating cells contralaterally to the tumor growth area cured five of 15 mice bearing 1-day-old tumors; injection of the same dose of proliferating cells into the tumor growth area cured two of 20 tumor-bearing mice. However, two 5-day courses with a nontoxic dose (0.1 microgram) of rIL-12 given intraperitoneally cured a similar proportion of these animals (six of 20). Only two of 20 mice with 7-day-old TSA tumors were cured by vaccination with proliferating TSA-IL12 cells, whereas 24 of 30 mice with such tumors were cured by intraperitoneal administration of rIL-12.

CONCLUSIONS

TSA cells engineered to release IL-12 are rejected by most mice; the ensuing immune memory for TSA parental cells, however, was less efficient than that elicited by proliferating TSA cells engineered to release other cytokines (e.g., IL-4, IL-10, and possibly interferon gamma). The immune reaction elicited by TSA-IL12 cells was the most efficient in curing mice with established TSA tumors; notably though, the same or a better cure rate was obtained with rIL-12 given intraperitoneally.