Regression of extensive pulmonary metastases in mice by adoptive transfer of antigen-specific CD8(+) CTL reactive against tumor cells expressing a naturally occurring rejection epitope

In this study, we developed a mouse model of adoptive immunotherapy reflecting immune recognition of syngeneic tumor cells naturally expressing an endogenous rejection Ag. Specifically, in a pulmonary metastases model, we examined the potency and maintenance of an antitumor CD8(+) CTL response in vivo, as well as its effectiveness against an "extensive" tumor burden. The approach taken was to first generate tumor-specific CTL from mice challenged with the CMS4 sarcoma coadministered with anti-CTLA4 mAb, which has been shown to facilitate the induction of Ag-specific T cell responses in vivo. An H-2L(d)-restricted nonamer peptide, derived from an endogenous murine leukemia provirus was identified as a CMS4-reactive CTL epitope based upon the following: CTL cross-recognition of another syngeneic tumor cell line (CT26 colon carcinoma) previously characterized to express that gene product; sensitization of Ag-negative lymphoblasts or P815 targets with the peptide; and by cold target inhibition assays. In vivo, the adoptive transfer of CMS4-reactive CTL (> or =1 x 10(6)) resulted in nearly the complete regression of 3-day established lung metastases. Furthermore, mice that rejected CMS4 following a single adoptive transfer of CTL displayed antitumor activity to a rechallenge 45 days later, not only in the lung, but also at a s.c. distal site. Lastly, the adoptive transfer of CTL to mice harboring extensive pulmonary metastases (> 150 nodules) led to a substantial reduction in tumor burden. Overall, these data suggest that the adoptive transfer of tumor-specific CTL may have therapeutic potential for malignancies that proliferate in or metastasize to the lung.     

The Fas/Fas ligand pathway is important for optimal tumor regression in a mouse model of CTL adoptive immunotherapy of experimental CMS4 lung metastases

The mechanisms of CTL-mediated tumor regression in vivo remain to be fully understood. If CTL do mediate tumor regression in vivo by direct cytotoxicity, this may occur via two major effector mechanisms involving the secretion of perforin/granzymes and/or engagement of Fas by Fas ligand (FasL) expressed by the activated CTL. Although the perforin pathway has been considered the dominant player, it is unclear whether Fas-mediated cytotoxicity is additionally required for optimal tumor rejection. Previously, we produced H-2L(d)-restricted CTL reactive against the CMS4 sarcoma, which expresses a naturally occurring rejection Ag recognized by these CTL and harbors a cytokine (IFN-gamma plus TNF)-inducible, Fas-responsive phenotype. The adoptive transfer of these CTL to syngeneic BALB/c mice with minimal (day 3 established) or extensive (day 10 established) experimental pulmonary metastases resulted in strong antitumor responses. Here we investigated whether a FasL-dependent CTL effector mechanism was important for optimal tumor regression in this adoptive immunotherapy model. The approach taken was to compare the therapeutic efficacy of wild-type to FasL-deficient (gld) CTL clones by adoptive transfer. In comparison with wild-type CTL, gld-CTL efficiently mediated tumor cytolysis and produced comparable amounts of IFN-gamma, after tumor-specific stimulation, as in vitro assessments of Ag recognition. Moreover, gld-CTL mediated comparably potent antitumor effects in a minimal disease setting, but were significantly less effective under conditions of an extensive tumor burden. Overall, under conditions of extensive lung metastases, these data revealed for the first time an important role for a FasL-dependent CTL effector mechanism in optimal tumor regression.     

The rationale and practice of CTL therapy against cancer in the mouse and human

It is essential to investigate and elucidate the immune response especially T cell response to either syngeneic or autologous tumor for establishing a rational immunotherapy of cancer. We reported that major immune effector cells capable of inducing tumor regression are cytotoxic T lymphocytes (CTL). We found that there are at least two distinct CTL subsets directed to syngeneic tumor. One CTL subset which is selectively induced by syngeneic solid tumor is independent from CD4 positive helper T cells but requires a soluble factor (s) released from macrophage-like accessory cells designated killer T cell activating factor (KAF) in its induction and generation directed to the homologous tumor. The other CTL subset which is usually induced by syngeneic tumor of hematocytic origin is dependent on CD4 positive helper T cells in its induction. On the basis of our findings regarding the induction and activation mechanism of CTL to syngeneic tumors in the mouse, we have investigated the mechanisms of human CTL generation to autochthonous tumor in peripheral blood mononuclear cells of cancer patients. It was found that the nature of human CTL and its generation to autochthonous tumor are similar to those of murine CTL to syngeneic solid tumor. We are now establishing a rational cancer specific immunotherapy utilizing intravenous passive cell transfer of in vitro activated CTL to autochthonous tumor into an original cancer patient.     

Induction of an effective anti-tumor immune response and tumor regression by combined administration of IL-18 and Apoptin

Immunization strategies using plasmid DNA can potentially improve humoral and cellular immune responses that protect against cancer and infectious diseases. The chicken anemia virus-derived Apoptin protein exhibits remarkable specificity in its ability to induce apoptosis in tumor cells, but not in normal diploid cells. Interleukin-18 (IL-18) is a Th1-type cytokine that has demonstrated potential as a biological adjuvant in murine tumor models. In this study, we analyzed the anti-tumor potential and mechanism of action of simultaneous Apoptin and IL-18 gene transfer in C57BL/6 mice bearing Lewis lung carcinoma (LLC). Here we report that the growth of established tumors in mice immunized with pAPOPTIN in conjunction with pIL-18 was significantly inhibited compared with the growth of tumors in mice immunized with the empty vector (EV) or pAPOPTIN alone. Furthermore, the immunization of mice with pAPOPTIN in conjunction with pIL-18 elicited strong natural killer activity and LLC tumor-specific cytotoxic T lymphocyte (CTL) responses in vitro. In addition, T cells from lymph nodes of mice vaccinated with pIL-18 or pAPOPTIN + pIL-18 secreted high levels of the Th1 cytokine IL-2 and IFN-γ, indicating that the regression of tumor cells is related to a Th1-type dominant immune response. These results demonstrate that vaccination with Apoptin together with IL-18 may be a novel and powerful strategy for cancer immunotherapy.     

A model for CD8+ CTL tumor immunosurveillance and regulation of tumor escape by CD4 T cells through an effect on quality of CTL.

Understanding immune mechanisms influencing cancer regression, recurrence, and metastasis may be critical to developing effective immunotherapy. Using a tumor expressing HIV gp160 as a model viral tumor Ag, we found a growth-regression-recurrence pattern, and used this to investigate mechanisms of immunosurveillance. Regression was dependent on CD8 T cells, and recurrent tumors were resistant to CTL, had substantially reduced expression of epitope mRNA, but retained the gp160 gene, MHC, and processing apparatus. Increasing CTL numbers by advance priming with vaccinia virus expressing gp160 prevented only the initial tumor growth but not the later appearance of escape variants. Unexpectedly, CD4 cell depletion protected mice from tumor recurrence, whereas IL-4 knockout mice, deficient in Th2 cells, did not show this protection, and IFN-gamma knockout mice were more susceptible. Purified CD8 T cells from CD4-depleted mice following tumor regression had more IFN-gamma mRNA and lysed tumor cells without stimulation ex vivo, in contrast to CD4-intact mice. Thus, the quality as well as quantity of CD8+ CTL determines the completeness of immunosurveillance and is controlled by CD4 T cells but not solely Th2 cytokines. This model of immunosurveillance may indicate ways to enhance the efficacy of surveillance and improve immunotherapy.     

CTLA-4 blockade enhances the therapeutic effect of an attenuated poxvirus vaccine targeting p53 in an established murine tumor model

p53 is overexpressed by half of all cancers, and is an attractive target for a vaccine approach to immunotherapy. p53 overexpression is frequently the result of point mutations, which leaves the majority of the protein in its wild-type form. Therefore, the majority of p53 sequence is wild type, making it a self-protein for which tolerance plays a role in limiting immune responses. To overcome tolerance to p53, we have expressed wild-type murine p53 in the nonpathogenic attenuated poxvirus, modified vaccinia virus Ankara (recombinant modified vaccinia virus Ankara expressing wild-type murine p53 (rMVAp53)). Mice immunized with rMVAp53 vaccine developed vigorous p53-specific CTL responses. rMVAp53 vaccine was evaluated for its ability to inhibit the outgrowth of the syngeneic murine sarcoma Meth A, which overexpresses mutant p53. Mice were inoculated with a lethal dose (5 x 10(5) cells injected s.c.) of Meth A tumor cells and vaccinated by i.p. injection 3 days later with 5 x 10(7) PFU of rMVAp53. The majority of mice remained tumor free and resistant to rechallenge with Meth A tumor cells. We wished to determine whether rMVAp53 immunization could effect the rejection of an established, palpable Meth A tumor. In subsequent experiments, mice were injected with 10(6) Meth A tumor cells, and treated 6 days later with anti-CTLA-4 Ab (9H10) and rMVAp53. The majority of treated mice had complete tumor regression along with lasting tumor immunity. In vivo Ab depletion confirmed that the antitumor effect was primarily CD8 and to a lesser extent CD4 dependent. These experiments demonstrate the potential of a novel cell-free vaccine targeting p53 in malignancy.     

Tumor regression induced by intratumor therapy with a disabled infectious single cycle (DISC) herpes simplex virus (HSV) vector, DISC/HSV/murine granulocyte-macrophage colony-stimulating factor, correlates with antigen-specific adaptive immunity

Direct intratumor injection of a disabled infectious single cycle HSV-2 virus encoding the murine GM-CSF gene (DISC/mGM-CSF) into established murine colon carcinoma CT26 tumors induced a significant delay in tumor growth and complete tumor regression in up to 70% of animals. Pre-existing immunity to HSV did not reduce the therapeutic efficacy of DISC/mGM-CSF, and, when administered in combination with syngeneic dendritic cells, further decreased tumor growth and increased the incidence of complete tumor regression. Direct intratumor injection of DISC/mGM-CSF also inhibited the growth of CT26 tumor cells implanted on the contralateral flank or seeded into the lungs following i.v. injection of tumor cells (experimental lung metastasis). Proliferation of splenocytes in response to Con A was impaired in progressor and tumor-bearer, but not regressor, mice. A potent tumor-specific CTL response was generated from splenocytes of all mice with regressing, but not progressing tumors following in vitro peptide stimulation; this response was specific for the gp70 AH-1 peptide SPSYVYHQF and correlated with IFN-gamma, but not IL-4 cytokine production. Depletion of CD8(+) T cells from regressor splenocytes before in vitro stimulation with the relevant peptide abolished their cytolytic activity, while depletion of CD4(+) T cells only partially inhibited CTL generation. Tumor regression induced by DISC/mGM-CSF virus immunotherapy provides a unique model for evaluating the immune mechanism(s) involved in tumor rejection, upon which tumor immunotherapy regimes may be based.     

Immunotherapy of a human papillomavirus type 16 E7-expressing tumor by administration of fusion protein comprised of Mycobacterium bovis BCG Hsp65 and HPV16 E7

Human papillomavirus type 16 (HPV16) infection has been linked to the development of cervical and anal dysplasia and cancer. One hallmark of persistent infection is the synthesis of the viral E7 protein in cervical epithelial cells. The expression of E7 in dysplastic and transformed cells and its recognition by the immune system as a foreign antigen make it an ideal target for immunotherapy. Utilizing the E7-expressing murine tumor cell line, TC-1, as a model of cervical carcinoma, an immunotherapy based on the administration of an adjuvant-free fusion protein comprised of Mycobacterium bovis BCG Hsp65 linked to HPV16 E7 (HspE7) has been developed. Initial in vitro analyses indicate that immunization with HspE7 results in the induction of a type 1 immune response based on the pattern of secreted cytokines and the presence of cytolytic activity following antigenic recall. It has been previously shown that prophylactic immunization with HspE7 protected mice against challenge with TC-1 cells and that these tumor-free animals are also protected against rechallenge with TC-1 cells. The present report shows that a single therapeutic immunization with HspE7 induces regression of palpable tumors, confers protection against tumor rechallenge, and is associated with long-term survival (>253 days). In vivo studies using mice with targeted mutations in CD8 or MHC class II or depleted of CD8 or CD4 lymphocyte subsets demonstrate that tumor regression following therapeutic HspE7 immunization is CD8 dependent and CD4 independent. These studies extend previous observations on the induction of CTL by Hsp fusion proteins and are consistent with the clinical application of HspE7 as an immunotherapy for human cervical and anal dysplasia and cancer.     

The coming of age of tumour immunotherapy

Compared with the earlier incidence of acute infectious diseases, the introduction of vaccines has been one of the major public health success achievements. In contrast, vaccine development to control some persisting infections such as HIV remains a major challenge. There are many similarities with this task and that of controlling tumours by immunotherapy. Generating CTL responses by using pulsed dendritic cells has become a popular approach and has led to success with the mouse model. With viral antigens, priming with DNA plasmids and boosting with a chimeric live vector results in high levels of CTL activity, and is worth trying with cancer. A recent review highlights three other difficulties posed by tumours: epitope stability, maiming or killing of CTL by the tumour, and accessibility of the tumour vasculature to immune components. The new ability to label CTL by staining with specific tetrameric peptide/MHC complexes offers the possibility of effectively studying this third aspect. Our increased knowledge of tumour-associated antigens, viral or otherwise, and our growing ability to manipulate the immune system, offers hope that control of at least some human tumours may be within reach.     

Cytotoxic effector T cells elicited by the killed tumor vaccine differ significantly from the effectors generated during active growth of a murine B-cell lymphoma

Active specific immunotherapy of neoplastic diseases is an elusive goal. Using a murine B lymphoma 2C3, we showed that vaccination with the killed tumor cells effectively induces protective immunity and a cytotoxic T cell (CTL) response. Similar protection, however, is rarely observed in mice bearing live tumor cells. These animals usually succumb to the progressively growing tumor. In this study, we inquired whether the splenic CTL induced during tumor progression in mice differ from those evoked by the killed tumor cells. Here we demonstrate that the CTL generated following vaccination are significantly different from those induced in the tumor-bearing hosts. Adding to the complexity, the CTL from the early tumor bearers also differ significantly from those induced at the late stages. These differences are based on their cytotoxic activity, MHC allele specificity, mitogen responsiveness, cytokine secretion profile and T cell receptor Vβ gene expression. The results clearly indicate that passive immunization with killed tumor is most effective, possibly because the CTL induced are not subject to the same regulatory pressure as those induced during active tumor growth. This decreasing effectiveness of CTL could be due to greater variability in antigenic stimulus, less involvement of innate immunity, changes in cytokine milieu and/or costimulatory factors. Received: 5 February 1999 / Accepted: 22 June 1999     

Irradiation of tumor cells up-regulates Fas and enhances CTL lytic activity and CTL adoptive immunotherapy

CD8(+) CTL play important roles against malignancy in both active and passive immunotherapy. Nonetheless, the success of antitumor CTL responses may be improved by additional therapeutic modalities. Radiotherapy, which has a long-standing use in treating neoplastic disease, has been found to induce unique biologic alterations in cancer cells affecting Fas gene expression, which, consequently, may influence the overall lytic efficiency of CTL. Here, in a mouse adenocarcinoma cell model, we examined whether exposure of these tumor cells to sublethal doses of irradiation 1) enhances Fas expression, leading to more efficient CTL killing via Fas-dependent mechanisms in vitro; and 2) improves antitumor activity in vivo by adoptive transfer of these Ag-specific CTL. Treatment of carcinoembryonic Ag-expressing MC38 adenocarcinoma cells with irradiation (20 Gy) in vitro enhanced Fas expression at molecular, phenotypic, and functional levels. Furthermore, irradiation sensitized these targets to Ag-specific CTL killing via the Fas/Fas ligand pathway. We examined the effect of localized irradiation of s.c. growing tumors on the efficiency of CTL adoptive immunotherapy. Irradiation caused up-regulation of Fas by these tumor cells in situ, based on immunohistochemistry. Moreover, localized irradiation of the tumor significantly potentiated tumor rejection by these carcinoembryonic Ag-specific CTL. Overall, these results showed for the first time that 1) regulation of the Fas pathway in tumor cells by irradiation plays an important role in their sensitization to Ag-specific CTL; and 2) a combination regimen of tumor-targeted irradiation and CTL promotes more effective antitumor responses in vivo, which may have implications for the combination of immunotherapy and radiation therapy.     

DC immunotherapy is highly effective for the inhibition of tumor metastasis or recurrence,although it is not efficient for the eradication of established solid tumors

Dendritic cell (DC)-based immunotherapy has not been as effective as expected in most solid tumors even in the murine model, particularly in renal cell carcinoma (RCC). Our investigation was initiated to identify what causes the limitations of DC-based immunotherapy in solid RCC. We have investigated immunosuppressive factors from tumors and their effects on DC migration, as well as cytotoxic T lymphocyte (CTL) response and lymphocyte infiltration into the tumor mass upon vaccination with mouse renal adenocarcinoma (Renca) cell lysate-pulsed bone marrow (Bm)-derived DC in tumor-bearing mice. We also investigated pulmonary metastasis- and tumor recurrence-inhibitory effects of DC-vaccination in the solid tumor-bearing mice. In these experiments, we found that the limitations of DC-based immunotherapy to solid RCC likely result from tumor-mediated TGF-β hindrance of immune attack rather than insufficient immune induction by DC therapy. In fact, the CTL response induced by DC therapy was quite sufficient and functional for the inhibition of tumor recurrence after surgery or of tumor metastasis induced by additional tumor-challenge to the tumor-bearing mice. Taken together, our present results obtained in mouse model suggest the potential of DC immunotherapy in tumor patients for hindering or blocking disease progression by inhibition of tumor metastasis and/or tumor recurrence after surgery.     

Vaccination with mRNAs encoding tumor-associated antigens and granulocyte-macrophage colony-stimulating factor efficiently primes CTL responses, but is insufficient to overcome tolerance to a model tumor/self antigen

Immunization of mice with dendritic cells transfected ex vivo with tumor-associated antigen (TAA)-encoding mRNA primes cytotoxic T lymphocytes (CTL) that mediate tumor rejection. Here we investigated whether direct injection of TAA mRNA, encapsulated in cationic liposomes, could function similarly as cancer immunotherapy. Intradermal and intravenous injection of ovalbumin (OVA) mRNA generated specific CTL activity and inhibited the growth of OVA-expressing tumors. Vaccination studies with DNA have demonstrated that co-administration of antigen (Ag)- and cytokine-encoding plasmids potentiate the T cell response; in analogous fashion, the inclusion of granulocyte-macrophage colony-stimulating factor (GM-CSF) mRNA enhanced OVA-specific cytotoxicity. The ability of this GM-CSF-augmented mRNA vaccine to treat an established spontaneous tumor was evaluated in the Transgenic Adenocarcinoma of Mouse Prostate (TRAMP) mouse, using the SV40 large T Ag (TAg) as a model tumor/self Ag. Repeated vaccination elicited vigorous TAg-specific CTL activity in nontransgenic mice, but tumor-bearing TRAMP mice remained tolerant. Adoptive transfer of naïve splenocytes into TRAMP mice prior to the first vaccination restored TAg reactivity, and slowed tumor progression. The data from this study suggests that vaccination with TAA mRNA is a simple and effective means of priming antitumor CTL, and that immunogenicity of the vaccine can be augmented by co-delivery of GM-CSF mRNA. Nonetheless, limitations of such vaccines in overcoming tolerance to tumor/self Ag may mandate prior or simultaneous reconstitution of the autoreactive T cell repertoire for this form of immunization to be effective.     

Potential of the Trifunctional Bispecific Antibody Surek Depends on Dendritic Cells: Rationale for a New Approach of Tumor Immunotherapy

Trifunctional bispecific antibodies (trAbs) used in tumor immunotherapy have the unique ability to recruit T cells toward antigens on the tumor cell surface and, moreover, to activate accessory cells through their immunoglobulin Fc region interacting with activating Fcγ receptors. This scenario gives rise to additional costimulatory signals required for T cell–mediated tumor cell destruction and induction of an immunologic memory. Here we show in an in vitro system that most effective trAb-dependent T-cell activation and tumor cell elimination are achieved in the presence of dendritic cells (DCs). On the basis of these findings, we devise a novel approach of cancer immunotherapy that combines the specific advantages of trAbs with those of DC-based vaccination. Simultaneous delivery of trAbs and in vitro differentiated DCs resulted in a markedly improved tumor rejection in a murine melanoma model compared with monotherapy.     

Individual analysis of mice vaccinated against a weakly immunogenic self tumor-specific antigen reveals a correlation between CD8 T cell response and antitumor efficacy

The weakly immunogenic murine P1A Ag is a useful experimental model for the development of new vaccination strategies that could potentially be used against human tumors. An i.m. DNA-based immunization procedure, consisting of three inoculations with the P1A-coding pBKCMV-P1A plasmid at 10-day intervals, resulted in CTL generation in all treated BALB/c mice. Surprisingly, gene gun skin bombardment with the pBKCMV-P1A vector did not induce CTL, nor was it protective against a lethal challenge with the syngeneic P1A-positive J558 tumor cell line. To speed up the immunization procedure, we pretreated the tibialis anterior muscles with cardiotoxin, which induces degeneration of myocytes while sparing immature satellite cells. The high muscle-regenerative activity observable after cardiotoxin inoculation was associated with infiltration of inflammatory cells and expression of proinflammatory cytokines. A single pBKCMV-P1A plasmid inoculation in cardiotoxin-treated BALB/c mice allowed for sustained expansion of P1A-specific CTL and the induction of strong lytic activity in <2 wk. Cardiotoxin adjuvanticity could not be replaced by another muscle-degenerating substance, such as bupivacaine, or by MF59, a Th1 response-promoting adjuvant. Although this vaccination schedule failed to induce tumor rejection in all immunized mice, the analysis of CD8 T cell responses at an individual mouse level disclosed that the cytotoxic activity of P1A-specific CTL was correlated to the antitumor efficacy. These results highlight the critical need to identify reliable, specific immunological parameters that may predict success or failure of an immune response against cancer.     

Induction of cytotoxic T cells and their antitumor activity in mice transgenic for carcinoembryonic antigen

In order to develop immunotherapy strategies that are based on eliciting immune responsiveness to the self-antigen, human carcinoembryonic antigen (CEA), we examined whether cytotoxic T lymphocyte (CTL) activity against CEA could be elicited in CEA-transgenic and nontransgenic mice. CEA-transgenic [C57BL/6-TGN(CEAGe)18FJP] and nontransgenic mice were primed with CEA-transfected syngeneic fibroblasts in combination with Corynebacterium parvum. Spleen cells from immunized mice were cultured with irradiated syngeneic MC-38 colon carcinoma cells transfected with CEA (MC-38.CEA) as stimulators prior to the measurement of CTL activity. Primed nontransgenic spleen cells showed augmented CTL activity against MC-38.CEA cells as compared with control parental MC-38 cells, nontransfected or transfected with vector only. Moreover, primed CEA transgenic spleen cells showed augmented CTL activity against MC-38.CEA cells that was similar to that observed in nontransgenic mice. All CTL clones derived from either transgenic or nontransgenic mice showed cross-reactivity with MC-38 cells expressing the CEA-related antigen, nonspecific cross-reacting antigen, but not biliary glycoprotein. CEA-specific CTL clones were not identified. Adoptive transfer of cloned CTL resulted in inhibition of MC-38.CEA but not MC-38.BGP tumor growth. Tumor cures were elicited in mice treated with a combination of cloned CTL and cyclophosphamide. Histopathological examination of CEA-expressing colons from either immunized mice or recipients of cloned CTL did not reveal any autoimmune reactions. These studies demonstrate that CTL recognizing cross-reactive class I epitopes on the CEA molecule can be induced in transgenic mice. The expression of these epitopes on tumor cells creates effective targets for CTL in vivo without inducing adverse reactions in CEA-expressing normal tissues. Since anti-CEA CTL have been generated in humans, CEA-transgenic mice may be a useful model to study vaccines that are based on CTL effector mechanisms. Received: 7 January 2000 / Accepted: 8 March 2000     

Costimulation of antitumor immunity by the B7 counterreceptor for the T lymphocyte molecules CD28 and CTLA-4.

Interaction of the B7 molecule on antigen-presenting cells with its receptors CD28 and CTLA-4 on T cells provides costimulatory signals for T cell activation. We have studied the effects of B7 on antitumor immunity to a murine melanoma that expresses a rejection antigen associated with the E7 gene product of human papillomavirus 16. While this E7+ tumor grows progressively in immunocompetent hosts, cotransfection of its cells with B7 led to tumor regression by a B7-dependent immune response mediated by CD8+ cytolytic T lymphocytes. The immune response induced by E7+B7+ tumor cells also caused regression of E7+B7- tumors at distant sites and was curative for established E7+B7- micrometastases. Our findings suggest that increasing T cell costimulation through the CD28 and CTLA-4 receptors may have therapeutic usefulness for generating immunity against tumors expressing viral antigens.     

Destructive and nondestructive patterns of immune rejection of syngeneic intraocular tumors

Two immunogenic, syngeneic murine tumors were used to analyze the immunopathological processes associated with the immune rejection of primary intraocular tumors. Intracameral inoculation of P91 mastocytoma, an immunogenic variant of P815 mastocytoma, into DBA/2 mice resulted in progressive tumor growth for several weeks before immune rejection eradicated the intraocular neoplasm. The histopathologic characteristics of the tumor rejection included: a) destruction of the vascular endothelium of the microvasculature feeding the tumor; b) ischemic bulk necrosis; c) extensive innocent bystander damage to normal ocular structures; and d) absence of direct inflammatory cell-to-tumor cell contact. Thus, the immunopathological features resembled a delayed-type hypersensitivity (DTH) lesion. A second intraocular tumor model was similarly studied. UV5C25 fibrosarcoma grew slowly in the eyes of syngeneic BALB/c hosts. In sharp contrast to P91 tumors, a mononuclear cellular infiltrate was prominent within the tumor. After 5 wk, the intraocular tumors were completely rejected without detectable damage to normal ocular structures. The rejection of UV5C25 tumors did not produce scar tissue, damage to vascular endothelium, bulk necrosis, or atrophy of the globe. Although tumor-specific cytotoxic T lymphocytes (CTL) and DTH responses were readily detected, there was no histological evidence for DTH-mediated tumor rejection. Moreover, in situ immunoperoxidase staining indicated that the majority of the infiltrating lymphocytes were CTL, based on their characteristic phenotype: Thy-1+, Lyt-2+. Furthermore, the growth of UV5C25 fibrosarcoma in athymic, natural killer (NK) cell competent BALB/c nude mice demonstrated progressive tumor growth without infiltrating host cells. Collectively, the results indicate that immunogenic intraocular tumors can undergo strikingly different patterns of immune rejection with profoundly different pathological consequences. In one case (P91), tumor rejection occurs by a process that strongly resembles DTH and produces extensive nonspecific damage to normal tissues, resulting in irrevocable loss of vision. In contrast, the second intraocular tumor undergoes an immune rejection that is characterized by precision and a notable absence of damage to normal ocular tissues. The weight of evidence presented here strongly supports the hypothesis that the latter form of tumor rejection is mediated by CTL. Thus, the immunologic pathway invoked for tumor rejection in the eye has a profound effect on the fate of this delicate organ and the preservation of vision.     

A mathematical analysis of the interactions between immunogenic tumor cells and cytotoxic T lymphocytes.

Recent developments of biotechnology have enabled us to use immunotherapy against certain kinds of tumors in patients. However, it is reasonable to doubt if the immunotherapy can completely aid the rejection of tumors that have escaped from the immune system. In this paper, we propose a new mathematical model of tumor immunity by tumor-specific cytotoxic T lymphocytes (CTLs), since tumor-specific CTLs play an important role in tumor immunity. Using this model, we have mathematically investigated the interactions between immunogenic tumor cells (TCs) and tumor-specific CTLs and evaluated the availability of immunotherapies for tumors. The findings herein demonstrate that three kinds of dynamics of tumor immunity exist: i.e. (1) TCs continue to proliferate with CTLs; (2) TCs are rejected by CTLs; and (3) TCs equilibrate with CTLs, but with little possibility of the equilibrium. The findings also demonstrate that a sufficient increase in CTLs by immunotherapy can aid the rejection of TCs, but an insufficient increase in CTLs by immunotherapy causes only a transient regression of TCs. Clinically the findings mean that increasing tumor-specific CTLs, e.g., by vaccination or adoptive transfer of tumor-specific CTLs expanded ex vivo, can theoretically aid the rejection of TCs.