Regression Of Large Established Tumors Research Articles

CD8+ T cell-intrinsic IL-6 signaling promotes resistance to anti-PD-L1 immunotherapy

Although immune checkpoint inhibitors (ICIs) are established as effective cancer therapies, overcoming therapeutic resistance remains a critical challenge. Here we identify interleukin 6 (IL-6) as a correlate of poor response to atezolizumab (anti-PD-L1) in large clinical trials of advanced kidney, breast, and bladder cancers. In pre-clinical models, combined blockade of PD-L1 and the IL-6 receptor (IL6R) causes synergistic regression of large established tumors and substantially improves anti-tumor CD8+ cytotoxic T lymphocyte (CTL) responses compared with anti-PD-L1 alone. Circulating CTLs from cancer patients with high plasma IL-6 display a repressed functional profile based on single-cell RNA sequencing, and IL-6-STAT3 signaling inhibits classical cytotoxic differentiation of CTLs invitro. In tumor-bearing mice, CTL-specific IL6R deficiency is sufficient to improve anti-PD-L1 activity. Thus, based on both clinical and experimental evidence, agents targeting IL-6 signaling are plausible partners for combination with ICIs in cancer patients.

A single local delivery of paclitaxel and nucleic acids via an immunoactive polymer eliminates tumors and induces antitumor immunity

Despite recent advances in cancer therapy, hard-to-reach, unidentified tumors remain a significant clinical challenge. A promising approach is to treat locatable and accessible tumors locally and stimulate antitumor immunity in situ to exert systemic effects against distant tumors. We hypothesize that a carrier of immunotherapeutics can play a critical role in activating antitumor immunity as an immunoadjuvant and a local retainer of drug combinations. Here, we develop a polyethyleneimine-lithocholic acid conjugate (2E′), which forms a hydrophobic core and cationic surface to codeliver hydrophobic small molecules and anionic nucleic acids and activates antigen-presenting cells via the intrinsic activities of 2E′ components. 2E′ delivers paclitaxel and small-interfering RNA (siRNA) targeting PD-L1 (or cyclic dinucleotide, [CDN]) to induce the immunogenic death of tumor cells and maintain the immunoactive tumor microenvironment, and further activates dendritic cells and macrophages, leveraging the activities of loaded drugs. A single local administration of 2E′ or its combination with paclitaxel and PD-L1–targeting siRNA or CDN induces strong antitumor immunity, resulting in immediate regression of large established tumors, tumor-free survival, an abscopal effect on distant tumors, and resistance to rechallenge and metastasis in multiple models of murine tumors, including CT26 colon carcinoma, B16F10 melanoma, and 4T1 breast cancer. This study supports the finding that local administration of immunotherapeutics, when accompanied by the rationally designed carrier, can effectively protect the host from distant and recurrent diseases.

A novel aptamer-based small RNA delivery platform and its application to cancer therapy

Major challenges such as nuclease degradation, rapid renal clearance, non-specific delivery, poor cellular uptake and inflammatory response have limited the clinical application of small RNA-mediated gene silencing. To overcome these challenges, we designed a novel targeting small RNA delivery platform comprising of three oligonucleotides: (1) a guide RNA sequence, (2) part of a passenger sequence linked to a DNA aptamer via a PEG linker, and (3) another passenger sequence conjugated to cholesterol, which assemble through complementary base pair annealing. Remarkably, in the presence of magnesium, this molecule self-assembled into a nanoparticle with a hydrophobic cholesterol core, hydrophilic RNA oligonucleotide shell and PEG-linked DNA aptamer flare. The nanoparticles conferred protection to the RNA oligonucleotides against nuclease degradation, which increased bioavailability, and reduced systemic inflammatory responses. The aptamer allowed targeted delivery of RNA therapeutics through cell-specific surface markers, and once inside the cell, the nanoparticles induced lysosomal leakage that released the RNA oligonucleotides into the cytosol to achieve gene silencing. We created a c-Kit-targeting miR-26a delivery particle that specifically accumulated in c-Kit+ breast cancer, significantly increased T cell recruitment, and inhibited tumor growth. Regression of large established tumors were achieved when the nanoparticle was used in combination with anti-CTLA-4 monoclonal antibody.

Abstract P5-04-03: Conversion of non-T cell-inflamed triple-negative breast cancer by in situ immunomodulation of induced intratumoral cross-presenting dendritic cells

Abstract Checkpoint inhibitor (CPI)-based immunotherapy such as PD-1/PD-L1 blockade has shown an unprecedented success for the treatment of a variety of malignancies; however, meaningful clinical activity is seen only in a subset of breast cancer patients. This is due, at least in part, to poor T-cell infiltration into the tumor prior to CPI therapy, which is negatively correlated with the treatment response (non-T cell-inflamed tumor). Effective priming and trafficking of tumor-specific T cells to the tumor microenvironment (TME) can theoretically overcome current limitations of immunotherapy for non-T cell-inflamed tumors such as breast cancer. Accumulating evidence indicates that tumor-residing Batf3-dependent CD103+ dendritic cells (DCs) play critical roles in not only priming of tumor-specific CD8+ T cells, but also trafficking of CD8+ T cells to the TME, thus enhancing responses to PD-1/PD-L1 blockade. In the present study, we hypothesized that mobilization and activation of cross-presenting CD103+ DCs in the TME would increase CD8+ T cell infiltrate to the tumor, and facilitate effective regression of breast cancer. To this end, we utilized two triple-negative syngeneic mammary cancer models, 4T1 on a H-2d background and AT3 derived from the PyMT-MMTV model on a H-2b background, and evaluated antitumor efficacy of a combinatorial therapeutic regimen comprised of intratumoral administration of Fms-like tyrosine kinase 3 receptor ligand (Flt3L) to mobilize CD103+ DCs to the TME, local radiotherapy (RT) to induce immunogenic cell death and maturation of DCs, and peritumoral administration of a toll-like receptor 3 (TLR3) agonist to activate DCs. We found intratumoral administration of Flt3L increased the number of CD103+ DCs in the tumor, blood and lymph nodes, and local RT induced upregulation of TLR3, CD40 and CD86 on the tumor-residing CD103+ DCs. Following intratumoral administration of Flt3L, local RT, and in situ delivery of a TLR3 agonist significantly increased CD4+ and CD8+ tumor-infiltrating lymphocytes (TILs), mediated effective regression of large established tumors, and significantly improved survival in multiple mouse tumor models. Phenotypic analysis of circulating T cells revealed that the combinatorial regimen increased the frequency of effector memory and central memory T cell subsets with upregulation of PD-1 and C-X3-C motif chemokine receptor 1 (CX3CR1), suggesting effective activation and differentiation of T cells. Interestingly, we found the frequency of macrophages significantly decreased in the tumor after combinatorial treatment, indicating remodeling of both the myeloid and lymphoid compartments in the TME. Furthermore, increased PD-1 expression on CD4+ and CD8+ TILs, and PD-L1 expression in the TME suggest that antitumor efficacy of the combinatorial regimen can be additionally enhanced by PD-1/PD-L1 blockade. Taken together, combinatorial in situ immunomodulation with intratumoral Flt3L administration, RT and, peritumoral administration of a TLR3 agonist can convert non-T cell-inflamed tumors to T-cell inflamed tumors, remodel an immunosuppressive TME, and potentially overcome primary resistance to PD-1/PD-L1 blockade for triple-negative breast cancer. Acknowledgement: This work was supported by Uehara Memorial Foundation (T.O.), NIH/NCI K08CA197966 (F.I.) and P30CA016056 involving the use of Roswell Park Comprehensive Cancer Center’s Flow Cytometry Core. Citation Format: Takaaki Oba, Tibor Keler, Henry C Marsh, Scott Abrams, Fumito Ito. Conversion of non-T cell-inflamed triple-negative breast cancer by in situ immunomodulation of induced intratumoral cross-presenting dendritic cells [abstract]. In: Proceedings of the 2019 San Antonio Breast Cancer Symposium; 2019 Dec 10-14; San Antonio, TX. Philadelphia (PA): AACR; Cancer Res 2020;80(4 Suppl):Abstract nr P5-04-03.

Abstract 5003: Vaccibody DNA vaccine platform VB10.NEO induces strong neo-antigen specific CD8+ T cell responses critical to cure established tumors in pre-clinical models

Abstract BACKGROUND: Recent advances in the field of cancer immunotherapy have identified CD8+ T cell responses against tumor-specific neoantigens as a key driver of tumor regression and prolonged survival. VB10.NEO is a highly potent DNA plasmid vaccine with intrinsic adjuvant effect designed for efficient delivery of personalized tumor-specific neoantigens. VB10.NEO plasmid is translated in vivo and the secreted protein will covalently bind to endocytic receptors on APC by a targeting unit expressing CCL3 (MIP-1α) allowing efficient uptake and presentation of the neoantigens. In addition, CCL3 will attract immune cells by chemotaxis and induce maturation of APC locally. The objective of this study is to demonstrate the potential of VB10.NEO to induce tumor-specific T cell responses and control tumor growth. METHODS: VB10.NEO was delivered i.m to study CD8+ and CD4+ neoantigen-specific T cell responses in four different pre-clinical mouse models. Immunogenicity was compared with delivery of neoantigen as traditional peptide-adjuvant immunization. The tumor protective effect of VB10.NEO in the presence or absence of anti-PD-1 therapy was investigated in the CT26 colon carcinoma model. RESULTS: Vaccibody DNA Vaccine Platform VB10.NEO is flexible and can hold up to at least 40 neoepitopes. VB10.NEO vaccination induced strong neoantigen-specific T cell responses. Homologous boost vaccinations further augmented the response. T cell responses against predicted CD8+ T cell epitopes previously reported as non-immunogenic or activating only weak T cell responses using a conventional peptide-adjuvant or RNA immunization showed strong CD8+ T cell responses when delivered in the Vaccibody format, demonstrating a unique and strong priming of CD8+ T cells using VB10.NEO. The response was also accompanied by CD4+ T cell responses. In a therapeutic tumor setting VB10.NEO vaccinated mice (monotherapy) induced tumor protective responses. The effect was augmented when combining VB10.NEO with anti-PD-1 where complete regression of large established tumors was observed. All tumour-free mice rechallenged with a lethal tumor dose were protected indicating induction of long-lasting memory responses. Furthermore, the critical role of CD8+ T cells for the observed tumour protection was confirmed when depleting CD8+ T cells. CONCLUSION: VB10.NEO immunotherapy induce strong CD8+ T cell responses critical for anti-tumor effect which demonstrate the unique characteristic of the Vaccibody platform to potentiate activation of CD8+ T cells. VB10.NEO in combination with anti-PD-1 further synergize the potent immune responses resulting in durable complete tumor regression in pre-clinical models supporting the scientific rational for the current ongoing clinical trial investigating VB10.NEO in combination with CPI in patients with advanced solid tumors. Citation Format: Elisabeth Stubsrud, Stine Granum, Helene Zell-Flagstad, Audun Bersaas, Lise Madelene Skullerud, Monika Sekelja, Karoline Schjetne, Agnete Fredriksen. Vaccibody DNA vaccine platform VB10.NEO induces strong neo-antigen specific CD8+ T cell responses critical to cure established tumors in pre-clinical models [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 5003.

Synergistic STING activation by PC7A nanovaccine and ionizing radiation improves cancer immunotherapy

Solid cancers are able to escape immune surveillance and are resistant to current treatment in immunotherapy. Recent evidence indicates the critical role of the stimulator of interferon genes (STING) pathway in antitumor immunity. STING-targeted activation is extensively investigated as a new strategy for cancer therapy. Previously, we reported a safe and efficacious STING-activating nanovaccine to boost systemic tumor-specific T cell responses in multiple tumor models. Local radiotherapy has been reported to not only reduce tumor burden but also enhance local antitumor immunity in a STING-dependent manner. In this study, we demonstrate that combination of these two modalities leads to a synergistic response with long-term regression of large established tumors in two mouse tumor models. The percentage of CD8+ T cells increased significantly in primary tumors after combination therapy. Mechanistically, the augmented T cell responses of radiotherapy and nanovaccine is STING pathway dependent. Furthermore, nanovaccine synergizes with radiotherapy to achieve a better therapeutic effect in distal tumors. These findings suggest that combination of local radiotherapy with systemic PC7A nanovaccine offers a useful strategy to improve the therapeutic outcome of late stage solid cancers.

Abstract 2642: Evaluation of the mechanism of MET-dependent cellular transformation and potent cytoreductive activity of MGCD265 in novel MET exon 14 mutation positive cancer models

Abstract MET splice site mutations that result in the deletion of exon 14 (METex14del) are implicated as oncogenic drivers in a subset of non-small cell lung cancer (NSCLC). MET exon 14 contains the Y1003 CBL ubiquitin ligase regulatory binding site that normally mediates CBL-dependent MET degradation and signal attenuation. Deletion of this exon results in sustained activation of MET and its downstream signaling pathways. The diverse splice site mutations leading to exon 14 skipping comprise a unique and unprecedented class of RTK activating mutations and the molecular mechanism by which these genetic alterations transform cancer cells is not fully understood. One major challenge in understanding the utility of MET inhibition of the METex14del class has been the lack of available pre-clinical models. In the present study, we generated and characterized multiple METex14del-driven cancer models to study the mechanism of MET-dependent cellular transformation as well as the response to MGCD265, a small molecule inhibitor of MET and AXL. METex14del models were identified via mining patient-derived xenograft (PDX) databases or were engineered using genome editing techniques to generate isogenic pairs of METex14del and WT cell lines. The METex14del cell lines formed increased size and number of colonies in anchorage independent growth assays compared to their WT counterparts. The transformation of METex14del cells was associated with an increase in durable HGF-dependent activation of MET and downstream signaling pathways potentially due to dysregulated MET processing and signaling attenuation. MGCD265 was shown to effectively inhibit this growth and MET-dependent signal transduction in a concentration-dependent manner. When evaluated in the amplified METex14del-driven gastric xenograft model Hs746T, significant tumor regression was observed following MGCD265 treatment. In addition, MGCD265 demonstrated substantial regression of large established tumors, in two novel NSCLC METex14del-positive PDX models. Together, these data confirm METex14del mutations are bona fide oncogenic drivers and sensitive to targeted therapeutics. Moreover, the models described in this study represent a relevant pre-clinical platform to further study receptor hyper-activation and drug action that is clinically actionable. Identification, development, and understanding of METex14del models will likely help further guide precision medicine strategies to treat NSCLC patients harboring these mutations. Citation Format: Lars D. Engstrom, Ruth W. Tang, David M. Briere, Harrah Chiang, Peter Olson, James G. Christensen. Evaluation of the mechanism of MET-dependent cellular transformation and potent cytoreductive activity of MGCD265 in novel MET exon 14 mutation positive cancer models. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2642.

A novel, native-format bispecific antibody triggering T-cell killing of B-cells is robustly active in mouse tumor models and cynomolgus monkeys.

Bispecific antibodies, while showing great therapeutic potential, pose formidable challenges with respect to their assembly, stability, immunogenicity, and pharmacodynamics. Here we describe a novel class of bispecific antibodies with native human immunoglobulin format. The design exploits differences in the affinities of the immunoglobulin isotypes for Protein A, allowing efficient large-scale purification. Using this format, we generated a bispecific antibody, REGN1979, targeting the B cell marker, CD20, and the CD3 component of the T cell receptor, which triggers redirected killing of B cells. In mice, this antibody prevented growth of B cell tumors and also caused regression of large established tumors. In cynomolgus monkeys, low doses of REGN1979 caused prolonged depletion of B cells in peripheral blood with a serum half-life of approximately 14 days. Further, the antibody induced a deeper depletion of B cells in lymphoid organs than rituximab. This format has broad applicability for development of clinical bispecific antibodies.

STAT3 Signaling Is Required for Optimal Regression of Large Established Tumors in Mice Treated with Anti-OX40 and TGFβ Receptor Blockade.

In preclinical tumor models, αOX40 therapy is often successful at treating small tumors, but is less effective once the tumors become large. For a tumor immunotherapy to be successful to cure large tumors, it will most likely require not only an agonist to boost effector T-cell function but also inhibitors of T-cell suppression. In this study, we show that combining αOX40 antibodies with an inhibitor of the TGFβ receptor (SM16) synergizes to elicit complete regression of large established MCA205 and CT26 tumors. Evaluation of tumor-infiltrating T cells showed that SM16/αOX40 dual therapy resulted in an increase in proliferating granzyme B(+) CD8 T cells, which produced higher levels of IFNγ, compared with treatment with either agent alone. We also found that the dual treatment increased pSTAT3 expression in both CD4 and CD8 T cells isolated from tumors. Because others have published that STAT3 signaling is detrimental to T-cell function within the tumor microenvironment, we explored whether deletion of STAT3 in OX40-expressing cells would affect this potent combination therapy. Surprisingly, we found that deletion of STAT3 in OX40-expressing cells decreased the efficacy of this combination therapy, showing that the full therapeutic potential of this treatment depends on STAT3 signaling, most likely in the T cells of tumor-bearing mice.

STAT3 signaling is required for anti-OX40/TGF-β receptor blockade-mediated regression of large established tumors

OX40 (CD134, TNFRSF4), a member of the tumor necrosis factor receptor (TNFR) superfamily is expressed on activated CD4+ and CD8+ T cells. In pre-clinical tumor models, agonist OX40 antibody (αOX40) therapy is often successful at treating small tumors but is less effective once the tumors have become established. For a tumor immunotherapy to be successful it will most likely require not only an agonist to boost effector T cell function but also an antagonist to eliminate T cell suppression. In this study, we show that agonist OX40 antibody synergizes with an orally bioavailable inhibitor of TGF-β (SM16) to elicit complete regression of large established tumors, resulting in long-term survival in 40-85% of αOX40/SM16 treated mice in two murine tumor models. Evaluation of tumor infiltrating T cells showed that SM16/αOX40 dual therapy resulted in an increase in OX40 and Granzyme B-expressing CD8+ T cells undergoing proliferation and which produced greater levels of IFNγ. We also found that this dual treatment led to an increase in pSTAT3 staining in both CD4+ and CD8+ T cells isolated from tumors. Therefore, we tested whether deletion of STAT3 in OX40 expressing cells would impact this potent combination therapy, since others have shown that pSTAT3 up-regulation is detrimental to T cell function within the tumor microenvironment. Surprisingly, deletion of STAT3 decreased the therapeutic efficacy of this combination therapy, suggesting that immune enhancement of T cells within tumor-bearing mice is reliant on signals through STAT3 to gain their full therapeutic potential.

Efficient Treg depletion induces T‐cell infiltration and rejection of large tumors

There are a number of factors that hamper immunotherapy of cancer. For example, tumors exhibit an aberrant vasculature that appears to form a barrier against T-cell infiltration. Another major obstacle is created by Treg. So far, conventional depletion of Treg with anti-CD25 antibodies, which eliminate only 70% of Treg, has failed to significantly reduce the growth of established tumors. Using Foxp3.LuciDTR-4 mice, we show here that 90-95% Treg depletion resulted in complete regression of large established tumors, whereas 70% depletion was ineffective. The extensive Treg depletion induced a number of processes that are critical for tumor rejection, including activation of tumor-specific CD8(+) T cells and enhanced infiltration of these cells into the tumor. The precise mechanism of enhanced infiltration is not known, but normalization of the tumor vasculature is assumed to assist infiltration. Indeed, we observed that 90% Treg depletion caused normalization of the tumor vasculature as indicated by a reduction in leakiness and the number of dilated vessels. These results suggest that for clinical immunotherapy of cancer, it would be desirable to have reagents that allow high-level depletion of Treg, which, in conjunction with treatment modalities such as vaccination, may concomitantly increase T-cell activation and infiltration.

Tumor-reactive CD4+ T cells develop cytotoxic activity and eradicate large established melanoma after transfer into lymphopenic hosts

Adoptive transfer of large numbers of tumor-reactive CD8+ cytotoxic T lymphocytes (CTLs) expanded and differentiated in vitro has shown promising clinical activity against cancer. However, such protocols are complicated by extensive ex vivo manipulations of tumor-reactive cells and have largely focused on CD8+ CTLs, with much less emphasis on the role and contribution of CD4+ T cells. Using a mouse model of advanced melanoma, we found that transfer of small numbers of naive tumor-reactive CD4+ T cells into lymphopenic recipients induces substantial T cell expansion, differentiation, and regression of large established tumors without the need for in vitro manipulation. Surprisingly, CD4+ T cells developed cytotoxic activity, and tumor rejection was dependent on class II–restricted recognition of tumors by tumor-reactive CD4+ T cells. Furthermore, blockade of the coinhibitory receptor CTL-associated antigen 4 (CTLA-4) on the transferred CD4+ T cells resulted in greater expansion of effector T cells, diminished accumulation of tumor-reactive regulatory T cells, and superior antitumor activity capable of inducing regression of spontaneous mouse melanoma. These findings suggest a novel potential therapeutic role for cytotoxic CD4+ T cells and CTLA-4 blockade in cancer immunotherapy, and demonstrate the potential advantages of differentiating tumor-reactive CD4+ cells in vivo over current protocols favoring in vitro expansion and differentiation.

Activity of the Bcl-2 Family Inhibitor ABT-263 in a Panel of Small Cell Lung Cancer Xenograft Models

The purpose of this study was to characterize the activity of the Bcl-2 protein family inhibitor ABT-263 in a panel of small cell lung cancer (SCLC) xenograft models. A panel of 11 SCLC xenograft models was established to evaluate the efficacy of ABT-263. Single agent activity was examined on a continuous dosing schedule in each of these models. The H146 model was used to further evaluate dose and schedule, comparison to standard cytotoxic agents, and induction of apoptosis. ABT-263 exhibited a range of antitumor activity, leading to complete tumor regression in several models. Significant regressions of tumors as large as 1 cc were also observed. The efficacy of ABT-263 was also quite durable; in several cases, minimal tumor regrowth was noted several weeks after the cessation of treatment. Antitumor effects were equal or superior to that of several clinically approved cytotoxic agents. Regression of large established tumors was observed through several cycles of therapy and efficacy was retained in a Pgp-1 overexpressing line. Significant efficacy was observed on several dose and therapeutic schedules and was associated with significant induction of apoptosis. ABT-263 is a potent, orally bioavailable inhibitor of Bcl-2 family proteins that has recently entered clinical trials. The efficacy data reported here suggest that SCLC is a promising area of clinical investigation with this agent.

Alphaviral vector-transduced dendritic cells are successful therapeutic vaccines against neu-overexpressing tumors in wild-type mice.

While dendritic cell (DC) vaccines can protect hosts from tumor challenge, their ability to effectively inhibit the growth of established tumors remains indeterminate. Previously, we have shown that human DCs transduced with Venezuelan equine encephalitis virus replicon particles (VRPs) were potent stimulators of antigen-specific T cells in vitro. Therefore, we investigated the ability of VRP-transduced DCs (VRP-DCs) to induce therapeutic immunity in vivo against tumors overexpressing the neu oncoprotein. Transduction of murine DCs with VRPs resulted in high-level transgene expression, DC maturation and secretion of proinflammatory cytokines. Vaccination with VRP-DCs expressing a truncated neu oncoprotein induced robust neu-specific CD8(+) T cell and anti-neu IgG responses. Furthermore, a single vaccination with VRP-DCs induced the regression of large established tumors in wild-type mice. Interestingly, depletion of CD4(+), but not CD8(+), T cells completely abrogated inhibition of tumor growth following vaccination. Taken together, our results demonstrate that VRP-DC vaccines induce potent immunity against established tumors, and emphasize the importance of the generation of both CD4(+) T cell and B cell responses for efficient tumor inhibition. These findings provide the rationale for future evaluation of VRP-DC vaccines in the clinical setting.

Immune competence of cancer-reactive T cells generated de novo in adult tumor-bearing mice

AbstractThe impact of timing of antigen introduction into fetus and neonates leads to the suggestion that pre-existing antigens are tolerogenic to immunocompetent cells generated thereafter. This hypothesis predicts that in patients with cancer who are undergoing bone marrow transplantation, newly produced T cells with specificity for pre-existing tumor cells will be inactivated by the tumor antigens in the host. Because the effect of tumor cells on developing cancer-reactive T cells has not been investigated, we set out to systematically analyze the impact of tumor cells in the periphery on the development of tumor-reactive T cells in the thymus and their immunocompetence in the periphery. Our data demonstrate that in the host in which a tumor is established in the periphery, the cancer-reactive T cells develop normally, remain fully immunocompetent, become activated in the periphery, and cause regression of large established tumors. The immunocompetence of T cells generated in an antigen-bearing host is also confirmed in a skin graft transplantation model.

Cellular requirements for the monoclonal antibody-mediated eradication of an established solid tumor.

Following subcutaneous implantation, the murine lymphoma E.G7 [a variant of EL-4, transfected with the chicken ovalbumin (OVA) gene] up-regulates the CD4 molecule. We previously showed that the administration of an anti-CD4 monoclonal antibody (mAb) to EG.7-bearing mice leads to a rapid and complete regression of large established tumors. This tumor regression was shown to require both CD8+ cells and functional Fcgamma receptors (FcgammaR), as it failed to occur in mice depleted of CD8 cells, or mice genetically deficient in FcgammaI/III (gamma-/-mice). Using adoptive transfer, we now show that the FcgammaR+ cells required for this regression are the CD11b+ (phagocytic) cells. Furthermore, experiments using peptide tolerization demonstrated that the critical CD8 CTL population in this model is tumor specific. Analysis of tumors at various stages of regression revealed a massive CD11b+FcgammaR+ and a marginal CD8 infiltration. In the presence of the CTL determinant OVA-8 on tumor cells and of the antitumor mAb, this CD8 infiltration became remarkable, and correlated with tumor regression. These results identify the specific cellular effectors essential for the mAb-mediated tumor regression, and suggest that FcgammaR-activated macrophages induced an expansion of tumor-eliminating CTL in situ.

Cellular requirements for the monoclonal antibody-mediated eradication of an established solid tumor

Following subcutaneous implantation, the murine lymphoma E.G7 [a variant of EL-4, transfected with the chicken ovalbumin (OVA) gene] up-regulates the CD4 molecule. We previously showed that the administration of an anti-CD4 monoclonal antibody (mAb) to EG.7-bearing mice leads to a rapid and complete regression of large established tumors. This tumor regression was shown to require both CD8+ cells and functional Fcγ receptors (FcγR), as it failed to occur in mice depleted of CD8 cells, or mice genetically deficient in FcγRI/III (γ− / − mice). Using adoptive transfer, we now show that the FcγR + cells required for this regression are the CD11b+ (phagocytic) cells. Furthermore, experiments using peptide tolerization demonstrated that the critical CD8 CTL population in this model is tumor specific. Analysis of tumors at various stages of regression revealed a massive CD11b+ FcγR + and a marginal CD8 infiltration. In the presence of the CTL determinant OVA-8 on tumor cells and of the antitumor mAb, this CD8 infiltration became remarkable, and correlated with tumor regression. These results identify the specific cellular effectors essential for the mAb-mediated tumor regression, and suggest that FcγR-activated macrophages induced an expansion of tumor-eliminating CTL in situ.

Gene replacement strategies for lung cancer

Advances in our understanding of the molecular genetics of cancer present an opportunity to develop prevention and treatment strategies based on the reversal of specific genetic lesions. This strategy is analogous to the classic concept of gene therapy for replacement of defective or nonfunctioning genes. The gene families implicated in carcinogenesis include dominant oncogenes and tumor suppressor genes. Regional administration of viral vectors expressing wildtype p53 and antisense K-ras prevents tumor growth for tumors with the specific genetic lesions in orthotopic tumor models and mediates regression of large established tumors. These studies provide a rationale for a new clinical protocol recently approved by the National Institutes of Health Recombinant DNA Advisory Committee and Food and Drug Administration to replace a defective p53 gene with intratumor injection of recombinant retrovirus expressing wild-type p53 or elimination of activated K-ras by expression of antisense K-ras messenger RNA. If these agents are efficacious, their lack of toxicity may provide a sufficiently high therapeutic index such that they could be used as an adjuvant to surgery to treat patients with earlier stages of cancer or as prevention for second primary cancers for individuals with genetic abnormalities in premalignant lesions. Although much research needs to be done, the possibility of specific gene targeting with a high therapeutic index makes this a promising area of investigation.