Characterization of the recognition and functional heterogeneity exhibited by cytokine-induced killer cell subsets against acute myeloid leukaemia target cell

SMAC Mimetic BV6 Enables Sensitization of Resistant Tumor Cells but also Affects Cytokine-Induced Killer (CIK) Cells: A Potential Challenge for Combination Therapy

Allogeneic hematopoietic stem cell transplantation (HSCT) is an established treatment option for high-risk hematological malignancies, and may also be offered to patients with solid malignancies refractory to conventional therapies. In case of patients' relapse, refractory tumor cells may then be targeted by cellular therapy-based combination strategies. Here, we investigated the potential of small molecule IAP (SMAC mimetic) BV6 in increasing cytokine-induced killer (CIK) cell-mediated cytotoxicity against different tumor targets. Four-hour pre-incubation with 2.5 μMol BV6 moderately enhanced CIK cell-mediated lysis of hematological (H9, THP-1, and Tanoue) and solid malignancies (RH1, RH30, and TE671). However, BV6 also increased apoptosis of non-malignant cells like peripheral blood mononuclear cells and most notably had an inhibitory effect on immune cells potentially limiting their cytotoxic potential. Hence, cytotoxicity increased in a dose-dependent manner when BV6 was removed before CIK cells were added to tumor targets. However, cytotoxic potential was not further increasable by extending BV6 pre-incubation period of target cells from 4 to 12 h. Molecular studies revealed that BV6 sensitization of target cells involved activation of caspases. Here, we provide evidence that SMAC mimetic may sensitize targets cells for CIK cell-induced cell death. However, BV6 also increased apoptosis of non-malignant cells like CIK cells and peripheral mononuclear cells. These findings may therefore be important for cell- and small molecule IAP-based combination therapies of resistant cancers after allogeneic HSCT.

Multivariate statistical data analysis as a tool to analyze ex vivo expansion dynamics of cytokine-induced killer cells

BACKGROUND

Cytokine-induced killer (CIK) cells, obtained after mononucleated cell stimulation with interferon-γ, interleukin-2, and anti-CD3 antibody, are constituted by CD3(+) CD56(+) (CIK) cells and a minority of natural killer (NK; CD3(-) CD56(+) ) cells and T-lymphocytes (CD3(+) CD56(-) ) with antitumor effect against hematological malignancies, thus representing a promising immunotherapy strategy. To ensure in vivo antitumor activity it is mandatory to maximize the percentage of CD3(+) 56(+) effector cells, which is highly variable depending on the starting sample and the harvesting day. Based on cytofluorimetric data, we have retrospectively applied multivariate statistical data analysis (MVDA) to 30 expansions building mathematical models able to predict the expansion fate and the optimal CIK harvesting day.

METHODS

Cell phenotype was monitored during culture; multivariate batch statistical process control was applied to monitor cell expansion and orthogonal projections to latent structures to predict CIK percentage.

RESULTS

Ten expansions had CD3(+) CD56(+) cells ≥ 40% (good batches) and 20 had CD3(+) CD56(+) cells ≤ 40%. In 36.7%, CD3(+) CD56(+) cells reached the highest concentration at day 17 and the others at day 21. We built a highly predictive regression model for estimating CD3(+) CD56(+) cells during culture. Three variables resulted highly informative: NK % at day 0, cytotoxic T-lymphocytes % (CTLs, CD3(+) CD8(+) ) at day 4, and CIK % at day 7. "Good batches" are characterized by a high percentage of CTLs and CD3(+) CD56(+) cells at day 4 and day 7, respectively.

CONCLUSION

By applying MVDA it is possible to optimize CIK expansion, deciding the optimal cell harvesting day. A predictive role for CTL and CIK was evidenced.

The phenotype of ex vivo generated cytokine-induced killer cells is associated with overall survival in patients with cancer

Cytokine-induced killer (CIK) cells are ex vivo generated heterogeneous NK-like T lymphocytes. It is not very clear whether the phenotype of CIK cells is associated with their therapeutic efficacy to cancer patients. Thus, in this study, the association of phenotype of CIK cells and the overall survival of 121 patients with hepatocellular carcinoma (HCC), 74 patients with lung cancer and 42 patients with colorectal cancer, all of whom underwent surgical resection and received autogenous CIK cell therapy, was analyzed. We found that high ratio of the CD3+CD4+ subset was associated with poorer overall survival in colorectal cancer, but not HCC or lung cancer. A high ratio of the CD3+CD8+ subset was associated with improved overall survival in all three types of cancer. A high ratio of the CD3+CD56+ NK-like subset was associated with improved overall survival in lung and colorectal cancer, but not HCC. A high ratio of the CD3-CD56+ NK subset was associated with poorer overall survival in lung and colorectal cancer, but not HCC. In conclusion, the CD3+CD8+ and CD3+CD56+ subsets, especially the CD3+CD8+ subset, may be the major phenotypes responsible for anti-tumor immunity in vivo after autogenous CIK cell therapy.

A phase I/II clinical trial of autologous cytokine-induced killer cells as adjuvant immunotherapy for acute and chronic myeloid leukemia in clinical remission

BACKGROUND AIMS

Cytokine-induced killer (CIK) cells have shown remarkable cytotoxicity against various tumors in vitro and in animal studies. We report on the clinical outcome of autologous CIK cells for patients with acute (AML) and chronic (CML) myeloid leukemia in remission.

METHODS

Eleven of the 13 recruited AML patients undergoing autologous peripheral blood stem cell transplant (autoPBSCT) were given autologous CIK cell infusion upon engraftment post-transplant and followed-up for disease relapse. Eleven CML patients on Imatinib with residual disease detectable by polymerase chain reaction (PCR) were given infusion and monitored by quantitation of the bcr-abl transcript.

RESULTS

Despite the presence of interferon (IFN)-γ-secreting T cells against various AML- and CML-associated peptides at sporadic time-points and demonstration of in vitro cytotoxicity of CIK cells against autologous and allogeneic AML targets, there was no survival benefit in AML patients post-autoPBSCT given CIK cells compared with historical controls. For CML patients, all continued to have a detectable bcr-abl transcript fluctuating within a range comparable to their pre-treatment baseline, although two had a transient but non-sustainable disappearance of bcr-abl transcript. There were no adverse reactions except for fever within the first day of infusion.

CONCLUSIONS

Our small series, while confirming safety, failed to demonstrate a clinical benefit of autologous CIK cells given in its current form for AML and CML. Further manipulation of CIK cells to improve anti-leukemic potency and specificity, together with the preparation of patients to create a more conducive milieu for in vivo expansion and persistence of infused CIK cells, should be explored.

CD8 T cell defect of TNF-α and IL-2 in DNAM-1 deficient mice delays clearance in vivo of a persistent virus infection

DNAM-1 gene-deficient (-/-) mice take significantly longer to clear an acute and persistent LCMV infection in vivo than DNAM-1 +/+ mice. During acute LCMV priming, at the single cell level, DNAM-1 -/- mice made significantly less cytoplasmic CD8 TNF-α and IL-2 but not IFN-γ than their DNAM-1 +/+ counterparts. Restimulated immune memory CD8 T cells from DNAM-1 -/- and DNAM-1 +/+ mice were equivalent in cytolytic activity against LCMV-infected target cells but DNAM-1 -/- CD8 T cells had significant reductions in TNF-α and IL-2 that were associated on adoptive transfer with the inability to terminate the persistent viral infection.

Cytokine-induced killer (CIK) cells as feasible and effective adoptive immunotherapy for the treatment of solid tumors

INTRODUCTION

Cytokine-induced killer (CIK) cells are heterogeneous ex vivo-expanded T lymphocytes with mixed T-NK phenotype and endowed with a wide MHC-unrestricted antitumor activity. CIK cells can be expanded from peripheral blood mononuclear cells (PBMC) cultured with the timed addition of IFN-γ, Ab anti-CD3 and IL2. A consistent subset of mature CIK cells presents a CD3(+)CD56(+) phenotype. The CD3(+)CD56(+) cellular subset is the main responsible for the tumor-killing activity, mostly mediated by the interaction of NKG2D receptor with MHC-unrestricted ligands (MIC A/B; ULBPs) on tumor cells.

AREAS COVERED

In the present work, we described the biologic characteristics of CIK cells, focusing on those aspects that may favor their clinical translation. We reviewed preclinical data and analyzed reports from clinical trials. A specific paragraph is dedicated to future research perspectives in the field.

EXPERT OPINION

CIK cells represent a realistic new option in the field of cancer immunotherapy. Crucial issues, favoring their clinical translation, are the easy availability of large amounts of expanded CIK cells and their MHC-unrestricted tumor killing, potentially effective against many tumor types. Intriguing future perspectives and open challenges are the investigation of synergisms with other immunotherapy approaches, targeted therapies or even conventional chemotherapy.

Improved activation toward primary colorectal cancer cells by antigen-specific targeting autologous cytokine-induced killer cells

Adoptive therapy of malignant diseases with cytokine-induced killer (CIK) cells showed promise in a number of trials; the activation of CIK cells from cancer patients towards their autologous cancer cells still needs to be improved. Here, we generated CIK cells ex vivo from blood lymphocytes of colorectal cancer patients and engineered those cells with a chimeric antigen receptor (CAR) with an antibody-defined specificity for carcinoembryonic antigen (CEA). CIK cells thereby gained a new specificity as defined by the CAR and showed increase in activation towards CEA⁺ colon carcinoma cells, but less in presence of CEA⁻ cells, indicated by increased secretion of proinflammatory cytokines. Redirected CIK activation was superior by CAR-mediated CD28-CD3ζ than CD3ζ signaling only. CAR-engineered CIK cells from colon carcinoma patients showed improved activation against their autologous, primary carcinoma cells from biopsies resulting in more efficient tumour cell lysis. We assume that adoptive therapy with CAR-modified CIK cells shows improved selectivity in targeting autologous tumour lesions.

The anti-tumour activity of allogeneic cytokine-induced killer cells in patients who relapse after allogeneic transplant for haematological malignancies

We performed a Phase I/II clinical trial to study the feasibility, toxicity and efficacy of allogeneic cytokine-induced killer (CIK) cell expansion, and treatment for patients with haematological malignancies who relapsed after allogeneic haemopoietic SCT (allo-HSCT). Allogeneic CIK cells were successfully generated for a total of 24 patients, including those from patients' own leukapheresis products in 5 patients who had no access to further donor cells. The median CD3(+) T-cell expansion was 9.33 (1.3-38.97) fold, and CD3(+)CD56(+) natural killer (NK)-like T-cell expansion was 27.77 (2.59-438.93) fold. A total of 55 infusions were done for 16 patients who had either failed or progressed after initial response to various individualized chemotherapy regimens and donor lymphocyte infusion (DLI), at doses ranging from 10 to 200 million CD3(+) cells/kg. Response attributable to CIK cell infusion was observed in five patients. These included two with ALL, two with Hodgkin's disease (HD) and one with AML, and two of whom had a response sustained for more than 2 years. Acute GVHD occurred in three and was easily treatable. This study provides some evidence suggestive of the efficacy of allogeneic CIK cells even after failure of DLI in some cases.

The cytotoxic potential of interleukin-15-stimulated cytokine-induced killer cells against leukemia cells

BACKGROUND AIMS

Cytokine-induced killer (CIK) cells may serve as an alternative approach to adoptive donor lymphocyte infusions (DLI) for patients with acute leukemia relapsing after haplo-identical hematopoietic stem cell transplantation (HSCT). We investigated the feasibility of enhancing CIK cell-mediated cytotoxicity by interleukin (IL)-15 against acute myeloid and lymphoblastic leukemia/lymphoma cells.

METHODS

CIK cells were activated using IL-2 (CIK(IL-2)) or IL-15 (CIK(IL-15)) and phenotypically analyzed by fluorescence-activated cell sorting (FACS). Cytotoxic potential was measured by europium release assay.

RESULTS

CIK(IL-2) cells showed potent cytotoxicity against the T-lymphoma cell line H9, T-cell acute lymphoblastic leukemia (T-ALL) cell line MOLT-4 and subtype M4 acute myeloid leukemia (AML) cell line THP-1, but low cytotoxicity against the precursor B (pB)-cell ALL cell line Tanoue. IL-15 stimulation resulted in a significant enhancement of CIK cell-mediated cytotoxicity against acute lymphoblastic leukemia/lymphoma cell lines as well as against primary acute myeloid and defined lymphoblastic leukemia cells. However, the alloreactive potential of CIK(IL-15) cells remained low. Further analysis of CIK(IL-15) cells demonstrated that the NKG2D receptor is apparently involved in the recognition of target cells whereas killer-cell immunoglobulin-like receptor (KIR)-HLA mismatches contributed to a lesser extent to the CIK(IL-15) cell-mediated cytotoxicity. In this context, CD3 (+) CD8 (+) CD25 (+) CD56(-) CIK(IL-15) cell subpopulations were more effective in the lysis of AML cells, in contrast with CD56 (+) CIK(IL-15) cells, which showed the highest cytotoxic potential against ALL cells.

CONCLUSIONS

This study provides the first evidence that CIK(IL-15) cells may offer a therapeutic option for patients with refractory or relapsed leukemia following haplo-identical HSCT.

Natural killer T cells subsets in cancer, functional defects in prostate cancer and implications for immunotherapy

Natural killer T cells are T lymphocytes with unique activation and effector properties. The majority of NKT cells, termed type-I or iNKT cells, recognize lipid antigens presented on MHC-like CD1d molecules. Type-I NKT cells have the capacity to rapidly secrete various cytokines upon activation, thereby regulate immune responses exerts dominant anti-tumor and anti-microbial effector functions. Specific activation of type-I NKT cells in mouse models boosts immunity and prevents metastasis, which has led to a number of phase I-II clinical trials. Since the discovery of NKT cells other subsets with different specificities and effector functions have been described. This article briefly reviews the physiological functions of NKT cell subsets, their implications in cancer and the attempts that have been made to employ NKT cells for immune therapy of cancer.

Synergistic effect of CH-296 and interferon gamma on cytokine-induced killer cells expansion for patients with advanced-stage malignant solid tumors

BACKGROUND

Cytokine-induced killer cells (CIKs) are heterogenous antitumor effectors including interferon gamma (IFN-γ)-amplified CD3(+)CD56(+) cells. CH-296 has been shown to stimulate T-cell proliferation in the presence of T cell receptor (TCR)-stimulating signals. The purpose of this study was to investigate the synergistic effect of CH-296 and IFN-γ on expansion of CIKs for treating patients with advanced-stage malignant solid tumors.

METHODS

CIKs were cultured with immobilized CH-296 in the presence (retronectin [RN]-CIKs) or absence of IFN-γ (RN-CIKs/del) for 14 days. Proliferation, apoptosis, phenotype, and cytotoxicity were detected. Twenty (20) patients (18 patients with stage IV solid tumors) received three cycles of RN-CIKs treatment. The clinical responses were evaluated using Karnofsky Performance Status scoring and computed-tomography scanning.

RESULTS

CH-296 promoted CIKs expansion in a time-dependent manner by inhibiting apoptosis and increasing proliferation. Costimulation of CH-296 and IFN-γ amplified more antitumor effectors of CIKs with activated T-cell phenotype, which displayed potent cytotoxicity and increased cytokines secretion upon antigen priming. Sixteen (16) patients receiving RN-CIKs experienced relief of clinical symptoms. The overall clinical response rate was 65% (13/20) and the mean overall survival was 16.95±6.10 months. No severe adverse events were observed in the clinical trial.

CONCLUSIONS

CH-296 and IFN-γ synergistically promote antitumor efficiency of CIKs by increasing proliferation, inhibiting apoptosis, and enhancing cytotoxicity.

Clinical scale expansion of cytokine-induced killer cells is feasible from healthy donors and patients with acute and chronic myeloid leukemia at various stages of therapy

OBJECTIVE

In our clinical studies involving cytokine-induced killer (CIK) cells for patients with hematological malignancies, starting cells came from a heterogeneous group of patients and donors. Here we study the feasibility of expansion and analyzed the characteristics of the end product from starting cells derived from different sources and at different disease states.

MATERIALS AND METHODS

Seventy-five clinical scale cultures were grown from 28 patients and 20 donors in Good Manufacturing Practices facilities under CIK condition.

RESULTS

CIK cells could be successfully expanded from healthy donors, patients with acute myeloid leukemia recovering from chemotherapy, untreated patients with acute myeloid leukemia or myelodysplastic syndrome with circulating leukemic blasts, and patients with chronic myeloid leukemia on imatinib. Furthermore, CIK cells of donor origin could be expanded from leukapheresis product collected from patients who relapsed post-allogeneic transplantation, thereby offering a useful method of obtaining activated donor cells in patients for whom further donor cells were unavailable. Interestingly, CIK cells cultured from patients with untreated acute myeloid leukemia and myelodysplastic syndrome had a significantly higher proportion of CD3(+)CD56(+) subset and higher fold expansion of CD3(+) cells as compared to other groups of patients or healthy donors. Multivariate analysis showed that fresh starting cells expanded better than frozen-thawed cells, while prior exposure to granulocyte colony-stimulating factor or imatinib before harvesting did not adversely affect CIK cell expansion.

CONCLUSIONS

Clinical scale expansion of CIK cells is feasible from both healthy donors and leukemia patients at various stages of treatment. This robust system allows clinical translation using CIK cells as immunotherapy in various clinical settings.

Cytokine induced killer cells as promising immunotherapy for solid tumors

Cytokine-induced killer (CIK) cells are a heterogeneous subset of ex-vivo expanded T lymphocytes which present a mixed T-NK phenotype and are endowed with a MHC-unrestricted antitumor activity. The main functional properties of CIK cells may address some of the main limitations that are currently preventing the successful clinical translation of adoptive immunotherapy strategies. Clinically adequate quantities of immune effectors, sufficient for multiple adoptive infusions, may be obtained based on their relatively easy and inexpensive ex-vivo expansion starting from peripheral blood mononuclear cells. The MHC-unrestricted tumor-killing is mainly based on the interaction between NKG2D molecules on CIK cells and MIC A/B or ULBPs molecules on tumor cells; it has been proved effective against several solid and hematological malignancies and does not require any HLA-restriction increasing the number of patients that might potentially benefit from such approach. Finally, CIK cells present a reduced alloreactivity across HLA-barriers with important clinical implications for their potential use as alternative to conventional Donor Lymphocyte Infusions after allogeneic hemopoietic cell transplant with a reduced risk of GVHD. In the present report we review the main functional characteristics of CIK cells discussing recent findings and future perspectives to improve their antitumor activity and potential clinical applications.

Anti-leukemia effect of ex vivo expanded DNT cells from AML patients: a potential novel autologous T-cell adoptive immunotherapy

CD3(+)CD56(-), CD4 and CD8 double negative T (DNT) cells comprise 1-3% of peripheral blood (PB) mononuclear cells. Their role in tumor immunity remains largely unknown due to their limited numbers and lack of effective methods to expand them. Here we developed a novel protocol by which DNT cells can be expanded ex vivo to therapeutic levels in 2 weeks from 13 of 16 acute myeloid leukemia (AML) patients during chemotherapy-induced complete remission. The expanded DNT cells expressed similar or higher levels of interferon-γ and tumor necrosis factor-α and Granzyme B as that seen in bulk activated CD8T cells from the same patient but significantly higher levels of perforin. The expanded DNT cells could effectively kill both allogeneic and autologous primary CD34(+) leukemic blasts isolated from PB of AML patients in a perforin-dependant manner. These results demonstrate, for the first time, that DNT cells from AML patients can be expanded ex vivo even after intensive chemotherapy, and are effective at killing both allogeneic and autologous primary leukemic blasts. These findings warrant studies further exploring the potential of DNT cells as a novel adjuvant immunotherapy to decrease the risk of relapse in patients with AML and, perhaps, other cancers.

Systemic effector and regulatory immune responses to chlamydial antigens in trachomatous trichiasis

Trachomatous trichiasis (TT) caused by repeated or chronic ocular infection with Chlamydia trachomatis is the result of a pro-fibrotic ocular immune response. At the conjunctiva, the increased expression of both inflammatory (IL1B, TNF) and regulatory cytokines (IL10) have been associated with adverse clinical outcomes. We measured in vitro immune responses of peripheral blood to a number of chlamydial antigens. Peripheral blood effector cells (CD4, CD69, IFNγ, IL-10) and regulatory cells (CD4, CD25, FOXP3, CTLA4/GITR) were readily stimulated by C. trachomatis antigens but neither the magnitude (frequency or stimulation index) or the breadth and amount of cytokines produced in vitro [IL-5, IL-10, IL-12 (p70), IL-13, IFNγ, and TNFα] were significantly different between TT cases and their non-diseased controls. Interestingly we observed that CD4+ T cells account for <50% of the IFNγ positive cells induced following stimulation. Further investigation in individuals selected from communities where exposure to ocular infection with C. trachomatis is endemic indicated that CD3-CD56+ (classical natural killer cells) were a major early source of IFNγ production in response to C. trachomatis elementary body stimulation and that the magnitude of this response increased with age. Future efforts to unravel the contribution of the adaptive immune response to conjunctival fibrosis should focus on the early events following infection and the interaction with innate immune mediated mechanisms of inflammation in the conjunctiva.

[Biological characteristics and antitumor activity of CIK cells activated by recombinant human fibronectin for human lung cancer cell lines in vitro]

背景与目的

CIK细胞是过继免疫治疗的重要手段之一，简化体外培养过程从而提高其增殖率和杀瘤活性仍是目前研究的一个热点课题。本研究观察重组人纤维连接蛋白（recombinant human fibronectin, RN）诱导CIK细胞的生物学特性，建立一种高效、简便的体外CIK细胞扩增方法。

方法

抽取10名健康人外周静脉血各50 mL，用淋巴细胞分离液分离单个核细胞，分别采用RN诱导法和传统方法培养CIK细胞，记录细胞增殖数；用流式细胞术测定免疫细胞表型和分泌IFN-γ、IL-4、穿孔素和颗粒酶B细胞的百分比；用MTT法测定CIK细胞对4种人肺癌细胞株的体外杀伤率。

结果

RN诱导的CIK细胞扩增倍数为传统方法的2.0倍-3.5倍，具有统计学差异（P < 0.05）；RN诱导组和传统方法组CD3⁺CD16⁺CD56⁺细胞绝对数分别增加了3 778倍和2 069倍；RN诱导组细胞中CD3⁺CD8⁺细胞比例明显高于传统方法组（P < 0.05）；但CD3⁺CD4⁺细胞比例无统计学差异（P > 0.05）；对4种肺癌细胞株的体外杀伤活性无统计学差异（P > 0.05）。RN诱导的CIK较诱导前：分泌IFN-γ的细胞比例明显增加；分泌IL-4的细胞比例略有降低；释放穿孔素、颗粒酶B的阳性细胞比例较诱导前增加。

结论

RN诱导法是一种高效、简便的体外扩增CIK方法，可以替代传统方法。

Cytokine-induced NK-like T cells: from bench to bedside

Cytokine-induced killer (CIK) cells are polyclonal T effector cells generated when cultured under cytokine stimulation. CIK cells exhibit potent, non-MHC-restricted cytolytic activities against susceptible tumor cells of both autologous and allogeneic origins. Over the past 20 years, CIK cells have evolved from experimental observations into early clinical studies with encouraging preliminary efficacy towards susceptible autologous and allogeneic tumor cells in both therapeutic and adjuvant settings. This paper is our attempt to summarize the available published literature related to CIK cells. Looking into the future, we anticipate that the continuous therapeutic application of CIK cells will likely be developed along two major directions: overcoming the challenge to organize large prospective randomized clinical trials to define the roles of CIK cells in cancer immunotherapy and expanding its spectrum of cytotoxicity towards resistant tumor cells through experimental manipulations.

Cytokine induced killer cells as adoptive immunotherapy strategy to augment graft versus tumor after hematopoietic cell transplantation

Donor lymphocyte infusion (DLI) is used to increase the graft versus tumor (GVT) effect after allogeneic hematopoietic cell transplant (HCT). The limited spectrum of activity and high risk of graft versus host disease (GVHD) remain major limitations of this approach. The finding of new cell populations for adoptive immunotherapy, with the ability to separate GVT from GVHD, would be useful. Here we review the main basic, preclinical and clinical research on cytokine-induced killer (CIK) cells, highlighting the aspects of their antitumor and alloreactive potentials that might favourably affect the balance between GVT and GVHD. CIK cells are ex vivo-expanded T lymphocytes sharing NK markers and endowed with a potent MHC-unrestricted antitumor activity against haematological and solid malignancies. Studies in preclinical animal models have demonstrated their low GVHD potential when infused across MHC-barriers, and recent clinical studies seem to confirm these findings in patients with hematological malignancies relapsing after HCT. If consolidated with larger clinical trials, adoptive immunotherapy with CIK cells might represent an effective alternative to classic DLI, helping HCT to succesfully meet current challenges like the extension across major HLA-barriers and application to solid tumors.