1.Background.
Kidney cancer is a common malignant tumor of the urinary system. According to the American Society of Oncology, there are about 40,000 new cases of kidney cancer in the United States each year, and the incidence of kidney cancer worldwide increases by 2% each year, and nearly 100,000 patients die of kidney cancer each year. Nearly half of the patients with kidney cancer are already in advanced stage when they are first diagnosed, and about 40% of them have recurrence and metastasis after surgery. The 3-year survival rate of untreated patients is less than 5%, and the related epidemiological survey in China also shows that the number of new kidney cancer cases in China is increasing year by year. At present, the main treatment method of kidney cancer is surgical resection, and radiotherapy and chemotherapy have no significant efficacy in the treatment of kidney cancer. However, the remission rate of IL-2 is low and the incidence of toxic side effects is high. The toxic side effects caused by IL-2, such as capillary leakage syndrome and gastrointestinal symptoms, make many kidney cancer patients who have spread unable to tolerate high doses.
In the 1980s, secondary cellular immunotherapy opened up a new field of biological treatment for kidney cancer. After more than 20 years of research and practice, biological cellular immunotherapy (DC-CIK) has become a new method for effective treatment of metastatic kidney cancer. Appropriate immunotherapy can help remove the remaining cancer cells in patients’ bodies and address subclinical metastases that are difficult to be resolved by conventional therapies, thus further improving and consolidating the efficacy of kidney cancer, reducing recurrence and improving the quality of life of tumor patients.
1.1. DC Tumor Vaccine
Tumor vaccine therapy is to stimulate specific anti-tumor immune response of patients by introducing tumor antigens into their bodies, which has the advantages of specificity and long maintenance of immune effect in vivo.
Since the core problem of tumor evasion from the immune system is that tumor antigens cannot be effectively delivered to T lymphocytes, the most effective way of antigen delivery is that antigen-presenting cells have both tumor antigens and functional 1st and 2nd signaling systems. Therefore, current tumor vaccines focus more on cellular vaccines, either by enhancing the 1st and 2nd signaling systems of tumor cells to become fully functional APCs, called modified tumor cell vaccines; or by using professional APCs to uptake, process, and deliver tumor antigens, mostly using DC vaccines with loaded tumor antigens.
Dendritic cells (DCs) are currently considered to be the most important antigen-presenting cells in tumor immunity, which induce, activate and proliferate cytotoxic T lymphocytes (CTL) by uptake of tumor antigens and presentation of antigens to T lymphocytes, mediating powerful and specific anti-tumor cellular immunity. DCs obtained from in vitro culture have the same antigen-presenting function as purified in vivo mature DCs, which is the basis for DCs to be used in clinical treatment of malignant tumors.
1.1.1 Main characteristics of mature DCs
(1) There are many dendritic irregular protrusions on the cell surface;
②The cell surface is rich in molecules that contribute to antigen presentation, such as MHC class I and II molecules, co-stimulatory molecules B721 and B722, cell adhesion molecules ICAM21 and ICAM23, and lymphocyte function-related antigens L FA21 and L FA23, etc;
(3) In the mixed lymphocyte response, both self-reactive T cells with the same MHC and allogeneic T cells with different MHC can be activated, and the most important feature is that it can significantly stimulate the proliferation of initial T cells (Naive T calls) and establish primary immune response;
④The ability to migrate to local lymphocyte T-cell areas;
⑤ The ability of DCs to stimulate T cell proliferation and antigen enhancement is 100-1000 times greater than that of macrophages and B cells.
(6) In addition to inducing antigen-specific cytotoxic T lymphocytes, DC can also affect the proliferation of B cells and activate humoral immune response in a direct or indirect manner.
1.1.2. DC- tumor cell vaccines
Currently, a large number of dendritic cells can be obtained by culturing patients’ peripheral blood or bone marrow single nucleated cells with cytokines such as GM-CSF, IL-4, TNF-α, and Fit3-L. Tumor antigens can be loaded to DCs in the form of genes, peptides, proteins, or even intact cells, so the preparation of DC cell vaccines is significantly easier than that of genetically modified tumor cell vaccines, thus facilitating the entry of DC vaccines into clinical trials.
The tumor antigen genes of most solid tumors are not yet clearly understood, and the number of clearly identified tumor antigens is still very small. Moreover, there is a lack of in vivo experimental evidence whether the known tumor-associated antigens truly represent tumor rejection antigens. Therefore, the fusion of tumor cells with DCs provides all cellular antigens, and the fused cells possess tumor cell antigenicity and DC antigen presentation and T-cell activation functions, so that the tumor antigen uptake, processing and presentation functions of DCs can be fully utilized.
1.2. CIK cells
Cytokine-induced killer (CIK) cells are a new class of tumor-killing cells prepared by Stanford University School of Medicine in 1991 based on CD3-activated killer cells (CD3AK cells), which are obtained by co-culturing human peripheral blood mononuclear cells with various cytokines (e.g. anti-CD3McAb, IL-2, IFN-γ, IL-1α, etc.) in vitro for a period of time. A heterogeneous population of cells obtained after co-culture for a period of time. CIK cells are also known as NK cell-like T lymphocytes because they express both CD3 and CD56 membrane protein molecules, and have the advantages of strong anti-tumor activity of T lymphocytes and non-MHC-restricted tumor killing of NK cells.
1.2.1. Characteristics of CIK cells
Fast proliferation rate: The problem of low number of cells obtained by in vitro expansion of effector cells has been solved.
High tumoricidal activity: It is due to their high survival rate and strong proliferation ability.
Broad tumor-killing spectrum: It can kill tumor cells of different tissue origins.
It is also sensitive to multi-drug resistant tumor cells.
Little toxicity to normal bone marrow hematopoietic precursor cells.
Resistant to tumor cell-triggered apoptosis of effector cells Fas-FasL.
1.2.2. Tumor killing mechanism of CIK cells
1.2.2.1 Recognition: Since the cell killing effect of CIK is non-MHC-restricted, CD4 and CD8 are not essential in their recognition of tumor cells.
1.2.2.2 Killing mechanism: CIK cells kill and lyse tumor cells through three pathways
Direct killing of tumor cells by CIK cells: CIK cells stimulated by exogenous anti-CD3McAb or sensitive target cells will release cytotoxic cytoplasmic granules to the extra-membrane space, these cytoplasmic granules have a direct killing effect on target cells.
The tumor-killing activity of a large number of inflammatory cytokines produced by CIK cell activation: such as IFN-γ, TNF-α, IL-2, etc., not only have a direct inhibitory effect on tumor cells, but also can indirectly kill tumor cells by regulating the responsiveness of the body’s immune system.
CIK cells induce tumor cell apoptosis: CIK cells expressing FasL in culture enhance their resistance to Fas-FasL apoptosis triggered by FasL+ tumor cells on the one hand, and also exercise their chronic killing effect on tumor cells by inducing apoptosis on Fas+ tumor cells to ensure the long-term durability of anti-tumor activity.
1.3. Synergistic antitumor effects of DC and CIK cells
DC and CIK are two important parts of tumor immunotherapy, the former recognizes antigens and activates the acquired immune system, while the latter kills tumor cells by exerting its own cytotoxicity and secreting cytokines, the combination of which ensures an efficient and harmonious immune system.
CIK cells are non-specific killer cells induced by various cytokines, which can secrete various cytokines (such as IL-4, IFN-γ, etc.) and have stronger killing activity than LAK and CD3AK cells. In clinical studies, it was found that some patients with less than satisfactory efficacy in the secondary immunotherapy with immune effector cells, which was thought to be due to the resistance of tumor cells to these immune effector cells, and might be related to the lack of functional DCs in tumor patients. Co-culture of CIK cells and DCs significantly increased the specificity of antigen delivery by dendritic cells and co-stimulatory molecules, in addition to promoting IL-12 secretion from dendritic cells and cytotoxicity of CIK cells, while blocking IL-12 uptake reduced the cytotoxicity of CIK cells. The cytotoxicity of CIK cells was diminished by blocked IL-12 uptake. Therefore, the combination of CIK cells and DCs for the treatment of malignant tumors will help to relieve the immune incompetence of T cells in some tumor patients, thus exerting a synergistic anti-tumor effect.