TCR-T uses autologous T cells derived from peripheral blood mononuclear cells via leukapheresis, which is followed by TCR gene transduction (typically by using lentivirus or various other gene delivery approaches) as well as T-cell expansion. TCR-T doses are typically transfused back to cancer patients following lymphodepleting chemotherapy with cyclophosphamide and fludarabine (to mediate the delivery of cytotoxic T-lymphocytes) followed by administration of interleukin (IL)-2 (Tsimberidou et al., 2021). TCR-T has already proved its durability, effectiveness, and safety in various solid tumors such as synovial sarcoma, melanoma, and human papillomavirus-associated tumors (Ma et al., 2024). Varying success rates were obtained in a number of TCR-based trials. A objective response rate (ORR) of 61% was obtained among individuals with soft tissue sarcomas, particularly the individuals with with resistant synovial sarcomas expressing New York esophageal squamous cell carcinoma-1 (NY-ESO1) (Robbins et al., 2015). On the other hand, an ORR of 20%–60% was observed in the case of melanomas, while an ORR of 17%–64%) was observed in the case of hepatocellular carcinoma as per the patient status as well as target (hepatitis B virus [HBV] or alpha-fetoprotein antigen-targeted) (Ma et al., 2024). An enhanced disease control rate (DCR) of around 80% was observed in the trials that primarily targeted esophageal cancers, non-small-cell lung cancer, and head and neck squamous cell carcinoma (Ma et al., 2024). In addition, TCR-T exhibited its durability and effectiveness in several solid tumor niches.

Conventional first-line anthracycline-based chemotherapies showed a 3-year survival of less than 20% and only 26% ORR in the case of soft tissue sarcoma, whereas a specific antigen-based TCR-T performed better in heavily treated conditions (Judson et al., 2014). In the case of metastatic synovial sarcoma, an ORR of 35.7%–66.7% was observed with NY-ESO1-specific TCR-T, along with 5- and 3-year survival rates of 14% and 38%, respectively. In addition, this NY-ESO1-specific TCR-T was found to perform better as compared to the programmed death-1 (PD-1) inhibitor, which had an ORR of 10% only (Robbins et al., 2015; Tawbi et al., 2017; Hong et al., 2020). Metastatic human papillomavirus (HPV)-related cancers are typically standard therapy-resistant and incurable, a DCR of 83.3% and ORR of 50% were observed with the HPV E7-targeted TCR-T, which further extends the applications of TCR-T for carcinomas induced by viruses (Nagarsheth et al., 2021). Even in tumors like refractory malignant pleural mesothelioma that are targetable by TCR-T and CAR, gavocabtagene autoleucel (a novel cell therapy based on autologous, genetically engineered T cells) showed a DCR of 100% and ORR of 50% in interim analysis, in comparison with the results of a phase I clinical trial of mesothelin-targeted CARs and PD-1 antibody (a DCR of 68.8%) (Adusumilli et al., 2021).

Advantages in terms of efficacy and safety were also observed with TCR-based bispecific protein as compared to standard therapy (Nathan et al., 2021; Olivier and Prasad, 2022). In the case of hepatocarcinoma, a median overall survival of 33.5 months was observed with the HBV antigen-targeted TCR-T, where a median overall survival of 10.7 months was observed with sorafenib and a median progression-free survival of only 5 months was observed with CD133 CAR-T (Wang et al., 2018). A specific TCR-T therapy’s The safety profile mainly relies on its on-target, off-tumor (OTOT) activity or off-target toxicity. These unwanted toxicities were carefully circumvented via preclinical investigations and optimizing target selection in the most recent clinical trials. Side effects commonly associated with ACT include cytokine release syndrome (CRS) and immune effector cell-associated neurotoxicity syndrome, which were found to be milder in association with the TCR-T as compared to CAR-T. In general, TCR-T-associated side effects were found to be better tolerated because of recent developments, thus a higher tolerable dosage can be administered to ameliorate effectiveness (Ma et al., 2024). As compared to ACTs, the benefits of using TCR-T in vivo have been validated via exploring clinical and pre-clinical data in terms of the mechanism of action. When aimed at the same target, synthetic TCRs and antigen receptors showed earlier and improved tumor infiltration than CAR-T, which was found to be linked with enhanced antitumor effectiveness at the preclinical level (Liu et al., 2021). However, there is a lack of clinical data in terms of direct comparisons of TCR-Ts with ACTs (Ma et al., 2024).

Indeed, iPSCs have been identified as a promising source of engineered off-the-shelf allogeneic cell therapies because of their ability for clonal selection following genetic modification, comparatively easier genetic engineering, unlimited expansion capacities, and removal of the necessity to collect cells from a donor at any given time (Zhu et al., 2018; Yamanaka, 2020; Zhou et al., 2022). Over the past decade, iPSCs technology has progressed substantially and demonstrated its application in malignant solid tumors. It has been observed that iPSCs obtained from readily available cells have the ability to expand indefinitely and can also differentiate into all specialised cell types, which can provide an unlimited and strong source for the generation of differentiated cells. Moreover, iPSCs obtained from individuals with an inherited predisposition towards cancer development might mimic the early stage of tumor development and can facilitate the understanding of tumor progression (He et al., 2023).

There is a growing interest in cancer cells reprogramming into iPSCs for resetting the identification of malignant cells without modifying the cell genome sequence. Various studies have already induced the transformation of malignant solid tumor cells, such as low-grade gliomas (Liu et al., 2019), sarcoma (Zhang et al., 2013), prostate cancer (Zhang et al., 2020b), lung cancer (Mahalingam et al., 2012), and human germ cell tumors (Taguchi et al., 2021), into a pluripotent state via utilizing targeted transcription factors. This iPSC technology has confirmed the capacity to markedly decrease the tumorigenicity of the original parental cancer cells (He et al., 2023). It has also been revealed that solid tumor cells are flexible, thus the cells can be reprogrammed by utilizing iPSCs technology to reverse the malignant tumor phenotypes. Furthermore, this technology has motivated novel approaches in the treatment of malignant tumor (He et al., 2023).

In the past few decades, CAR-T cell-based therapies have revolutionized cancer therapy, since they are capable of producing durable and effective clinical responses (June et al., 2018). It is now well-known that CARs are engineered synthetic receptors that can redirect T cells to detect and eradicate the cells that express targeted antigens (Sterner and Sterner, 2021). There are 3 major functional domains present in the CAR structure including the intracellular domain, transmembrane domain, and extracellular domain (Figure 1). An intracellular domain containing only CD3ζ is present in first-generation CARs, while they lack co-stimulatory signals (Lindner et al., 2020). In contrast, a co-stimulatory domain like CD28 or 4-1BB is present in second-generation CARs, while 2 or more co-stimulatory domains are involved in third-generation CARs. On the other hand, the fourth-generation CARs were developed as per the second-generation CAR, which includes expressions of certain cytokines. Finally, co-stimulatory domains activating various other signalling cascades are incorporated in the fifth-generation CARs (Chen et al., 2024).

The use of CAR-T is well-established in cancer treatment, thus the use of CAR engineering to alter other types of immune cells has greatly motivated researchers (Figure 2). In the case of solid tumors, most of the earlier phase clinical trials utilized second-generation CAR T-cell-based therapies, however limited antitumor properties were observed as compared to what was observed in blood cancers (Srour and Akin, 2023). Therefore, two costimulatory domains were incorporated in third-generation CARs to enhance the antitumor properties (Sadelain et al., 2013). Remarkable outcomes obtained with CAR T-cell-based therapies in blood cancers encouraged an expectation for similar outcomes in the case of solid tumors. A growing number of preclinical and clinical studies over the past few years have explored the mechanisms and applications of CAR T-cells in the case of solid tumors (Dhaliwal et al., 2024). Even though their effectiveness in solid tumor treatment is yet to be demonstrated, numerous tumor-linked neoantigens and antigens have been detected as potential targets (Keshavarz et al., 2022).

TIL therapy is an outstanding immunotherapeutic approach, which provides prospects for the management of difficult cancers (Hong et al., 2024). TILs are mononuclear cells that occur naturally and infiltrate the solid TME, which play roles as part of the broader group of immune cells at the sites of tumors (Savas et al., 2016; Mohammad Hossein et al., 2022). In the case of TIL therapy, lymphocytes are extracted from a tumor and then expanded outside of the body (ex vivo), which are then reintroduced to improve immune responses against tumor cells (Betof Warner et al., 2024). TILs efficiently eradicate cancer cells and have less chance to cause injury to normal cells, offering greater therapeutic potential with fewer side effects, therefore they have superior therapeutic properties along with lesser side effects (Hong et al., 2024). In humans, the first use of TIL therapy resulted in a 60% regression in the case of metastatic melanoma (Dhaliwal et al., 2024).

Solid tumors were found to be highly heterogeneous and they often do not contain an ideal tumor marker, notwithstanding blood cancers along with lineage-specific markers (Roshandel et al., 2021; Wang et al., 2021). Interestingly, TILs are polyclonal cells containing various receptors thus able to detect multiple tumor-associated antigens, therefore TILs as genetically-modified immune cells show superiority in the treatment of solid tumors. Immune escape and heterogeneity of tumors can be overcome by TILs, which can offer better clinical responses as compared to CAR-T cell-based therapies in the treatment of solid tumors with greater mutation rates, for example, melanoma (Titov et al., 2021). In addition, within the TME, TILs show greater tumor-specificity and have the capacity to target even unknown tumor neoantigens, which removes the need for previous understanding regarding major histocompatibility complex (MHC) restriction or tumor-associated antigens (Fernandez-Poma et al., 2017).

Stromal TILs (sTILs) and intratumoral TILs (iTILs) are the major types of TILs. It has been observed that sTILs are easily detectable and commonly found in the tumor stroma, while iTILs are rarely found in tumor cell clusters thus their identification process is complex (Savas et al., 2016). Most of the TILs are effector memory T cells that show high effectiveness in antitumor properties and proliferation, which are activated by tumor-associated antigens in vivo and can also proliferate in vitro up to 10⁵ times. Since TILs have the capacity to infiltrate TME, thus they contain chemokine receptors that are required for migration toward the TME following administration (Fernandez-Poma et al., 2017). Lower off-target toxicity is another advantage provided by TILs as compared to CAR-T cells, which perhaps owing to the negative selection of TCRs during T cell maturation (Wang et al., 2021).

MSCs are self-renewing, versatile cells that can be obtained from various sources, for example, bone marrow, amniotic fluid, adipose tissue, and umbilical cord (Zhang et al., 2020a). MSCs has shown promising outcomes in cancer immunotherapy via providing oncolytic immunotherapy and increasing CAR-T cell activities, thus being able to exert substantial antitumor actions. Exosomes derived from MSCs might possess similar properties (Hombach et al., 2020). Nonetheless, varying research outcomes have been observed regarding the capacity of MSCs to modify CAR-associated products. Perplexingly, the role of MSCs has also been indicated in mediating metastasis and tumor growth in certain scenarios (Holthof et al., 2021). MSCs are currently being investigated as a delivery vehicle for various therapies including oncolytic viruses (Zhu et al., 2017) and tumor necrosis factor (TNF)-related apoptosis-inducing ligands (Shaik Fakiruddin et al., 2018).

Former studies involving tumors and MSCs were mainly associated with the exploration of the effects of naive (unmodified) MSCs (N-MSCs) on tumors. It has been observed that N-MSCs can be isolated from various natural tissue sources and can be homed to tumors to efficiently target the TME and assess their uses as antitumor agents. In addition to this, N-MSCs can be co-cultured with in vitro tumor cells, which may suppress the proliferation of tumor cells (Shams et al., 2023). In a study, it was confirmed that N-MSCs may avert in vitro proliferation of solid tumors and leukemia cell lines (Ramasamy et al., 2007). Furthermore, the suppressive effect of N-MSCs was found to be dose-dependent, and the suppression rate was decreased at higher proportions of N-MSCs (Ramasamy et al., 2007). Future studies should optimize their engineering, clarify the contribution of MSCs in tumor growth, and explore them as part of combination therapies (D’Avanzo et al., 2024).

Unlike T cells, NK cells have the capacity to detect and target various abnormal or stressed cells without preceding sensitization, such as metastatic and MHC-I-deficient tumor cells (Laskowski et al., 2022). In recent times, NK cell engagers have markedly advanced NK cell therapy, which can direct NK cells precisely to tumors (Vivier et al., 2024). Methods on ex vivo cytokine induction are also utilized to increase NK cell activities and offer a memory-like phenotype, such as feeder cell approaches by utilizing soluble IL-12, -15, and −18 and membrane-bound IL-15 (Terrén et al., 2022). In the case of solid tumors, there is a high chance of the occurrence of abnormal tumor vasculature, where solid stress caused by the growing tumor may compress tumor vasculature to reduce blood flow into the tumor bed (Figure 3) (Portillo et al., 2023). Another drawback of using NK cell-based therapies is the shorter duration, which can decrease their long-term therapeutic effectiveness and might necessitate repeated administrations (Terrén et al., 2022).

Furthermore, the therapeutic effectiveness of NK cells is largely determined by their sources, where functional heterogeneity can influence clinical outcomes. In recent times, NK cells derived from cord blood have indicated this issue, which confirmed that a higher level of effector-related genes is present in NK cells derived from optimal cord blood units (CBUs) and showed enhanced activities than NK cells derived from suboptimal CBUs (Marin et al., 2024). Still, there is a debate regarding the requirement for conditioning regimens in the case of allogeneic NK cell therapies, therefore more clinical trials are needed to elucidate their requirement (Kerbauy et al., 2021). More studies are also essential to improve the trafficking of NK cells, effector capacity, and metabolic profiles (Laskowski et al., 2022; Berrien-Elliott et al., 2023; Marin et al., 2024). Other important areas that need to be considered include maintaining cell viability after cryopreservation and the development of a scalable manufacturing process. Along with CAR-NK cell therapy, novel approaches are also emerging, for example, the combination of a bispecific CD30/CD16 antibody along with blood-derived NK cells and cytokine-activated cord blood (Kerbauy et al., 2021).

Cytokine-induced killer (CIK) cells also have already demonstrated their effectiveness and an outstanding safety profile in several clinical trials, even across HLA barriers in an allogeneic setting (Magnani et al., 2020; Wu and Schmidt-Wolf, 2022). CIK cells showed strong anti-tumor ability against several solid and hematological malignancies (Sharma et al., 2024). In addition to this, CIK cells show a heterogenous T cell population with a mixed NK cell phenotype and combine adaptive T cell-mediated with MHC-unrestricted functions of the innate immune system (Moser et al., 2025). CIK cells were found to be compatible with nearly all kinds of immune checkpoint inhibitors, epigenetic drugs, and CAR-CIK therapy. It has been reported that CAR-CIK therapy is at least as effective as CAR-T cells. In addition, CAR-CIK therapy has favorable allogeneic applicability and a safety profile (Moser et al., 2025).

Various endogenous danger signals can trigger an immune response, including fragments of dying cells and microbial products (known as pathogen-associated molecular patterns). These danger signals are detected by various immune cells (Li and Wu, 2021). Among them, DCs play a role as the major link between adaptive and innate immune responses. It has been observed that pulsing DCs with whole tumor cell lysates in vitro and in vivo can trigger therapeutic antitumor immune responses following vaccination (Rosenblatt et al., 2011). Nonetheless, there are several challenges (such as antigen loading and method optimization for DC generation) that need to be addressed before using DC-based therapies to treat solid tumors (Jung et al., 2018; Sheykhhasan et al., 2025). Interestingly, blocking suppressive molecules like PD-1, cytotoxic T-lymphocyte-associated protein 4 (CTLA-4), and programmed death-ligand 1 (PD-L1) on immune and tumor cells restored tumor-specific T cell functions (Baumeister et al., 2016; Vreeland et al., 2016). In a clinical trial, administration of a combination of radiotherapy (35 Gy) and in situ DC therapy utilizing GM-CSF in individuals with metastatic solid tumors triggered an abscopal effect in 11 of 41 participants, which was markedly greater than the abscopal effects mediated by radiotherapy alone (Golden et al., 2015).

There are several approved checkpoint inhibitors that are used in solid tumor treatments owing to their outstanding clinical outcomes such as anti-PD-L1 (avelumab, durvalumab, and atezolizumab), anti-CTLA-4 (durvalumab and ipilimumab), and anti-PD-1 (nivolumab and pembrolizumab), It has been reported that effectiveness of these checkpoint inhibitors, particularly the monoclonal antibodies that block PD-L1, usually linked with the mutational burden, expression of PD-L1 in the TME, and the number of TILs (Snyder et al., 2014; Tumeh et al., 2014; Dammeijer et al., 2017; Fennell et al., 2018; Yi et al., 2018). DC-based therapies enhance the infiltration of CD8⁺ T cells that are specific to tumors and increase the expressions of PD-1 on these TILs, which may make tumors with lower numbers of TILs receptive to anti-PD-L1 therapy (Antonios et al., 2016). Most of the DC-based clinical trials were successful in producing tumor-specific CTLs in individuals with cancers, however the activities against most solid tumors were found to be rather disappointing (Butterfield, 2013). There are several factors that can result in insufficient efficacy of DC vaccine-mediated immune responses against solid tumors. One such factor is the inadequate number of CD8⁺ CTL induction in response to DC vaccination alone (Lou et al., 2004). CTLs produced in this manner might contain suboptimal antitumor properties in vivo, perhaps because of inadequate migration or weak activation at the tumor sites. The responsiveness of such cells to host-derived regulatory processes also seems to be an issue (Jung et al., 2018).

Multiple limitations of CAR-T cell-based therapies include graft versus host disease, OTOT toxicity, immune effector cell-associated neurotoxicity syndrome, CRS, time-consuming production, and high cost (Bonifant et al., 2016; Yadav et al., 2020). In solid tumor treatment, CAR-T cell has limited effectiveness because of various reasons including high complexity of TME, incompetent homing and infiltration, limited T cell fitness, antigen escaping, and heterogeneity (Wagner et al., 2020). Macrophages have the capacity to exert various effector activities that can mediate support tumor clearance. In recent times, CAR-Ms have been generated by the genetic engineering of macrophages to express targeted proinflammatory transgenes (Brempelis et al., 2020; Gardell et al., 2020; Kaczanowska et al., 2021). CAR-M has emerged as a potential therapy and its use can prove beneficial in the solid tumor treatment (Hadiloo et al., 2023). In the case of both in vitro and in vivo studies, CAR-Ms have resulted in great results in the of solid and blood cancer treatment. Indeed, CAR-Ms were found to possess strong anti-cancer properties as compared to macrophages alone or various other macrophage-based therapies (Liu et al., 2022). Several studies demonstrated significant outcomes of cytotoxicity in the CAR-manner through multiple target antigens including CD19 (Morrissey et al., 2018), mesothelin (Anderson et al., 2022), human epidermal growth factor receptor 2 (HER2) (Klichinsky et al., 2020), transmembrane glycoprotein mucin 1 (MUC1) (Eisenberg et al., 2021), and GD2 (Zhang et al., 2023).

CAR-Ms and their killing capacity can regulate and modify the immune system and associated factors to enhance their anti-cancer properties. CAR-Ms can directly cause cytotoxicity in tumor cells (Figure 4). Macrophages activated by lipopolysaccharide were found to release various harmful substances that can cause the disintegration of tumor cells, such as nitric oxide, reactive oxygen species, and TNF (Lu et al., 2024). A number of preclinical studies of CAR M cells confirmed substantial anti-tumor properties in the case of both in vitro and in vivo studies. For instance, CAR M exerted anti-tumor properties on leukemia cells through luciferase reporter assays or ovarian cancer cell line HO8910 expressing a high level of mesothelin in vivo (Zhang et al., 2020a). On the other hand, MUC1-targeting CAR-Ms exhibited strong anti-tumor activities via phagocytosis and release of various pro-inflammatory cytokines including TNFα, IL-8, and IL-1β in the presence of MUC1 expressing tumor cells from malignant pleural effusions or solid lung tumors (Eisenberg et al., 2021). Despite their therapeutic promises, there are several limitations of CAR-Ms in terms of solid tumor treatment because of the complex TME and unique features of solid tumors. Even though CAR-Ms showed good outcomes in several preclinical studies, multiple problems were faced afterwards including cell exhaustion, the suppressive activities of TME, antigen escape, and tumor heterogeneity. Nonetheless, human cancer-associated TMEs possess a more complex scenario as compared to animal models (Kochneva et al., 2020; Toor et al., 2020).