In head and neck squamous carcinoma (HNSCC), the primary mechanism underlying tumor recurrence or metastasis lies in the interplay between PD-L1 on the surface of CD8 T lymphocytes and PD-1. This interaction weakens the cytolytic activity of CD8 T cells against tumor cells, subsequently suppressing the immune system's ability to eliminate cancer cells, leading to immune escape. Notably, immunotherapeutic approaches for HNSCC, such as nivolumab and pembrolizumab, both immune checkpoint inhibitors, are humanized IgG4 antibodies targeting programmed cell death 1 (PD-1). These agents are particularly effective for patients expressing PD-L1, as they modulate the immune response to cancer. In 2016, they were approved for the treatment of platinum-refractory recurrent and metastatic HNSCC[7, 10, 26].Recent years have witnessed significant advances in verifying the immunogenicity of HNSCC and the development of related immunosuppressive agents. These novel agents boast low toxicity and invasiveness while demonstrating superior efficacy[6, 8–11]. Consequently, it is essential to comprehend the present state of HNSCC research within the realm of immunity over the past decade and delve into further in-depth analysis.
Based on the current research landscape of HNSCC and its immune aspects over the last decade, we embarked on a bibliometric analysis to explore the knowledge base and structural dynamics within this domain. Employing the cutting-edge tools of Citespace and VOSviewer, we artfully evaluated the collaborative network map encompassing countries, institutions, and authors. In addition, through the analysis of the journal co-citation graph, we discerned the trajectory of knowledge transfer within the subject area. Lastly, the literature co-citation and keyword co-occurrence analyses allowed us to unravel the knowledge base, structural elements, and research hotspots pertaining to the role of immunity in HNSCC.
Over the past 11 years, HNSCC and immune-related research have gained ever-increasing academic attention, manifesting a remarkable surge in the past four years. In his seminal work, American sociologist Freeman L. (Freeman, 1979) proposed the concept of "number centrality" (betweenness centrality) as a metric to gauge the centrality of a node relative to others in a graph. This measure primarily assesses the bridge function of a node within the entire network structure, thus evaluating its influential position among the set of nodes[27, 28].
Henceforth, the United States, China, and Germany have ascended as the top three prolific nations. From our data analysis, it emerges that the United States holds the highest centrality. Following the United States, the United Kingdom, Italy, Japan, and Spain shine on the stage of significance. However, China, despite securing the second position in the number of publications, lacks centrality, possibly due to the plethora of standalone publications in the country.
Delving deeper into the scientific contributions and collaborative network map, we find that among the top ten institutions in terms of publications, six hail from the United States and four from China. The University of Pittsburgh in the United States embarked on research early on, boasting the highest number of publications (n = 89), and exhibiting profound collaborations with diverse institutions, thus radiating its strong centrality (c = 0.17). Similarly, Shanghai Jiao Tong University, despite ranking fifth in the number of articles (38), exhibits commendable centrality (c = 0.16). In contrast, Sun Yat-sen University from China possesses the second-highest number of publications (58), but its research centrality remains relatively low (c = 0.08). To enhance its collaborative ties with other institutions worldwide, fostering cooperation would be judicious.
Shifting our gaze to the scientific contributions and cooperative network map, we discern that Ferris and Robert L occupy the forefront with the largest number of posts (n = 53), followed by Sun, Zhi-Jun (n = 23), Zhang, Wen-Feng (n = 19), Deng, Wei-Wei (n = 18), and Uppaluri, Ravindra (n = 18). However, among these five esteemed authors, only Ferris, Robert L commands a centrality value greater than 0.1 (c = 0.24), emblematic of their research's bridging effect and significant influence across the field. The high quality of their work and their emphasis on cooperation with others contribute to this distinction. On the contrary, the remaining four authors exhibit low centrality, indicative of their relatively independent stance, possibly lacking in communication and cooperation.
An interesting observation is the notable centrality (c = 0.1) of Thomas K. Hoffmann, despite not being within the top five in terms of publications. Such high centrality reflects the constructive impact and influence of his research on related investigations across the entire research landscape. Our investigation has illuminated that the top 10 most active journals account for approximately one-third (31.32%) of the total publications in this domain, indicating a notable concentration of research endeavors within this cluster. Notably, the journal "CANCERS" takes the lead with the highest number of publications (110), while "CLIN CANCER RES" emerges as the most cited, as corroborated by the double graph superposition analysis. This recurrent citation pattern pertains to papers published in journals classified under the purview of molecular/biology/genetics and molecular/biology/immunology/medicine/medical/clinical, accentuating the prevailing research focus on the molecular biology and clinical medicine aspects of immunity in HNSCC.
Of noteworthy significance, the majority of journals within the top 10 rankings for both publications (80%) and citations (90%) boast an impressive impact factor (IF > 5). Such a trend underscores the substantial academic contributions and research achievements associated with these journals. Moreover, it serves as a testament to the elevated research quality in the realm of HNSCC immune-related investigations. The analysis of co-cited authors unveils influential figures within specific fields and brings to light their frequently co-cited papers[23]. Among all the co-cited authors, two luminaries have garnered over 400 citations each: FERRIS RL (n = 730) and SEIWERT TY (n = 404). However, upon closer examination, it becomes apparent that only FERRIS RL enjoys a high centrality (c = 0.1). FERRIS RL and his team are actively engaged in unraveling the roles of immunosuppressive molecules, such as immune checkpoint receptors like PD-1[29–32], CTLA-4[33], and TIM-3[34–37], as well as investigating the intricacies of the immune microenvironment in personalized cancer immunotherapy[38–40]. In parallel, they keenly focus on the clinical application of immunization in HNSCC[8, 26, 41, 42]. Notably, alongside conducting relevant clinical trials, FERRIS RL provides consensus suggestions for emerging immunotherapy[43], thereby not only enlightening clinicians on the potential of immunotherapy in HNSCC but also contributing to the standardization of immunotherapeutic approaches in this domain. Our co-cited literature analysis reveals the remarkable frequency of citations for FERRIS RL papers within this research domain, a fact further substantiated by the co-cited author analysis. Through literature co-citation analysis, we have successfully identified the most influential works in immune-related studies of HNSCC[44]. Among the top 10 cited articles, two notable ones, authored by Ferris and Robert L, stand as randomized clinical studies investigating the effects of navuzumab in the treatment of HNSCC[8, 26].Simultaneously, the chronicle presentation of the topic classification within the co-cited literature aids us in gaining a deeper understanding of the research trends (Fig. 7F). Evidently, the research focal points have undergone a gradual shift, evolving from "premalignant" and "warburg effect" to encompass "cupropotosis", "prognosis", "metastatic", "radiotherapy", "exosomes", "tumor-infiltrating lymphocytes", and other intriguing facets. Our quest for knowledge continues as we delve into the research hotspots and frontiers of HNSCC immunity through keyword co-occurrence analysis. This analysis represents a profound extension and expansion of the aforementioned hotspots. Unlike co-citation analysis, keyword co-occurrence analysis unveils novel terminologies that may emerge as hotspots in future research endeavors.
The keywords "open label" (n = 208), "t cell" (n = 200), "t cell" (n = 200), "immunotherapy" (n = 185), and "tumor microenvironment" (n = 160) have emerged as prominent focal points in the realm of research. The co-occurrence of terms such as "t-cells" and "regulatory t cell" signifies their early prominence, indicating that they were the subjects of intense investigation in the initial stages. On the other hand, keywords like "tumor microenvironment", "open label", "immunotherapy", "immune checkpoint inhibitor", "pembrolizumab", and "nivolumab" have prominently emerged in recent years, suggesting their significance as potential future research areas. Furthermore, while the keywords "immune infiltration" (n = 26), "prognostic signature" (n = 18), "prognostic factor" (n = 14), and "durvalumab" (n = 11) exhibit a lower frequency of co-occurrence, they have gained considerable traction after the year 2021.
The fundamental constituents comprising the Tumor Microenvironment (TME) in Head and Neck Squamous Cell Carcinoma (HNSCC) encompass an array of intricate cellular elements, including immune cells, fibroblasts, mesenchymal cells, hematopoietic and bone marrow-derived cells, vascular endothelial cells, and nerves[45, 46]. Notably, among these cellular components, T cells occupy a position of paramount significance within the TME. They primarily consist of CD4 and CD8 T lymphocytes, each with unique roles, wherein CD4 T cells exhibit the potential for further differentiation into regulatory T (Treg) and helper T (Th) cells. Of particular importance, cytotoxic CD8 T lymphocytes, endowed with the remarkable ability to recognize and dismantle tumor cells, play a pivotal role in exerting profound antitumor activities[47].
Th cells, through their orchestration of intricate molecular interactions, serve as potent promoters of the anti-tumor prowess exhibited by CD8 T cells, bestowing upon them a harmonious synergy in their mission against malignancy[48]. On the other hand, Treg cells, though wielding their own significance, present a contrasting role as they manifest an inhibitory influence on the immune response within the Tumor Microenvironment (TME).In the intricately woven fabric of the TME, immune checkpoint receptors emerge as pivotal players, holding the delicate balance between controlling the immune system, curbing autoimmunity, and finely regulating the inflammatory responses. Remarkably, the activation of immune checkpoint receptors on CD8 T cells exerts a multifaceted impact, tempering their potent tumor-inhibitory capabilities[49–51].
At present, LAG-3, CTLA-4, TIM-3, and PD-1 stand as eminent immune checkpoint receptors, gracefully gracing the surface of CD8 T cells. The enchanting interplay of PD1/PDL1 has been the focus of in-depth investigations in the realm of HNSCC. Admirably, navulumumab and pabolizumab, enchanting as the most studied immune checkpoint inhibitors, embark on a profound journey, targeting the exquisite PD/PD-L1 pathway. Alas, as they navigate this path, they unravel the delicate balance within CD8 T cells, evoking both admiration and concern, as they bestow upon them the gift of hyperactivation, which at once infuses them with profound potential and yet, at the same time, gently attenuates their anti-tumor ardor[52].In the realm of immune cells, LAG-3 takes its place with dignity and grace, adorning the noble NK cells, the esteemed CD4 and CD8 T lymphocytes, the virtuous B lymphocytes, and the wise DC. The expression of LAG-3 on Treg is a symphony of elegance, elevating their function to greater heights, while the gentle act of blocking its expression, like a soft breeze, gently diminishes Treg numbers, allowing the radiant CD8 T cells to ascend in their splendor and embrace the stage of enhanced antitumor effects[53].In the realm of immune cells, TIM-3 graces the NK cells and T lymphocytes with its presence. In the captivating AML mouse model, the union of CD M-3 with PD-1[54] accentuated the presence of CD8 T cells, bearing the hallmarks of PD-1 and TIM-3, in HNSCC patients undergoing cetuximab monotherapy. Alas, this union seemed to cast a shadow upon the efficacy of cetuximab treatment, perhaps stemming from the subtle induction of immune tolerance[55].In the days to come, the limelight shall continue to grace the PD-1 / PD-L1 pathway, along with its companion immune checkpoint inhibitors[56]. The union of immune checkpoint inhibitors with chemotherapy, radiotherapy, and surgical interventions in clinical research shall gain ever-increasing popularity[57]. Moreover, the quest for hitherto undiscovered immune checkpoints and their translation from fundamental research to clinical practice shall emerge as a scintillating hotspot within this domain. Nonetheless, as chemotherapy and immunotherapy exert their influence on the tumor microenvironment, a more profound investigation of the TME shall be required to elucidate the intricate biological landscape of HNSCC. In this vein, I anticipate that exploring the TME shall serve as one of the frontiers and hotspots in the future of HNSCC immunization research[58].