Helicobacter pylori reversing the landscape of neoadjuvant immunotherapy for microsatellite stable gastric cancer: a multicenter cohort study

Abstract

Background

Microsatellite stable (MSS) gastric cancer (GC) is largely unresponsive to immunotherapy, presenting a persistent and formidable challenge in the field. Patients with advanced GC and Helicobacter pylori (H. pylori) infection have shown benefits from immunotherapy. However, it remains unreported whether neoadjuvant immunotherapy is beneficial for H. pylori-positive MSS GC patients.

Methods

This retrospective cohort study analyzed data from GC patients treated at three medical centers in China between January 1, 2014, and July 1, 2024. Patients with gastric adenocarcinoma or adenocarcinoma of the gastroesophageal junction underwent testing for H. pylori infection prior to receiving neoadjuvant therapy.

Results

In this retrospective analysis, those positive for H. pylori had a higher objective response rate of 63.77% (95% CI, 51.98–74.11%) compared to 47.73% (95% CI, 39.39–56.19%) in H. pylori-negative patients. Pathological complete remission was higher in H. pylori-positive patients at 17.39% (95% CI, 10.24–27.98%) versus 15.91% (95% CI, 10.65–23.10%). Logistic regression analysis revealed a strong correlation between H. pylori positivity and increased objective remission rate (P = 0.031, OR = 1.928, 95% CI 1.06–3.51). In H. pylori-positive MSS GC patients receiving neoadjuvant immunotherapy pCR rates can reach 27.27% (95% CI, 15.07–44.21%), much higher than the 8.33% (95% CI, 2.87–21.82%) in neoadjuvant chemotherapy patients. Survival analysis showed a 3-year OS rate of 74.2% (95% CI, 56.75–86.30%) in the H. pylori-positive group and 64.3% (95% CI, 51.20–75.55%) in the H. pylori-negative group, and the hazard ratio (HR) of these two groups was 0.50 (95% CI, 0.28–0.87; P <.001). Multivariable analysis for OS further showed the survival benefit of H. pylori, with HRs of 0.51 (95% CI, 0.29–0.91; P = 0.02).

Conclusions

H. pylori infection has emerged as a favorable factor for neoadjuvant immunotherapy in MSS GC, underscoring the importance of considering H. pylori status in preoperative treatment strategies.

Background

MSS GC accounts for approximately 90% of advanced GC [1]. Unlike tumors with high microsatellite instability (MSI-H), MSS GC is largely unresponsive to immunotherapy[2–5]. In the neoadjuvant therapy, immune checkpoint blockade (ICB) has emerged as one of the effective strategies for treating malignancies. By inhibiting immune checkpoints, ICB aims to restore T-cell function and stimulate antitumor immunity[6]. However, only a subset of GC patients derive benefit from this approach. The efficacy of immunotherapy for MSS GC has been limited.

While the role of H. pylori in GC has been extensively studied, its impact on treatment remains to be explored. Recent studies have suggested that H. pylori infection can shape a “hot” tumor microenvironment, thereby becoming a favorable factor for immunotherapy in GC [7]. Meanwhile, there is a close association between H. pylori infection and the expression of PD-L1 in GC patients [8]. These revealed a previously unknown protective effect of H. pylori infection on immunotherapy for GC.

However, the relationship between H. pylori status and response to neoadjuvant therapy in GC patients has not been thoroughly investigated. Exploring the relationship could have significant implications for treatment strategies and patients’ outcomes. Based on previous reports, we hypothesized that H. pylori infection might influence the treatment outcomes of neoadjuvant therapy in GC. To test this hypothesis, our study aimed to explore the relationship between H. pylori infection status and the efficacy of neoadjuvant treatment through a retrospective analysis.

Methods

Patients

We retrospectively analyzed data from GC patients at the Cancer Hospital Chinese Academy of Medical Sciences, Tianjin Medical University Cancer Institute & Hospital, The Second Affiliated Hospital Zhejiang University School of Medicine, between January 1, 2014, and July 1, 2024. Eligible patients met the inclusion criteria: (1) diagnosis of gastric adenocarcinoma confirmed by enhanced CT, gastroscopy, and pathological biopsy; (2) curative gastrectomy and D2 lymphadenectomy after neoadjuvant therapy for GC; (3) age ≥ 18 years (4) H. pylori infection status was clarified before neoadjuvant therapy; (5) clinical T3 - 4 N + M0 gastric adenocarcinoma. The exclusion criteria are (1) preoperative radiotherapy or interventional procedures and (2) uncertain H. pylori status.

A total of 201 cases meeting the above criteria were included in the research. Patients were categorized into H. pylori-positive and negative groups based on their pre-treatment H. pylori testing status. We collected comprehensive demographic and clinicopathologic data, including age, gender, blood type, comorbidities (hypertension, diabetes), body mass index (BMI), smoking and alcohol consumption history, family history, tumor sites, histologic grade, Lauren classification, lymph node metastasis, MSI/MSS and ypTNM staging, Her- 2 expression, maximum tumor diameter, surgical details (type of gastrectomy and anastomosis), and neoadjuvant therapy specifics (regimens, cycles and complications), was evaluated according to the eighth edition of the American Joint Committee on Cancer’s Cancer Staging Manual [9]. In addition, neoadjuvant immunotherapy indicates whether the patient received a PD- 1/PD-L1 inhibitor during neoadjuvant chemotherapy.

Evaluation of H. pylori infection status

All patients enrolled in the study underwent histologic examination with Giemsa staining method, ¹³C urea breath test, or a rapid urease test to determine their H. pylori infection status before neoadjuvant therapy. Positive H. pylori status was defined as a history of previous prior or active infection prior to neoadjuvant therapy ¹³C-urea breath test, H. pylori stool antigen tests, and/or histopathological findings from medical records, endoscopic procedures, and pathology reports. Negative H. pylori status was defined as a definitively negative test for infection by at least one of the above tests prior to neoadjuvant therapy. Patients with unknown H. pylori test results or not clearly stated in the electronic medical record were excluded.

Pathological assessments

Radiological response is assessed by the local radiologist using RECIST (version 1.1), based on CT or MRI findings according to the number of lesions and the short axis of the target lymph node, including complete remission (CR), partial remission (PR), stable disease (SD) and progressive disease (PD)[10]. The objective remission rate (ORR) was defined as the sum of the proportion of patients with CR and PR. Pathological response assessment Surgical specimens were stained with hematoxylin and eosin and analyzed by the pathologist for the percentage of residual live tumor cells in the tumor bed. Pathological complete remission (pCR) was defined as the absence of live tumor cells. Major pathological response (MPR) was defined as no more than 10% live tumor cells [11]. In addition, tumor regression was classified using the Mandard Tumor Regression Grading (TRG) system, which includes the following categories: TRG 1 (complete tumor regression), TRG 2 (dispersed tumor cells within fibrosis), TRG 3 (predominantly fibrotic tumor cells and fibrosis), TRG 4 (predominantly tumor cell-based tumor cells and fibrosis), and TRG 5 (no tumor regression) [12,13,14]. Patients were divided into three groups: major histopathological response (MjHR) defined as TRG 1–2, partial histopathological response (PHR) defined as TRG 3, and no histological response (NHR) defined as TRG 4–5 [15].

Patient follow-up and outcome

Patients are regularly followed up for review every 3 to 6 months for 2 years and every 6 months for 3 to 5 years after surgery. The main follow-up examinations included physical examination, measurement of tumor markers, computed tomography scanning, ultrasonography, and endoscopy to observe whether the tumor had recurred and metastasized. The median follow-up time in this study was 34 months (interquartile range 18–57). The primary endpoint was OS, defined as the time from the date of neoadjuvant therapy to death from any cause. The last follow-up date for patients in our study was 1 October 2024.

Data analysis

All statistical analyses were performed using GraphPad Prism 9 software (GraphPad Software, San Diego, CA), IBM SPSS Statistics version 27.0, and R version 4.3.2. Descriptive statistics were presented as means with standard deviations for continuous variables, and frequencies with percentages for categorical variables. A two-sided p-value < 0.05 was considered as statistically significant. Patients were stratified based on H. pylori infection status, neoadjuvant therapy regimens, and pathological and radiological assessment results. Group differences were examined using the chi-square test. To analyze factors influencing neoadjuvant therapy outcomes in GC patients, we conducted stepwise univariate and multivariate logistic regression. Furthermore, we performed subgroup analyses based on patient characteristics and generated forest plots to further investigate the relationship between H. pylori infection and neoadjuvant therapy prognosis. Kaplan–Meier analysis was used to generate the survival curves, and log-rank tests were used to compare the survival differences between the H. pylori-positive and H. pylori-negative groups. To ensure reliable results and to control for potential confounding variables, we used univariate and multivariate Cox proportional risk models to calculate hazard ratios (HRs) and 95% confidence intervals (CIs) for OS of H. pylori infection status. An interaction term between H. pylori status and treatment modality was included in the Cox proportional hazards model to assess its impact on OS and pCR. All statistical analyses were 2-sided, with P < 0.05 considered statistically significant.

Results

Patient characteristics

This study included 201 GC patients who received neoadjuvant therapy (Fig. 1), of which 132 (65.7%) patients were negative for H. pylori and 69(34.3%) were positive (median (IQR) age of the patients was 61 (53–67) years, 45 (22.3%) female and 156 (77.6%) male). The median weight (IQR) index score for neoadjuvant GC patients was 22.9 (20.3–25.6) (calculated as weight in kilograms divided by height in meters squared) (Additional file 1: Table 1). In addition, patients were treated with a variety of neoadjuvant chemotherapy regimens. Detailed protocols for neoadjuvant immunotherapy and neoadjuvant chemotherapy are provided (Additional file 1: Table 2 and Table 3). The average duration of neoadjuvant therapy was 3.7 cycles, with 62 (30.9%) patients experiencing adverse reactions and 98 (48.8%) patients underwent distal gastrectomy. Postoperatively, 83 (41.0%) patients were pathologically diagnosed with ypTNM stage III disease. Histologic grading showed that 135 (67.2%) patients were poorly differentiated, and the intestinal type was predominant in 63 (31.3%) patients according to the Lauren classification. Assessment of treatment efficacy using the Mandard criteria for TRG revealed the following distribution: 68 (33.8%) patients in TRG grades 1 and 2, 64 (31.8%) in TRG grade 3, and 69 (34.3%) in TRG grades 4 and 5 (Fig. 2). The objective remission rate showed that 107 (53.2%) patients achieved CR or PR, 94 (46.8%) achieved SD or PD. Furthermore, 33 (16.4%) patients achieved pCR, and 66 (32.8%) achieved MPR, signifying a substantial treatment response in a subset of the study population.

Fig. 1

Flowchart of Patients inclusion and exclusion. Patients with pathologically diagnosed gastric adenocarcinoma or adenocarcinoma of the esophagogastric junction, who underwent neoadjuvant therapy and radical gastrectomy, and who were tested for ah status of Helicobacter pylori infection prior to treatment during the period January 1, 2014, to July 1, 2024, were included in the study

Fig. 2

Changes in five Helicobacter pylori-positive GC patients before and after neoadjuvant therapy from TRG 1–5, respectively

Analysis of treatment outcomes in different subgroups of patient

In this study, we conducted an in-depth analysis of the impact of H. pylori infection status on the efficacy of neoadjuvant therapy. By stratifying patients according to their H. pylori infection status, we observed significant differences in treatment response (Table 1). H. pylori-positive patients achieved a significantly higher objective remission rate of 63.8% (44/69) compared to 47.7% (63/132) in H. pylori-negative patients (p = 0.043) (Additional file 1: Table 4). In terms of pCR, 17.4% (12/69) of patients in the H. pylori-positive group achieved pCR, compared to 15.9% (21/132) in the uninfected group. Additionally, we analyzed the relationship between H. pylori status and other clinical variables. The results showed no significant association between these factors and the relationship between H. pylori status and treatment outcomes, thus excluding the potential for confounding. In the subgroup analysis of MPR and pCR (Additional file 1: Table 5), we found that patients with poorly differentiated, lymph node metastasis, and HER- 2-positive GC had significantly lower MPR and pCR rates (P < 0.001). Thus, ypTNM staging was in stage I MPR and pCR rates were higher than stage II and III. (P < 0.001). Grouped according to the neoadjuvant regimen (Additional file 1: Table 6), the MPR and pCR rates were found to be significantly higher in the neoadjuvant immunization group at 44.2% (38/86) and 24.4% (21/86) than in the neoadjuvant chemotherapy group at 24.4% (28/115) and 10.4% (12/115) (Additional file 1: Table 7). Among the 86 patients receiving neoadjuvant immunotherapy, H. pylori-positive patients achieved CR or PR in 63.6% (21/33) of objective remission rate, significantly higher than 49.1% (26/53) of H. pylori-negative patients (Table 2).

Table 1 Demographic, clinical and pathological characteristics of 201 patients undergoing neoadjuvant therapy for GC by Helicobacter pylori infection status

Table 2 Treatment response and pathological staging in Helicobacter pylori–stratified neoadjuvant immunotherapy and chemotherapy patients

In our analysis of prognostic factors associated with MPR, pCR, and objective remission rate using logistic regression models, we identified several significant predictors. H. pylori infection status was also associated with objective remission rate, with positive infection status associated with increased odds of objective remission rate (P = 0.031, OR = 1.93, 95% CI, 1.06–3.51) (Fig. 3). For MPR, univariable and multivariable logistic regression revealed that tumor maximum diameter of 4 cm or less was significantly associated with higher odds of MPR (P = 0.019, OR = 2.17, 95% CI 1.14–4.15), as was the absence of lymph node transfer (P < 0.001, OR = 0.118, 95% CI 0.056–0.245) and negative Her2 expression (P < 0.001, OR = 0.178, 95% CI 0.079–0.401) in multivariable analysis (Additional file 1: Fig. S1). For pCR, lymph node metastasis (P < 0.001, OR = 0.02, 95% CI 0.00–0.18) and Her2 expression (P = 0.021, OR, 0.10, 95% CI 0.02–0.44) were the most significant predictors in multivariate analyses, and a positive lymph node and Her2 expression were associated with reduced odds of pCR. Chemotherapy was associated with reduced odds of pCR compared with chemoimmunotherapy regimens (P = 0.010, OR = 0.36, 95% CI 0.17–0.78) (Additional file 1: Fig. S2). In the analysis of objective remission rate, the presence of adverse reactions to treatment was associated with reduced odds of objective remission rate (P = 0.033, OR = 0.52, 95% CI 0.28–0.95), while positive H. pylori infection status was associated with increased odds of objective remission rate (P = 0.031, OR = 1.93, 95% CI 1.06–3.51) (Fig. 3).

Fig. 3

Univariate and multivariate logistic regression analysis of ORR and clinical baseline indicators after neoadjuvant therapy in 201 GC patients

Survival analysis of patients in different subgroups

We performed survival analyses to compare the overall survival (OS) of GC patients in the H. pylori-positive and negative groups before neoadjuvant therapy (Fig. 4A). Survival analysis showed a 3-year OS rate of 74.2% (95% CI, 56.75–86.30%) in the H. pylori-positive group and 64.3% (95% CI, 51.20–75.55%) in the H. pylori-negative group, and the hazard ratio (HR) of these 2 groups was 0.50 (95% CI, 0.28–0.87; P < 0.001). Next, we analyzed the OS by subgroups (Additional file 1: Fig. S1). In most subgroups, HER- 2 presence or absence of expression in the H. pylori-negative versus positive group was consistent, as well as in the neoadjuvant treatment cycle and maximum tumor diameter (Additional file 1: Fig. S3). Meanwhile, patients were categorized into two groups based on whether or not they had previously received H. pylori eradication therapy, and there were no significant differences in the primary outcomes between the two groups (HR = 1.07, 95% CI 0.67–1.73, P = 0.80) (Additional file 1: Fig. S4). Multivariable analysis for OS further showed the survival benefit of H. pylori, with HRs of 0.51 (95% CI, 0.29–0.91; P = 0.02). Meanwhile, we performed OS analysis for the presence or absence of postoperative lymph node metastasis (Fig. 4B) and found a marked difference between the two groups (HR, 1.88; 95% CI, 1.13–3.12; P = 0.01). Subsequently, the absence of lymph node metastasis (HR, 0.36; 95% CI, 0.14–0.92; P = 0.03) and the objective remission rate were assessed as CR/PR (HR, 0.42; 95% CI, 0.19–0.93; P = 0.03) there was a significant benefit in the H. pylori-positive group in GC. In contrast, H. pylori infection status in GC with metastatic lymph nodes (HR, 0.78; 95% CI, 0.38–1.57; P = 0.47) and in patients with poorly assessed SD/PD (HR, 0.64; 95% CI, 0.27–1.46; P = 0.28) did not make a significant difference in OS (Fig. 4C–F). Significant differences in OS were found according to TRG subgroups (P = 0.02), with OS benefit in MjHR and PHR compared with NHR, in addition to a significant difference between H. pylori-positive and negative patients in MjHR (HR, 0.25; 95% CI, 0.07–0.99; P = 0.04) after neoadjuvant therapy. The difference was not significant in PHR (HR, 0.44; 95% CI, 0.16–1.20; P = 0.10) and NHP (HR, 0.70; 95% CI, 0.28–1.75; P = 0.44) (Fig. 5A–D). In terms of ypTNM staging, we found that the difference in OS (HR, 0.78; 95% CI, 0.27–2.41; P = 0.66) between H. pylori-positive and negative in stage I patients was not significant. However, the difference in OS (HR, 0.45; 95% CI, 0.23–0.90; P = 0.02) between these two groups was significant in stage II/III patients (Fig. 5E,F).

Fig. 4

Kaplan-Meyer analysis of overall survival in different subgroups of GC patients. A Survival analysis of the H. pylori-positive and negative groups; (B–D) survival analysis of lymph nodes with and without metastasis and different subgroups of H. pylori-positive and negative groups; (E,F)Survival analysis of the H. pylori-positive and negative groups in ypTNM staging

Fig. 5

Kaplan-Meyer analysis of overall survival in a subgroup of patients with GC in the H. pylori-positive and negative groups for indicators of tumor regression. A–D Survival analysis of the H. pylori-positive and negative groups in different subgroups of the TRG; (E,F) survival analysis of the H. pylori-positive and negative groups in different subgroups of the ORR

Prognostic factor analysis with Cox proportional hazards regression model

Univariable and multivariable analyses using the Cox proportional hazards regression model were performed. Age, sex, maximum tumor diameter, neoadjuvant therapy cycle, Her- 2 expression status, and neoadjuvant therapy regimen were not significantly associated with one-way and multifactorial OS. However, for the presence of H. pylori infection during type-adjuvant therapy was independently associated with unifactorial (HR, 0.50; 95% CI, 0.28–0.87; P = 0.015) and multifactorial (HR, 0.51; 95% CI, 0.29–0.91; P = 0.021) factors for OS (Additional file 1: Table 8). To evaluate potential effect modification, we assessed the interaction between H. pylori infection status and therapeutic regimen in relation to OS and pCR. No statistically significant interaction effects were observed for either OS (P for interaction = 0.474) or pCR (P for interaction = 0.492) (Additional file 1: Table 9 and Table 10).

Discussion

GC can be divided into two immunologically distinct subtypes [2]. The microsatellite instability (MSI) phenotype is associated with a high mutation burden and significant T-cell infiltration, whereas the MSS phenotype is characterized by a low mutation burden and minimal T-cell infiltration [16]. The MSI subtype represents a favorable group for GC immunotherapy, while the success rate of immunotherapy in MSS GC remains limited. Notably, only about 10% of GCs are classified as MSI, with the remaining 90% being MSS, which accounts for the generally low response rate to immunotherapy among GC patients [17]. However, the study found that H. pylori-infected GC patients responded better to immunotherapy than uninfected GC patients [3].

In this retrospective analysis, we pioneered the investigation into the relationship between H. pylori infection status and the efficacy of neoadjuvant therapy in MSS GC. Our findings indicated a significant influence of H. pylori infection on the therapeutic efficacy in our cohort. Specifically, patients positive for H. pylori exhibited a substantial improvement in objective remission rate, TRG, and MPR compared with H. pylori-negative patients. Univariate logistic regression analysis confirmed the independent association of H. pylori infection with achieving an objective remission rate. Despite previous studies have shown that MSS GC is typically associated with low sensitivity to immunotherapy, we were surprised to find that H. pylori positivity group receiving neoadjuvant immunotherapy achieved a much higher MjHR and PHR than in the negative control within the cohort of GC patients with MSS status. While the observed difference in pCR rates between H. pylori-positive and negative groups was modest (17.39% vs. 15.91%), this finding may be influenced by limited statistical power due to sample size constraints. Nonetheless, the higher pCR rate in H. pylori-positive patients suggests a potential immune-primed tumor microenvironment that could be more responsive to neoadjuvant therapy. H. pylori-positive group had a longer and more beneficial OS than the negative group during neoadjuvant therapy. Cox proportional risk regression univariate and multivariate analyses showed that H. pylori was independently associated with OS. H. pylori infection may play a favorable role in treatment responsiveness, highlighting the importance of performing the H. pylori test as a part of immunotherapy for MSS GC. While H. pylori infection is associated with favorable clinical outcomes, our analysis revealed no significant interaction between H. pylori status and neoadjuvant treatment modalities in modifying therapeutic efficacy. The retrospective nature of this study and its limited cohort size may have reduced the statistical power to detect such interactions. Future investigations should integrate strain-specific virulence profiling with multi-omics characterization of the tumor microenvironment to elucidate potential mechanistic interactions between microbial factors and therapeutic agents. The underlying mechanism for this improved response may involve H. pylori-induced modification to the tumor microenvironment, subsequently influencing the outcomes of both chemotherapy and immunotherapy. Interestingly, in a study by Jia et al. [7], H. pylori-positive patients with GC treated with anti-PD- 1/PD-L1 showed superior immune-related progression-free survival (irPFS) and overall survival (irOS) compared to negative patients, with median irPFS of 6.97 months versus 5.03 months and a 4-month longer irOS. Meanwhile, they revealed a higher expression of PD-L1 and more non-exhausted CD8 T cells in the tumor microenvironment of H. pylori-infected patients. On one hand, both transcriptional and protein levels of PD-L1 are elevated in H.pylori-positive GC, resulting in higher Combined Positive Score (CPS) values. H. pylori drives immune evasion by upregulating PD-L1 through activation of NF-κB, JAK/STAT, and PI3 K/Akt signaling pathways, highlighting the potential of immunotherapy to counteract these mechanisms [4, 18]. Furthermore, the CagA virulence factor stabilizes PD-L1 via squalene epoxidase (SQLE)-mediated enhancement of palmitoylation and suppression of ubiquitination, thereby reinforcing tumor immune tolerance [19]. This suggests that ICB therapies could more effectively disrupt the PD- 1/PD-L1, thereby restoring T cell function and stimulating antitumor immunity. On the other hand, H. pylori-positive GC exhibits a"hot"tumor phenotype, characterized by enhanced immunogenicity and sensitivity to immunotherapeutic interventions. The density of non-exhausted CD8 T cells is higher in H. pylori-positive GC, indicating enhanced tumor-killing capability [20]. Chronic H. pylori infection induces a Th1-polarized immune profile characterized by cytotoxic T-cell activation and antitumor effects [21]. Microbial nucleic acids engage TLR9 and RIG-I receptors on dendritic cells (DCs), triggering IFN-β secretion and Th1-skewed immunity. This Th1-dominant milieu promotes M1 macrophage polarization and cytotoxic T lymphocyte (CTL)-mediated tumor apoptosis, contrasting sharply with the immunosuppressive Th2-rich environments associated with inferior immunotherapy responses [22]. Paradoxically, H. pylori lipopolysaccharide (LPS)—exhibiting weak TLR4 agonism due to tetra-acylated lipid A—may temper excessive immunosuppression. Although VacA-dependent NFAT inhibition facilitates regulatory T-cell (Treg) infiltration, Th1 polarization likely counteracts Treg-mediated suppression [21]. Studies in GC demonstrate enhanced CD8 + T-cell infiltration and survival in H. pylori-colonized tissues [23]. Virulence factor CagA, translocated via the type IV secretion system (T4SS), activates NF-κB and STAT3 pathways in gastric epithelia, driving pro-inflammatory cytokine release (IL- 1β, IL- 8, TNF-α) and MHC class II upregulation on antigen-presenting cells (APCs) [18, 23]. This MHC class II induction may potentiate CD4 + T-cell recognition of tumor antigens. Chronic H. pylori-induced inflammation in GC may amplify antitumor immunity by reshaping the tumor microenvironment [24]. The CagA virulence factor activates NF-κB and MAPK signaling pathways, driving upregulation of pro-inflammatory cytokines (IL- 6, IL- 1β, IL- 8), which recruit neutrophils, macrophages, and lymphocytes to establish an immunologically active tumor niche [18, 23]. Furthermore, H. pylori primes M1-polarized tumor-associated macrophages (TAMs) via IFN-γ and LPS-like components, augmenting phagocytic capacity and antigen presentation efficiency [25]. Following chronic infection, the activation of dendritic cells and M1 macrophages leads to the production of cytokines such as IL- 12, IL- 15, IL- 21, and IFN-γ. These cytokines play a pivotal role in inducing the activation of CD8 + T cells [24]. The inflammatory milieu rich in cytokines and chemokines further augment the infiltration and activity of immune cells, thus improving the efficacy of neoadjuvant therapy. Cancer-associated fibroblasts (CAFs) play a promoting role in tumor initiation, progression, and metastasis [26]. CagA interacts with stromal cells to upregulate CAF-derived factors, such as VEGF, MMP- 7, which remodel the extracellular matrix and facilitate immune cell infiltration [23]. In H. pylori-positive GC, the level of CAF infiltration is relatively low [7]. These characteristics confer an opportunity for H. pylori-positive GC subtypes to benefit from immunotherapy. Emerging evidence indicates that H. pylori strain virulence stratification (CagA + vs. CagA −) differentially modulates the tumor immune microenvironment and immunotherapy responsiveness through distinct mechanisms. CagA + strains activate STAT3/NF-κB signaling to upregulate pro-inflammatory cytokines and PD-L1 expression, while concurrently enhancing CD8 + T-cell infiltration via Th1 polarization. Conversely, CagA − strains exhibit attenuated STAT3/NF-κB activation but secrete VacA toxin, which suppresses NFAT signaling to reduce regulatory T-cell (Treg) infiltration, potentially augmenting immunotherapy susceptibility [25]. However, strain-specific heterogeneity, particularly geographic variations in CagA virulence (East Asian EPIYA-C/D motifs linked to heightened oncogenicity and immune remodeling), may underlie regional disparities in therapeutic outcomes [27]. The β-catenin pathway interaction of East Asian-prevalent CagA + strains could further potentiate immunotherapy benefits. Aging-associated immunosenescence exacerbates H. pylori pathogenicity, as elderly patients’ compromised immunity and chronic inflammation foster persistent colonization. Sustained CagA-driven microenvironmental remodeling in these individuals may impair immunotherapy efficacy. While eradication strategies hold therapeutic promise, their implementation requires careful risk–benefit analysis considering antibiotic resistance and comorbidities like gastroesophageal reflux disease. Future research should delineate age-dependent host–pathogen interactions. Despite limited research exploring the impact of H. pylori on the efficacy of ICI treatment for GC, findings remain controversial. Magahis et al. [28]. included 215 stage IV GC patients undergoing ICI treatment with recorded H. pylori status. They found a significant association between H. pylori infection and shortened progression-free survival (PFS) and OS in GC patients undergoing ICI treatment. Similarly, Che et al. [29] also analyzed 77 GC patients retrospectively, and patients in the H. pylori-negative group had longer OS and PFS than those in the positive group. Although prior studies propose a detrimental role of H. pylori infection in immunotherapy efficacy, our data demonstrate its paradoxical benefit in locally advanced MSS GC. These conflicting observations may arise from heterogeneity in disease staging, strain-specific virulence profiles, and therapeutic protocols. For example, neoadjuvant chemoimmunotherapy could synergize with H. pylori-mediated PD-L1 upregulation via immunogenic cell death mechanisms. Furthermore, the predominance of CagA + strains in East Asian populations—associated with pro-inflammatory tumor microenvironment (TME) activation—contrasts with VacA-dominant strains enriched in advanced/metastatic cohorts, which may drive immunosuppression. Due to the limited sample size, the results may be influenced by factors such as the duration of prior infection, treatment duration, and eradication protocols, making it challenging to directly establish a causal relationship between H. pylori infection and the efficacy of ICIs.

While this study represents the largest investigation to date, several limitations warrant consideration. The retrospective nature of our study, coupled with its extended time span, resulted in missing data for key parameters such as CPS, tumor mutational burden (TMB), and systemic inflammatory markers. This limitation may constrain our ability to fully characterize the tumor immune microenvironment. Future prospective studies should integrate standardized PD-L1 CPS assessment, TMB analysis, and spatially resolved inflammatory profiling to refine immunotherapy response prediction. Additionally, the lack of H. pylori strain subtyping (vacuolating cytotoxin secretion status) represents a critical gap. To address this, we propose a multi-dimensional framework combining strain-specific genotyping (CagA/VacA), host genetic polymorphisms, and multi-omics tumor analyses (immune infiltration mapping, spatial transcriptomics) in a planned multicenter trial enrolling locally advanced MSS GC (cT3 - 4/N +) patients receiving neoadjuvant immunotherapy. This initiative aims to mechanistically link H. pylori virulence determinants, tumor microenvironmental dynamics, and clinical outcomes, advancing precision immunotherapy strategies. Meanwhile, further validation will include prospective enrollment of MSI-H patients to systematically compare H. pylori’s immunomodulatory effects across MSI subtypes. Multi-omics integration will elucidate potential interactions between MSI status and H. pylori-mediated immune activation, addressing current knowledge gaps in microbial-host oncogenic crosstalk.

Conclusions

In H. pylori-positive MSS GC, the objective remission rate and pCR following neoadjuvant therapy can reach up to 63.8% and 17.4%, respectively. Although MSS GC is generally unresponsive to immunotherapy, it is unexpectedly observed that H. pylori-positive MSS GC benefits from neoadjuvant immunotherapy. H. pylori infection has emerged as a favorable factor in the neoadjuvant immunotherapy of GC.