The goal of this clinical trial is to learn the safety of tumor neoantigen vaccine combined with neoantigen vaccine induced T-cell in treating advanced gastric cancer in adults. It will also learn if the combined treatment works to treat advanced gastric cancer.

The main questions it aims to answer are:

What medical problems do participants have when using the combined treatment? Does tumor neoantigen vaccine combined with neoantigen vaccine induced T-cell eliminate or shrink the tumor, and can it prolong the patient's survival period?

Inclusion Criteria:

1. Provision of signed and dated informed consent form.
2. Aged between 18 and 70 years old, male or female.
3. Advanced gastric cancer that has been diagnosed by histological and/or cellular pathology, and which has failed to respond to second-line standard treatment or is intolerant to it, or is not suitable for standard treatment at this stage.
4. According to the RECIST 1.1 criteria for evaluating the efficacy of solid tumors, there must be at least one measurable lesion as the target lesion for efficacy evaluation. The total diameter of the overall tumor lesion (excluding bone metastases) should be ≤ 100mm, and the diameter of a single tumor lesion should be ≤ 30mm. If the lesion that has received local treatment (radiotherapy, ablation, vascular intervention, etc.) is the only lesion, then there must be clear imaging evidence of disease progression for this lesion.
5. Expected survival duration ≥ 12 weeks.
6. Adequate organ and bone marrow function.

Exclusion Criteria:

1. Requires long-term systemic administration of antiallergic drugs, or has severe hypersensitivity reactions (≥Grade 3) to XH001 injection and/or any of its excipients.
2. Central nervous system metastases with symptoms and without prior treatment, and/or meningeal metastases.
3. Having received immunomodulatory drug therapy within 2 weeks prior to the first administration day (D1) of XH001 injection.
4. Suffer from skin diseases that may prevent the intradermal injection from reaching the target area (such as psoriasis).
5. Subjects with toxic side effects from previous treatment that have not recovered to CTCAE grade≤2, excluding hair loss.
6. Subjects who received systemic steroid treatment (daily dose exceeding 10mg of prednisone equivalent) or any other form of immunosuppressive treatment within 7 days before the first administration of XH001 injection, excluding:1) Intranasal inhalation of local steroids or local steroid injection (such as intra-articular injection); 2) Systemic corticosteroid treatment not exceeding 10mg/day of prednisone or its equivalent physiological dose.
7. Subjects who have previously received therapeutic tumor vaccines or therapeutic cell therapy products.
8. Previously received allogeneic hematopoietic stem cell or allogeneic bone marrow transplantation, or previously received solid organ transplantation, or currently using immunosuppressive drugs.
9. Have active or poorly controlled severe infections during screening period.
10. Virological tests show positive for human immunodeficiency virus antibodies, hepatitis B surface antigen and/or hepatitis B core antibody with hepatitis B virus DNA > 1000 IU/ml, positive for hepatitis C virus antibodies, and positive for Treponema pallidum specific antibodies.
11. Patients with other malignancies within 5 years before enrollment, except for those with a history of appropriately treated and cured cervical carcinoma in situ, breast carcinoma in situ, or skin basal cell carcinoma.
12. Any history of autoimmune diseases.
13. Known to have active pulmonary tuberculosis (TB).
14. Patients who have received systemic chemotherapy, radiotherapy, molecular targeted therapy, biological immunotherapy, hormone therapy or unapproved clinical trial drugs/instruments within 2 weeks before screening.
15. Subjects who are still participating in other clinical trials during the screening period.
16. Pregnant or lactating women.
17. Other severe, acute, or chronic medical or psychiatric conditions, or laboratory abnormalities, that, to the investigator's discretion, may increase the risks of participating in the trial or may interfere with the interpretation of the trial results.