This is a single center, open-label, dose increasing study to evaluate the safety, tolerability, pharmacokinetic(PK) profile, and antitumor efficacy of KL340399 injection in patients with advanced solid tumors.

This is a single center, open-label, dose increasing study to evaluate the safety, tolerability, pharmacokinetic(PK) profile, and antitumor efficacy of KL340399 injection in patients with advanced solid tumors.The dose increasing method of "BLRM" is used to explore the safety, tolerance and determine the maximum tolerated dose(MTD).

Inclusion Criteria:

1. Patient is at least ≥18 years of age (male or female);
2. Patients with histologically and/or cytologically confirmed advanced solid tumors who have failed standard of care, or who have no available standard of care regimen, or who are unqualified for standard of care. Presence of at least one measurable lesion based on Response Evaluation Criteria in Solid Tumors (RECIST) v1.1;
3. Eastern Cooperative Oncology Group (ECOG) score of 0 or 1, estimated survival ≥ 3 months;
4. Adequate organ and bone marrow function (no blood components and cytokines are allowed within 14 days prior to the first dose) ;
5. More than 4 weeks from the last radiotherapy, chemotherapy, surgery, hormone treatment, target therapy, and toxicity from previous antitumor therapy returned to baseline or CTCAE≤ grade 1;
6. Patients of childbearing potential (male or female) must use effective medical contraception during the study and for 3 months after the end of dosing;
7. Patients voluntarily participate in the study, sign the ICF, and will be able to comply with the protocol-specified visits and relevant procedures.

Exclusion Criteria:

1. Known history of severe allergies, or allergy to any component of KL340399;
2. Received any previous therapy of STING-activating, or received any immunostimulant therapy within 28 days；
3. Have other malignancies within 5 years;
4. Concomitant or known metastases to brain or central nervous system;
5. Active autoimmune disease;
6. History of major cardiovascular diseases;
7. Uncontrolled systemic diseases；
8. Known of coagulation disorders, hemorrhagic disease;
9. Confirmed serious lung disease or lung disease;
10. Subjects with third space fluid that can not be controled by drainage or other methods;
11. Known active infection;
12. Known HIV, active hepatitis B/C virus;
13. Pregnant or lactating women;
14. Received immunotherapy and had immune related adverse reactions ≥ grade 3;
15. Have received stem cell transplantation or organ transplantation;
16. Receive any live or attenuated live vaccine within 4 weeks;
17. History of serious dementia, altered mental status, or any psychiatric disorder;
18. Evidence of alcohol or drug abuse;
19. Participated in any other clinical trials and received treatment within 4 weeks;
20. Have other factors based on which the investigator considers that the subjects are not appropriate to participate in the study.