For limited-stage small cell lung cancer (SCLC), neoadjuvant chemotherapy plus PD-1 antibody is recommended. However, most patients cannot achieve a complete pathological response (CPR). A new immunotherapeutic strategy is needed to achieve a higher CPR rate. JS004 is a new antibody targeting B and T lymphocyte attenuator (BTLA), which restrains immune cells' function and leads to immune escape of tumor cells. The combination of PD-1 and BTLA antibodies has shown a good therapeutic effect in solid tumors. This trial aims to investigate the efficacy and safety of the therapeutic regimen of toripalimab and JS004 plus etoposide and platinum Chemotherapy in limited-stage SCLC.

Inclusion Criteria:

1. The patient shall sign the Informed Consent Form.
2. Aged 18 ≥ years.
3. Histological or cytological diagnosis of SCLC by needle biopsy, and limited stage confirmed by imageological examinations (CT, PET-CT or EBUS).
4. Eastern Cooperative Oncology Group (ECOG) performance-status score of 0 or 1.
5. Life expectancy is at least 12 weeks.
6. At least 1 measurable lesion according to RECIST 1.1.
7. Patients with good function of other main organs (liver, kidney, blood system, etc.)
8. Without systematic metastasis (including M1a, M1b and M1c);
9. Expected to be completely resected
10. Patients with lung function can tolerate surgery
11. Fertile female patients must voluntarily use effective contraceptives not less than 120 days after chemotherapy or the last dose of toripalimab (whichever is later) during the study period, and urine or serum pregnancy test results within 7 days prior to enrollment are negative.
12. Unsterilized male patients must voluntarily use effective contraception during the study period not less than 120 days after chemotherapy or the last dose of toripalimab (whichever is later).

Exclusion Criteria:

1. Participants who have received any systemic anti-cancer treatment for thymic epithelial tumor, including surgical treatment, local radiotherapy, cytotoxic drug treatment, targeted drug treatment and experimental treatment;
2. Patients with a malignancy other than SCLC within five years prior to the start of this trial;
3. Participants with any unstable systemic disease (including active infection, uncontrolled hypertension), unstable angina pectoris, angina pectoris starting in the last three months, congestive heart failure (>= NYHA) Grade II), myocardial infarction (6 months before admission), severe arrhythmia requiring drug treatment, liver, kidney or metabolic diseases;
4. With activate or suspectable autoimmune disease, or autoimmune paracancer syndrome requiring systemic treatment;
5. Participants who are allergic to the test drug or any auxiliary materials;
6. Participants with Interstitial lung disease currently;
7. Participants with active hepatitis B, hepatitis C or HIV;
8. Pregnant or lactating women;
9. Any malabsorption;
10. Participants suffering from nervous system diseases or mental diseases that cannot cooperate
11. Other factors that researchers think it is not suitable for enrollment.

The researchers will consider whether IPD is available to other researchers only after the paper is published.