SCREENING: Patient eligibility will be determined by protocol inclusion/exclusion criteria including HLA (human leukocyte antigen) screening and a biopsy for biomarker screening. If the patient is eligible, white blood cells will be taken during leukapheresis for the manufacture of the IMA203 product.

MANUFACTURING: IMA203 product will be made from the patient's white blood cells.

TREATMENT: Lymphodepletion with cyclophosphamide and fludarabine will occur in the days before the IMA203 product infusion to improve the duration of time that IMA203 product stays in the body. The patient will be admitted to the hospital during the T-cell infusion.

After the IMA203 product infusion, a low dose of IL-2 will be given subcutaneously daily for 10 days.

In Extension Cohort B (IMA203 plus nivolumab), nivolumab will be administered intravenously.

Patients will be monitored closely throughout the study. The follow-up phase ends 5 years post infusion.

Inclusion Criteria:

• Patients must have recurrent/progressing and/or refractory solid tumors and must have received or not be eligible for all available indicated standard of care treatment.
• Eastern Cooperative Oncology Group (ECOG) performance status 0-1
• HLA phenotype positive for the study
• Measurable disease according to RECIST 1.1
• Adequate selected organ function per protocol
• Patient's tumor must express tumor antigen by "IMADetect® RT-qPCR
• Life expectancy more than 3 months
• Patients must have recurrent/progressing and/or refractory solid tumors and must have received or not be eligible for all available indicated standard of care treatment.
• For hepatocellular carcinoma (HCC) patients only, Child-Pugh score of ≤ 6
• Female patient of childbearing potential must use adequate contraception prior to study entry until 12 months after the infusion of IMA203
• Male patient must agree to use effective contraception or be abstinent while on study and for 6 months after the infusion of IMA203
• The patient must have recovered from any side effects of prior therapy to Grade 1 or lower prior to lymphodepletion.

Exclusion Criteria:

• History of other malignancies (except for adequately treated basal or squamous cell carcinoma or carcinoma in situ) within the last 3 years
• Solid tumors with low likelihood of tumor biomarker expression per protocol
• Pregnant or breastfeeding
• Serious autoimmune disease Note: At the discretion of the investigator, these patients may be included if their disease is well controlled without the use of immunosuppressive agents.
• History of cardiac conditions as per protocol
• Prior stem cell transplantation or solid organ transplantation
• Concurrent severe and/or uncontrolled medical disease that could compromise participation in the study
• History of or current immunodeficiency disease or prior treatment compromising immune function at the discretion of the treating physician
• HIV infection, active hepatitis B virus (HBV), active hepatitis C virus (HCV) infection, ongoing active anti-HCV treatment or detectable HBV or HCV viral load at the most recent laboratory report. Patients with both HBV and HCV infections will be excluded from screening
• Patients who have received more than 4 prior systemic treatment lines for treatment of advanced and/or metastatic disease.
• Patients who are known to have at least one single tumor lesion that exceeds 10 cm in diameter
• Any condition contraindicating leukapheresis, lymphodepletion, low-dose IL-2, and/or IMA203 treatment
• Patients with active brain metastases
• Concurrent participation in an interventional part of another clinical trial.
• For nivolumab treatment, patients must not have a history of severe immune-related toxicities, defined as any Grade 3 or 4 toxicities related to prior PD1/PD-L1 inhibitor therapy (e.g., atezolizumab, pembrolizumab or nivolumab etc.).

Other protocol defined inclusion/exclusion criteria could apply