Safety and Preliminary Efficacy of MBS8(1V270) in Cancer Patients With Advanced Solid Tumours

Stage I Inclusion Criteria 1. Male or female aged ≥18 years. 2. Diagnosis of a histologically or cytologically confirmed solid tumour that was advanced and with progression. No standard treatment existed, or the participant refused standard treatment. Experimental immunotherapy appeared as a feasible exploratory treatment option as per Investigator's assessment. 3. Tumour lesion(s) accessible to serial biopsies. 4. Was willing and able to comply with scheduled visits, treatment schedule, laboratory tests, and tumour biopsies. Mandatory Baseline and on-treatment tumour biopsies were required. However, a biopsy may have been omitted if the procedure was deemed medically unsafe or not feasible, based on the Investigator's clinical judgment and after discussion with the Medical Monitor (or Sponsor's designee). 5. Measurable disease according to RECIST v1.1. Previously irradiated lesions were measurable if subsequent progression was documented. 6. Eastern Cooperative Oncology Group (ECOG) performance status 0 to 1. 7. Life expectancy \>3 months as assessed by the Investigator. 8. Adequate bone marrow, cardiopulmonary, renal and hepatic functions: • Haemoglobin ≥5.6 mmol/L (≥90 g/dL) (without transfusion or erythropoietin therapy within 4 weeks prior to therapy) • Neutrophils ≥1.5×109/L, without growth factor stimulation within 3 weeks prior to the blood test • Platelet count ≥75×109/L • Serum creatinine ≤1.25×ULN or creatinine clearance ≥50 mL/min (by CKD-EPI formula) • Hepatic function: AST and ALT ≤2.5×ULN; (5×ULN in the case of liver metastases); bilirubin ≤1.5×ULN except in the case of Gilbert's syndrome and 2×ULN in the case of liver metastases. 9. All participants of childbearing potential (defined as \<2 years after last menstruation or not surgically sterile) must have had a negative highly sensitive pregnancy test at Screening (urine/serum) and agreed to use highly effective method for contraception according to the European Union (EU) Clinical Trial Facilitation Group guidance from time of signing the informed consent form (ICF) until at least 120 days after the last administration of trial drug. The partners of participants with childbearing potential must have also applied contraceptive methods and were recommended not to donate sperm. 10. Ability to understand and sign the ICF. Stage II General Inclusion Criteria The following general inclusion criteria apply to all participants unless cohort criteria specify otherwise. 1. Male and female aged ≥18 years. 2. Eastern Cooperative Oncology Group performance status 0 to 1. 3. Life expectancy ≥3 months as assessed by the Investigator. 4. Adequate organ function within 7 to 14 days prior to Day 1. • Absolute neutrophil count ≥1.5×10⁹/L; platelets ≥100×10⁹/L; haemoglobin ≥9 g/dL (transfusion allowed per site's policy) • Aspartate transaminase/ALT ≤3×ULN (≤5×ULN in case of liver metastases) • Total bilirubin ≤1.5×ULN (≤3×ULN in case of Gilbert's syndrome) * Creatinine clearance ≥50 mL/min (Cockcroft-Gault or measured) * International normalised ratio (INR)/activated partial thromboplastin time (APTT) within institutional limits (unless on stable anticoagulation). 5. Prior systemic anti-cancer therapy with a washout period of ≥14 days plus resolution of drug-related AEs before C1D1. Participants should have recovered from prior therapy-related toxicities to Baseline or Grade ≤1 (except alopecia and other non-clinically significant AEs) and meet all Baseline laboratory criteria. Any deviation requires documented approval from the Sponsor/Medical Monitor with justification in the source record. 6. Major surgery ≥4 weeks, palliative radiotherapy ≥2 weeks, stereotactic body radiation therapy to lung/liver ≥3 weeks. 7. No systemic steroids \>10 mg/day prednisone-equivalent within 14 days before C1D1. Note: Physiologic/replacement doses (e.g., adrenal insufficiency) up to 10 mg/day prednisone-equivalent, topical, inhaled, intra-articular, intranasal, or ophthalmic steroids are allowed. 8. All participants of childbearing potential (defined as \<2 years after last menstruation or not surgically sterile) must have a negative highly sensitive pregnancy test at Screening (urine/serum) and agree to use highly effective method for contraception according to the EU Clinical Trial Facilitation Group guidance from the time of signing the ICF until at least 120 days after the last administration of trial drug. The partners of participants with childbearing potential must also apply contraceptive methods and are recommended not to donate sperm. 9. Ability to provide informed consent and comply with trial procedures. 10. Lactate dehydrogenase ≤2.0×ULN at Screening (single repeat allowed, if confounded). Stage II - Cohort A (Cutaneous Melanoma; Pembrolizumab in Combination with MBS8(1V270)) Specific Inclusion Criteria The following inclusion criteria apply specifically to Stage II - Cohort A. 11A. Histologically/cytologically confirmed metastatic cutaneous melanoma. 12A. Prior exposure to pembrolizumab, nivolumab, nivolumab + ipilimumab, or nivolumab + relatlimab with documented SD lasting ≥6 months, or any CR or PR followed by disease progression. 13A. No untreated or unstable brain metastases. Participants with treated/stable CNS metastasis are eligible if the condition is radiographically stable for ≥4 weeks, no new/worsening neurologic symptoms, and off steroids or on stable/declining ≤10 mg/day prednisone-equivalent for ≥14 days. 14A. Last dose of pembrolizumab, nivolumab, nivolumab + ipilimumab, or nivolumab + relatlimab was given ≤12 weeks prior to Screening, and with no other therapy started. 15A. No prior Grade ≥3 irAE leading to permanent discontinuation of prior anti-PD1/PD L1. 16A. Willing to receive pembrolizumab per SmPC/label-concordant schedule. Stage II - Cohort B (Uveal Melanoma; MBS8(1V270) Monotherapy) Specific Inclusion Criteria The following inclusion criteria apply specifically to Stage II - Co