A Study to Investigate ALE.P02 as a Monotherapy or in Combination With Pembrolizumab in Adult Patients With Selected CLDN1+ Solid Tumors

The purpose of this study is to evaluate the safety, tolerability, pharmacokinetic, pharmacodynamic, preliminary anti-tumor activity, and to determine the recommended Phase II dose (RP2D) of the ALE.P02 as a monotherapy or in combination with pembrolizumab in adult patients with selected squamous solid tumors.

Inclusion Criteria: * Have disease and treatment history as: histologically or cytologically confirmed advanced locally recurrent and inoperable or metastatic SqNSCLC, HNSCC (nasopharyngeal cancer included), ESCC or CSCC. * Phase I Dose Escalation: Have received at least one systemic standard of care regimen and being refractory or intolerant to the treatment. * Phase I Monotherapy RDE and Phase II: Have received no more than 2 lines of systemic standard of care regimen and being refractory or intolerant to the treatment. * Phase I Combination Therapy RDE: Have received no previous systemic therapy in incurable recurrent or metastatic setting * Have provided tissue for CLDN1 analysis in a central laboratory. * Have a performance status of 0 or 1 on the Eastern Cooperative Oncology Group Performance Scale. * Demonstrate adequate bone marrow and organ function. * Patients must have recovered from all toxicities led by prior treatment. * Have measurable disease based on RECIST 1.1 as determined by the site. Exclusion Criteria: * Diagnosed with cancers of predominantly non-squamous histology (eg, adenosquamous carcinoma) or adenocarcinoma. * Has received antineoplastic therapies prior to study intervention within specified time frame. * Has rapidly progressing disease (eg, tumor bleeding, uncontrolled tumor pain). * Patients with uncontrolled diabetes. * Has known active central nervous system (CNS) metastases and/or carcinomatous meningitis. * Has clinically significant gastrointestinal bleeding and has an active infection requiring systemic treatment and has a history or current evidence of any condition, therapy, or laboratory abnormality that might confound the results of the clinical study, interfere with the patient's participation for the full duration of the clinical study, or is not in the best interest of the patient to participate. * Concomitant use of drugs that are known to prolong or shorten QT and/or have known risk of Torsades de Pointes.