Combining DCSZ11 With Radiation and Chemotherapy as Neoadjuvant Treatment for pMMR Locally Advanced Rectal Cancer

Inclusion Criteria: * Age ≥18 years. * Eastern Cooperative Oncology Group (ECOG) performance status 0 - 1. * Rectal cancer (with tumor tissue present at or below the peritoneal reflection) as determined by MRI pelvis or endoscopic ultrasound. * Have histologically proven mismatch repair proficient (pMMR) or microsatellite stable (MSS) rectal adenocarcinoma. * Must not have received any prior systemic treatment or radiation. * Patients have the following clinical staging: * cT4 any node status * Any T stage cN2 node status * Any T or N status, evidence of suspicious lateral lymph nodes \> 10 mm in size in short axis * Evidence of extramural vascular invasion on MRI pelvis * Absence of distant metastases on CT or MRI imaging * Patients must have adequate organ and marrow function defined by study-specified laboratory tests and procedures. * Left ventricular ejection fraction (LVEF) assessment with documented LVEF ≥ 50% by either TTE or Multigated Acquisition (MUGA) (TTE preferred) within 6 months from first study drug administration. * For both Women and Men, must use acceptable form of birth control while on study. * Ability to understand and willingness to sign a written informed consent document. Exclusion Criteria: * Have received an investigational agent or used an investigational device within 28 days of the first dose of study drug. * Have expected to require any other form of systemic or localized antineoplastic therapy while on study. * Have had surgery within 28 days of dosing of investigational agent, excluding minor procedures (dental work, skin biopsy, etc.). * History of severe hypersensitivity reaction to any monoclonal antibody. * History of encephalitis, meningitis, dementia, Parkinson's or uncontrolled seizures within 1 year prior to the first dose of study drug. * Uncontrolled infection of HIV, hepatitis B virus (HBV), hepatitis C virus (HCV), or Tuberculosis. * Uncontrolled intercurrent illness including, but not limited to, uncontrolled infection, symptomatic congestive heart failure, unstable angina, cardiac arrhythmia, metastatic cancer, or psychiatric illness/social situations that would limit compliance with study requirements. * Any tissue or organ allograft, regardless of need for immunosuppression, including corneal allograft. * Patient has a pulse oximetry of \<92% on room air. * Patient is on supplemental home oxygen. * Has clinically significant heart disease. * Conditions, including alcohol or drug dependence that would affect the patient's ability to comply with study visits and procedures. * Patient is pregnant or breastfeeding. * Unwilling or unable to follow the study schedule for any reason. * Patient received a live vaccine within 30 days of planned start of study medication. * Receipt of COVID-19 vaccination within 1 week of planned start of study medication or for which the planned COVID-19 vaccinations would not be completed 1 week prior to start of study medication.