A Clinical Trial of MK-1045 and Rituximab in People With Follicular Lymphoma (MK-1045-007)

Researchers are looking for new ways to treat follicular lymphoma (FL). A standard (usual) treatment for FL includes a targeted therapy called rituximab and chemotherapy. In this study, researchers want to learn if giving a study medicine called MK-1045 and rituximab can treat FL. MK-1045 is a type of treatment called immunotherapy. The goals of this study are to learn: * About the safety of MK-1045 and rituximab, and if people tolerate them when given together * If people who receive MK-1045 and rituximab have the cancer go away * If people who receive MK-1045 and rituximab live longer without their cancer getting worse compared to those who receive standard treatment (rituximab and chemotherapy)

Inclusion Criteria: * Has biopsy-proven, previously untreated, histologically confirmed cluster of differentiation (CD)19-positive and CD20-positive classical follicular lymphoma (FL), with Ann Arbor Stage II-IV disease and a Follicular Lymphoma International Prognostic Index (FLIPI) score of 2-5. * Has radiographically measurable disease per the Lugano Response Criteria. * Has provided a newly obtained core or excisional biopsy or archival tissue of a tumor lesion not previously irradiated. * If human immunodeficiency virus (HIV)-positive, has well-controlled HIV on antiretroviral therapy (ART). * If hepatitis B surface antigen (HBsAg)-positive, has undetectable hepatitis B virus (HBV) viral load and has received HBV antiviral therapy for at least 4 weeks and will continue it. * If history of hepatitis C virus (HCV) infection, has undetectable HCV viral load. Exclusion Criteria: * Has received prior systemic anticancer therapy or radiotherapy for FL. * Has follicular large B-cell lymphoma or any other subtype of FL other than classical FL. * Has FL that has transformed into a more aggressive type of lymphoma. * History or presence of clinically relevant central nervous system (CNS) diseases. * Has history of serious cardiovascular and cerebrovascular diseases. * Is HIV-infected with a history of Kaposi's sarcoma and/or Multicentric Castleman's Disease. * Has received a live or live-attenuated vaccine within 30 days before the first dose of study intervention. * Has a diagnosis of immunodeficiency or is receiving chronic systemic steroid therapy. * Has a known additional malignancy that is progressing or has required active treatment within the past 3 years. * Has known active CNS lymphoma or involvement. * Has an active autoimmune disease that has required systemic treatment in the past 2 years. * Has active infection requiring systemic therapy. * Has chronic liver disease, including liver cirrhosis of Child-Pugh class B or C. * Has not adequately recovered from major surgery or has ongoing surgical complications.