DLTs will be defined as follows unless determined to be unrelated to study intervention: any Grade 4 nonhematologic toxicity (not laboratory); any Grade 4 hematologic toxicity lasting \>7 days (Grade 4 lymphopenia lasting ≥21 days); Grade 3 platelet count decreased if associated with clinically significant hemorrhage; any Grade 3 nonhematologic toxicity (not laboratory) lasting \>3 days despite optimal supportive care; any clinically significant Grade 3 or Grade 4 nonhematologic laboratory abnormality if: medical intervention is required to treat participant, or abnormality leads to hospitalization, or abnormality persists for \>1 week (or bilirubin if persists \>4 weeks); aspartate aminotransferase (AST)/ alanine aminotransferase (ALT) \>10.0 times upper limit of normal (ULN) or \>10.0 times baseline if baseline \>ULN; any febrile neutropenia Grade 3 or Grade 4; any treatment-related AE that causes the participant to discontinue study intervention during the DLT window; any Grade 5 toxicity

An AE is any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. The number of participants with an AE will be reported.

An AE is any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. An SAE is defined as any untoward medical occurrence that, at any dose: results in death, is life-threatening, requires inpatient hospitalization or prolongation of existing hospitalization, results in persistent or significant disability/incapacity, is a congenital anomaly/birth defect, or is another important medical event. The number of participants with an SAE will be reported.

An AE is any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. AEs associated with MK-1308A exposure may represent an immune-related response. irAEs pre-specified for this study include pneumonitis, diarrhea/colitis, Type 1 diabetes mellitus (T1DM) or hyperglycemia, hypophysitis, hyperthyroidism, hypothyroidism, nephritis (grading according to increased creatinine or acute kidney injury), and myocarditis. The number of participants with an irAE will be reported.

An AE is any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. Hepatic events of clinical interest (ECIs) include any of the following events if the event is considered not due to disease progression as judged by the investigator: among participants with Baseline ALT \<2 × ULN: ALT ≥5 × ULN; among participants with Baseline ALT ≥2 × ULN: ALT \>3 × the Baseline level; ALT \>500 U/L regardless of baseline level; total bilirubin \>3.0 mg/dL; hepatic decompensation diagnosed clinically (regardless of laboratory values) including new onset clinically detectable ascites requiring intervention for \>3 days, hepatic encephalopathy, or gastrointestinal bleeding suggestive of portal hypertension. The number of participants with a hepatic AE will be reported.

An AE is any untoward medical occurrence in a participant, temporally associated with the use of study treatment, whether or not considered related to the study treatment. The number of participants that discontinue study treatment due to an AE will be reported.

ORR is defined as the percentage of participants who achieve a confirmed Complete Response (CR: disappearance of all target lesions) or a Partial Response (PR: at least a 30% decrease in the sum of diameters \[SOD\] of target lesions) per RECIST 1.1 adjusted for this study to allow a maximum of 10 target lesions in total and 5 per organ, and assessed by BICR.