An Adverse Event (AE) is any new untoward medical occurrence or worsening of a preexisting medical condition in a study participant administered study treatment and that does not necessarily have a causal relationship with this treatment. An AE can be any unfavorable and unintended sign (such as an abnormal laboratory finding), symptom, or disease temporally associated with the use of study treatment, whether or not considered related to the study treatment.

A Serious Adverse Event (SAE) is any untoward medical occurrence that, at any dose:

• Results in death
• Is life-threatening (defined as an event in which the participant was at risk of death at the time of the event)
• Requires inpatient hospitalization or causes prolongation of existing hospitalization
• Results in persistent or significant disability/incapacity
• Is a congenital anomaly/birth defect.

All treated participants. Participants who started in the Part A1 group but transitioned to Part B are accounted for in both treatment groups.

The number of participants who died during the study.

All treated participants. Participants who crossed over from part A1 are accounted for under their original arm assignment.

Dose-limiting toxicity (DLT) refers to a side effect or adverse reaction caused by a drug that is severe enough to prevent an increase in dose or level of that drug. It is typically identified during clinical trials to determine the highest dose of a drug that can be given safely without causing unacceptable side effects.

A participant was considered DLT evaluable if they received 1 dose of BMS-986258 in Part A or 1 dose of BMS-986258 and nivolumab 480mg in Part B and completed the DLT observation period.

Participants who withdraw from the study during the 4-week DLT evaluation period for reasons other than a DLT may be replaced with a new participant at the same dose level.

All treated participants who were evaluable for DLTs.

Objective response rate (ORR) is defined as the percent of treated participants whose best overall response (BOR) is either complete response (CR) or partial response (PR) per RECIST v1.1.

Complete Response (CR): Disappearance of all target lesions. Partial Response (PR): At least a 30% decrease in the sum of the diameters of target lesions, taking as reference the baseline sum diameters.

All treated participants. Prespecified to be reported collectively per Part. Participants who crossed over from part A1 to Part B are accounted for in both arms.

Median duration of response (mDOR) for a participant with a best overall response (BOR) of complete response (CR) or partial response (PR) is defined as the time between the date of first response and the date of the first objectively documented disease progression (DP) per RECIST v1.1 or death, whichever occurred first.

Complete Response (CR): Disappearance of all target lesions. Partial Response (PR): At least a 30% decrease in the sum of the diameters of target lesions, taking as reference the baseline sum diameters.

Disease Progression (DP): At least a 20% increase in the sum of the diameters of target lesions, with an absolute increase of at least 5 mm, or the appearance of new lesions.

Based on Kaplan-Meier estimates.

All treated participants witha complete or partial response. Prespecified to be reported collectively per Part. Response evaluable participants who crossed over from part A1 to Part B are accounted for in both arms.

Progression free survival (PFS) for a participant is defined as the time from the first dosing date to the date of first objectively documented disease progression or death due to any cause, whichever occurred first.

Disease Progression (DP): At least a 20% increase in the sum of the diameters of target lesions, with an absolute increase of at least 5 mm, or the appearance of new lesions.

All treated participants. Prespecified to be reported collectively per Part. Treated participants who crossed over from part A1 to Part B are accounted for in both arms.

Cmax (Maximum Concentration) is the highest level of a drug in the blood after it has been taken. It shows the peak level of the drug, which helps in understanding how much of the drug is absorbed and how strong its effects might be.

All treated participants with available PK results. PK evaluable participants who crossed over from Part A1 to Part B are accounted for in both arms.

AUC (0-T) is the total exposure to the drug over a specific period; from the time you take it until a specified time.

It helps in understanding the overall amount of drug that has been in your body over that time period.

All treated participants with available PK results. PK evaluable participants who crossed over from Part A1 to Part B are accounted for in both arms.

AUC(TAU) (Area Under the Curve over the Dosing Interval) is the total exposure to the drug over one complete dosing interval (the time between doses). It helps in understanding how much of the drug is in your body over the entire period between doses, which is important for determining the right dosing schedule.

All treated participants with available PK results. PK evaluable participants who crossed over from Part A1 to Part B are accounted for in both arms.

Ctau (Concentration at the End of the Dosing Interval) is the level of the drug in the blood just before the next dose is due. It shows how much of the drug remains in your body before taking the next dose, which helps in ensuring that the drug levels stay effective without dropping too low.

All treated participants with available PK results. PK evaluable participants who crossed over from Part A1 to Part B are accounted for in both arms.

Tmax (Time to Reach Maximum Concentration) is the time it takes for the drug to reach its highest level in the blood after taking it. It helps in understanding how quickly the drug starts to work and reaches its peak effect.

All treated participants with available PK results. PK evaluable participants who crossed over from Part A1 to Part B are accounted for in both arms.

Baseline ADA-positive participant is defined as a participant who has an ADA-detected sample at baseline. ADA-positive participant is a participant with at least 1 ADA-positive sample relative to baseline after initiation of the treatment

All treated participants with baseline and at least one post-baseline pre-infusion ADA assessment. Prespecified to be reported collectively per Part. PK evaluable participants who crossed over from Part A1 to Part B are accounted for in both arms.