DLT was defined as any of the treatment-emergent adverse events (TEAEs) that occurred during Cycle 1 and were considered by the investigator to be at least possibly related to modakafusp alfa. Toxicity was evaluated according to national cancer institute common terminology criteria for adverse events (NCI CTCAE) Version 5.0.

The Dose Limiting Toxicity (DLT)-evaluable Population included all participants from the Phase 1 dose escalation portion who experienced a DLT in Cycle 1 in the treatment phase of the study or had completed the Cycle 1 dose of modakafusp alfa and at least 75% of the planned dose of daratumumab SC.

An adverse event (AE) is defined as any untoward medical occurrence in a clinical investigation participant administered a drug; it does not necessarily have to have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (e.g., a clinically significant abnormal laboratory finding), symptom, or disease temporally associated with the use of a drug, whether or not it is considered related to the drug. A TEAE is defined as an adverse event with an onset that occurs after receiving study drug. Severity grades for TEAEs were evaluated as per the NCI CTCAE Version 5.0.

The Safety Population included all participants who received at least 1 dose, even an incomplete dose, of any study drug.

ORR is defined as the percentage of participants who achieve a confirmed partial response (PR) or better during the study in the safety population. ORR will be assessed by the investigator per International Myeloma Working Group (IMWG) criteria.

After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons. Thus, no participants were enrolled for Phase 2a and no data was collected for this outcome measure due to study termination.

ORR is defined as the percentage of participants who achieved a confirmed PR or better during the study in the safety population. ORR will be assessed by the investigator per IMWG criteria.

The Response-evaluable Population included all participants who received at least 1 dose, even an incomplete dose, of any study drug, have a disease assessment at screening (baseline evaluation), and at least 1 postbaseline disease assessment.

DOR is defined as the time from the date of first documentation of a confirmed PR or better to the date of first documentation of confirmed progressive disease or death due to any cause, whichever occurs first. DOR will be calculated for confirmed responders only (PR or better). DOR will be assessed by the investigator as per IMWG criteria.

PFS is defined as the time from the date of the first dose administration of any study drug to the first documentation of confirmed progressive disease or death due to any cause, whichever occurs first. PFS will be assessed by the investigator as per IMWG criteria.

OS is defined as the time from the date of the first dose administration of any study drug to the documentation of death due to any cause. OS will be assessed by the investigator as per IMWG criteria.

After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons and hence no participants were enrolled for Phase 2a.

Immunogenicity-evaluable Population included participants who received at least 1 dose of modakafusp alfa in combination with daratumumab SC (partial or complete) with a baseline assessment & at least 1 postbaseline immunogenicity assessment. No data was collected for this outcome measure due to study termination. Overall number of participants analyzed is the number of participants with data available for analyses.

MRD[-] CR rate is defined as the percentage of participants who achieve confirmed CR assessed by the investigator and MRD[-] status using a threshold of 10^-5. The analysis will be based on the response-evaluable population. No participants had sCR or CR in Phase 1 thus the overall number of participants analyzed is zero.

Only participants who had a confirmed stringent CR (sCR) or complete response (CR) were to be analyzed for this outcome measure. After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons. Thus, no participants were enrolled for Phase 2a & no data was collected for this outcome measure due to study termination.

Duration of MRD negativity for participants achieving MRD negativity is defined as the time from the date of first documentation of MRD negativity to the first documentation of MRD positivity or confirmed progressive disease, whichever occurs first. It will be calculated for participants achieving MRD negativity only. No participants had sCR or CR in Phase 1 thus the overall number of participants analyzed is zero.

Only participants who had a confirmed stringent CR (sCR) or complete response (CR) were to be analyzed for this outcome measure. After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons. Thus, no participants were enrolled for Phase 2a & no data was collected for this outcome measure due to study termination.

CBR is defined as the percentage of participants who had a confirmed response of stringent complete response (sCR), complete response (CR), very good partial response (VGPR), partial response (PR), or minimal response based on investigators' disease assessment per IMWG criteria.

After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons. Thus, no participants were enrolled for Phase 2a & no data was collected for this outcome measure due to study termination.

DCB is defined as the time from the date of first documentation of a minimal response or better to the date of first documentation of confirmed progressive disease or death due to any cause, whichever occurs first. DCB will be calculated for only participants who achieved a minimal response or better. DCB will be assessed by the investigator as per IMWG criteria.

After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons (no safety concerns). Thus, no participants were enrolled for Phase 2a & no data was collected for this outcome measure due to study termination.

DCR is defined as the percentage of participants with a confirmed response of sCR, CR, VGPR, PR, minimal response, or stable disease (SD) based on investigators' disease assessment per IMWG criteria.

After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons (no safety concerns). Thus, no participants were enrolled for Phase 2a & no data was collected for this outcome measure due to study termination.

Duration of disease control is defined as the time from date of first documentation of SD or better to the date of first documentation of confirmed progressive disease or death due to any cause. Duration of disease control will be calculated for only patients who achieved SD or better. It will be assessed by the investigator per IMWG criteria.

After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons (no safety concerns). Thus, no participants were enrolled for Phase 2a & no data was collected for this outcome measure due to study termination.

TTP is defined as the time from the date of randomization to the first documentation of confirmed progressive disease as defined by IMWG criteria, assessed by the investigator. Participants without documentation of confirmed progression will be censored at the date of last adequate disease assessment. The analysis will be based on the intent-to-treat (ITT) population.

After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons (no safety concerns). Thus, no participants were enrolled for Phase 2a & no data was collected for this outcome measure due to study termination.

TTR is defined as time from the date of first dose administration of any study drug to the date of the first documentation of a confirmed PR or better. TTR will be calculated for responders only. TTR will be assessed by the investigator per IMWG criteria.

After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons (no safety concerns). Thus, no participants were enrolled for Phase 2a & no data was collected for this outcome measure due to study termination.

TTNT is defined as the time from the date of first dose administration of any study drug to the date of the first dose initiation of the next line of anticancer therapy for any reason or death from any cause, whichever comes first. Participants who have not started the next-line therapy will be censored at the date last known to be alive before subsequent anticancer therapy.

After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons (no safety concerns). Thus, no participants were enrolled for Phase 2a & no data was collected for this outcome measure due to study termination.

An AE is defined as any untoward medical occurrence in a clinical investigation participant administered a drug; it does not necessarily have to have a causal relationship with this treatment. An AE can therefore be any unfavorable and unintended sign (e.g., a clinically significant abnormal laboratory finding), symptom, or disease temporally associated with the use of a drug, whether or not it is considered related to the drug. A TEAE is defined as an adverse event with an onset that occurs after receiving study drug. Severity grades for TEAEs will be evaluated as per the NCI CTCAE Version 5.0.

After completion of Phase 1 Dose Escalation of this study the sponsor decided not to proceed with Phase 2a due to strategic reasons (no safety concerns). Thus, no participants were enrolled for Phase 2a & no data was collected for this outcome measure due to study termination.