Background: AFM24 is a novel tetravalent bispecific IgG1-scFv fusion antibody (scFv-IgAb) binding specifically to EGFR on target cells and CD16A on NK cells, mediating specific lysis of EGFR⁺ tumor cells via NK cell-mediated antibody-dependent cellular cytotoxicity. SNK01 cell therapy is an NK cell-derived adoptive cellular immunotherapy technology that can produce large scale ex vivo expanded and activated autologous NK cells (1,000–10,000-fold expansion of NK cells with >95% cell purity), even in patients with low primary NK cell counts. The antitumor activity of SNK01 may be enhanced when combined with AFM24. Methods: This is a proof-of-concept phase 1, 3+3 dose escalation study to determine the maximum tolerated dose and/or recommended phase 2 dose of AFM24 in combination with SNK01 (NCT05099549). Secondary endpoints are safety/tolerability, preliminary efficacy and pharmacokinetics (PK). Patients with advanced or metastatic, histologically or cytologically confirmed EGFR⁺ solid tumors (≥1% of positive tumor cells) refractory to standard-of-care therapies were enrolled. AFM24 starting dose was 160 mg followed by 480 mg. AFM24 is administered once weekly, concomitantly with 4.0 x10⁹ SNK01 cells once weekly until disease progression, intolerable toxicity, patient withdrawal. Cycles are 28 days and CTs are at screening, cycle 2, 4, 6, 8, and every 3 cycles thereafter. Results: As of January 27, 2023, 6 patients (5 microsatellite stable colorectal and 1 head and neck cancer) received combination therapy, 3 in each cohort. Median (range) age was 59 (41–64), mean number (range) of prior therapies was 5 (3–7). ECOG performance status was 0 for 3 patients and 1 for the other 3. No dose limiting toxicities or unexpected toxicities were observed. Preliminary results suggest consistent safety events with both drugs in monotherapy. The most frequent treatment-emergent adverse events related to AFM24 was Grade 1/2 infusion related reactions occurring in 5/6 patients. There were no Grade ≥3 events related to AFM24 or SNK01. In the low dose cohort (160 mg), 2 patients had stable disease for 106 days (15 weeks) and 100 days (14 weeks), respectively. At 480 mg, 1 patient with SD had 2% tumor burden reduction and 2 subsequent carcinoembryonic antigen reductions. The patient proceeded to Cycle 3. No difference in PK data was observed in comparison to AFM24 alone. Enrollment continues at 480 mg. Conclusions: In this first study combining a bispecific NK cell engager with autologous NK cell infusions; two dose cohorts have completed, and escalation has proceeded. Early PK data are consistent with AFM24 monotherapy with no new safety signals, suggesting that the combination of AFM24 and SNK01 cells is tolerated and warrants further investigation. Clinical trial information: NCT05099549.